Swift observations of the bright uncatalogued X-ray transient MAXI J1535-571

Abstract

The black hole candidate MAXI J1535-571 is a recently discovered X-ray transient. We report on the monitoring observations of Swift Gamma-Ray Burst Mission during outburst. The source transits from the hard state to the intermediate state, and reaches the soft state; near the end of the outburst, it returns to the hard state passing through the low intermediate state, following a typical Q-shaped loop in the hardness-intensity diagram. During the high intermediate state, detailed spectral analyses using a multitemperature disc model reveal that the disc luminosity is flatter than the inner disc temperature to the fourth power, and the disc temperature profile varies as the disc radius raised to the power of -0.5, consistent with the behavior of a slim disc, implying that the disc structure has been modified due to the high luminosity of similar to 10(39) ergs(-1). Meanwhile, the column density increases with the Eddington ratio, suggesting that the outflow matters are driven by radiation pressure due to the high accretion rate.