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Abstract

We present the analysis of 9.7 years Fermi-LAT data of the middle-aged
supernova remnant W44 and the massive molecular gas complex that surrounds it.
We derived a high-quality spectral energy distribution of gamma-radiation of
the shell over three decades. The very hard spectrum below 1 GeV supports the
earlier claims regarding the hadronic origin of radiation. We also confirm the
presence of two extended $\gamma$-ray structures located at two opposite edges
of the remnant along its major axis. Based on the high-resolution gas maps, we
demonstrate that the gamma-ray structures are caused by the enhanced cosmic-ray
density rather than the gradient of the gas distribution. We argue that the
revealed cosmic-ray "clouds" suggest an anisotropic character of the escape of
high-energy particles from the shell along the magnetic field of the remnant.