Sv. Vadawale et al., Spectral differences between the radio-loud and radio-quiet low-hard states of GRS 1915+105: Possible detection of synchrotron radiation in X-rays, ASTRON ASTR, 372(3), 2001, pp. 793-802
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-har
d states, one with steady radio emission and the other without any signific
ant radio emission. We present the results of a detailed X-ray spectroscopi
c study of GRS 1915+105, using data from the Rossi X-ray Timing Explorer ob
tained during various episodes of the low-hard states of the source. We sho
w that there are distinct X-ray spectral differences between the radio-quie
t and radio-loud low-hard states of the source. The X-ray spectra of the ra
dio-quiet low-hard state is best described by a model consisting of a multi
color disk-blackbody and a Comptonized component, whereas the X-ray spectra
of radio-loud low-hard state requires a model consisting of three componen
ts: a multicolor disk-blackbody, a Comptonized component and a power-law, f
or statistically and physically acceptable fits. We attempt to model the pr
esence of this additional power-law component as due to synchrotron radiati
on which is responsible for the radio and infrared radiation from the sourc
e. We show that a simple adiabatically expanding jet model for the synchrot
ron radiation can account for the observed X-ray flux for reasonable values
of the magnetic field and the mass out ow rate. This is the first report o
f detection of the synchrotron radiation in the X-ray band for this source.