A Very High Energy γ-Ray Survey toward the Cygnus Region of the Galaxy

Abstract

We present results from deep observations towards the Cygnus region using 300 hours of very-high-energy (VHE) γ-ray data taken with the VERITAS Cherenkov telescope array and over seven years of high-energy γ-ray data taken with the Fermi satellite at an energy above 1 GeV. As the brightest region of diffuse γ-ray emission in the northern sky, the Cygnus region provides a promising area to probe the origins of cosmic rays. We report the identification of a potential Fermi-LAT counterpart to VER J2031+415 (TeV J2032+4130), and resolve the extended VHE source VER J2019+368 into two source candidates (VER J2018+367* and VER J2020+368*) and characterize their energy spectra. The Fermi-LAT morphology of 3FGL J2021.0+4031e (the Gamma-Cygni supernova remnant) was examined and a region of enhanced emission coincident with VER J2019+407 was identified and jointly fit with the VERITAS data. By modeling 3FGL J2015.6+3709 as two sources, one located at the location of the pulsar wind nebula CTB 87 and one at the quasar QSO J2015+371, a continuous spectrum from 1 GeV to 10 TeV was extracted for VER J2016 +371 (CTB 87). An additional 71 locations coincident with Fermi-LAT sources and other potential objects of interest were tested for VHE γ-ray emission, with no emission detected and upper limits on the differential flux placed at an average of 2.3% of the Crab Nebula flux. We interpret these observations in a multiwavelength context and present the most detailed γ-ray view of the region to date.

Cosmic-ray acceleration and escape from post-adiabatic supernova remnants

“…7 The formula was derived assuming Bohm diffusion, a magneticfield compression at the shock by √ 11 and only considering the upstream diffusion coefficient as important for the acceleration time. 8 The flux for G69.7 is taken from Abeysekara et al (2018) and a conservative distance of 7.1 kpc was adopted (Kilpatrick et al 2016). Fig.…”

AGILE Study of the Gamma-Ray Emission from the SNR G78.2+2.1 (Gamma Cygni)

“…In the same region of the shell a bright source, VER J2019+407, is visible above 10 GeV by Fermi -LAT (Fraija & Araya 2016;Ackermann et al 2017) and at TeV energies by VERITAS (Aliu et al 2013;Abeysekara et al 2018). This high-energy feature is consistent with the NW bright excess of the radio synchrotron shell.…”

“…In our models we took into account only the non-thermal contributions to the overall multiwavelength SED. Together with the AG-ILE data, we considered radio data (from Higgs 1977a; et al 1977b;Pineault & Chastenay 1990;Wendker et al 1991;Zhang et al 1997;Kothes et al 2006;Gao et al 2011) and Fermi -LAT data (from Ackermann et al 2017 andAbeysekara et al 2018). The γ-ray data from Fermi -LAT are related to an energy band for which the emission of the pulsar is naturally turned off (cut-off energy E cut−of f 2.4 GeV).…”

“…During the last few years, several works on the γray emission from this SNR (Lande et al 2012;Aliu et al 2013;Fraija & Araya 2016;Ackermann et al 2017;Abeysekara et al 2018) have been published but, because of the presence of the pulsar, all the analyses were focused at energies above 1 GeV, where its contribu- tion becomes subdominant. In this paper, the off-pulsed analysis of the γ-ray emission from the region allowed us to extract the SNR contibution down to hundreds of MeV energies.…”

“…Above 10 GeV, Fermi -LAT detected a significant extended source that is consistent with the spherical shell of the SNR detected at radio wavelengths (Lande et al 2012;Ackermann et al 2017). Furthermore, a bright γray excess is detected in the North-Western (NW) rim of the remnant at GeV (Fermi -LAT, Fraija & Araya 2016) and TeV energies (VERITAS, Aliu et al 2013;Abeysekara et al 2018), VER J2019+407 (see Fig. 4).…”