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Nustar and integral observations of a low/hard state of 1E1740.7-2942

  • Author(s): Natalucci, L
  • Tomsick, JA
  • Bazzano, A
  • Smith, DM
  • Bachetti, M
  • Barret, D
  • Boggs, SE
  • Christensen, FE
  • Craig, WW
  • Fiocchi, M
  • Fürst, F
  • Grefenstette, BW
  • Hailey, CJ
  • Harrison, FA
  • Krivonos, R
  • Kuulkers, E
  • Miller, JM
  • Pottschmidt, K
  • Stern, D
  • Ubertini, P
  • Walton, DJ
  • Zhang, WW
  • et al.

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. © 2014. The American Astronomical Society. All rights reserved.

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