The prompt emission of the extremely bright long-duration GRB 230307A 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 761s. The GRB was detected within the extended FoV (about 0.6 deg outside the nominal 18.6 deg x 18.6 deg 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 200s. 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 4000s and no significant emission was detected. The derived upper limit of the LEIA is around 1e-11 erg cm-2s-1 in the energy band of 0.5-4.0 keV.
The preliminary results have been posted at GCN Circular as GCN Circular 33466. Click here for more EP/LEIA GCN Circulars.