GCN Circular 33472
Subject
GRB 230307A: INTEGRAL upper limit on Hard X-ray afterglow
Event
Date
2023-03-13T16:54:30Z (3 years ago)
From
Volodymyr Savchenko at ISDC,U of Geneve <savchenk@in2p3.fr>
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/).