EDP Sciences
Free access
Volume 372, Number 3, June IV 2001
Page(s) 793 - 802
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20010574

A&A 372, 793-802 (2001)
DOI: 10.1051/0004-6361:20010574

Spectral differences between the radio-loud and radio-quiet low-hard states of GRS 1915+105: Possible detection of synchrotron radiation in X-rays

S. V. Vadawale1, A. R. Rao1 and S. K. Chakrabarti2

1  Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
2  S.N. Bose National Center for Basic Sciences, Salt Lake, Calcutta 700 091, India

(Received 22 December 2000 / Accepted 28 March 2001 )

The Galactic microquasar GRS 1915+105 exhibits several episodes of steady X-ray emission characterized by a hard power-law spectrum and intense Quasi Periodic Oscillations. It is known that there are two types of such low-hard states, one with steady radio emission and the other without any significant radio emission. We present the results of a detailed X-ray spectroscopic study of GRS 1915+105, using data from the Rossi X-ray Timing Explorer obtained during various episodes of the low-hard states of the source. We show that there are distinct X-ray spectral differences between the radio-quiet and radio-loud low-hard states of the source. The X-ray spectra of the radio-quiet low-hard state is best described by a model consisting of a multicolor disk-blackbody and a Comptonized component, whereas the X-ray spectra of radio-loud low-hard state requires a model consisting of three components: a multicolor disk-blackbody, a Comptonized component and a power-law, for statistically and physically acceptable fits. We attempt to model the presence of this additional power-law component as due to synchrotron radiation which is responsible for the radio and infrared radiation from the source. We show that a simple adiabatically expanding jet model for the synchrotron radiation can account for the observed X-ray flux for reasonable values of the magnetic field and the mass outflow rate. This is the first report of detection of the synchrotron radiation in the X-ray band for this source.

Key words: accretion, accretion disks -- black hole physics -- stars: winds, outflows -- stars: individual: GRS1915+105 -- X-rays: stars

Offprint request: S. V. Vadawale, santoshv@tifr.res.in

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