Fermi large area telescope discovery of GeV gamma-ray emission from the vicinity of snr W44

Abstract

We report the detection of GeV γ-ray emission from the molecular cloud complex that surrounds the supernova remnant (SNR) W44 using the Large Area Telescope on board Fermi. While the previously reported γ-ray emission from SNR W44 is likely to arise from the dense radio-emitting filaments within the remnant, the γ-ray emission that appears to come from the surrounding molecular cloud complex can be ascribed to the cosmic rays (CRs) that have escaped from W44. The non-detection of synchrotron radio emission associated with the molecular cloud complex suggests the decay of π0 mesons produced in hadronic collisions as the γ-ray emission mechanism. The total kinetic energy channeled into the escaping CRs is estimated to be W esc (0.3-3) × 1050 erg, in broad agreement with the conjecture that SNRs are the main sources of Galactic CRs. © 2012. The American Astronomical Society. All rights reserved.