LEIA observations of Swift J1727.8-1613

ATel #16210; H. Y. Liu (NAOC, CAS), D. Y. Li (NAOC, CAS), H. W. Pan (NAOC, CAS), 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), D. Y. Li (NAOC, CAS), Q. X. Li (BNU), M. J. Liu (NAOC, CAS), H. Sun (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 26 Aug 2023; 05:31 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report LEIA observations of the new X-ray transient Swift J1727.8-1613, which was initially recognized as a GRB (GRB 230824A, GCN #34536, GCN #34537), and then was confirmed as a low-mass X-ray binary candidate by the following observations in both X-ray and optical bands (ATel #16205, #16206, #16207, #16208).

The two observations of LEIA were carried out at 00:20:38 UT and 03:29:00 UT on 2023-08-25, respectively. The 0.5-4 keV spectra can be well fitted by an absorbed powerlaw plus a black body (the column density is fixed to that derived by NICER), and the flux is consistent with that given by NICER (ATel #16207). The results are listed below.

 
Time                | Unabsorbed Flux  | NH            | Photon Index |  kT          |  Exposure  
                    | (10^-8 erg/s/cm2)| (10^22 cm^-2) |              | (keV)        |  (seconds)  
2023-08-25T00:20:38 |  1.96+/-0.04     | 0.226 (fixed) | 1.35+/-0.18  |  0.25+/-0.02 |  273  
2023-08-25T03:29:00 |  2.83+/-0.03     | 0.226 (fixed) | 1.30+/-0.08  |  0.37+/-0.03 |  420  

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 SATech-01 satellite of CAS, launched on July 27, 2022.