Evolution of MAXI J1631–479 during the January 2019 outburst observed by INTEGRAL/IBIS

We report on a recent bright outburst from the new X-ray binary transient MAXIJ1631−479, observed in January 2019. In particular, we present the 30-200 keV anal-ysis of spectral transitions observed withINTEGRAL/IBIS during its Galactic Planemonitoring program. In the MAXI and BAT monitoring period, we observed twodifferent spectral transitions between the high/soft and low/hard states. TheINTE-GRALspectrum from data taken soon before the second transition, is best describedby a Comptonised thermal component with a temperature ofkTe∼30 keV and a highluminosity value of L2−200 keV∼3×1038erg s−1(assuming a distance of 8 kpc). Duringthe second transition, the source shows a hard, power-law spectrum. The lack of highenergy cut-off indicates that the hard X-ray spectrum from MAXI J1631−479 is dueto a non-thermal emission. Inverse Compton scattering of soft X-ray photons from anon-thermal or hybrid thermal/non-thermal electron distribution can explain the ob-served X-ray spectrum although a contribution to the hard X-ray emission from a jetcannot be determined at this stage. The outburst evolution in the hardness-intensitydiagram, the spectral characteristics and the rise and decay times of the outburst aresuggesting this system is a black hole candidate.