NuSTAR and INTEGRAL Observations of a Low/Hard State of 1E1740.7-2942
Hailey, Charles J.; Fürst, Felix; Pottschmidt, Katja; Walton, Dominic J.; Miller, Jon M.; Stern, Daniel; Kuulkers, Erik; Boggs, Steven E.; Harrison, Fiona A.; Christensen, Finn E.; Craig, William W.; Grefenstette, Brian W.; Zhang, William W.; Tomsick, John A.; Krivonos, Roman; Bachetti, Matteo; Ubertini, Pietro; Bazzano, Angela; Fiocchi, Mariateresa; Natalucci, Lorenzo; Barret, Didier; Smith, David M.
Italy, United States, France, Denmark, Spain
Abstract
The microquasar 1E1740.7-2942, also known as the "Great Annihilator," was observed by NuSTAR in the summer of 2012. We have analyzed in detail two observations taken ~2 weeks apart, for which we measure hard and smooth spectra typical of the low/hard state. A few weeks later the source flux declined significantly. Nearly simultaneous coverage by INTEGRAL is available from its Galactic Center monitoring campaign lasting ~2.5 months. These data probe the hard state spectrum from 1E1740.7-2942 before the flux decline. We find good agreement between the spectra taken with IBIS/ISGRI and NuSTAR, with the measurements being compatible with a change in flux with no spectral variability. We present a detailed analysis of the NuSTAR spectral and timing data and upper limits for reflection of the high energy emission. We show that the high energy spectrum of this X-ray binary is well described by thermal Comptonization.