A new X-ray nova MAXI J1910-057 (= Swift J1910.2-0546) and mass accretion inflow
Abstract
We report on 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 the MAXI Gas Slit Camera (GSC) and the Swift Burst Alert Telescope (BAT) almost simultaneously. We analyzed X-ray and UV data for 270 d following the outburst onset taken by repeated MAXI scans and Swift pointing observations. The obtained X-ray light curve for the inital 90 d is roughly represented by a fast-rise and exponential-decay profile. However, it re-brightened at ∼ 110 d after the onset and finally went down below both GSC and BAT detection limits after 240 d. 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 was 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 > 2.9 M⊙ 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 modeled 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 d 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.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- October 2014
- DOI:
- 10.1093/pasj/psu060
- arXiv:
- arXiv:1406.0613
- Bibcode:
- 2014PASJ...66...84N
- Keywords:
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- accretion;
- accretion disks;
- black hole physics;
- stars: individual (MAXI J1910-057);
- X-rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 11 pages, 5 figures, PASJ in print