Papers for Monday, Aug 23 2021

Recently, an increasing number of wide binaries has been discovered. Their chemical and dynamical properties are studied through extensive surveys and pointed observations. However, the formation of these wide binaries is far from clear, although several scenarios have been suggested. In order to investigate the chemical compositions of these systems, we analysed high-resolution spectroscopy of three wide binary pairs belonging to the Galactic halo. In total, another three candidates from our original sample of 11 candidates observed at various resolutions with various instruments were refuted as co-moving pairs because their radial velocities are significantly different. Within our sample of wide binaries, we found homogeneity amongst the pair components in dynamical properties (proper motion and line-of-sight velocities) and also in chemical composition. Their metallicities are -1.16, -1.42, and -0.79 dex in [Fe/H] for each wide binary pair, which places these stars on the metal-poor side of wide binaries reported in the literature. In particular, the most metal-poor pair in our sample (WB2 = HD134439/HD134440) shows a lower [$\alpha$/Fe] abundance ratio than Milky Way field stars, which is a clear signature of an accreted object. We also confirmed that this wide binary shares remarkably similar orbital properties with stars and globular clusters associated with the Sequoia event. Thus, it appears that the WB2 pair was formed in a dwarf galaxy environment and subsequently dissolved into the Milky Way halo. Although the other two wide binaries appear to arise from a different formation mechanism, our results provide a novel opportunity for understanding the formation of wide binaries and the assembly process of the Milky Way.

The 23 Myr system V1298 Tau hosts four transiting planets and is a valuable laboratory for exploring the early stages of planet evolution soon after formation of the star. We observe the innermost planet, V1298 Tau c, during transit using LBT PEPSI to obtain high spectral resolution characterization of escaping material near the H-alpha line. We find no strong evidence for atmospheric material escaping at the orbital velocity of the planet. Instead, we find a deep stellar feature that is variable on the few percent level, similar to a previous observation of the planet and can be explained by stellar activity. We attempted to monitor the broadband optical transit with LBT MODS but do not achieve the precision needed to characterize the atmosphere or improve the ephemeris.

We make the most precise determination to date of the number density of extragalactic 21-cm radio sources as a function of their spectral line widths - the HI velocity width function (HIWF) - based on 22832 sources from the final 7000 deg$^2$ data release of the Arecibo Legacy Fast ALFA (ALFALFA) survey. The number density of sources as a function of their neutral hydrogen masses - the HI mass function (HIMF) - has previously been reported to have a significantly different low-mass slope and 'knee mass' in the two sky regions surveyed during ALFALFA. In contrast with this, we find that the shape of the HIWF in the same two sky regions is remarkably similar, consistent with being identical within the confidence intervals implied by the data (but the overall normalisation differs). The spatial uniformity of the HIWF implies that it is likely a stable tracer of the mass function of dark matter haloes, in spite of the environmental processes to which the measured variation in the HIMF are attributed, at least for galaxies containing enough neutral hydrogen to be detected. This insensitivity of the HIWF to galaxy formation and evolution can be exploited to turn it into a powerful constraint on cosmological models as future surveys yield increasingly precise measurements. We also report on the possible influence of a previously overlooked systematic error affecting the HIWF, which may plausibly see its low-velocity slope steepen by $\sim$40 per cent in analyses of future, deeper surveys.

Stellar feedback in dwarf galaxies plays a critical role in regulating star formation via galaxy-scale winds. Recent hydrodynamical zoom simulations of dwarf galaxies predict that the periodic outward flow of gas can change the gravitational potential sufficiently to cause radial migration of stars. To test the effect of bursty star formation on stellar migration, we examine star formation observables and sizes of 86 local dwarf galaxies. We find a correlation between the R-band half-light radius (R$_e$) and far-UV luminosity (L$_{FUV}$) for stellar masses below 10$^8 $ M$_{\odot}$ and a weak correlation between the R$_e$ and H$\alpha$ luminosity (L$_{H\alpha}$). We produce mock observations of eight low-mass galaxies from the FIRE-2 cosmological simulations and measure the similarity of the time sequences of R$_e$ and a number of star formation indicators with different timescales. Major episodes of R$_e$ time sequence align very well with the major episodes of star formation, with a delay of $\sim$ 50 Myrs. This correlation decreases towards SFR indicators of shorter timescales such that $R_e$ is weakly correlated with L$_{FUV}$ (10-100 Myr timescale) and is completely uncorrelated with L$_{H\alpha}$ (a few Myr timescale), in agreement with the observations. Our findings based on FIRE-2 suggest that the R-band size of a galaxy reacts to star formation variations on a $\sim50$ Myr timescale. With the advent of a new generation of large space telescopes (e.g., JWST), this effect can be examined explicitly in galaxies at higher redshifts where bursty star formation is more prominent.

Baryonic feedback effects consist of a major systematic for upcoming weak-lensing and galaxy-clustering surveys. In this paper, we present an emulator for the baryonic suppression of the matter power spectrum. The emulator is based on the baryonification model, containing seven free parameters that are connected to the gas profiles and stellar abundances in haloes. We show that with the baryonic emulator, we can not only recover the power spectra of hydro-dynamical simulations at sub-percent precision but also establish a connection between the baryonic suppression of the power spectrum and the gas and stellar fractions in haloes. This connection allows us to predict the expected deviation from a dark-matter-only power spectrum using measured X-ray gas fractions of galaxy groups and clusters. With these measurements, we constrain the suppression to exceed the percent-level at k = 0.1-0.4 h/Mpc and to reach a maximum of 20-28 percent at around k = 7 h/Mpc (68 percent confidence level). As a further step, we also perform a detailed parameter study and we present a minimum set of four baryonic parameters that are required to recover the scale and redshift dependence observed in hydro-dynamical simulations. The baryonic emulator can be found at https://github.com/sambit-giri/BCMemu.

We suggest that the hotspot of ultrahigh energy cosmic rays (UHECR) detected by the Telescope Array (TA) from the direction of M82 might be the echo of UHECR emitted by Centaurus A in a more powerful phase approximately 20Myr ago. Echoes from other starburst galaxies may contribute to the UHECR flux at the Earth.

In the standard scenario of planet formation, terrestrial planets, ice giants, and cores of gas giants are formed by the accumulation of planetesimals. However, there are few N-body simulation studies of planetesimal accretion that correctly take into account the merging condition of planetesimals. In order to investigate a realistic accretion process of planetesimals, it is necessary to clarify the merging criteria of planetesimals at collision. We perform numerical collision experiments using smoothed particle hydrodynamics and obtain the merging criteria as a function of planetesimal mass and impact parameters for undifferentiated rocky and icy planetesimals and differentiated icy planetesimals. We vary the total mass of colliding planetesimals, their mass ratios, and the impact angle and obtain the critical impact velocity as the merging criteria distinguishing merging from hit-and-run collision. We find that the critical impact velocity normalized by the two-body surface escape velocity decreases with increasing impact angle. The critical impact velocity does not depend on the total mass, while it has a weak positive dependence on the mass ratio. These results barely depend on the composition and internal structure of the planetesimals.

