GRS 1739-278 has been at an outburst state since 2023 June 22, as detected with LEIA
ATel #16102; GRS 1739-278 has been at an outburst state since 2023 June 22, as detected with LEIA
on 28 Jun 2023; 15:36 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
Subjects: X-ray, Binary, Black Hole
Negoro et al. (ATel #16097) report the detection of a possible new outburst of GRS 1739-278 on June 26, 2023, which is confirmed by a Swift/XRT observation on June 27, 2023 (Kennea et al., ATel #16100). We report that around this position a source (RA=265.676, Dec=-27.73, 90% uncertainty=2 arcmin) was detected with LEIA at a flux of (4.6 +/- 2.0)E-9 erg/s/cm^2 at 2023-06-22T09:43:27, which is spatially consistent with GRS 1739-278. We thus suggest that GRS 1739-278 has already been at an outburst state since June 22, 2023, and exhibits flux variations by a factor of ~3.
Prior to June 7, GRS 1739-278 remained undetected in all observations of LEIA with a typical cadence of ~10 days and a typical exposure time of ~700s each, setting an upper limit of ~4e-11 erg/s/cm2. The X-ray spectrum taken at 2023-06-22T09:43:27 can be well fitted with an absorbed powerlaw with N_H=(2.2 +/- 0.7)E22 cm^-2, and a photon index of 2.9+/-0.8. The unabsorbed 0.5-4.0 keV flux was (4.6 +/- 2.0)E-9 erg/s/cm^2, which increased by a factor of ~3 about 11 hours later. There have been 8 detections of the outburst with LEIA since June 22, 2023. In the latest LEIA observation at 2023-06-25T10:00:19, the source remains in the outburst state with 0.5 - 4.0 keV unabsorbed flux to be (2.6 +/- 0.8)E-8 erg/s/cm^2.
LEIA (Zhang et al, ApJL, 941, 2) is a soft X-ray lobster-eye imager (0.5 - 4.0 keV) with a FoV of 340 square degrees aboard the experimental satellite SATech-01 of the CAS, launched on July 27, 2022. The above result is preliminary and the final result will be published elsewhere.
