出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We report preliminary results of mid-infrared and X-ray observations of GRS 1915+105 that we
carried out between 2004 October 2 and 2006 June 5. Our main goals were to study its variability,
to detect the presence of dust, and to investigate the possible links between mid-infrared and X-ray
emissions.
We performed photometric and spectroscopic observations of GRS 1915+105, using the IRAC
photometer and the IRS spectrometer mounted on the Spitzer Space Telescope. We completed our
set of MIR data with quasi-simultaneous high-energy data obtained with RXTE and INTEGRAL.
In the hard state, we detect PAH emission features in the MIR spectrum of GRS 1915+105, which
prove the presence of dust in the system. The dust is confirmed by the detection in the hard state of
a warm MIR excess in the broadband spectral energy distribution of GRS 1915+105. This excess
cannot be explained by the MIR synchrotron emission from the compact jets as GRS 1915+105
was not detected at 15 GHz with the Ryle telescope. We also show that the MIR emission of
GRS 1915+105 is strongly variable; it is likely correlated to the soft X-ray emission as it increases
in the soft state. We suggest that, beside the dust emission, part of the MIR excess in the soft state
is non-thermal, and could be due either to free-free emission from an X-ray driven wind or X-ray
reprocessing in the outer part of the accretion disc.
