Cosmic-ray acceleration and escape from supernova remnant W44 as probed by Fermi-LAT and MAGIC

The supernova remnant (SNR) and its surroundings are a prime target for studying the acceleration of cosmic rays (CRs). Several previous studies established an extended gamma-ray emission that is set apart from the radio shell of This emission is thought to originate from escaped high-energy CRs that interact with a surrounding dense molecular cloud complex. We present a detailed analysis of data with an emphasis on the spatial and spectral properties of and its surroundings. We also report the results of the observations performed with the MAGIC telescopes of the northwestern region of Finally, we present an interpretation model to explain the gamma-ray emission of the SNR and its surroundings. We first performed a detailed spatial analysis of 12,years of data at energies above 1,GeV, in order to exploit the better angular resolution, while we set a threshold of 100,MeV for the spectral analysis. We performed a likelihood analysis of 174,hours of MAGIC data above 130,GeV using the spatial information obtained with The combined spectra of and MAGIC, extending from 100,MeV to several TeV, were used to derive constraints on the escape of CRs. Using a time-dependent model to describe the particle acceleration and escape from the SNR, we show that the maximum energy of the accelerated particles has to be ≃ 40,GeV. However, our gamma-ray data suggest that a small number of lower-energy particles also needs to escape. We propose a novel model, the broken-shock scenario, to account for this effect and explain the gamma-ray emission.