GRB 180626B

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,

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

The short-duration GRB 180626B was detected by
Konus-Wind, Mars-Odyssey (HEND), INTEGRAL (SPI-ACS),
and Swift (BAT) at about 6441 s UT (01:47:21).
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:
   214.555 (14h 18m 13s) +12.412 (+12d 24' 43")
  Corners:
   212.075 (14h 08m 18s)  +4.864 ( +4d 51' 52")
   213.948 (14h 15m 48s) +11.502 (+11d 30' 08")
   217.782 (14h 31m 08s) +21.164 (+21d 09' 51")
   215.173 (14h 20m 42s) +13.338 (+13d 20' 17")
  ---------------------------------------------
The error box area is 4.7 sq. deg, and its maximum
dimension is 17.2 deg (the minimum one is 29 arcmin).
The Sun distance was 109 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB180626_T06442/IPN/

The localization of this burst is inconsistent with that of the short 
burst GRB 180626C, which is being reported in the next GCN Circular.

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 short-duration GRB 180626B
(IPN Triangulation: Hurley et al., GCN Circ. 22863
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 )
triggered Konus-Wind at T0=6442.786 s UT (01:47:22.786).

The burst light curve shows a single pulse which starts
at ~T0-0.1 s and has a total duration of ~0.3 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 7.69(-1.24,+1.35)x10^-7 erg/cm2,
and a 16-ms peak flux, measured from T0+0.004 s,
of 7.35(-2.79,+3.01)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.192 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.13(-0.54,+0.73)
and Ep = 218(-43,+60) keV (chi2 = 23/26 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 23/25 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model
with  alpha = -0.08(-0.59,+0.87)
and Ep = 294(-70,+116) keV (chi2 = 14/16 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.3
(chi2 = 14/15 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180626_T06442/

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

J.Lyman, D.Steeghs, K.Ulaczyk, A.Levan, B.Gompertz (U. Warwick),
N.Tanvir (U. Leicester), M.Dyer (U. Sheffield), K. Ackley, D.Galloway,
E.Rol (Monash U.), G.Ramsay (Armagh O.), V.Dhillon (U. Sheffield),
P.O'Brien (U. Leicester), S.Poshyachinda (NARIT),
D.Pollacco (U. Warwick), E.Thrane (Monash U.)

report on behalf of the GOTO collaboration:


In response to the short-duration GRB 180626B (GCN 22863
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 , 22866
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 ), the
Gravitational-wave Optical Transient Observer (GOTO) observed the IPN
triangulation region as reported in Hurley et al. (GCN 22863
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 ).

Observations were spread over several telescope array pointings,
beginning 2018-06-26T21:52 UT (20.1 hours after the burst) and
employed sets of 3x120s exposures in our wide L filter (400-700nm).
Approximately 83% of the IPN region was covered on-chip. These fields
were repeated in subsequent nights to permit difference imaging
analysis and typically achieved a 5 sigma limiting magnitude of
V=19.9-20.1 (based on zeropoints derived from APASS crossmatching).

We made use of the GLADE galaxy catalog to pay particular attention to
possible source candidates near galaxies within 200 Mpc. No
significant sources that could be credibly associated with the GRB were
detected.

GOTO is operated at the La Palma observing facilities of the
University of Warwick on behalf of a consortium including the
University of Warwick, Monash University, Armagh Observatory, the
University of Leicester, the University of Sheffield, the National
Astronomical Research Institute of Thailand (NARIT) and the Instituto
de Astrofisica de Canarias (IAC)

https://goto-observatory.org/