2025/03/12 by Archer, A., Bangale, P., Bartkoske, J. T. +55
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2503.09778
Observations of GeV gamma-ray emission from the well-studied mixed-morphology supernova remnant (SNR) W44 by Fermi-LAT and AGILE imply that it is a site of significant cosmic ray acceleration. The spectral energy distribution (SED) derived from the GeV data suggest that the gamma-ray emission likely originates from the decay of neutral pions generated by cosmic-ray interactions. It is essential to measure the SED of W44 in the X-ray and very high energy (VHE) gamma-ray bands to verify the hadronic origin of the emission and to gauge the potential contributions from leptonic emission. We report an upper-limit of the nonthermal X-ray flux from W44 of 5 × 10-13 erg cm-2 s-1 in the 0.5 - 8.0 keV band based on ∼ 300 ks of XMM-Newton observations. The X-ray upper limit is consistent with previously estimated hadronic models, but in tension with the leptonic models. We estimate the VHE flux upper limit of ∼ 1.2 × 10-12 erg s-1 cm-2 in the 0.5 - 5.0 TeV range from W44 using data from the Very Energetic Radiation Imaging Telescope Array System (VERITAS). Our non-detection of W44 at VHE wavlengths is in agreemnent with observations from other imaging atmospheric Cherenkov telescopes (IACTs) and is perhaps consistent with the evolutionary stage of the SNR.