The Galactic Center region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. We present the analysis of the very-high-energy gamma-ray emission above 2 TeV of the region around the Galactic Center known as the Central Molecular Zone using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. This analysis employs new shower reconstruction algorithms and instrument response functions optimized for data taken at large zenith angles such as the Galactic Center sources. We report positions and spectra for point sources VER J1745-290, G0.9+0.1, and HESS J1746-285, along with a light curve for VER J1745-290, the brightest source in the region consistent with the position of the supermassive black hole Sagittarius A*. We also measure the spectrum of the diffuse emission from the Galactic Center ridge region, which has been claimed as evidence of a Galactic PeVatron.

We present new Spitzer transit observations of four K2 transiting sub-Neptunes: K2-36c, K2-79b, K2-167b, and K2-212b. We derive updated orbital ephemerides and radii for these planets based on a joint analysis of the Spitzer, TESS, and K2 photometry. We use the EVEREST pipeline to provide improved K2 photometry, by detrending instrumental noise and K2's pointing jitter. We used a pixel level decorrelation method on the Spitzer observations to reduce instrumental systematic effects. We modeled the effect of possible blended eclipsing binaries, seeking to validate these planets via the achromaticity of the transits (K2 versus Spitzer). However, we find that Spitzer's signal-to-noise ratio for these small planets is insufficient to validate them via achromaticity. Nevertheless, by jointly fitting radii between K2 and Spitzer observations, we were able to independently confirm the K2 radius measurements. Due to the long time baseline between the K2 and Spitzer observations, we were also able to increase the precision of the orbital periods compared to K2 observations alone. The improvement is a factor of 3 for K2-36c, and more than an order of magnitude for the remaining planets. Considering possible JWST observations in 1/2023, previous 1 sigma uncertainties in transit times for these planets range from 74 to 434 minutes, but we have reduced them to the range of 8 to 23 minutes.

The behavior of an adaptive optics (AO) system for ground-based high contrast imaging (HCI) dictates the achievable contrast of the instrument. In conditions where the coherence time of the atmosphere is short compared to the speed of the AO system, the servo-lag error becomes the dominate error term of the AO system. While the AO system measures the wavefront error and subsequently applies a correction (taking a total of 1 to 2 milli-seconds), the atmospheric turbulence above the telescope has changed. In addition to reducing the Strehl ratio, the servo-lag error causes a build-up of speckles along the direction of the dominant wind vector in the coronagraphic image, severely limiting the contrast at small angular separations. One strategy to mitigate this problem is to predict the evolution of the turbulence over the delay. Our predictive wavefront control algorithm minimizes the delay in a mean square sense and has been implemented on the Keck II AO bench. In this paper we report on the latest results of our algorithm and discuss updates to the algorithm itself. We explore how to tune various filter parameters on the basis of both daytime laboratory tests and on-sky tests. We show a reduction in residual-mean-square wavefront error for the predictor compare to the leaky integrator implemented on Keck. Finally, we present contrast improvements for both day time and on-sky tests. Using the L-band vortex coronagraph for Keck's NIRC2 instrument, we find a contrast gain of 2.03 at separation of 3~$\lambda/D$ and up to 3 for larger separations (4-6~$\lambda/D$).

Song et al. (Song et al., 2021) published "Thresholds of temperature changes for mass extinctions" on 4 August 2021. They described the correlation between an increase in global-average temperature and Mass Extinction Events. This response intends to provide a more comprehensive evaluation of the environmental thresholds required to sustain a habitable planet. Our approach includes consideration of sustainable development goals (SDGs).

We consider whether the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells may reveal the past histories of these stars as having undergone helium shell flashes (thermal pulses) on the AGB. We exploit newly available Gaia parallaxes and photometry, along with archival infrared photometry, to obtain refined estimates of the luminosities of all (12) known detached shell carbon stars. We examine the relationship between these luminosities and the estimated dynamical ages (ejection times) of the detached shells associated with the 12 stars, which range from $\sim$1000 to $\sim$30000 yr. When arranged according to detached shell dynamical age, the (implied) luminosity evolution of the known detached shell carbon stars closely follows the predicted "light curves" of individual thermal pulses obtained from models of AGB stars. The comparison between data and models suggests that detached shell carbon stars are descended from $\sim$2.5-4.0 $M_\odot$ progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses.

We investigate a kinematic scaling relation between the baryonic mass and the flat velocity dispersion, i.e. mass-velocity dispersion relation (MVDR), from the brightest cluster galaxies (BCGs) to the galaxy clusters. In our studies, the baryonic mass of BCGs is mainly estimated by photometry. The velocity dispersion profiles are explored with the integrated field unit (IFU) by Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). For the first time, we reveal two significant results with 54 MaNGA BCGs: (1) the flat velocity dispersion profiles; (2) a tight empirical relation on the BCG-cluster scale together with cluster samples, i.e., MVDR, $\log(M_\mathrm{bar}/M_\odot)=4.1^{+0.1}_{-0.1}\log(\sigma_{\mathrm{los}}/\mathrm{km}\,\mathrm{s}^{-1})+1.6^{+0.3}_{-0.3}$, with a tiny lognormal intrinsic scatter of $10^{+2}_{-1}\%$. This slope is identical to the acceleration relation in galaxy clusters, which is reminiscent of the spiral galaxies, albeit at a larger characteristic acceleration scale. The residuals of the MVDR represent a Gaussian distribution, displaying no correlations with four properties: baryonic mass, scale length, surface density, and redshift. Notably, the MVDR on the BCG-cluster scale provides a strict test, which disfavors the general prediction of the slope of three in the dark matter model.

Systematic surveys of massive clumps have been carried out to study the conditions leading to the formation of massive stars. These clumps are typically at large distances and unresolved, so their physical properties cannot be reliably derived from the observations alone. Numerical simulations are needed to interpret the observations. To this end, we generate synthetic Herschel observations using our large-scale star-formation simulation, where massive stars explode as supernovae driving the interstellar-medium turbulence. From the synthetic observations, we compile a catalog of compact sources following the exact same procedure as for the Hi-GAL compact source catalog. We show that the sources from the simulation have observational properties with statistical distributions consistent with the observations. By relating the compact sources from the synthetic observations to their three-dimensional counterparts in the simulation, we find that the synthetic observations overestimate the clump masses by about an order of magnitude on average due to line-of-sight projection, and projection effects are likely to be even worse for Hi-GAL Inner Galaxy sources. We also find that a large fraction of sources classified as protostellar are likely to be starless, and propose a new method to partially discriminate between true and false protostellar sources.

