A new X-ray nova MAXI J1910-057 (= Swift J1910.2-0546) and mass-accretion inflow

Abstract

We report on a long-term monitoring of a newly discovered X-ray nova, MAXI J1910-057 (= Swift J1910.2-0546), by MAXI and Swift. The new X-ray transient was first detected on 2012 May 31 by MAXI Gas Slit Camera (GSC) and Swift Burst Alert Telescope (BAT) almost simultaneously. We analyzed X-ray and UV data for 270 days since the outburst onset taken by repeated MAXI scans and Swift pointing observations. The obtained X-ray light curve for the inital 90 days is roughly represented by a fast-rise and exponential-decay profile. However, it re-brightened on the ~110 days after the onset and finally went down below both GSC and BAT detec- tion limits on the 240 day. All the X-ray energy spectra are fitted well with a model consisting of a multi-color-disk blackbody and its Comptonized hard tail. During the soft-state periods, the inner-disk radius of the best-fit model were almost constant. If the radius represents the innermost stable circular orbit of a non-spinning black hole and the soft-to-hard transitions occur at 1-4% of the Eddington luminosity, the mass of the compact object is estimated to be > 2.9Mo and the distance to be > 1.70 kpc. The inner-disk radius became larger in the hard / hard-intermediate state. This suggests that the accretion disk would be truncated. We detected an excess of the UV flux over the disk blackbody component extrapolated from the X-ray data, which can be modelled as reprocessed emission irradiated by the inner disk. We also found that the UV light curve mostly traced the X-ray curve, but a short dipping event was observed in both the UV and the X-ray bands with a 3.5-day X-ray time lag. This can be interpreted as the radial inflow of accreting matter from the outer UV region to the inner X-ray region.

arXiv comment11 pages, 5 figures, PASJ in print

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• Discovery of the black hole X-ray binary transient MAXIJ1348-630
• X-ray, Optical, and Near-infrared Monitoring of the New X-ray Transient MAXI J1820+070 in the Low/hard State
• Accretion Flow Evolution of a New Black Hole Candidate MAXI J1348-630 During the 2019 Outburst
• Discovery and state transitions of the new Galactic black hole candidate MAXI J1535-571
• Discovery of the new X-ray transient MAXI J1807+132: a Candidate of a Neutron Star Low-mass X-ray binary
• Seven reflares, a mini-outburst and an outburst : High amplitude optical variations in the black hole X-ray binary Swift J1910.2-0546
• X-ray and Optical Observations of the Black Hole Candidate MAXI J1828-249
• Accretion Flow Properties of MAXI J1910-057/Swift J1910.2-0546 During Its 2012-13 Outburst
• Evolution of broad-band SED during outburst rise in NS X-ray Nova Aql X-1
• A Dependable Distance Estimator to Black Hole Low-Mass X-ray Binaries
• Clockwise evolution in the hardness-intensity diagram of the black hole X-ray binary Swift J1910.2-0546
• Characterising the short-orbital period X-ray transient Swift J1910.2-0546
• Swift/BAT and MAXI/GSC Broadband Transient Monitor