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Register a new userMid-Infrared observations of GRS 1915+105 during plateau and flaring states
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Yael Fuchs
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We present mid-infrared (4-18 micron) observations of the microquasar GRS 1915+105 obtained with ISOCAM, the camera on board the Infrared Space Observatory (ISO), in 1996 April and 1997 October. The first observation probably occurred during a flaring event with oscillating synchrotron emission. The 1997 observation occurred a few days before a major relativistic ejection, during a plateau state of inverted-spectrum radio emission and hard quasi-stable X-ray emission. The K-M giant donor star in GRS 1915+105 cannot account for the mid-IR emission and we discuss the possible additional components depending on two absorption laws. Thermal emission from dust seems unlikely. The flat mid-IR spectrum obtained during the plateau state is likely to be synchrotron emission. It would be the first evidence of the infrared extension of the radio synchrotron emission from the compact jets, although optically thin free-free emission from an X-ray driven-wind from the accretion disc cannot be excluded.
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We report preliminary results of mid-infrared (MIR) 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 MIR 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.
We present data from the first of six monitoring Open Time observations of GRS 1915+105 undertaken with the orbiting INTEGRAL satellite. The source was clearly detected with all three X-ray and gamma-ray instruments on board. GRS 1915+105 was in a highly variable state, as demonstrated by the JEM X-2 and ISGRI lightcurves. These and simultaneous RXTE/PCA lightcurves point to a novel type of variability pattern in the source. In addition, we fit the combined JEM X-2 and ISGRI spectrum between 3-300 keV with a disk blackbody + powerlaw model leading to typical parameter values found earlier at similar luminosity levels. A new transient, IGR J19140+098, was discovered during the present observation.
GRS1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however -- referred to as the plateau state -- may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates. In order to investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105s relationship to canonical black hole candidates.
Millimeter observations of the galactic source of relativistic ejections GRS 1915+105 (Mirabel & Rodriguez 1994) are consistent with this source being at a kinematic distance D = 12.5 +/- 1.5 kpc from the Sun, behind the core of a molecular cloud at 9.4 +/- 0.2 kpc. At this distance, GRS 1915+105, frequently radiating nearly 3 x 10^{38} erg/s in the X-rays, becomes the most luminous X-ray source in the Galaxy. The total hydrogen column density Nh = 4.7 +/- 0.2 x 10^{22} cm-2 along the line of sight corresponds to a visual absorption Av = 26.5 +/- 1 magnitude. The infrared counterpart of GRS 1915+105 exhibits in the 1.2 micrometre - 2.2 micrometre band variations of nearly 1 magnitude in a few hours and of nearly 2 magnitudes over longer intervals of time. In the infrared, GRS 1915+105 is strikingly similar to SS 433, and unlike any other known stellar source in the Galaxy. The infrared resemblance in absolute magnitude, color, and time variability, between these two sources of relativistic ejections suggests that GRS 1915+105, as SS 433, consists of a collapsed object (neutron star or black hole) with a thick accretion disk in a high-mass-luminous binary system.
We present the result of multi-wavelength observations of the microquasar GRS 1915+105 in a plateau state with a luminosity of ~7.5x10^{38) erg s-1 (~40% L_Edd), conducted simultaneously with the INTEGRAL and RXTE satellites, the ESO/NTT, the Ryle Telescope, the NRAO VLA and VLBA, in 2003 April 2-3. For the first time were observed concurrently in GRS 1915+105 all of the following properties: a strong steady optically thick radio emission corresponding to a powerful compact jet resolved with the VLBA, bright near-IR emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without any cutoff in the 3-400 keV range.
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