GRB 230309A

G. Waratkar (IITB), M. Dixit (IITB), P K. Navaneeth (IUCAA), 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 bright long GRB 230309A.

The source was clearly detected in the 20-200 keV energy range. The 
light curve peaks at 2023-03-09 12:32:21.5 UTC. The measured peak count 
rate associated with the burst is 1281.2 (+67.7 -66.2) counts/s above 
the background in the combined data of all quadrants, with a total of 
7527 (+432 -435) counts. The local mean background count rate was 479.4 
(+2.8 -3.5) counts/s. Using cumulative rates, we measure a T90 of 24.96 
(+2.51 -1.55) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve peaks at 2023-03-09 
12:32:21.5 UTC. The measured peak count rate is 7339.3 (+150.2 -163.3) 
counts/s above the background in the combined Veto data of all 
quadrants, with a total of 36415 (+702 -758) counts. The local mean 
background count rate was 1750.4 (+5.3 -6.0) counts/s. We measure a T90 
of 25.01 (+0.59 -0.59) s from the cumulative Veto light curve.

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

A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the MGNS/BepiColombo team,

J. Benkhoff on behalf of the BepiColombo team,

A. Ridnaia, D. Frederiks, D. Svinkin, A. Lysenko,
and T. Cline on behalf of the Konus-Wind team,

and

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team, report:

The bright, long-duration GRB 230309A
(AstroSat CZTI detection: Waratkar et al., GCN Circ. 33464
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 )
was detected by Konus-Wind, Swift (BAT), AstroSat (CZTI),
and BepiColombo (MGNS), at about 45138 s UT (12:32:18).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
   88.882 (05h 55m 32s) -62.196 (-62d 11' 45")
 Corners:
   88.454 (05h 53m 49s) -63.663 (-63d 39' 48")
   88.326 (05h 53m 18s) -63.585 (-63d 35' 05")
   89.273 (05h 57m 06s) -60.728 (-60d 43' 40")
   89.391 (05h 57m 34s) -60.806 (-60d 48' 20")
 ---------------------------------------------
The error box area is 712 sq. arcmin, and its maximum
dimension is 2.9 deg (the minimum one is 4 arcmin).
The Sun distance was about 90 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB230309_T45138/IPN/

The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.

A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 230309A
(AstroSat CZTI detection: Waratkar et al., GCN Circ. 33464
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 ;
IPN triangulation: Kozyrev et al., GCN Circ. 33484
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 )
triggered Konus-Wind at T0=45138.667 s UT (12:32:18.667).

The burst light curve shows a multipeaked structure
which starts at ~T0-6.1 s and has a total duration of ~68.9 s.
The emission is seen up to ~4 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230309_T45138/

As observed by Konus-Wind, the burst
had a fluence of 1.69(-0.11,+0.12)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+3.232 s,
of 3.12(-0.39,+0.40)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+62.976 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.80(-0.07,+0.08),
the high energy photon index beta = -2.27(-0.15,+0.11),
the peak energy Ep = 305(-25,+29) keV
(chi2 = 96/97 dof).

The spectrum near the maximum count rate
(measured from T0+2.816 to T0+3.584 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.55(-0.10,+0.12),
the high energy photon index beta = -2.80(-0.63,+0.31),
the peak energy Ep = 483(-64,+66) keV
(chi2 = 57/55 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.