Evolution of disc and corona in MAXI J1348−630 during the 2019 reflare: NICER and Insight-HXMT view

Abstract

ABSTRACT In this work, using Neutron star Interior Composition Explorer and Insight-Hard X-ray Modulation Telescope observations, we present a study of the broad-band spectral and timing evolution of the source throughout the first reflare, which occurred about 4-month after the major outburst. Our findings suggest that during the reflare, below a critical luminosity Lcrit ∼ 2.5 × 1036 (D/2.2 kpc)2 erg s−1, the scale of the corona shrinks in the radial direction, whereas the inner radius of the disc does not change considerably; however, the inner radius of the disc starts to move inward when the source exceeds the critical luminosity. We conclude that at low luminosity the increase in accretion rate only heats up the inner zone of the accretion disc without the transfer of angular momentum which occurs above a certain luminosity.