Swift XRT confirms outburst of GRS 1739-278
ATel #16100; J. A. Kennea (PSU), A. Bahramian (Curtin) and H. Negoro (Nihon U)
on 28 Jun 2023; 11:57 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Black Hole
Negoro et al. (ATEL #16097) report the MAXI detection of a possible new transient, MAXI J1741-276, or new outburst of GRS 1739-278. In response, we performed a Swift Target-of-Opportunity observation of the MAXI error circle, consisting of 4 pointings of 250-300s each, beginning at 18:02UT on June 27, 2023.
We find a bright, piled up source at the following UVOT enhanced localization: RA/Dec(J2000) = 265.66723, -27.74793, which is equivalent to:
RA(J2000) = 17h 42m 40.13s,
Dec(J2000) = 27d 44m 52.5s,
with an error radius 2.6 arc-seconds (90% confidence). This position is consistent is the source GRS 1739-278, AKA V2606 Oph, lying 1.4 arc-seconds from the catalog position.
GRS 1739-278 is in outburst, with a Swift/XRT count rate of 56.0 +/- 2.3 count/s. The spectrum is well fit by an absorbed disk blackbody (XSPEC diskbb) model with N_H = (2.3 +/- 0.4) x 10^22 cm^-2,
and kT = 0.92 +/- 0.1 keV. Additional power-law component is not required, and the power-law only fit is soft (photon index = 3.4).
Therefore we report that GRS 1739-278 is source of the MAXI outburst, and that this BH appears to be outbursting in a soft state.