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We present the analysis of Fermi Large Area Telescope (LAT) $gamma$-ray observations of HB~21 (G89.0+4.7). We detect significant $gamma$-ray emission associated with the remnant: the flux >100 MeV is $9.4pm0.8(stat)pm1.6(syst)times10^{-11}$ erg cm$^{-2}$ s$^{-1}$. HB 21 is well modeled by a uniform disk centered at $l= 88{deg}.75pm 0{deg}.04$, $b = +4{deg}.65 pm 0{deg}.06$ with a radius of $1{deg}.19 pm 0{deg}.06$. The $gamma$-ray spectrum shows clear evidence of curvature, suggesting a cutoff or break in the underlying particle population at an energy of a few GeV. We complement $gamma$-ray observations with the analysis of the WMAP 7-year data from 23 to 93 GHz, achieving the first detection of HB 21 at these frequencies. In combination with archival radio data, the radio spectrum shows a spectral break which helps to constrain the relativistic electron spectrum, hence parameters of simple non-thermal radiation models. In one-zone models multiwavelength data favor the origin of $gamma$ rays from nucleon-nucleon collisions. A single population of electrons cannot produce both $gamma$ rays through bremsstrahlung and radio emission through synchrotron radiation. A predominantly inverse-Compton origin of the $gamma$-ray emission is disfavored because it requires lower interstellar densities than are inferred for HB 21. In the hadronic-dominated scenarios accelerated nuclei contribute a total energy of $sim 3 times10^{49}$ ergs, while in a two-zone bremsstrahlung-dominated scenario the total energy in accelerated particles is $sim1times10^{49}$ ergs.
In this paper we report on the detection of $gamma$-ray emission coincident with the Galactic supernova remnant Kesteven 79 (Kes 79). We analysed approximately 52 months of data obtained with the Large Area Telescope (LAT) on board the Fermi Gamma-ra
To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources d
We present an analysis of gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region around SNR S147 (G180.0-1.7). A spatially extended gamma-ray source detected in an energy range of 0.2--10
We investigate the nature of the accelerated particles responsible for the production of the gamma-ray emission observed from the middle-aged supernova remnant (SNR) HB 21. The analysis of more than nine years of Fermi LAT data leads to the observati
The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). $gamma$-ray o