A repeating fast radio burst (FRB), FRB 20180916B (hereafter FRB 180916), was reported to have a 16.35-day period. This period might be related to a precession period. In this paper, we investigate two precession models to explain the periodic activity of FRB 180916. In both models, the radio emission of FRB 180916 is produced by a precessing jet. For the first disk-driven jet precession model, an extremely low viscous parameter (i.e., the dimensionless viscosity parameter $\alpha \lesssim 10^{-8}$) is required to explain the precession of FRB 180916, which implies its implausibility. For the second tidal force-driven jet precession model, we consider a compact binary consists of a neutron star/black hole and a white dwarf; the white dwarf fills its Roche lobe and mass transfer occurs. Due to the misalignment between the disk and orbital plane, the tidal force of the white dwarf can drive jet precession. We show that the relevant precession periods are several days to hundreds of days, depending on the specific accretion rates and component masses. The duration of FRB 180916 generation in the binary with extremely high accretion rate will be several thousand years.

One of the major science goals of the Visible Emission Line Coronagraph (VELC) payload aboard the Aditya-L1 mission is to map the coronal magnetic field topology and the quantitative estimation of longitudinal magnetic field on routine basis. The infrared (IR) channel of VELC is equipped with a polarimeter to carry out full Stokes spectropolarimetric observations in the Fe XIII line at 1074.7~nm. The polarimeter is in dual-beam setup with continuously rotating waveplate as the polarization modulator. Detection of circular polarization due to Zeeman effect and depolarization of linear polarization in the presence of magnetic field due to saturated Hanle effect in the Fe~{\sc xiii} line require high signal-to-noise ratio (SNR). Due to limited number of photons, long integration times are expected to build the required SNR. In other words signal from a large number of modulation cycles are to be averaged to achieve the required SNR. This poses several difficulties. One of them is the increase in data volume and the other one is the change in modulation matrix in successive modulation cycles. The latter effect arises due to a mismatch between the retarder's rotation period and the length of the signal detection time in the case of VELC spectropolarimeter (VELC/SP). It is shown in this paper that by appropriately choosing the number of samples per half rotation the data volume can be optimized. A potential solution is suggested to account for modulation matrix variation from one cycle to the other.

We have analyzed the data from a large-scale CO survey toward the northern region of the Small Magellanic Cloud (SMC) obtained with the Atacama Compact Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to comprehensively understand the behavior of CO as an H$_2$ tracer in a low-metallicity environment ($Z\sim0.2~Z_{\odot}$). The total number of mosaic fields is $\sim$8000, which results in a field coverage of 0.26$~$degree$^{2}$ ($\sim$2.9 $\times$10$^{5}$$~$pc$^2$), corresponding to $\sim$10$\%$ area of the galaxy. The sensitive $\sim$2$~$pc resolution observations reveal the detailed structure of the molecular clouds previously detected in the single-dish NANTEN survey. We have detected a number of compact CO clouds within lower H$_2$ column density ($\sim$10$^{20}$$~$cm$^{-2}$) regions whose angular scale is similar to the ACA beam size. Most of the clouds in this survey also show peak brightness temperature as low as $<$1$~$K, which for optically thick CO emission implies an emission size much smaller than the beam size, leading to beam dilution. The comparison between an available estimation of the total molecular material traced by thermal dust emission and the present CO survey demonstrates that more than $\sim$90$\%$ H$_2$ gas cannot be traced by the low-$J$ CO emission. Our processed data cubes and 2-D images are publicly available.

We investigate the low-luminosity supernova SN 2016bkv and its peculiar early-time interaction. For that, we compute radiative transfer models using the CMFGEN code. Because SN 2016bkv shows signs of interaction with material expelled by its progenitor, it offers a great opportunity to constrain the uncertain evolutionary channels leading to low-luminosity supernovae. Our models indicate that the progenitor had a mass-loss rate of (6.0 +- 2.0) x 1e-4 Msun/yr (assuming a velocity of 150 km/s). The surface abundances of the progenitor are consistent with solar contents of He and CNO. If SN 2016bkv's progenitor evolved as a single star, it was an odd red supergiant that did not undergo the expected dredge up for some reason. We propose that the progenitor more likely evolved through binary interaction. One possibility is that the primary star accreted unprocessed material from a companion and avoided further rotational and convective mixing until the SN explosion. Another possibility is a merger with a lower mass star, with the primary remaining with low N abundance until core collapse. Given the available merger models, we can only put a loose constraint on the pre-explosion mass around 10-20 Msun, with lower values being favored based on previous observational constraints from the nebular phase.

We compare the characteristics of flare-accelerated energetic electrons at the Sun with those injected into interplanetary space. We have identified 17 energetic electron events well-observed with the SEPT instrument aboard STEREO which show a clear association with a hard X-ray (HXR) flare observed with the RHESSI spacecraft. We compare the spectral indices of the RHESSI HXR spectra with those of the interplanetary electrons. Because of the frequent double-power-law shape of the in situ electron spectra, we paid special attention to the choice of the spectral index used for comparison. The time difference between the electron onsets and the associated type III and microwave bursts suggests that the electron events are detected at 1 AU with apparent delays ranging from 9 to 41 minutes. While the parent solar activity is clearly impulsive, also showing a high correlation with extreme ultraviolet jets, most of the studied events occur in temporal coincidence with coronal mass ejections (CMEs). In spite of the observed onset delays and presence of CMEs in the low corona, we find a significant correlation of about 0.8 between the spectral indices of the HXR flare and the in situ electrons. The correlations increase if only events with significant anisotropy are considered. This suggests that transport effects can alter the injected spectra leading to a strongly reduced imprint of the flare acceleration. We conclude that interplanetary transport effects must be taken into account when inferring the initial acceleration of solar energetic electron events. Although our results suggest a clear imprint of flare acceleration for the analyzed event sample, a secondary acceleration might be present which could account for the observed delays. However, the limited and variable pitch-angle coverage of SEPT could also be the reason for the observed delays.

Two dozens of radio loud active galactic nuclei (AGNs) have been observed with Urumqi 25 m radio telescope in order to search for intra-day variability (IDV). The target sources are blazars (namely flat spectrum radio quasars and BL Lac objects) which are mostly selected from the observing list of RadioAstron AGN monitoring campaigns. The observations were carried out at 4.8 GHz in two sessions of 8-12 February 2014 and 7-9 March respectively. We report the data reduction and the first results of observations. The results show that the majority of the blazars exhibit IDV in 99.9% confidence level, some of them show quite strong IDV. We find the strong IDV of blazar 1357 + 769 for the first time. The IDV at centimeter-wavelength is believed to be predominately caused by the scintillation of blazar emission through the local interstellar medium in a few hundreds parsecs away from Sun. No significant correlation between the IDV strength and either redshift or Galactic latitude is found in our sample. The IDV timescale along with source structure and brightness temperature analysis will be presented in a forthcoming paper.

I found that ASASSN-V J205543.90+240033.5 shows large-amplitude (1.2-1.4 mag) nearly sinusoidal variations with a period of 10.803(2) d and very short period variations with a period of 0.0068 d using Public Data Release of Zwicky Transient Facility observations. The only known object that shows a similar combination of nearly sinusoidal reflection variations and very short period, large-amplitude variations is the unique white dwarf pulsar AR Sco. ASASSN-V J205543.90+240033.5 appears to be very similar to AR Sco and observations at various wavelengths are desired.

