M.J. Liu, Y.L. Wang, Y. Liu, C. Zhang, Z.X. Ling, H.Q. Cheng, C.Z. Cui, D.W. Fan,
H.B. Hu, J.W. Hu, M.H. Huang, C.C. Jin, D.Y. Li, J.Q. Li, H.Y. Liu, H. Sun, H.W. Pan,
W.X. Wang, Q.Y. Wu, X.P. Xu, Y.F. Xu, H.N. Yang, M. Zhang, W.D. Zhang, Z. Zhang,
D.H. Zhao, and W. Yuan (NAOC, CAS), report on behalf of the LEIA and Einstein Probe team:
The prompt emission of the extremely bright long-duration GRB 230307A (Fermi/GBM
detection: GCN 33405, 33407, 33411, 33414; GECAM-B detection: GCN 33406;
Solar Orbiter STIX detection: GCN 33410; AGILE/MCAL detection: GCN 33412, 33444;
IPN triangulation: GCN 33413; AstroSat detection: GCN 33415; BALROG
localization: GCN 33416; GRBAlpha detection: 33418, VZLUSAT-2: GCN 33424,
Konus-Wind GCN 33427, AstroSat CZIT: 33415, Swift/BAT upper limits: GCN 33431,
AstroSat LAXPC detection: GCN 33437, ASO-S/HXI detection: GCN 33438, MAXI/GSC
upper limit: GCN 33448) was detected by LEIA (Lobster Eye Imager for Astronomy)
in the soft X-ray 0.5-4 keV band during one of its monitoring observations of
the Large Magellanic Cloud.
The observation was conducted from 2023-03-07T15:43:41 (25 s earlier than the
Fermi GBM trigger time at 2023-03-07T15:44:06) to 2023-03-07T16:02:00 with
a net exposure of 761 s. The GRB was detected within the extended FoV
(about 0.6 deg outside the nominal 18.6deg x 18.6deg FoV) of LEIA, and the
on-ground calculated position is RA=60.6, Dec=-75.4, with an estimated 3-sigma
error of 10 arcmin, which is consistent with the IPN localizaition (GCN 33461).
The lightcurve shows a burst profile which peaked at 2023-03-07T15:44:13
in 0.5 - 4.0 keV, and droped quickly to a level comparable to the detection
sensitivity within about 200 s. Given that the source is outside the nominal FoV,
the estimation of the source flux is complex and subject to further
investigation and will be published later.
LEIA also conducted follow-up observations in 6 successive orbits covering
the entire IPN error box from 2023-03-09UT00:47:26 to 2023-03-09UT10:32:34.
The total good exposure is around 4000 s and no significant emission was detected.
The derived upper limit of the LEIA is around 1e-11 erg/cm^2/s
in the energy band of 0.5 - 4.0 keV.
LEIA (Zhang et al, ApJL, 941, 2) is a soft X-ray monitor (0.5 - 4.0 keV)
with a FoV of 340 square degrees aboard the SATech-01 satellite of the CAS,
launched on July 27, 2022. The above result is preliminary and the final
result will be published elsewhere.