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 \sim 110 days after the onset and finally went down below both GSC and BAT detection 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 > 2.9 M _ { \odot } 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 .