Map-making is an important step for the data analysis of Cosmic Microwave Background (CMB) experiments. It consists of converting the data, which are typically a long, complex and noisy collection of measurements, into a map, which is an image of the observed sky. We present in this paper a new map-making code named PICASSO (Polarization and Intensity CArtographer for Scanned Sky Observations), which was implemented to construct intensity and polarization maps from the Multi Frequency Instrument (MFI) of the QUIJOTE (Q-U-I Joint TEnerife) CMB polarization experiment. PICASSO is based on the destriping algorithm, and is suited to address specific issues of ground-based microwave observations, with a technique that allows the fit of a template function in the time domain, during the map-making step. This paper describes the PICASSO code, validating it with simulations and assessing its performance. For this purpose, we produced realistic simulations of the QUIJOTE-MFI survey of the northern sky (approximately $\sim 20,000\,$deg$^2$), and analysed the reconstructed maps with PICASSO, using real and harmonic space statistics. We show that, for this sky area, PICASSO is able to reconstruct, with high fidelity, the injected signal, recovering all the scales with $\ell>10$ in TT, EE and BB. The signal error is better than 0.001% at $20<\ell<200$. Finally, we validated some of the methods that will be applied to the real wide-survey data, like the detection of the CMB anisotropies via cross-correlation analyses. Despite that the implementation of PICASSO is specific for QUIJOTE-MFI data, it could be adapted to other experiments.

Relativistic corrections are estimated for classical Cepheids and the Tip of the Red Giant Branch (TRGB stars), to enable future unbiased 1% measurements of Hubble's constant, $H_0$. We considered four effects: $K-$corrections, time-dilation, the apparent change of host dust extinction due to non-comoving reference frames, and the change of observed color due to redshift. Extinction-dependent $K-$corrections were computed using stellar atmosphere models applicable to giant stars for $0.005 < z < 0.03$ in HST, JWST, and 2MASS filters. The optical-NIR Wesenheit function advantageously combines filters with oppositely signed $K-$corrections and avoids complications due to host extinction. For TRGB stars, the JWST/NIRCAM F277W filter combines insensitivity to reddening with $K-$corrections $<1$% at Coma cluster distances. Missing corrections for host extinction due to circumgalactic or circumstellar material are discussed as potential systematics for TRGB distances although their impacts are insufficient to explain differences between $H_0$ based on Cepheid or TRGB supernova calibrations. All stellar standard candles require relativistic corrections to achieve an unbiased 1% $H_0$ measurement in the future. The combined relativistic correction involving $K$, redshift-Leavitt bias, and the redshift-dependence of the Wesenheit function yield an increase of the Cepheid-based $H_0$ by $0.45 \pm 0.05$ km/s/Mpc to $73.65 \pm 1.30$ km/s/Mpc and raises the tension with the {\it Planck} value from $4.2\sigma$ to $4.4\sigma$. For TRGB stars, we estimate a $\sim 0.5\%$ increase of $H_0$ reported by Freedman et al. (to $70.2\pm1.7$km/s/Mpc) and a small decrease by $-0.15\%$ for $H_0$ reported by Anand et al. (to $71.4 \pm 1.8$km/s/Mpc). The opposite sign of these corrections is due to different reddening systematics and reduces the difference between the studies by $\sim 0.46$km/s/Mpc.[abridged]

High-energy gamma rays are promising tools to constrain or reveal the nature of dark matter, in particular Weakly Interacting Massive Particles. Being well into its pre-construction phase, the Cherenkov Telescope Array (CTA) will soon probe the sky in the 20 GeV - 300 TeV energy range. Thanks to its improved energy and angular resolutions as well as significantly larger effective area when compared to the current generation of Cherenkov telescopes, CTA is expected to probe heavier dark matter, with unprecedented sensitivity, reaching the thermal annihilation cross-section at ~1 TeV. This talk will summarise the planned dark matter search strategies with CTA, focusing on the signal from the Galactic centre. As observed with the Fermi LAT at lower energies, this region is rather complex and CTA will be the first ground-based observatory sensitive to the large scale diffuse astrophysical emission from that region. We report on the collaboration effort to study the impact of such extended astrophysical backgrounds on the dark matter search, based on Fermi-LAT data in order to guide our observational strategies, taking into account various sources of systematic uncertainty.

High-frequency-peaked BL Lacs (HBLs) dominate the extragalactic TeV sky, with more than 50 objects detected by the current generation of TeV observatories. Still, the properties of TeV-emitting HBLs as a population are poorly understood due to biases introduced by the observing strategies of Cherenkov Telescopes, limiting our ability to estimate the potential contribution of TeV blazars to the diffuse neutrino, gamma-ray, and cosmic-ray background as well as their role in the late-stage evolution of active galactic nuclei. The VERITAS telescope array has designed a program to quantify and minimize observational biases by selecting a sample of 36 HBLs and measuring their TeV flux at times that are not weighted towards high-flux states. Such a survey could form the basis for a measurement of the luminosity function of TeV-emitting HBLs.

(Abriged) Blue compact galaxies (BCGs) are low-luminosity, metal-poor, gas-rich objects that form stars at high rates, excellent analogs to the high-redshift star-forming galaxy population. Being low-mass starbursts, they also constitute ideal laboratories for investigating star formation and massive stellar feedback. This work presents results from integral field spectroscopic observations of the BCG Haro 14 taken with the Multi Unit Spectroscopic Explorer (MUSE). The large MUSE field of view enables simultaneous observations of the starburst and the host galaxy. We built galaxy maps in continuum and in emission lines and generated synthetic VRI images, from which we produced color index maps and surface brightness profiles. We detected numerous clumps spread throughout the galaxy, both in continuum and in emission lines, and produced a catalog with their position, size, and photometry. This analysis allowed us to study the morphology and stellar populations of Haro 14 in detail. The stellar distribution shows a pronounced asymmetry; the intensity peak in continuum is not centered with respect to the stellar host but is displaced by about 500 pc southwest. At the position of the continuum peak we find a bright stellar cluster that with M$_{V}=-12.18$ appears as a strong super stellar cluster candidate. We also find a highly asymmetric, blue, but nonionizing stellar component that occupies almost the whole eastern part of the galaxy. We conclude that there are at least three different stellar populations in Haro 14: the current starburst of about 6 Myr; an intermediate-age component of between ten and several hundred million years; and a red and regular host of several gigayears. The pronounced lopsidedness in the continuum and also in the color maps, and the presence of numerous stellar clusters, are consistent with a scenario of mergers or interactions acting in Haro 14.

