GCN Circular 33565

P K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. 
Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao 
(IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat 
CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 
2021, JApA, 42, 73) showed the detection of a long GRB 230404A which was 
also detected by Fermi (Fermi GBM Team, GCN 33564
Not found
 
 
).

The source was detected in the 20-200 keV energy range. The light curve 
peaks at 2023-04-04 23:00:07.5 UTC. The measured peak count rate 
associated with the burst is 75 (+30, -10) counts/s above the background 
in the combined data of two quadrants (out of four), with a total of 753 
(+275, -296) counts. The local mean background count rate was 224 (+1, 
-2) counts/s. Using cumulative rates, we measure a T90 of 29 (+10, -12) 
s.

The source was also detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve peaks at 2023-04-04 
23:00:07.0 UTC. The measured peak count rate associated with the burst 
is 246 (+67, -54) counts/s above the background in the combined data of 
all quadrants, with a total of 3668 (+1002, -1058) counts. The local 
mean background count rate was 1491 (+6, -6) counts/s. We measure a T90 
of 48 (+7, -12) s from the cumulative Veto light curve.

While the two T90 measurements agree within error bars, the difference 
is higher than typical measurements. There are two possibilities for 
this: firstly, there may be an intrinsic energy dependence in T90, with 
it being higher at higher energies. The second is that at the instant of 
this GRB, AstroSat was relatively close to the South Atlantic Anomaly, 
which increased the background and hence the uncertainty in our T90 
measurements.

CZTI is built by a TIFR-led consortium of institutes across India, 
including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research 
Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb