GRB 180728B

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

K. Hurley, on behalf of the IPN,

A. Goldstein, M. S. Briggs, and C. Wilson-Hodge
on behalf of the Fermi GBM 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

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

The short-duration GRB 180728B was detected by
Fermi (GBM; trigger 554505003), INTEGRAL (SPI-ACS), Konus-Wind,
and Swift (BAT), at about 76199 s UT (21:09:59).
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:
   222.078 (14h 48m 19s) +15.942 (+15d 56' 32")
  Corners:
   221.253 (14h 45m 01s) +11.625 (+11d 37' 29")
   221.537 (14h 46m 09s) +11.383 (+11d 23' 00")
   222.836 (14h 51m 21s) +20.467 (+20d 28' 01")
   222.533 (14h 50m 08s) +20.757 (+20d 45' 26")
  ---------------------------------------------
The error box area is 2.88 sq. deg, and its maximum
dimension is 9.423 deg (the minimum one is 18.8 arcmin).
The Sun distance was 88 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB180728_T76197/IPN

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

R. Hamburg, P. Veres, and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 21:09:58.91 UT on 28 July 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180728B (trigger 554505003 / 180728882).
which was also localized by IPN (GCN 23056
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 ).

The angle from the Fermi LAT boresight at the GBM trigger time is 96
degrees.

The GBM light curve shows a structured spike
with a duration (T90) of about 0.6 s (50-300 keV).
The time-averaged spectrum from T0-0.06 s to T0+0.38 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.18 +/- 0.15 and
the cutoff energy, parameterized as Epeak, is 504 +/- 61 keV.

The event fluence (10-1000 keV) in this time interval is
(1.36 +/- 0.90)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.19 s in the 10-1000 keV band
is 16.5 +/- 1.7 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

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

The short-duration GRB 180728B
(IPN triangulation Svinkin et al., GCN Circ. 23056
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 )
triggered Konus-Wind at T0=76197.29 s UT (21:09:57.290).

The burst light curve shows a multi-peaked structure
which starts at ~T0-0.2 s and has a total duration of ~0.4 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180728_T76197/

As observed by Konus-Wind, the burst
had a fluence of 1.35(-0.22,+0.25)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-0.004 s,
of 9.59(-3.38,+3.55)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 - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = 0.25(-0.61,+0.88)
and Ep = 404(-74,+118) keV (chi2 = 15/17 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.2
(chi2 = 15/16 dof).

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

V. Lipunov, E. Gorbovskoy, P.Balanutsa, N.Tiurina, D.Vlasenko, V.Kornilov, 
A.Kuznetsov,  V.Chazov, I.  Gorbunov, D.Zimnukhov, D.Kuvshinov, 
V.Vladimirov,
Lomonosov Moscow State University,SAI

D.Svinkin (Ioffe Institute, StPetersburg, Russia)

D. Buckley,
South African Astronomical Observatory (SAAO)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias (IAC)

A. Tlatov, V.Senik, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

H.Levato,
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

A. Gabovich, V. Yurkov, Yu. Sergienko
Blagoveschensk Educational State University (BSPU)

MASTER-SAAO  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in SAAO was starting survey on the IPN  GRB180728B error-box 
(Svinkin et al., GCN Circ #23056
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 ; Hamburg et al., GCN Circ #23057
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 )  14269 
sec after notice time and 70698 
sec after trigger time at 2018-07-29 16:48:15 UT. The 5-sigma upper limit 
on our first (180s exposure)  set is about 18mag.

The typical limit of coadded images is about 20 mag.
We marginally found one candidate to uncataloged object source near 
PGC052927 galaxy:

MASTER OT J144922.8+164418.2

RA,DEC = 14h 49m 22.8s +16d 44' 18.2"    error = 0.7 arcsec
mag = 19.7;
The offset from galaxy is 10.8W	and 22.2N arcsec.

====================================================================

The observations made on zenit distance = 50 degrees, galactic latitude b 
=  61 degree.
The moon (97 % bright part) below the horizon (The altitude of the Moon is 
-8 deg.
Observations started at twilight.
The sun  altitude  is -11.1 deg.
The object can be observed till sunrise at 2018-07-30 05:26:48.


The covered map is available at
http://master.sai.msu.ru/static//IPN/db/GRB180728.88/img/ligo_master_2018-07-30-16-09-11.eb.zoom.1.png


We reobserved possible transient on the next night starting 2018-07-30
16:57:46 UT. We do not find the
object brighter than  20.5 .

D.Steeghs, J.Lyman (U. Warwick), G.Ramsay (Armagh O.), M.Dyer
(U. Sheffield), K.Ulaczyk, A.Levan, R.Cutter (U. Warwick)
K. Ackley, D.Galloway, E.Rol (Monash U.), V.Dhillon (U. Sheffield),
P.O'Brien, R.Starling (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 180728B (GCN 23056
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 , 23057
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 , 23060
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 ),
the Gravitational-wave Optical Transient Observer (GOTO) observed the
IPN triangulation region as reported in Svinkin et al. (GCN 23056
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 ).

Observations were spread over four telescope array pointings,
beginning 2018-07-29T21:24 UT (24.25 hours after the burst) and employ
sets of 3x120s exposures in our wide L filter(400-700nm). These fields
were repeated on 2018-07-30 to permit difference imaging analysis.
Conditions were affected by dust, typically achieved a 5 sigma limiting
magnitude of V=19.8-20.1 on 2018-07-29 and V=20.4-20.6 on 2018-07-30.

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

Furthermore, we see no evidence for a source at the position reported
in Lipunov et al. (GCN 23065
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 ), noting that our observations started
4.7 hours later than the MASTER observations and thus the source
may have faded below our detection limit by then.


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/

Authors: Michael W. Coughlin (Caltech), Tom��s Ahumada (UMD), S.
Bradley Cenko (NASA GSFC), Shaon Ghosh (UWM), Virginia Cunningham
(UMD), Eric C. Bellm (UW), Mansi M. Kasliwal (Caltech) and Leo P.
Singer (NASA GSFC) on behalf of the ZTF and GROWTH collaborations

We observed the localization region of the short GRB 180728B (trigger
554505003) detected by the Gamma-Ray Burst Monitor (GBM) on the Fermi
satellite with the Palomar 48-inch telescope equipped with the 47
square degree Zwicky Transient Facility (ZTF) camera. The observations
taken during the night of July 29 did not cover the IPN updated
localization of GRB 180628B available the next day.  The IPN region
was observed with ZTF beginning at 04:06 UT on 2018 July 30 (30:58
hours after the trigger time). The observations covered 334 square
degrees, corresponding to ~ 76% of the probability enclosed in the
localization region.

The images were processed through the ZTF reduction and image
subtraction pipelines at IPAC to search for potential counterparts. 7
high-significance transient and variable candidates were identified by
our pipeline in the area observed, all of which had previous
detections with ZTF in the days and weeks prior to the GRB trigger
time (e.g., supernovae, active galactic nuclei). No viable optical
counterparts were thus identified.

The median 5-sigma upper limit for an isolated point source in our
images was r > 18.7 and g > 20. mag for the observations made on July
30.

ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL
#11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA;
UW, USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA.
ZTF acknowledges the generous support of the NSF under AST MSIP Grant
No 1440341. Alert distribution service provided by DIRAC@UW. Alert
filtering is being undertaken by the GROWTH marshal system, supported
by NSF PIRE grant 1545949.