Volume 448, Number 2, March III 2006
|Page(s)||677 - 687|
|Section||Stellar structure and evolution|
|Published online||24 February 2006|
The XMM-Newton view of GRS 1915+105
CNRS / Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: firstname.lastname@example.org
2 Dipartimento di Fisica, Università degli Studi “Roma Tre”, Via della Vasca Navale 84, 00146 Roma, Italy
3 INAF / Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
4 INAF / IASF, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
5 Astronomical Institute, Academy of Sciences, Boční II, 140 31 Prague, Czech Republic
6 INAF / IASF, Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
7 Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
8 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
Accepted: 20 October 2005
Two XMM-Newton observations of the black-hole binary GRS 1915+105 were triggered in 2004 (April 17 and 21), during a long “plateau” state of the source. We analyzed the data collected with EPIC-pn in timing and burst modes, respectively. Reflection Grating Spectrometers were used only on April 21st. The source 2–10 keV flux is ~0.6 (unabsorbed: ) 10-8 in cgs units. While the light curves show only small amplitude variations (a few percent) at timescales longer than a few seconds, a QPO is seen at about 0.6 Hz – as expected in χ variability modes of GRS 1915+105, when the phenomenological correlation with the source flux is taken into account – possibly with a harmonic signal at 1.2 Hz. The pn spectrum is well fitted without invoking thermal disk emission, on the basis of four main components: a primary one (either a simple power law or thermal Comptonization models), absorbed by cold matter with abundances different than those of standard ISM; reprocessing from an ionized disk; emission and absorption lines; and a soft X-ray excess at ~1 keV. However, the last is not confirmed by the RGS spectra, whose difference from the EPIC-pn ones lacks a fully satisfactory explanation. If real, the soft X-ray excess may be due to reflection from an optically thin, photoionized disk wind; in this case it may lead to a way to disentangle intrinsic from interstellar absorption.
Key words: black hole physics / line: formation / accretion, accretion disks / X-rays: binaries / X-rays: individuals: GRS 1915+105
© ESO, 2006
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