GRB 180611A

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

The long-duration GRB 180611A was detected by
Fermi (GBM; trigger 550380546), INTEGRAL (SPI-ACS), Konus-Wind,
and Mars-Odyssey (HEND), at about 12541 s UT (03:29:01).

We have triangulated it to a preliminary, 3 sigma error box whose
coordinates are:
---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
   46.471 (03h 05m 53s) -48.835 (-48d 50' 05")
 Corners:
   47.883 (03h 11m 32s) -52.743 (-52d 44' 36")
   50.103 (03h 20m 25s) -53.759 (-53d 45' 33")
   45.101 (03h 00m 24s) -44.765 (-44d 45' 54")
   43.190 (02h 52m 46s) -43.503 (-43d 30' 10")
 ---------------------------------------------
The error box area is 8.7 sq. deg, and its maximum
dimension is 11.2 deg (the minimum one is 53.9 arcmin).
The Sun distance was 75 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB180611_T12541/IPN/

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

E. Bissaldi (Politecnico & INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 03:29:01.46 UT on 11 June 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180611A (trigger 550380546 / 180611145),
which was also reported by Hurley et al. 2018 (GCN 22767
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 ).
The GBM location is consistent with the IPN triangulated box.

The angle from the Fermi LAT boresight at the GBM trigger time is 62 degrees.

The GBM light curve shows a multipeaked emission episode
with a duration (T90) of about 9 s (50-300 keV).
The time-averaged spectrum from T0-1 s to T0+10 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.95 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 253 +/- 22 keV.

The event fluence (10-1000 keV) in this time interval is
(5.4 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 in the 10-1000 keV band
is 8.4 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak = 219 +/- 30 keV, alpha = -0.9 +/- 0.1 and
beta = -2.4 +/- 0.3.


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

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

The long-duration GRB 180611A
(IPN Triangulation: Hurley et al., GCN 22767
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 ;
Fermi GBM observation: Bissaldi &�� Meegan, GCN 22768
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 )
triggered Konus-Wind at T0=12541.046 s UT (03:29:01.046).

The burst light curve shows several peaks with a total duration of ~7 s.
The emission is seen up to ~1.5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.61(-0.56,+0.72)x10^-6 erg/cm2,
and a 64-ms peak energy flux, measured from T0+0.148 s,
of 5.04(-2.18,+3.14)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 1.5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with�� alpha = -0.80(-0.26,+0.30),
and Ep = 250(-47,+77) keV (chi2 = 52/60 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.25 (chi2 = 52/59 dof).

The spectrum near the peak count rate
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 20 MeV range
by the power law with exponential cutoff model
with�� alpha = -1.05(-0.29,+0.38),
and Ep = 668(-304,+856) keV (chi2 = 23/19 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -1.80 (chi2 = 23/18 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180611_T12541/

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

V. Sharma 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 180611A, which was also detected by IPN Triangulation (Hurley K. et al., GCN 22767
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 ), Fermi-GBM (Bissaldi E. et al., GCN 22768
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 ), Konus-Wind (Tsvetkova A. et al., GCN 22770
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 03:29:02.5 UT. The measured peak count rate is 265.9 cts/s above the background in combined data of four quadrants, with a total of 1173 cts. The local mean background count rate was 478.1 cts/s. Using cumulative rates, we measure a T90 of 11.5 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.