2005/10/31 by A. Martocchia, Andrea Martocchia, Giorgio Matt +9
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #High-pressure geophysics and materials #astro-ph
paper · pdf · doi:10.1051/0004-6361:20053446
published as Astron.Astrophys.448:677,2006 · 11 pages, 7 figures. Accepted for publication on Astronomy and Astrophysics
openalex publication_date 2006/02/24 · arxiv created 2006/03/08 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
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.