We report on a recent bright outburst from the new X-ray binary transient MAXI J1631-479, observed in January 2019. In particular, we present the 30-200 keV analysis of spectral transitions observed with INTEGRAL/IBIS during its Galactic Plane monitoring program. In the MAXI and BAT monitoring period, we observed two different spectral transitions between the high/soft and low/hard states. The INTEGRAL spectrum from data taken soon before the second transition, is best described by a Comptonised thermal component with an electron temperature of 30 keV and a high luminosity value of 3x10^38 erg/s in 2-200 keV energy range (assuming a distance of 8 kpc). During the second transition, the source shows a hard, power-law spectrum. The lack of high energy cut-off indicates that the hard X-ray spectrum from MAXI J1631-479 is due to a non-thermal emission. Inverse Compton scattering of soft X-ray photons from a non-thermal or hybrid thermal/non-thermal electron distribution can explain the observed X-ray spectrum although a contribution to the hard X-ray emission from a jet cannot be determined at this stage. The outburst evolution in the hardness-intensity diagram, the spectral characteristics and the rise and decay times of the outburst are suggesting this system is a black hole candidate.
@article{arxiv.2001.03034,
title = {Evolution of MAXI J1631-479 during the January 2019 outburst observed by INTEGRAL/IBIS},
author = {M. Fiocchi and F. Onori and A. Bazzano and A. J. Bird and A. Bodaghee and P. A. Charles and V. A. Lepingwell and A. Malizia and N. Masetti and L. Natalucci and P. Ubertini},
journal= {arXiv preprint arXiv:2001.03034},
year = {2020}
}