The hard to soft state transition of the outbursts in X-ray binaries (XRBs) is triggered by the rising of the mass accretion rate due to the disk instability. In order to explain the observed correlation between the hard X-ray transition luminosity and the soft X-ray peak luminosity in the soft state, we construct a magnetic disk-outflow model for the state transition in XRBs. We assume that the large-scale magnetic field in the outer thin disk is formed through inverse cascade of small-scale dynamo generated field, and it is then advected by the inner advection dominated accretion flow (ADAF), which accelerates a fraction of the gas into the outflows. During the outbursts, the heating front moves inwards, and the field strength at the heating front of the outer disk is proportional to the accretion rate of the disk. Much angular momentum of the inner ADAF is carried away by the outflows for a stronger magnetic field, which leads to a high radial velocity of the ADAF. This makes the critical mass accretion rate of the ADAF increases with the field strength, and it therefore leads to a correlation between transition luminosity and the peak luminosity in the thermal state. We found that the values of the viscosity parameter $\alpha$ of the neutron star XRBs are systematically higher for those of the black hole (BH) XRBs ($\alpha\sim 0.05-0.15$ for BHs, and $\alpha\sim 0.15-0.4$ for neutron stars). Our model predicts the transition luminosity may be higher than the peak luminosity provided $\alpha$ is sufficiently high, which is able to explain a substantial fraction of outbursts in BHXRBs not reaching the thermally dominant accretion state.

This article implements a Convolutional Neural Network (CNN)-based deep learning model for solar-wind prediction. Images from the Atmospheric Imaging Assembly (AIA) at 193\.A wavelength are used for training. Solar-wind speed is taken from the Advanced Composition Explorer (ACE) located at the Lagrangian L1 point. The proposed CNN architecture is designed from scratch for training with four years' data. The solar-wind has been ballistically traced back to the Sun assuming a constant speed during propagation, to obtain the corresponding coronal intensity data from AIA images. This forecasting scheme can predict the solar-wind speed well with a RMSE of 76.3 km\s and an overall correlation coefficient of 0.57 for the year 2018, while significantly outperforming benchmark models. The threat score for the model is around 0.46 in identifying the HSEs with zero false alarms.

We report the follow-up of 10 pulsars discovered by the Five-hundred-meter Aperture Spherical radio-Telescope (FAST) during its commissioning. The pulsars were discovered at a frequency of 500-MHz using the ultra-wide-band (UWB) receiver in drift-scan mode, as part of the Commensal Radio Astronomy FAST Survey (CRAFTS). We carried out the timing campaign with the 100-m Effelsberg radio-telescope at L-band around 1.36 GHz. Along with 11 FAST pulsars previously reported, FAST seems to be uncovering a population of older pulsars, bordering and/or even across the pulsar death-lines. We report here two sources with notable characteristics. PSR J1951$+$4724 is a young and energetic pulsar with nearly 100% of linearly polarized flux density and visible up to an observing frequency of 8 GHz. PSR J2338+4818, a mildly recycled pulsar in a 95.2-d orbit with a Carbon-Oxygen white dwarf (WD) companion of $\gtrsim 1\rm{M}_{\odot}$, based on estimates from the mass function. This system is the widest WD binary with the most massive companion known to-date. Conspicuous discrepancy was found between estimations based on NE2001 and YMW16 electron density models, which can be attributed to under-representation of pulsars in the sky region between Galactic longitudes $70^o<l<100^o$. This work represents one of the early CRAFTS results, which start to show potential to substantially enrich the pulsar sample and refine the Galactic electron density model.

Current models predict that binary interactions are a major ingredient for the formation of bipolar planetary nebulae (PNe) and pre-planetary nebulae (PPNe). Despite years of radial velocity (RV) monitoring, the paucity of known binaries amongst the latter systems is insufficient to examine this relationship in detail. In this paper, we report on the discovery of a long period (P=2654$\pm$124 d) binary at the centre of the Galactic bipolar PPN, IRAS 08005-2356 (V510 Pup) determined from long-term spectroscopic and near-infrared time series data. The spectroscopic orbit is fit with an eccentricity of 0.36$\pm$0.05 that is similar to other long period post-AGB binaries. Time resolved H$\alpha$ profiles reveal high-velocity outflows (jets) with de-projected velocities up to 231$_{-27}^{+31}$ km s$^{-1}$ seen at phases when the luminous primary is behind the jet. The outflow traced by H$\alpha$ is likely produced via accretion onto a main sequence companion for which we calculate a mass of 0.63$\pm$0.13 M$_\odot$. This discovery is one of the first cases of a confirmed binary PPN and demonstrates the importance of high-resolution spectroscopic monitoring surveys on large telescopes in revealing binarity among these systems.

Precise spectral diagnostic modelling of H~{\sc i} and He~{\sc ii} recombination spectra can constrain theoretical models which describe many astrophysical environments. Simple analytic expressions are of interest for collisional $l$-changing rate coefficients that are used by large-scale population modelling codes. We review, clarify and improve-upon the modified Pengelly \& Seaton formulae of Guzm\'an \etal We show that the recent poor results for it shown by Vrinceanu \etal are due to their misinterpretation of its usage. We also detail efficient numerical algorithms which should enable the full quantum mechanical expression for such rate coefficients to be used much more routinely by modelling codes. We illustrate with some collisional-radiative population modelling for hydrogen.

Recently, the evidence for gamma-ray emission has been found in the $Fermi$-LAT observation for the outer halo of Andromeda galaxy (M31). The dark matter (DM) annihilation offers a possible explanation on the gamma-ray radiation. In this work, we focus on the dark matter annihilation within minispikes around intermediate-mass black holes (IMBHs) with masses ranging from $100~\mathrm{M_\odot}$ to $10^6~\mathrm{M_\odot}$. When the thermal annihilation relic cross section $\left\langle \sigma v \right\rangle = 3 \times 10^{-26}~\mathrm {cm} ^{3}\;\mathrm {s} ^{-1}$ is adopted, we conduct an investigation on the population of IMBHs in the spherical halo area of M31. We find that there could be more than 65 IMBHs with masses of $ 100~ \mathrm{M_\odot}$ surrounded by the DM minispikes as the remnants of Population III stars in the M31 spherical halo, and it is almost impossible for the existence of minspikes around IMBHs with masses above $10^4~ \mathrm{M_\odot}$ which could be formed by the collapse of primordial cold gas, for both dark matter annihilation channels $b\bar{b}$ and $\tau^{+}\tau^{-}$. The properties of dark matter have been further explored with the simulation of these two scenarios for IMBHs formation.

Soft Ultra-Luminous X-ray (ULXs) sources are a subclass of the ULXs that can switch from a supersoft spectral state, where most of the luminosity is emitted below 1 keV, to a soft spectral state with significant emission above 1 keV. In a few systems, dips have been observed. The mechanism behind this state transition and the dips nature are still debated. To investigate these issues, we obtained a long XMM-Newton monitoring campaign of a member of this class, NGC 247 ULX-1. We computed the hardness-intensity diagram for the whole dataset and identified two different branches: the normal branch and the dipping branch, which we study with four and three hardness-intensity resolved spectra, respectively. All seven spectra are well described by two thermal components: a colder ($kT_{\rm bb}$ $\sim$ 0.1-0.2 keV) black-body, interpreted as emission from the photo-sphere of a radiatively-driven wind, and a hotter ($kT_{\rm disk}$ $\sim$ 0.6 keV) multicolour disk black-body, likely due to reprocessing of radiation emitted from the innermost regions. In addition, a complex pattern of emission and absorption lines has been taken into account based on previous high-resolution spectroscopic results. We studied the evolution of spectral parameters and the flux of the two thermal components along the two branches and discuss two scenarios possibly connecting the state transition and the dipping phenomenon. One is based on geometrical occultation of the emitting regions, the other invokes the onset of a propeller effect.

