GRB 180526A

V. Sharma, A. Vibhute and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration:

Analysis of Astrosat CZTI data showed the detection of a long GRB 180526A at 11:04:09 UT.

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 11:04:20.50 UT. The measured peak count rate is 660.8 cts/s above the background in combined data of four quadrants, with a total of 4580 cts. The local mean background count rate was 510.1 cts/s. Using cumulative rates, we measure a T90 of 23.8 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 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.

S. Matsukawa, A. Yoshida, T. Sakamoto, V. Pal'shin, Y. Kawakubo,
A. Tezuka, H. Onozawa (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (RIKEN), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa,
S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long, bright GRB 180526A (INTEGRAL SPI-ACS trigger #8067,
Konus-Wind trigger time on 11:03:36.006, AstroSat CZTI detection:
Sharma et al., GCN circ. 22742
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 ) triggered the CALET Gamma-ray
Burst Monitor (CGBM) at 11:03:36.200 UTC on 26 May 2018.
No real-time CGBM GCN notice was distributed about this
trigger because the real-time communication from the ISS was off
(loss of signal). The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure which starts
at T-2.2 sec, peaks at T+44.4 sec and ends at T+79.2 sec.
The T90 and the T50 durations measured by the SGM data are
56.9 +- 2.8 sec and 16.3 +- 1.3 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1211367794/

The CALET data used in this analysis are provided by the Waseda CALET
Operation Center located at the Waseda University.

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,

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

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, and

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

The long-duration GRB 180526A (Sharma et al., GCN Circ. 22742
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 )
was detected by Konus-Wind, INTEGRAL (SPI-ACS), Mars-Odyssey (HEND),
and AstroSat (CZTI) at about 39814 s UT (11:03:34).

We have triangulated it to a preliminary, 3 sigma error box whose
coordinates are:
---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   108.576 (07h 14m 18s)  +3.677 ( +3d 40' 36")
  Corners:
   109.188 (07h 16m 45s)  +3.834 ( +3d 50' 02")
   108.877 (07h 15m 31s)  +2.756 ( +2d 45' 23")
   107.965 (07h 11m 52s)  +3.525 ( +3d 31' 31")
   108.274 (07h 13m 06s)  +4.632 ( +4d 37' 57")
  ---------------------------------------------
The error box area is 1.2 sq. deg, and its maximum
dimension is 1.97 deg (the minimum one is 1 deg).
The Sun distance was 47 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB180526_T39816/IPN/

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

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

The long-duration GRB 180526A
(AstroSat CZTI detection: Sharma et al., GCN 22742
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 ;
CGBM detection: Matsukawa et al., GCN 22744
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 ;
IPN Triangulation: Hurley et al., GCN 22745
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 )
triggered Konus-Wind at T0=39816.006 s UT (11:03:36.006).

The burst light curve shows a multipeaked structure
started at ~T0-9 s with a total duration of ~87 s.
The emission is seen up to ~4 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.12(-0.13,+0.13)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+42.048 s,
of 1.61(-0.28,+0.29)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+76.032 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.11(-0.13,+0.15),
the high energy photon index beta = -2.23(-0.24,+0.14),
the peak energy Ep = 207(-31,+38) keV
(chi2 = 76/69 dof).

The spectrum near the maximum count rate
(measured from T0+41.216 to T0+43.264 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.52(-0.17,+0.19),
the high energy photon index beta = -2.49(-0.31,+0.20),
the peak energy Ep = 224(-25,+27) keV
(chi2 = 56/58 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180526_T39816/

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