An OH(1720 MHz) Maser and a Nonthermal Radio Source in Sgr B2(M): An SNR-Molecular Cloud Interaction Site?
Abstract
Sgr B2 is a well-known star-forming molecular cloud complex in the Galactic center region showing evidence of high energy activity as traced by the Kα neutral Fe I line at 6.4 keV, as well as GeV and TeV γ-ray emission. Here, we present Very Large Array and GMRT observations with respective resolutions of ≈ 3\buildrel{\prime\prime}\over{.} 5× 1\buildrel{\prime\prime}\over{.} 2 and 25\prime\prime × 25\prime\prime and report the detection of an OH(1720 MHz) maser, with no accompanying OH 1665, 1667, and 1612 MHz maser emission. The maser coincides with a 150 MHz nonthermal radio source in Sgr B2(M). This rare class of OH(1720 MHz) masers or the so-called supernova remnant (SNR) masers, with no main line transitions, trace shocked gas and signal the interaction of an expanding SNR with a molecular cloud. We interpret the 150 MHz radio source as either the site of a SNR-molecular gas interaction or a wind-wind collision in a massive binary system. The interaction of the molecular cloud and the nonthermal source enhances the cosmic-ray ionization rate, allows the diffusion of cosmic rays into the cloud, and produces the variable 6.4 keV line, GeV, and TeV γ-ray emission from Sgr B2(M). The cosmic-ray electron interaction with the gas in the Galactic center can not only explain the measured high values of cosmic-ray ionization and heating rates but also contribute to nonthermal bremsstrahlung continuum emission, all of which are consistent with observations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2016
- DOI:
- 10.3847/2041-8205/819/2/L35
- arXiv:
- arXiv:1603.00883
- Bibcode:
- 2016ApJ...819L..35Y
- Keywords:
-
- cosmic rays;
- Galaxy: center;
- ISM: molecules;
- ISM: supernova remnants;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 15 pages, 4 figures, ApJL (in press)