Long-term multi-wavelength studies of GRS 1915+105 I. A high-energy and mid-infrared focus with RXTE, INTEGRAL, and Spitzer

摘要

To date, mid-infrared properties of Galactic black hole binaries have barelybeen investigated in the framework of multi-wavelength campaigns. Yet, studiesin this spectral domain are crucial to get complementary information on thepresence of dust and/or on the physical processes such as dust heating andthermal bremsstrahlung. Here, we report a long-term multi-wavelength study ofthe microquasar GRS 1915+105. On the one hand, we aimed at understanding theorigins of the mid-infrared emission, and on the other hand, at searching forcorrelation with the high-energy and/or radio activities. We observed thesource at several epochs between 2004 and 2006 with the photometer IRAC andspectrometer IRS, both mounted on the Spitzer Space Telescope. When available,we completed our set of data with quasi-simultaneous RXTE and INTEGRALhigh-energy and/or Ryle radio observations from public archives. We thenstudied the mid-infrared environment and activities of GRS 1915+105 throughspectral analysis and broad band fitting of its radio to X-ray spectral energydistributions. We detected polycyclic aromatic hydrocarbon molecules in all butone IRS spectra of GRS 1915+105 which unambiguously proves the presence of adust component, likely photoionised by the high-energy emission. We also arguethat this dust is distributed in a disc-like structure heated by the companionstar, as observed in some Herbig Ae/Be and isolated cool giant stars. Moreover,we show that some of the soft X-ray emission emanating from the inner regionsof the accretion disc is reprocessed and thermalised in the outer part. Thisleads to a mid-infrared excess that is very likely correlated to the soft X-rayemission. We exclude thermal bremsstrahlung as contributing significantly inthis spectral domain.