LS I +61$^\circ$ ~303 is one of around ten gamma-ray binaries detected so far which has a spectral energy distribution dominated by MeV-GeV photons. It is located at a distance of 2 kpc and consists of a compact object (black hole or neutron star) in an eccentric orbit around a 10-15 $M_{\odot}$ Be star, with an orbital period of 26.496 days. The binary orbit modulates the emission ranging from radio to TeV energies. A second, longer, modulation period of 1667 days (the super-orbital period) has also been detected from radio to TeV observations. The VERITAS imaging atmospheric Cherenkov telescope array has been observing LS I +61$^\circ$ ~303 since 2006, and has accumulated a dataset that fully covers the entire orbit. Increased coverage of the source in the very-high-energy band is currently underway to provide more results on the modulation pattern, super-orbital period, and orbit-to-orbit variability at the highest energies. The spectral measurements at the highest energies will reveal more information about gamma-ray production/absorption mechanisms, the nature of the compact object, and the particle acceleration mechanism. Using >150 hrs of VERITAS data, we present a detailed study of the spectral energy distribution and periodic behavior of this rare gamma-ray source type at very-high energy.

The VERITAS Imaging Air Cherenkov Telescope array (IACT) was augmented in 2019 with high-speed focal plane electronics to allow the use of VERITAS for Stellar Intensity Interferometry (SII) observations. Since that time, several improvements have been implemented to increase the sensitivity of the VERITAS Stellar Intensity Interferometer (VSII) and increase the speed of nightly data processing. This poster will describe the use of IACT arrays for performing ultra-high resolution (sub-milliarcsecond) astronomical observations at short visible wavelengths. The poster presentation will include a description of the VERITAS-SII focal plane, data acquisition, and data analysis systems. The poster concludes with a description of plans for future upgrades of the VSII instrument.

Inspired by the recent conjecture that the universe has transitioned from AdS vacua to dS vacua in the late universe made via graduated dark energy, we extend the $\Lambda$CDM model by a cosmological `constant' ($\Lambda_{\rm s}$) that switches sign at certain redshift, $z_\dagger$, and name it as $\Lambda_{\rm s}$CDM. We discuss the construction and theoretical features of this model, and find out that, when the consistency of $\Lambda_{\rm s}$CDM with the CMB data is ensured, (i) $z_\dagger\gtrsim1.1$ is implied by the condition that the universe monotonically expands, (ii) $H_0$ is inversely correlated with $z_\dagger$ and reaches $\approx74.5~{\rm km\, s^{-1}\, Mpc^{-1}}$ for $z_\dagger=1.5$, (iii) $H(z)$ presents an excellent fit to the Ly-$\alpha$ measurements provided that $z_\dagger\lesssim 2.34$. We further investigate the model constraints by using the full Planck CMB data, with and without BAO data. We find that the CMB data alone does not constrain $z_\dagger$ but CMB+BAO dataset favors the sign switch of $\Lambda_{\rm s}$ providing the constraint: $z_\dagger=2.44\pm0.29$ (68\% CL). Our analysis reveals that the lower and upper limits of $z_\dagger$ are controlled by the Galaxy and Ly-$\alpha$ BAO measurements, respectively, and the larger $z_{\dagger}$ values imposed by the Galaxy BAO data prevent the model from achieving the highest local $H_0$ measurements. In general, $\Lambda_{\rm s}$CDM (i) relaxes the $H_0$ tension while being fully consistent with the TRGB measurement, (ii) removes the discrepancy with the Ly-$\alpha$ measurements, (iii) relaxes the $S_8$ tension, and (iv) finds a better agreement with the BBN constraints of physical baryon density. We find no strong statistical evidence to discriminate between the $\Lambda_{\rm s}$CDM and $\Lambda$CDM models. However, interesting and promising features of $\Lambda_{\rm s}$CDM provide an upper edge over $\Lambda$CDM.

The results of multiwavelength observations of the very massive galaxy cluster SRGe CL2305.2-2248 detected in X-rays during the first SRG/eROSITA all-sky survey are discussed. This galaxy cluster was also detected earlier in microwave band through the observations of Sunyaev-Zeldovich effect in South Pole Telescope (SPT-CL J2305-2248), and in Atacama Cosmological Telescope (ACT-CL J2305.1-2248) surveys. Spectroscopic redshift measurement, $z=0.7573$, was measured at the Russian 6-m BTA telescope of SAO RAS, in good agreement with its photometric estimates, including a very accurate one obtained using machine learning methods. In addition, deep photometric measurements were made at the Russian-Turkish 1.5-m telescope (RTT150), which allows to study cluster galaxies red sequence and projected galaxies distribution. Joint analysis of the data from X-ray and microwave observations show that this cluster can be identified as a very massive and distant one using the measurements of its X-ray flux and integral comptonization parameter only. The mass of the cluster estimated according to the eROSITA data is $M_{500}=(9.0\pm2.6)\cdot10^{14}\, M_\odot$. We show that this cluster is found among of only several dozen of the most massive clusters in the observable Universe and among of only a few the most massive clusters of galaxies at $z>0.6$.

With n-body simulations, we model terrestrial circumbinary planet (CBP) formation with an initial surface density profile motivated by hydrodynamic circumbinary gas disc simulations. The binary plays an important role in shaping the initial distribution of bodies. After the gas disc has dissipated, the torque from the binary speeds up the planet formation process by promoting body-body interactions but also drives the ejection of planet building material from the system at an early time. Fewer but more massive planets form around a close binary compared to a single star system. A sufficiently wide or eccentric binary can prohibit terrestrial planet formation. Eccentric binaries and exterior giant planets exacerbate these effects as they both reduce the radial range of the stable orbits. However, with a large enough stable region, the planets that do form are more massive, more eccentric and more inclined. The giant planets remain on stable orbits in all our simulations suggesting that giant planets are long-lived in planetary systems once they are formed.

