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Register a new userThe outburst of the X-ray nova GRS 1739-278 in September, 2016
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I.A. Mereminskiy
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During the scanning observations of the Galactic Center region in August - September 2016 we detected the new outburst of the historical X-ray nova GRS 1739-278, the black hole candidate LMXB system. In this letter we present results of INTEGRAL and Swift-XRT observations taken during the outburst. In hard X-ray band (20-60 keV) the flux from the source raised from $sim$11 to $sim$30 mCrab between 3 and 14 of September. For nearly 8 days the source has been observed at this flux level and then faded to $sim$15 mCrab. The broadband quasi-simultaneous spectrum obtained during the outburst is well described by the absorbed powerlaw with the photon index $Gamma=1.86pm0.07$ in broad energy range 0.5-150 keV, with absorption corresponding to ${N_{H}}=2.3times10^{22}$ cm$^{-2}$ assuming solar abundance. Based on this we can conclude that the source was in the low/hard state. From the lightcurve and spectra we propose that this outburst was `failed, i.e. amount of accreted matter was not sufficient to achieve the high/soft spectral state with dominant soft blackbody component as seen in normal outbursts of black hole candidates.
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We report on the X-ray spectral analysis and time evolution of GRS 1739$-$278 during its 2014 outburst based on MAXI/GSC and Swift/XRT observations. Over the course of the outburst, a transition from the low/hard state to the high/soft state and then back to the low/hard state was seen. During the high/soft state, the innermost disk temperature mildly decreased, while the innermost radius estimated with the multi-color disk model remained constant at $sim18 (frac{D}{8.5 mathrm{kpc}}) {(frac{cos i}{cos 30^{circ}})}^{-1/2}$ km, where $D$ is the source distance and $i$ is the inclination of observation. This small innermost radius of the accretion disk suggests that the central object is more likely to be a Kerr black hole rather than a Schwardzschild black hole. Applying a relativistic disk emission model to the high/soft state spectra, a mass upper limit of $18.3 mathrm{M_{odot}}$ was obtained based on the inclination limit $i<60^{circ}$ for an assumed distance of 8.5 kpc. Using the empirical relation of the transition luminosity to the Eddington limit, the mass is constrained to $4.0-18.3 mathrm{M_{odot}}$ for the same distance. The mass can be further constrained to be no larger than $9.5 mathrm{M_{odot}}$ by adopting the constraints based on the fits to the NuSTAR spectra with relativistically blurred disk reflection models (Miller et al. 2015).
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In $2016-17$, the Galactic transient black hole candidate GRS 1716-249 exhibited an outburst event after a long period of quiescence of almost 23 years. The source remained in the outbursting phase for $sim 9$ months. We study the spectral and temporal properties of the source during this outburst using archival data from four astronomy satellites, namely MAXI, Swift, NuSTAR and AstroSat. Initial spectral analysis is done using combined disk black body and power-law models. For a better understanding of the accretion flow properties, we studied spectra with the physical two component advective flow (TCAF) model. Accretion flow parameters are extracted directly from the spectral fits with the TCAF model. Low frequency quasi-periodic oscillations are also observed in the Swift/XRT and AstroSat/LAXPC data. From the nature of the variation of the spectral and temporal properties, we find the source remains in hard state during the entire outburst. It never had a transition to other states which makes this event a `failed outburst. An absence of the softer spectral states is consistent with the class of short orbital period objects, where the source belongs to. From the spectral fit, we also estimate the probable mass of GRS~1716-249 to be in the range of $4.50-5.93 M_odot$ or $5.02^{+0.91}_{-0.52} M_odot$.
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