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

TL;DR

This paper reports Swift observations of the X-ray transient MAXI J1535-571, revealing its spectral state transitions, disk structure modifications consistent with a slim disk, and outflow behavior driven by radiation pressure at high luminosity.

Contribution

It provides detailed spectral analysis during the outburst, demonstrating the presence of a slim disk and radiation-pressure-driven outflows in a black hole candidate.

Findings

Disk luminosity flatter than T^4, indicating slim disk behavior

Disk temperature profile varies as radius^-0.5, consistent with slim disk models

Column density increases with Eddington ratio, suggesting radiation-driven outflows

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 multi-temperature disk model reveal that the disk luminosity is flatter than the inner disk temperature to the fourth power, and the disk temperature profile varies as the disk radius raised to the power of -0.5, consistent with the behavior of a slim disk, implying that the disk structure has been modified due to the high luminosity of ~ 10^{39} erg/s. 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.