Swift Spectroscopy of the Black Hole GS 1354-645 in Outburst

ATel #7614; J. M. Miller, M. T. Reynolds (University of Michigan), J. Kennea (Penn State)
on 10 Jun 2015; 16:21 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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We report on a Swift/XRT observation of GS 1354-645 obtained in windowed timing mode. The 0.45 ks observation started on 2015-06-10 at 09:55:15. The fast read-out of windowed timing mode prevents photon pile-up and yields robust spectra and flux measurements for bright sources.

After binning to require 10 counts per bin, an absorbed power-law is found to provide an acceptable fit to the 1-10 keV spectrum. The column density is measured to be N_H = 6.4 +/- 1.2 E+21 cm^-2, the power-law index is found to be 1.5 +/- 0.1 (1 sigma errors). This model implies an absorbed flux of 1.7 E-10 erg/s/cm^2 in the 0.5-10.0 keV band, or an unabsorbed flux of 2.25 E-10 erg/s/cm^2. The luminosity of the source is then 1.7 E+37 (d/25 kpc)^2 erg/s (Casares et al. 2009).

The windowed timing mode spectrum is softer, and the source is more luminous than implied by the photon counting mode XRT observation, as anticipated in ATEL #7612. The source is currently 1500 times brighter than its quiescent level (Reynolds & Miller 2011).

Continued X-ray observations, and radio observations, are strongly encouraged.

Casares, J., et al., 2009, ApJS, 181, 238
Reynolds, M. T., & Miller, J. M., 2011, ApJ, 734, L17