LEIA detected brightening from 4U 1907+09 and GRS 1915+105
ATel #16180; D. Y. Li (NAOC, CAS), Q. X. Li (BNU), Y. Liu (NAOC, CAS), Z. X. Ling (NAOC, CAS), C. Zhang (NAOC, CAS), H. Q. Cheng (NAOC, CAS), C. Z. Cui (NAOC, CAS), D. W. Fan (NAOC, CAS), H. B. Hu (NAOC, CAS), J. W. Hu (NAOC, CAS), M. H. Huang (NAOC, CAS), C. C. Jin (NAOC, CAS), D. M. Li (BNU), H. Y. Liu (NAOC, CAS), M. J. Liu (NAOC, CAS), H. Sun (NAOC, CAS), H. W. Pan (NAOC, CAS), C. Y. Wang (THU), W. X. Wang (NAOC, CAS), Y. L. Wang (NAOC, CAS), Q. Y. Wu (NAOC, CAS), X. P. Xu (NAOC, CAS), Y. F. Xu (NAOC, CAS), H. N. Yang (NAOC, CAS), M. Zhang (NAOC, CAS), W. D. Zhang (NAOC, CAS), W. J. Zhang (NAOC, CAS), Y. J. Zhang (THU), D. H. Zhao (NAOC, CAS) and W. Yuan (NAOC, CAS), on behalf of the LEIA and Einstein Probe team
on 10 Aug 2023; 13:53 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
Subjects: X-ray, Black Hole, Neutron Star, Transient
We report on the brightening of the X-ray binaries 4U 1907+09 and GRS 1915+105 detected by LEIA (Lobster Eye Imager for Astronomy). The detected source positions by LEIA are R.A. = 287.457 deg, DEC = 9.783 deg (uncertainty = 7.3 arcmin, 90% C.L. statistical and systematic) and R.A. = 288.787 deg, DEC = 10.937 deg (uncertainty = 2.3 arcmin, 90% C.L. statistical and systematic), which are spatially consistent with 4U 1907+09 and GRS 1915+105, respectively.
4U 1907+09 and GRS 1915+105 remained undetected in all previous observations of LEIA with a typical cadence of ~10 days and a typical exposure time of ~700s from this April, indicating an upper limit of ~ 4e-11 erg/s/cm2. 4U 1907+09 was first detected in the latest observation at 2023-08-08T11:08:49. Assuming a spectral shape of absorbed powerlaw with a photon index of 1.1 and NH of 3e+22 cm-2 (Ferrigno et al. 2022, A&A, 664, A99), its unabsorbed 0.5 - 4.0 keV flux is (3.7 +/- 1.6)e-10 erg/s/cm2, which is comparable to the brightest soft X-ray flux as recorded by Swift in an outburst in 2015 August. GRS 1915+105 was detected in the last two observations at 2023-08-08T09:34:37 and 2023-08-08T11:08:49, respectively. Assuming a spectral shape of absorbed powerlaw with NH=5e+22 cm-2 and a photon index of 1.7 (Peris et al. 2016, ApJ, 822, 60), the unabsorbed 0.5 - 4.0 keV fluxes are (7.8 +/- 2.8)e-10 erg/s/cm2 and (6.2 +/- 2.8)e-10 erg/s/cm2, respectively.
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.
