We report on results of the on-ground X-ray calibration of the Wide-field X-ray Telescope (WXT) built from novel lobster-eye micro-pore optics, onboard the Einstein Probe (EP) satellite. To fully characterize the instrumental performance and properties, a series of tests and calibrations have been carried out at different levels of devices, assemblies and the complete module before the launch of EP. In this paper, we present the calibration results of three flight model modules (FM1, FM5 and FM11) obtained during their end-to-end module calibration experiments carried out at the 100-m X-ray Test Facility (100XF) of IHEP, CAS. Measurements of the Point Spread Function (PSF), effective area, and energy response were performed for multiple incident directions and several characteristic X-ray emission line energies. Specifically, the distributions of the PSF and effective areas are found to be roughly uniform across the FoV, in large agreement with the prediction of lobster-eye optics. Their energy dependence behavior aligns well with theoretical predictions and Monte Carlo simulations. At 1.25 keV, the full width at half maximum (FWHM) of the focal spot is in range of 3-7 arcmin (a median of 4.2) and the effective area in range of 2-3 $cm^2$. Noticeably, the flight model instruments demonstrate a $\sim1.5$ arcmin spatial resolution improvement over the previously launched Lobster Eye Imager for Astronomy. The properties of the complementary metal-oxide semiconductor (CMOS) sensors were also calibrated. The gain coefficients are in range of 6.4-6.9 eV/DN. The energy resolutions are in range of 120-140 eV at 1.25 keV, meeting design requirements. These calibration results have been ingested into the first version of calibration database (CALDB) and applied to the analysis of the scientific data acquired by WXT after the launch of EP.
We present the results of low-resolution spectroscopic and densely sampled multiband simultaneous optical imaging ($ugi$ and $vrz$ bands) follow-up of supernova (SN) 2024aecx. The photometric data is supplemented with $Swift$/UVOT and ATLAS survey observations. The SN was discovered in the spiral galaxy NGC 3521 (distance $\sim$11 Mpc) within a day after the explosion. The early spectra of SN 2024aecx show a weak signature of hydrogen lines, which disappeared in $\sim$30 days after the explosion. Light curves in all bands show a distinct feature of two peaks, and the first peak is likely due to the shock cooling emission. The early phase light curve evolution of SN 2024aecx has similarity with the typical Type IIb events, but the decay rate in different bands (e.g., $\rm \Delta m_{15}$ = 1.60 $\pm$ 0.05 mag, $g$-band) is significantly faster in the post-peak phase. It attained the secondary maximum in $\sim$19 days ($g$-band) with a peak absolute magnitude of M$_{g}$= -17.94 $\pm$ 0.10 mag. The color evolution of SN 2024aecx is displaying a red-blue-red trend between days $\sim$8 to 40. The analytical model fitting to the light curves reveals an envelope mass and progenitor radii in the range of $\sim$0.03 - 0.24 $M_\odot$ and $\sim$169 - 200 $R_\odot$, respectively. Modeling of the pseudo-bolometric light curve suggests that synthesized $^{56}$Ni in the explosion was $\sim$0.15 M$_{\odot}$ with ejecta mass and kinetic energy of $\sim$0.7 M$_{\odot}$ and $\sim$0.16 x 10$^{51}$ erg, respectively. The observational properties and modeling indicate that the SN 2024aecx progenitor belongs to the extended progenitor category.
New extragalactic measurements of the cloud population-averaged star formation (SF) efficiency per freefall time $\rm\epsilon_{\rm ff}$ from PHANGS show little sign of theoretically predicted dependencies on cloud-scale virial level or velocity dispersion. We explore ways to bring theory into consistency with observations, highlighting systematic variations in internal density structure that must happen together with an increase in virial level typical towards galaxy centers. To introduce these variations into conventional turbulence-regulated SF models we adopt three adjustments motivated by the host galaxy's influence on the cloud-scale: we incorporate self-gravity and a gas density distribution that contains a broad power-law (PL) component and resembles the structure observed in local resolved clouds, we let the internal gas kinematics include motion in the background potential and let this regulate the onset of self-gravitation, and we assume that the gas density distribution is in a steady-state for only a fraction of a freefall time. The combined result is a strong reduction to $\rm\epsilon_{\rm ff}$ predicted in multi-freefall (MFF) scenarios compared to purely lognormal probability density functions and variations that are tied to the PL slope $\alpha$. The $\alpha$ needed to match PHANGS $\rm\epsilon_{\rm ff}$'s vary systematically with environment in the sense that gas sitting furthest from virial balance contains more gas at high density. With this `galaxy regulation' behavior included, our `self-gravitating' sgMFF models function similar to the original, roughly `virialized cloud' single-freefall models. However, outside disks with their characteristic regulation, the flexible MFF models may be better suited.