* Astronomy

Blobrana · L

RE: GRS 1915+105

Blobrana · L

Title: GRS 1915+105 as a Galactic Analog of a Fanaroff-Riley II Quasar
Authors: Brian Punsly, Jerome Rodriguez

We study the long term time averaged kinetic luminosity, \bar{Q}, of the major flares of the Galactic microquasar GRS 1915+105 and the relationship to the intrinsic X-ray (bolometric) luminosity, L_{bol}, and scale it to that of a complete sample of SDSS/FIRST FR II quasars. If the scale invariance hypothesis for black holes (BHs) holds then we show that the expected distribution in the \bar{Q} - L_{bol} scatter plane of GRS 1915+105 is consistent with FR II quasars for distances D = 10.7 - 11 kpc. We compare the specific values of kinetic luminosity and L_{bol} during flares of GRS 1915+105 to that predicted by several 3-D MHD simulations of BH accretion flows with relativistic ejections. If FR II quasars are a scaled up version of GRS 1915+105, the data are consistent with numerical models when they contain an ergospheric disk jet and the BH spin is a/M= 0.99 or a/M=0.998 (we estimate a/M>0.984). In the framework of scale invariance of BHs, our results may imply that FR II quasars also hold rapidly rotating BHs.

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Blobrana · L

Title: The mass of the black hole in GRS 1915+105: new constraints from IR spectroscopy
Authors: D. J. Hurley, P. J. Callanan, P. Elebert, M. T. Reynolds

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large. Here we present spectroscopic analysis of medium-resolution IR VLT archival data of GRS 1915+105 in the K-band. We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radial velocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandhead emission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrain the black hole mass. We report on a possible way to measure the radial velocity utilising apparent H-band atomic absorption features and also discuss the general uncertainty of the system parameters of this well-studied object

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Blobrana · L

Title: On the harmonics of the low-frequency quasi-periodic oscillation in GRS 1915+105
Authors: E.M. Ratti, T.M. Belloni, S.E. Motta

GRS 1915+105 is a widely studied black hole binary, well known because of its extremely fast and complex variability. Flaring periods of high variability alternate with "stable" phases (the plateaux) when the flux is low, the spectra are hard and the timing properties of the source are similar to those of a number of black hole candidates in hard spectral state. In the plateaux the power density spectra are dominated by a low frequency quasi periodic oscillation (LFQPO) superposed onto a band limited noise continuum and accompanied by at least one harmonic. In this paper we focus on three plateaux, presenting the analysis of the power density spectra and in particular of the LFQPO and its harmonics. While plotting the LFQPO and all the harmonics together on a frequency-width plane, we found the presence of a positive trend of broadening when the frequency increases. This trend can shed light in the nature of the harmonic content of the LFQPO and challenges the usual interpretation of these timing features.

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Blobrana · L

Title: The complex behaviour of the microquasar GRS 1915+105 in the rho class observed with BeppoSAX. II: Time resolved spectral analysis
Authors: T. Mineo, E. Massaro, A. D'Ai, F. Massa, M. Feroci, G. Ventura, P. Casella, C. Ferrigno, T. Belloni

BeppoSAX observed GRS 1915+105 on October 2000 with a long pointing lasting about ten days. During this observation the source was mainly in the rho class characterized by busts with recurrence time between 40 and 100 s. We identified five segments in the burst structure and accumulated the average spectra of these segments during each satellite orbit. We present a detailed spectral analysis aimed at determining variations along the burst and understanding the physical process that produces them. MECS, HPGSPC and PDS spectra have been compared with several models, and under the assumption that a single model is able to fit all spectra, we find that the combination of a multi-temperature blackbody disk plus an hybrid corona is able to give a consistent physical explanation of the source behaviour. The variations of KT_el, tau, KT_in and R_in exhibit properties either of correlation or anti-correlation with the count rate in the range 1.6-10 keV. The strongest variations are detected along the burst segments: almost all parameters exhibit significant variations in the segments with the highest fluxes (Pulse) with the exception of R_in that varies continuously and reaches the maximum just before the peak. The flux of the multi-temperature disk strongly increases in the Pulse and simultaneously the corona contribution is significantly reduced. The disk luminosity increases in the Pulse and the R_in-T_in correlation can be better interpreted with the slim disk model and the reduction of the corona luminosity at the bursts could indicate its condensation on the disk.