Issue |
Astron. Astrophys. Suppl. Ser.
Volume 128, Number 1, February II 1998
|
|
---|---|---|
Page(s) | 145 - 151 | |
DOI | https://doi.org/10.1051/aas:1998131 | |
Published online | 15 February 1998 |
X-ray variability of GRS 1915+105 during the low-hard state observed with the Indian X-ray astronomy experiment (IXAE)
1
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
2
ISRO Satellite Centre, Airport Road, Vimanpura P.O. Bangalore 560 017, India
Send offprint request to: B. Paul
Received:
9
June
1997
Accepted:
20
June
1997
The galactic superluminal transient X-ray source GRS 1915+105 was
observed with the pointed proportional counters (PPCs) onboard the
Indian satellite IRS-P3 during 1996 July 23-27. We report here
details of the behavior of this source during the relatively quiet
and low luminosity state. Large intensity variations by a factor
of 2 to 3, generally seen in black-hole candidates, are observed
at a time scale of 100 ms to few seconds. No significant variation
is detected over larger time scale of minute or more. The intensity
variations are described as sum of shots in the light curve, and
the number distribution of the shots are found to be exponential
function of the fluence and duration of the shots. The cross
correlation spectrum between keV and
keV X-rays is
found to have asymmetry signifying a delay of the hard X-rays by
about 0.2 to 0.4 s. This supports the idea of hard X-rays being
generated by Compton up-scattering from high energy clouds near
the source of soft X-rays. Very strong and narrow quasi periodic
oscillations in the frequency range 0.62 to 0.82 Hz are observed.
We discuss about a model which explains a gradual change in the
QPO frequencies with corresponding changes in the mass accretion
rate of the disk.
Key words: accretion, accretion disks / black hole physics / X-rays: stars / stars: individual: GRS 1915+105
© European Southern Observatory (ESO), 1998