2024/06/21 by Andrew Mummery, Jiachen Jiang, Mummery, Andrew +3
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Gamma-ray bursts and supernovae
paper · pdf · doi:10.48550/arxiv.2406.14957
On the second of November 2019 the black hole X-ray binary MAXI J0637-430 went into outburst, at the start of which it was observed in a thermal ``disc-dominated'' state. High photon energy (extending above 10 keV) observations taken by the NuSTAR telescope reveal that this thermal spectrum can not be fit by conventional two-component (disc plus corona) approaches which ignore disc emission sourced from within the plunging region of the black hole's spacetime. Instead, these models require a third ``additional'' thermal component to reproduce the data. Using new disc solutions which extend classical models into the plunging region we show that this ``additional'' thermal emission can be explained self-consistently with photons emitted from the accretion flow at radii within the innermost stable circular orbit of the black hole. This represents the second low mass X-ray binary, after MAXI J1820+070, with a detection of plunging region emission, suggesting that signatures of this highly relativistic region may well be widespread but not previously widely appreciated. To allow for a detection of the plunging region, the black hole in MAXI J0637-430 must be at most moderately spinning, and we constrain the spin to be a_\bullet < 0.86 at 99.9% confidence. We finish by discussing the observational requirements for the robust detection of this region.