An oh(1720 MHZ) maser and a nonthermal radio source insgr b2(m): An snr-molecular cloud interaction site?

F. Yusef-Zadeh, W. Cotton, M. Wardle, H. Intema

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5 Citations (Scopus)


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 and 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.

Original languageEnglish
Article numberL35
Pages (from-to)1-6
Number of pages6
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 10 Mar 2016


  • Cosmic rays
  • Galaxy: center
  • ISM: molecules
  • ISM: supernova remnants


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