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Register a new userPeriods of two enigmatic black hole candidates GRS 1915+105 and IGR J17091-3624
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Galactic black hole candidates GRS 1915+105 and IGR J17091-3624 have many similarities in their light curves and spectral properties. However, very little is known about the orbital elements of their companions. In case the orbits are eccentric, tidal forces by the black hole on the companion can cause modulations of accretion rates in orbital time scale. We look for these modulations in the light curves of these two objects and find that their periodicities are around 28.3 d (29.0 d) and 32.2 d respectively. Eccentricities are at the most 0.071 and 0.46 respectively. We conclude that both these objects have long orbital periods and are eccentric. This could be a reason why light curves have several similar variability class transitions as reported in the literature.
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We report on the long-term monitoring campaign of the black hole candidate IGR J17091-3624 performed with INTEGRAL and Swift during the peculiar outburst started on January 2011. We have studied the two month spectral evolution of the source in detail. Unlike the previous outbursts, the initial transition from the hard to the soft state in 2011 was not followed by the standard spectral evolution expected for a transient black hole binary. IGR J17091-3624 showed pseudo periodic flare-like events in the light curve, closely resembling those observed from GRS 1915+105. We find evidence that these phenomena are due to the same physical instability process ascribed to GRS 1915+105. Finally we speculate that the faintness of IGR J17091-3624 could be not only due to the high distance of the source but to the high inclination angle of the system as well.
We present here the main characteristics of the BHC IGR J17091-3624 outbursts occurred several times since 1994. Since 2003, the source has been extensively observed by INTEGRAL and Swift. In particular, we report results on the last 2011 outburst that showed a rare variability behaviour observed before only in the galactic BH GRS 1915+105 but at a different level of flux. Several hypotheses have been proposed in order to explain this particular behaviour. They are all discussed here, in the light of their apparent contradiction. Finally, based on all available informations, we attempt to give an overall view of this enigmatic source and we speculate on the evolutionary state of the binary system.
We performed an analysis of all RXTE observations of the Low Mass X-ray Binary and Black Hole Candidate IGR J17091-3624 during the 2011-2013 outburst of the source. By creating lightcurves, hardness-intensity diagrams and power density spectra of each observation, we have created a set of 9 variability `classes that phenomenologically describe the range of types of variability seen in this object. We compare our set of variability classes to those established by Belloni et al. (2000) to describe the similar behaviour of the LMXB GRS 1915+105, finding that some types of variability seen in IGR J17091-3624 are not represented in data of GRS 1915+105. We also use all available X-ray data of the 2011-2013 outburst of IGR J17091-3624 to analyse its long-term evolution, presenting the first detection of IGR J17091-3624 above 150 keV as well as noting the presence of `re-flares during the latter stages of the outburst. Using our results we place new constraints on the mass and distance of the object, and find that it accretes at <33% of its Eddington limit. As such, we conclude that Eddington-limited accretion can no longer be considered a sufficient or necessary criterion for GRS 1915+105-like variability to occur in Low Mass X-Ray Binaries.
IGR J17091--3624 is a transient galactic black hole which has a distinct quasi-periodic variability known as `heartbeat, similar to the one observed in GRS 1915+105. In this paper, we report the results of $sim 125$ ks textit{AstroSat} observations of this source during the 2016 outburst. For the first time a double peaked QPO (DPQ) is detected in a few time segments of this source with a difference of $delta f ~sim12$ mHz between the two peaks. The nature of the DPQ was studied based on hardness ratios and using the static as well as the dynamic power spectrum. Additionally, a low frequency (25--48 mHz) `heartbeat single peak QPO (SPQ) was observed at different intervals of time along with harmonics ($50-95$ mHz). Broadband spectra in the range $0.7-23$ keV, obtained with textit{SXT} and textit{LAXPC}, could be fitted well with combination of a thermal Comptonisation and a multicolour disc component model. During textit{AstroSat} observation, the source was in the Soft-Intermediate State (SIMS) as observed with textit{Swift/XRT}. We present a comparative study of the `heartbeat state variability in IGR J17091--3624 with GRS 1915+105. Significant difference in the timing properties is observed although spectral parameters ($Gammasim2.1-2.4$ and $T_mathrm{max}sim0.6-0.8$ keV) in the broad energy band remain similar. Spectral properties of segments exhibiting SPQ and DPQ are further studied using simple phase resolved spectroscopy which does not show a significant difference. Based on the model parameters, we obtain the maximum ratio of mass accretion rate in GRS 1915+105 to that in IGR J17091--3624 as $sim25:1$. We discuss the implications of our findings and comment on the physical origin of these exotic variabilities.
We explore the nonlinear properties of IGR J17091-3624 in the line of the underlying behaviour for GRS 1915+105, following correlation integral method. We find that while the latter is known to reveal the combination of fractal (or even chaotic) and stochastic behaviours depending on its temporal class, the former mostly shows stochastic behaviour. Therefore, although several observations argue IGR J17091-3624 to be similar to GRS 1915+105 with common temporal classes between them, underlying nonlinear time series analyses offer differently. Nevertheless, the Poisson noise to $rms$ variation value for IGR J17091-3624 turns out to be high, arguing them to be Poisson noise dominated and hence may plausibly lead to suppression of the nonlinear character, if any. Indeed, it is a very faint source compared to GRS 1915+105. However, by increasing time bin some of the temporal classes of IGR J17091-3624 show deviation from stochasticity, indicating plausibility of higher fractal dimension. Along with spectral analysis, overall IGR J17091-3624 argues to reveal three different accretion classes: slim, Keplerian and advective accretion discs.
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