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The black hole X-ray transient GRS 1739-278 is still active

ATel #10137; Zhen Yan, Wenfei Yu (Shanghai Astronomical Observatory )
on 28 Feb 2017; 12:14 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Zhen Yan (zyan@shao.ac.cn)

Subjects: X-ray, Black Hole, Transient

INTEGRAL detected a new outburst of the black hole X-ray transient GRS 1739-278 in September 2016 (ATel#9517), which was confirmed by the following Swift observation (ATel #9541). Then a Swift monitoring campaign had been carried out to track the evolution of the outburst until November 2016, when GRS 1739-278 was not observable due to the Sun constraint. All the Swift/XRT spectra the monitoring campaign were well-fitted with an absorbed power law spectral component and the power indices varied in the range 1.4-2.0, which indicates the source stayed in the hard state through all the observations (see also Mereminskiy et al. 2016). The Swift observations covered the decay phase of the outburst reported in Mereminskiy et al. (2016), and the rise phase of the other one. The unabsorbed 0.3-10 keV flux varied in the range of 0.2-2.7E10^-10 erg s^-1 cm^-2, which indicates that it is a faint outburst for a distance of 7.25 kpc (Greiner et al. 1996).

Recently, immediately after the black hole transient came out of Sun constraint, we proposed a Swift/XRT ToO observation and detected the source on February 23, 2017. The X-ray spectrum was well-fitted by an absorbed power law spectral component with a power index ~ 1.8+-0.5, which indicates the source is still in the hard state. The unabsorbed 0.3-10 keV flux is 1.2+-0.2E10^-11 erg s^-1 cm^-2. It is not yet known if the source is on the way to quiescence or in a new outburst. We encourage follow-up observations of this source at all wavelengths.

We would like to thank the Swift team for scheduling these observations.