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X-Ray Observations of GRS 1915+105

Published online by Cambridge University Press:  12 April 2016

J. Greiner
Affiliation:
Max-Planck-Institute for extraterrestrial Physics, 85740 Garching, FRG
B.A. Harmon
Affiliation:
Marshall Space Flight Center, Huntsville, AL 35812, USA
W.S. Paciesas
Affiliation:
Marshall Space Flight Center, Huntsville, AL 35812, USA
E.H. Morgan
Affiliation:
Center for Space Research, MIT, Cambridge, MA 02139, USA
R.A. Remillard
Affiliation:
Center for Space Research, MIT, Cambridge, MA 02139, USA

Extract

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After the discovery of GRS 1915+105 (Castro-Tirado et al. 1992) we obtained pointed ROSAT observations every six months (12 until now). The flux in the ROSAT (0.1–2.4 keV) band is strikingly different from the simultaneous BATSE (25–50 keV) flux which was obtained by integrating the best fit power law (Fig. 1). Motivated by the different intensity evolution in the soft and hard X-ray band we have selected BATSE monitoring data collected simultaneously to ROSATdata and performed joint spectral fitting with XSPEC. As a result, we never got an acceptable fit (see Fig. 2): The BATSE power law (upper dotted line) is too steep to match the ROSAT band, and even allowing for an increased absorbing column (lower dotted line) does not solve the problem. Alternatively, neither a thermal bremsstrahlung fit (solid line) nor a power law fit (lower dash-dot line) to the ROSAT data match the BATSE flux. The upper dash-dot line is a -2.5 powerlaw which would match the BATSE data while giving too much 1–2 keV emission. A similar, but less stringent result is obtained when folding the best fit BATSE power law models with the HRI detector response to compare the expected count rate with the observed one. We therefore conclude that the spectrum during all simultaneous ROSAT/BATSE observations seemingly consists of two different spectral components.

Type
Part 15. Poster Papers
Copyright
Copyright © Astronomical Society of the Pacific 1997

References

Castro-Tirado, A.J., Brandt, S., Lund, N., 1992, IAU Circ. 5590 Google Scholar
Greiner, J., Morgan, E.H., Remillard, R.A., 1996, ApJ Lett. (in press)Google Scholar
Pooley, G., 1996, IAU Circ. 6411 Google Scholar