GCN Circular 33472

At the time of the very bright GRB 230307A (GCN #33405, GCN #33406, GCN 
#33407, GCN #33410, GCN #33411, GCN #33412, GCN #33413, GCN #33414, GCN 
#33415, GCN #33416, GCN #33418, GCN #33419, GCN #33424, GCN #33425, GCN 
#33427, GCN #33428, GCN #33429, GCN #33430, GCN #33431, GCN #33434, GCN 
#33437, GCN #33438, GCN #33439, GCN #33442, GCN #33443, GCN #33444, GCN 
#33447, GCN #33448, GCN #33449, GCN #33453, GCN #33459, GCN #33461, GCN 
#33465, GCN #33466), INTEGRAL was pointing 74 deg from the GRB 
direction. Such an exceptionally high flux lead to a detection in 
various ratemeters of INTEGRAL often causing saturation. From moderately 
saturated SPI-ACS observation, we can estimate a likely close lower 
limit on the total flux in 75 - 2000 keV energy range at the level of 
0.0015 erg cm-2 s-1 in the time range T0 to T0+130.0s where T0 = 
2023-03-07T15:44:07.

We note that despite the GRB brightness, both SPI-ACS and PICsIT 
observations do not reveal early afterglow and no emission past 
T0+129~s, with an approximate upper limit on average 75-2000 keV flux 
between T0+129s and of T0+259 s at the level of 5.8e-09 erg cm-2 s-1 
(see also GCN#33431).

A ToO pointed observation was carried out from 2023-03-08 11:35:00 (T0 + 
19.8 hours) to 2023-03-09 02:18:20 (T0 + 34.6 hours) with a total 
exposure time of 28.2 ks (for ISGRI). Since the observation was 
scheduled when the refined IPN localization was not yet available, the 
position of the candidate GRB optical and X-ray afterglow ((GCN #33429, 
GCN #33439, GCN #33443, GCN #33447, GCN #33449, GCN #33459, GCN #33465)) 
was observed at an offset of 1.3 deg, reducing somewhat the effective 
exposure of JEM-X compared to an optimal pointing.

We do not find any significant signal, and put a limit on any source 
within the IPN error box, including also to the possible X-ray and 
optical afterglow, at the level of 4.2e-11 erg cm-2 s-1 in the 3-200 keV 
energy range, assuming a powerlaw spectrum with a slope of -2. This 
limit is about 1.2 orders of magnitude lower than the detection in the 
case of GRB 221009A.

We are grateful to the INTEGRAL Ground Segment team for the quick 
scheduling of these observations.

All of the results except PICsIT were produced MMODA platform 
(https://www.astro.unige.ch/mmoda/).