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Register a new userOn the origin of the various types of radio emission in GRS 1915+105
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We investigate the association between the radio ``plateau states and the large superluminal flares in GRS 1915+105 and propose a qualitative scenario to explain this association. We identify several candidate superluminal flare events from available monitoring data on this source and analyze the contemporaneous RXTE pointed observations. We detect a strong correlation between the average X-ray flux during the ``plateau state and the total energy emitted in radio during the subsequent radio flare. We find that the sequence of events is similar for all large radio flares with a fast rise and exponential decay morphology. Based on these results, we propose a qualitative scenario in which the separating ejecta during the superluminal flares are observed due to the interaction of the matter blob ejected during the X-ray soft dips, with the steady jet already established during the ``plateau state. This picture can explain all types of radio emission observed from this source in terms of its X-ray emission characteristics.
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We propose a scenario for a periodic filling and emptying of the accretion disc of GRS 1915+105, by computing the mass transfer rate from the donor and comparing it with the observed accretion rate. The binary parameters found by Greiner et al. (2001) predict evolutionary expansion of the donor along the giant branch with a conservative mass transfer rate (1 - 2)E-8 solar masses per year. This reservoir can support the present accretion with a duty cycle 0.05 - 0.1 (the active time as a fraction of the total life time). The viscosity time scale at the circularization radius (15 solar radii from the primary 14 solar mass black hole) is identified as the recurrent quiescent time during which a new disc is formed once consumed by the BH. For small viscosity (alpha = 0.001) it equals to 300 - 400 years. The microquasar phase, with the duty cycle, will last around 10 million years ending with a long period black hole + white dwarf system.
We combine a complete sample of 113 pointed observations taken with the Rossi X-ray Timing Explorer between 1996-1999, monitoring observations taken with the Ryle telescope and the Green Bank Interferometer, and selected observations with the Very Large Array to study the radio and X-ray properties of GRS 1915+105 when its X-ray emission is hard and steady. We establish that radio emission always accompanies the hard-steady state of GRS 1915+105, but that the radio flux density at 15.2 GHz and the X-ray flux between 2-200 keV are not correlated. Therefore we study the X-ray spectral and timing properties of GRS 1915+105 using three approaches: first, by describing in detail the properties of three characteristic observations, then by displaying the time evolution of the timing properties during periods of both faint and bright radio emission, and lastly by plotting the timing properties as a function of the the radio flux density. We find that as the radio emission becomes brighter and more optically thick, 1) the frequency of a ubiquitous 0.5-10 Hz QPO decreases, 2) the Fourier phase lags between hard (11.5-60 keV) and soft (2-4.3 keV) in the frequency range of 0.01-10 Hz change sign from negative to positive, 3) the coherence between hard and soft photons at low frequencies decreases, and 4) the relative amount of low frequency power in hard photons compared to soft photons decreases. We discuss how these results reflect upon basic models from the literature describing the accretion flow around black holes and the possible connection between Comptonizing electrons and compact radio jets.
The X-ray spectrum of GRS 1915+105 is known to have a ``broad iron spectral feature in the spectral hard state. Similar spectral features are often observed in Active Galactic Nuclei (AGNs) and other black-hole binaries (BHBs), and several models have been proposed for explaining it. In order to distinguish spectral models, time variation provides an important key. In AGNs, variation amplitude has been found to drop significantly at the iron K-energy band at timescales of ~10 ks. If spectral variations of black-holes are normalized by their masses, the spectral variations of BHBs at timescales of sub-seconds should exhibit similar characteristics to those of AGNs. In this paper, we investigated spectral variations of GRS 1915+105 at timescales down to ~10 ms. This was made possible for the first time with the Suzaku XIS Parallel-sum clocking (P-sum) mode, which has the CCD energy-resolution as well as a time-resolution of 7.8 ms. Consequently, we found that the variation amplitude of GRS 1915+105 does not drop at the iron K-energy band at any timescales from 0.06 s to 63000 s, and that the entire X-ray flux and the iron feature are independently variable at timescales of hours. These are naturally understood in the framework of the ``partial covering model, in which variation timescales of the continuum flux and partial absorbers are independent. The difference of energy dependence of the variation amplitude between AGN and BHB is presumably due to different mechanisms of the outflow winds, i.e., the partial absorbers are due to UV-line driven winds (AGN) or thermally-driven winds (BHB).
We present the first detections of the black hole X-ray binary GRS 1915+105 at sub-millimetre wavelengths. We clearly detect the source at 350 GHz on two epochs, with significant variability over the 24 hr between epochs. Quasi-simultaneous radio monitoring indicates an approximately flat spectrum from 2 - 350 GHz, although there is marginal evidence for a minimum in the spectrum between 15 - 350 GHz. The flat spectrum and correlated variability imply that the sub-mm emission arises from the same synchrotron source as the radio emission. This source is likely to be a quasi-steady partially self-absorbed jet, in which case these sub-mm observations probe significantly closer to the base of the jet than do radio observations and may be used in future as a valuable diagnostic of the disc:jet connection in this source.
We present multiepoch VLBA observations of the compact jet of GRS 1915+105 conducted at 15.0 and 8.4 GHz during a {it plateau} state of the source in 2003 March-April. These observations show that the compact jet is clearly asymmetric. Assuming an intrinsically symmetric continuous jet flow, using Doppler boosting arguments and an angle to the line of sight of $theta=70degr$, we obtain values for the velocity of the flow in the range 0.3--0.5$c$. These values are much higher than in previous observations of such compact jet, although much lower than the highly relativistic values found during individual ejection events. These preliminary results are compatible with current ideas on the jet flow velocity for black holes in the low/hard state.
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