The non-uniform surface temperature distribution of rotating active stars is routinely mapped with the Doppler Imaging technique. Inhomogeneities in the surface produce features in high-resolution spectroscopic observations that shift in wavelength depending on their position on the visible hemisphere. The inversion problem has been systematically solved using maximum a-posteriori regularized methods assuming smoothness or maximum entropy. Our aim in this work is to solve the full Bayesian inference problem, by providing access to the posterior distribution of the surface temperature in the star. We use amortized neural posterior estimation to produce a model that approximates the high-dimensional posterior distribution for spectroscopic observations of selected spectral ranges sampled at arbitrary rotation phases. The posterior distribution is approximated with conditional normalizing flows, which are flexible, tractable and easy to sample approximations to arbitrary distributions. When conditioned on the spectroscopic observations, they provide a very efficient way of obtaining samples from the posterior distribution. The conditioning on observations is obtained through the use of Transformer encoders, which can deal with arbitrary wavelength sampling and rotation phases. Our model can produce thousands of posterior samples per second. Our validation of the model for very high signal-to-noise observations shows that it correctly approximates the posterior, although with some overestimation of the broadening. We apply the model to the moderately fast rotator II Peg, producing the first Bayesian map of its temperature inhomogenities. We conclude that conditional normalizing flows are a very promising tool to carry out approximate Bayesian inference in more complex problems in stellar physics, like constraining the magnetic properties.

Wolf-Rayet stars are amongst the rarest but also most intriguing massive stars. Their extreme stellar winds induce famous multi-wavelength circumstellar gas nebulae of various morphologies, spanning from circles and rings to bipolar shapes. This study is devoted to the investigation of the formation of young, asymmetric Wolf-Rayet gas nebulae and we present a 2.5-dimensional magneto-hydrodynamical toy model for the simulation of Wolf-Rayet gas nebulae generated by wind-wind interaction. Our method accounts for stellar wind asymmetries, rotation, magnetisation, evolution and mixing of materials. It is found that the morphology of the Wolf-Rayet nebulae of blue supergiant ancestors is tightly related to the wind geometry and to the stellar phase transition time interval, generating either a broadened peanut-like or a collimated jet-like gas nebula. Radiative transfer calculations of our Wolf-Rayet nebulae for dust infrared emission at 24 ?m show that the projected diffuse emission can appear as oblate, bipolar, ellipsoidal or ring structures. Important projection effects are at work in shaping observed Wolf-Rayet nebulae. This might call a revision of the various classifications of Wolf-Rayet shells, which are mostly based on their observed shape. Particularly, our models question the possibility of producing pre-Wolf-Rayet wind asymmetries, responsible for bipolar nebulae like NGC 6888, within the single red supergiant evolution channel scenario. We propose that bipolar Wolf-Rayet nebulae can only be formed within the red supergiant scenario by multiple/merged massive stellar systems, or by single high-mass stars undergoing additional, e.g. blue supergiant, evolutionary stages prior to the Wolf-Rayet phase.

The search for cosmic polarization rotation or birefringence in the CMB is well-motivated because it can provide powerful constraints on parity-violating new physics, such as axion-like particles. In this paper we point out that since the CMB polarization is produced at two very different redshifts - it is generated at both reionization and recombination - new parity-violating physics can generically rotate the polarization signals from these different sources by different amounts. We explore two implications of this. First, measurements of CMB birefringence are challenging because the effect is degenerate with a miscalibration of CMB polarization angles; however, by taking the difference of the reionization and recombination birefringence angles (measured from different CMB angular scales), we can obtain a cosmological signal that is immune to instrumental angle miscalibration. Second, we note that the combination with other methods for probing birefringence can give tomographic information, constraining the redshift origin of any physics producing birefringence. We forecast that the difference of the reionization and recombination birefringence angles can be competitively determined to within ~0.05 degrees for future CMB satellites such as LiteBIRD. Although much further work is needed, we argue that foreground mitigation for this measurement should be less challenging than for inflationary B-mode searches on similar scales due to larger signals and lower foregrounds.

We conduct intensity mapping to probe for extended diffuse Ly$\alpha$ emission around Ly$\alpha$ emitters (LAEs) at $z\sim2-7$, exploiting very deep ($\sim26$ mag at $5\sigma$) and large-area ($\sim4.5$ deg$^2$) Subaru/Hyper Suprime-Cam narrow-band (NB) images and large LAE catalogs consisting of a total of 1781 LAEs at $z=2.2$, $3.3$, $5.7$, and $6.6$ obtained by the HSC-SSP SILVERRUSH and CHORUS projects. We calculate the spatial correlations of these LAEs with $\sim1-2$ billion pixel flux values of the NB images, deriving the average Ly$\alpha$ surface brightness (${\rm SB_{Ly\alpha}}$) radial profiles around the LAEs. By carefully estimating systematics such as fluctuations of sky background and point spread functions, we detect diffuse Ly$\alpha$ emission ($\sim10^{-20}-10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$) at $100-1000$ comoving kpc around $z=3.3$ LAEs at the $4.1\sigma$ level and tentatively ($\sim2\sigma$) at the other redshifts, beyond the virial radius of a dark-matter halo with a mass of $10^{11}\ M_\odot$. While the observed ${\rm SB_{Ly\alpha}}$ profiles have similar amplitudes at $z=2.2-6.6$ within the uncertainties, the intrinsic ${\rm SB_{Ly\alpha}}$ profiles (corrected for the cosmological dimming effect) increase toward high redshifts. This trend may be explained by increasing hydrogen gas density due to the evolution of the cosmic volume. Comparisons with theoretical models suggest that extended Ly$\alpha$ emission around a LAE is powered by resonantly scattered Ly$\alpha$ photons in the CGM and IGM that originates from the inner part of the LAE, and/or neighboring galaxies around the LAE.

The Far-UV Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS) has been successful in maturing technologies for carrying out multi-object spectroscopy in the far-UV, including: the successful implementation of the Next Generation of Microshutter Arrays; large-area microchannel plate detectors; and an aspheric "dual-order" holographically ruled diffraction grating with curved, variably-spaced grooves with a laminar (rectangular) profile. These optical elements were used to construct an efficient and minimalist "two-bounce" spectro-telescope in a Gregorian configuration. However, the susceptibility to Lyman alpha (Ly$\alpha$) scatter inherent to the dual order design has been found to be intractably problematic, motivating our move to an "Off-Axis" design. OAxFORTIS will mitigate its susceptibility to Ly$\alpha$ by enclosing the optical path, so the detector only receives light from the grating. The new design reduces the collecting area by a factor of 2, but the overall effective area can be regained and improved through the use of new high efficiency reflective coatings, and with the use of a blazed diffraction grating. This latter key technology has been enabled by recent advancements in creating very high efficiency blazed gratings with impressive smoothness using electron beam lithography and chemical etching to create grooves in crystalline silicon. Here we discuss the derivation for the OAxFORTIS grating solution as well as methods used to transform the FORTIS holographic grating recording parameters (following the formalism of Noda et al.1974a,b), into curved and variably-spaced rulings required to drive the electron beam lithography write-head in three dimensions. We will also discuss the process for selecting silicon wafers with the proper orientation of the crystalline planes and give an update on our fabrication preparations.

