Letter to the Editor

Evidence for synchrotron bubbles from GRS 1915+105

¹ Space Astronomy and Instrumentation Division, ISRO Satellite Center, Bangalore 560 017, India
² Tata Institute of Fundamental Research, Homi Bhaba Road, Mumbai 400 005, India
³ National Center for Radio Astrophysics, Post Bag No. 3, Ganeshkhind, Pune 411 007, India

Corresponding author: C. H. Ishwara-Chandra, ishwar@ncra.tifr.res.in

Received: 18 February 2002
Accepted: 12 April 2002

Abstract

We present GMRT observations of the Galactic microquasar GRS 1915+105 at 1.28 GHz for 8 days from 2001 June 18 to July 1. We have seen several isolated radio flares of varying magnitudes (20–50 mJy) and durations (6–35 min) and we model them as due to adiabatically expanding synchrotron emitting clouds (synchrotron bubbles) ejected from the accretion disk. By applying this model, we provide a new method to estimate the electron power-law index p, hence the spectral index, from single frequency radio observations. This method does not require correction for the optical time delay effects which may be important in the case of optically thick radio emission. Using our estimated value of p and simultaneous multiwavelength data from literature, we have calculated the time of ejection of the synchrotron plasma and the time delays at different observed frequencies. Our estimates are in good agreement with the observed time delays.