MAXI GSC observations of a spectral state transition in the black hole candidate XTE J1752-223

TL;DR

This study reports on MAXI GSC observations of XTE J1752-223, revealing a spectral state transition from low/hard to high/soft, with implications for accretion processes and jet ejection in black hole candidates.

Contribution

First detailed MAXI GSC monitoring of XTE J1752-223's spectral transition, providing insights into accretion disk formation and jet activity in black hole candidates.

Findings

Observed spectral transition from low/hard to high/soft state.

Detected potential transient radio jet during intermediate state.

Long initial low/hard state suggests slow accretion rate variation.

Abstract

We present the first results on the black hole candidate XTE J1752-223 from the Gas Slit Camera (GSC) on-board the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of the outburst reported by the Proportional Counter Array on-board the Rossi X-ray Timing Explorer on 2009 October 23, the MAXI/GSC has been monitoring this source approximately 10 times per day with a high sensitivity in the 2-20 keV band. XTE J1752-223 was initially in the low/hard state during the first 3 months. An anti-correlated behavior between the 2-4 keV and 4-20 keV bands were observed around January 20, 2010, indicating that the source exhibited the spectral transition to the high/soft state. A transient radio jet may have been ejected when the source was in the intermediate state where the spectrum was roughly explained by a power-law with a photon index of 2.5-3.0. The unusually long period in the initial low/hard state implies a slow variation in the mass accretion rate, and the dramatic soft X-ray increase may be explained by a sudden appearance of the accretion disk component with a relatively low innermost temperature (0.4-0.7 keV). Such a low temperature might suggest that the maximum accretion rate was just above the critical gas evaporation rate required for the state transition.