Long-term Monitoring of the Black Hole Candidate Swift J1753.5-0127 with INTEGRAL/SPI

Abstract

The black hole candidate (BHC) Swift J1753.5-0127 went into outburst in 2005 June. Rather than fade into quiescence as most BHC transients do, it has remained in a low hard spectral state for most of the ∼9 years after its outburst. Its persistent emission during the hard state is reminiscent of the black hole Cyg X-1 and the BHCs 1E 1740.7-2942 and GRS 1758-258. Thus far, hard X-ray/soft gamma-ray results have mainly focused on the 2005 flare, with a few additional observations during 2007. Here, we present results from INTEGRAL/SPI observations from 2005-2010 spanning the 22-650 keV energy range. Spectral analysis shows a weak high-energy excess (∼ 2.9σ ) above a cutoff power-law model that is well fit by a power law, suggesting an additional spectral component. Observations of Cyg X-1, 1E 1740.7-2942, and GRS 1758-258 have shown similar spectra requiring an additional high-energy component. The SPI results are compared to previously reported results for Swift J1753.5-0127 as well as observations of other sources.