Speaker
Description
Extended TeV gamma-ray emission around middle-aged pulsars, commonly referred to as TeV halos, provides evidence for strongly inhibited cosmic-ray transport near these sources. The few well-established TeV halos have characteristic radii of approximately 20–30 pc and inferred diffusion coefficients 100–1000 times smaller than the Galactic average. Using 2860 days of data from the High Altitude Water Cherenkov Observatory, we detect extended TeV emission around HAWC~J0542+2315, a pulsar closely analogous to those associated with known TeV halos. Its spectral and morphological properties are consistent with a TeV-halo interpretation. However, the measured radial profile indicates a physical extent roughly $\sim3$ times as large as those of previously identified halos, implying a diffusion coefficient that is about an order of magnitude less suppressed. Independent analysis methods and systematic tests disfavor background contamination as the origin of this unusually large extension. These results provide the first evidence for a spread in the characteristic TeV-halo sizes and suggest that particle transport around pulsars may depend on local environmental conditions, potentially including the strength of turbulence and the geometry of the surrounding magnetic field.