GRB 170311B

V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IITB), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed clear detection of GRB170311B (IPN Triangulation detection: K. Hurley et al., GCN Circ. 20859
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 ) in the 40-200 keV energy range. The light curve shows multiple peak structure with peak counts at 13:45:15.0 UT, ~10 s after Konus-Wind trigger (Konus-Wind observation: D. Frederiks et al., GCN Circ. 20865
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 ). For initial few seconds from the trigger time the light curve doesn't show excess counts above the background. The measured peak count rate is 412.9 counts/s above the background in combined data of four quadrants, with a total 1979 counts. The local mean background count rate was 378.1 counts/s. Using cumulative rates, we measure a T90 of 13.4 s.

It was clearly detected in the CsI anticoincidence detector (Veto) also as bright detection in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The long, very intense GRB 170311B (IPN triangulation:
Hurley et al., GCN 20859
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 ) triggered Konus-Wind
at T0=49504.661 s UT (13:45:04.661).

The burst light curve shows a bright, multi-peaked structure,
that is preceded and followed by a weaker emission.
The total duration of the burst is ~30 s.
The emission is seen up to ~8 MeV.

As observed by Konus-Wind, the burst had a fluence of
(8.0 �� 0.6)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+5.888, of (2.5 �� 0.3)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+15.360 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.61 (-0.06,+0.06),
the high energy photon index beta = -2.85 (-0.49,+0.25),
the peak energy Ep = 440 (-28,+30) keV,
chi2 = 105/97 dof.

The spectrum near the peak count rate (measured from T0+4.608
to T0+6.114 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.48 (-0.12,+0.13),
the high energy photon index beta = -2.60 (-0.44,+0.23),
the peak energy Ep = 408 (-48,+55) keV,
chi2 = 67/74 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170311_T49504/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova,
and T. Cline on behalf of the Konus-Wind team,

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

and

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

A long-duration, very intense GRB 170311B
has been detected by Konus-Wind, Mars-Odyssey (HEND),
and Swift (BAT), so far, at about 49490 s UT (13:44:50).
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:
   354.919 (23h 39m 40s) +31.187 (+31d 11' 14")
  Corners:
   355.382 (23h 41m 32s) +31.782 (+31d 46' 54")
   355.104 (23h 40m 25s) +31.806 (+31d 48' 21")
   354.474 (23h 37m 54s) +30.587 (+30d 35' 13")
   354.747 (23h 38m 59s) +30.567 (+30d 34' 01")
  ---------------------------------------------
The error box area is 1076 sq. arcmin, and its maximum
dimension is 1.42 deg (the minimum one is 13.4 arcmin).
The Sun distance was 34 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170311_T49504/IPN

The time history and spectrum will be given in forthcoming GCN Circulars.