Extended gamma-ray emission around isolated pulsars at TeV energies, also known as TeV halos, have been found around a handful of middle-aged pulsars. The halos are significantly more extended than their pulsar wind nebulae but much smaller than the particle diffusion length in the interstellar medium. The origin of TeV halos is unknown. Interpretations invoke either local effects related to the environment of a pulsar or generic particle transport behaviors. The latter scenario predicts that TeV halos would be a universal phenomena for all pulsars. We searched for extended gamma-ray emission around 36 isolated middle-aged pulsars identified by radio and gamma-ray facilities using 2321 days of data from the High-Altitude Water Cherenkov (HAWC) Observatory. Through a stacking analysis comparing TeV flux models against a background-only hypothesis, we identified TeV halo-like emission at a significance level of $5.10\,\sigma$. Our results imply that extended TeV gamma-ray halos may commonly exist around middle-aged pulsars. This reveals a previously unknown feature about pulsars and opens a new window to identify the pulsar population that is invisible to radio, x-ray, and GeV gamma-ray observations due to magnetospheric configurations.
TeV halos are extended very-high-energy (VHE; 0.1-100 TeV) gamma-ray emission around middle-aged pulsars. So far they have only been found around isolated pulsars, but it has been suggested that they may also be powered by millisecond pulsars (MSPs). We searched for VHE gamma-ray emission from MSPs reported by radio and GeV gamma-ray observatories in 2565 days of data from the High Altitude Water Cherenkov (HAWC) Observatory. We found no significant emission from individual pulsars. By combining the likelihood profiles of all MSPs accessible to HAWC, our analysis suggests that the excess emission around the MSP population is consistent with a background. Our result suggests that MSPs are not as efficient as isolated pulsars in producing TeV halos. This finding has strong implications on the physics interpretation of the Galactic Center GeV excess and high-latitude Galactic diffuse emission.
We present an analysis of the young stellar moving group ASCC 127 using Gaia DR3 data, significantly expanding its membership to 3,971 stars -- double the number identified in previous studies. Using kinematic and distance criteria, ASCC 127 is divided into five subgroups (Groups 1-5) with ages spanning from 15 to 32 Myr. Groups 1-5 are spatially linked to the Cepheus Flare star-forming region, revealing potential evidence of four sequential star formation episodes at approximately 32 Myr, 20 Myr, 15 Myr, and 7 Myr. Through dust and gas mapping, we identify a spatial cavity extending several tens of parsecs, which may have resulted from feedback processes such as supernovae associated with earlier generations of stars in the region. This structure, along with the larger Loop III feature, indicates that feedback from massive stars likely influenced the interstellar medium (ISM). By integrating young stellar populations with ISM studies, we provide a detailed picture of the feedback-driven star formation history in the Cepheus Flare region.
Recent measurements of baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI) show hints of tension with data from the cosmic microwave background (CMB) when interpreted within the standard model of cosmology. In this short note we discuss the consequences of one solution to this tension, a small but negative spatial curvature with $R_k = 21 H_0^{-1}$, which DESI measures at $2\sigma$. We describe the physical role of curvature in cosmological distance measures tied to recombination, i.e. the CMB and BAO, and the relation to neutrino mass constraints which are relaxed to $\sum m_\nu < 0.10$ eV when curvature is allowed to deviate from zero. A robust detection of negative curvature would have significant implications for inflationary models: improved BAO measurements, particularly from future high-redshift spectroscopic surveys, will be able to distinguish curvature from other solutions to the DESI-CMB tension like phantom dark energy at high significance.