We introduce a set of generic conditions for the slow contracting Universe and for a narrowed-down category of models called fast-roll models. We present general conditions for super horizon freeze-out of scalar and tensor perturbations and show that any fast-roll model satisfies them, as in the case of inflation. We are interested in the "Sourced Bounce" scenario, where perturbations are sourced by a $U(1)$ gauge field coupled to a bouncer scalar field. The requirement of a slightly red tilted scalar spectrum greatly restricts the allowed couplings between the scalar and the gauge field. We show that a viable slightly red scalar spectrum is achievable. However, within the fast-roll approximation, the tensor-to-scalar ratio is in general $r\simeq 1/9$, inconsistent with current observations. We demonstrate the general result with an explicit example we dub "Intermediate contraction". We prove that small modifications in fast-roll that do not alter the Green's functions do not result in $r<0.06$ consistent with the data for more than an e-fold. Hence, a successful "Sourced Bounce" requires a different source or a significant deviation from fast-roll.

We introduce a numerical method and python package, https://github.com/andillio/CHiMES, that simulates quantum systems initially well approximated by mean field theory using a second order extension of the classical field approach. We call this the field moment expansion method. In this way, we can accurately approximate the evolution of first and second field moments beyond where the mean field theory breaks down. This allows us to estimate the quantum breaktime of a classical approximation without any calculations external to the theory. We investigate the accuracy of the field moment expansion using a number of well studied quantum test problems. Interacting Bosonic systems similar to scalar field dark matter are chosen as test problems. We find that successful application of this method depends on two conditions: the quantum system must initially be well described by the classical theory, and that the growth of the higher order moments be hierarchical.

In our recent companion paper [arXiv:2106.00022], we pointed out a novel signature of ultralight kinetically mixed dark-photon dark matter. This signature is a quasi-monochromatic, time-oscillating terrestrial magnetic field that takes a particular pattern over the surface of the Earth. In this work, we present a search for this signal in existing, unshielded magnetometer data recorded by geographically dispersed, geomagnetic stations. The dataset comes from the SuperMAG collaboration and consists of measurements taken with one-minute cadence since 1970, with $\mathcal{O}(500)$ stations contributing in all. We aggregate the magnetic field measurements from all stations by projecting them onto a small set of global vector spherical harmonics (VSH) that capture the expected vectorial pattern of the signal at each station. Within each dark-photon coherence time, we use a data-driven technique to estimate the broadband background noise in the data, and search for excess narrowband power in this set of VSH components; we stack the searches in distinct coherence times incoherently. Following a Bayesian analysis approach that allows us to account for the stochastic nature of the dark-photon dark-matter field, we set exclusion bounds on the kinetic mixing parameter in the dark-photon dark-matter mass range $2\times10^{-18} \text{eV} \lesssim m_{A'} \lesssim 7\times10^{-17} \text{eV}$ (corresponding to frequencies $6\times 10^{-4} \text{Hz}\lesssim f_{A'} \lesssim 2\times 10^{-2} \text{Hz}$). These limits are complementary to various existing astrophysical constraints. Although our main analysis also identifies a number of candidate signals in the SuperMAG dataset, these appear to either fail or be in strong tension with various additional robustness checks we apply to those candidates: we report no robust and significant evidence for a dark-photon dark-matter signal in the SuperMAG dataset.

The twisted local magnetic field at the front or rear regions of the magnetic clouds (MCs) associated with interplanetary coronal mass ejections (ICMEs) is often nearly opposite to the direction of the ambient interplanetary magnetic field (IMF). There is also observational evidence for magnetic reconnection (MR) outflows occurring within the boundary layers of MCs. In this paper a MR event located at the western flank of the MC occurring on 2000-10-03 is studied in detail. Both the large-scale geometry of the helical MC and the MR outflow structure are scrutinized in a detailed multi-point study. The ICME sheath is of hybrid propagation-expansion type. Here the freshly reconnected open field lines are expected to slip slowly over the MC resulting in plasma mixing at the same time. As for MR, the current sheet geometry and the vertical motion of the outflow channel between ACE-Geotail-WIND spacecraft was carefully studied and tested. The main findings on MR include: (1) First-time observation of non-Petschek-type slow-shock-like discontinuities in the inflow regions; (2) Observation of turbulent Hall magnetic field associated with a Lorentz force deflected electron jet; (3) Acceleration of protons by reconnection electric field and their back-scatter from the slow shock-like discontinuity; (4) Observation of relativistic electron near the MC inflow boundary/separatrix; these electron populations can presumably appear as a result of non-adiabatic acceleration, gradient B drift and via acceleration in the electrostatic potential well associated with the Hall current system; (5) Observation of Doppler shifted ion-acoustic and Langmuir waves in the MC inflow region.

Forbush decrease (FD), discovered by Scott E. Forbush about 80 years ago, is reffered to as the non-repetitive short-term depression in galactic cosmic ray (GCR) flux, presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field (IMF). It is the most spectacular variability in the GCR intensity which appear to be the compass for investigators seeking solar-terrestrial relationships. The method of selection and validation of FD events are very important to cosmic ray scientists. We have deployed a new computer software to determine the amplitude and timing of FDs from daily-averaged cosmic ray (CR) data at OULU neutron monitor station. The code selected 230 FDs between 1998 and 2002. In an attempt to validate the new FD automated catalog, the relationship between the amplitude of FDs, and IMF, solar wind speed (SWS) and geomagnetic storm indices (Dst, kp, ap) is tested here. A two-dimensional regression analysis indicates significant linear relationship between large FDs (CR(\%) $\leq-3$) and solar wind data and geomagnetic storm indices in the present sample. The implications of the relationship among these parameters are discussed.

The departure of particle distributions from the Maxwellian is commonly observed in space plasmas. These non-Maxwellian distributions which are typical for plasmas that are not in thermal equilibrium, can be modeled with $\kappa$-distribution. Kinetic simulations of quasi-parallel collisionless shocks show that proton distribution is a composite of thermal, suprathermal, and non-thermal parts. By using particle-in-cell shock simulations, we show that $\kappa$-distribution adequately fits thermal and suprathermal parts together, as a single continuous distribution in early proton spectra. We derive suprathermal proton distribution directly from the generalized entropy of non-extensive statistical mechanics, and show that thermal and suprathermal populations are both naturally embedded in $\kappa$-distribution. We find that the index $\kappa$ of the distribution increases with the distance from the shock, following the decrease in suprathermal part. The non-equilibrium plasma distribution which is continuously being enriched with suprathermal particles at the reforming shock barrier, reaches the thermal equilibrium in the far downstream. The suprathermal part completely fades there, and the shape of proton distribution becomes a Maxwellian from which directly emerges a power-law.

Neutron star tidal deformability extracted from gravitational wave data provides a novel probe to the interior neutron star structures and the associated nuclear equation of state (EOS). Instead of the popular composition of nucleons and leptons in neutron stars, we include hyperons and examine the role of hyperons in the tidal deformability and its impact on the symmetry energy in a relativistic mean-field approach with the density-dependent parametrizations. The hyperons are found to have significant impact on the deformability, correlated sensitively with the onset density and fraction of hyperons in neutron star matter. Moderately lower onset density of hyperons can yield considerable modification to the tidal deformability and shift its inference on the nuclear EOS. The future measurements of the tidal deformability at multi-fiducial star masses are anticipated to lift the degeneracy between the contributions from the hyperon component and symmetry energy.

Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.