INTEGRAL and Swift observations of the hard X-ray transient MAXI J1828-249

¹ ISDC, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
e-mail: Ekaterina.Filippova@unige.ch
² Space Research Institute, 117997 Moscow, Russia

Received: 25 December 2013
Accepted: 16 February 2014

Abstract

In this paper we report on the observations performed with INTEGRAL and Swift of the first outburst detected from the hard X-ray transient MAXI J1828-249. During the first about two days of the outburst, the source was observed by MAXI to undergo a very rapid transition from a hard to a softer spectral state. While the hard state was not efficiently monitored because the transition occurred so rapidly, the evolution of the source outburst in the softer state was covered quasi-simultaneously in a broad energy range (0.6−150 keV) by the instruments on board INTEGRAL and Swift. During these observations, the spectra measured from the source displayed both a prominent thermal emission with temperature kT ~ 0.7 keV and a power-law hard component with a photon index Γ ~ 2.2 extending to 200 keV. The properties of the source in the X-ray domain are reminiscent of those displayed by black hole transients during the soft intermediate state, which supports the association of MAXI J1828-249 with this class of objects.