GRB 170527A

M. Stanbro (UAH), C. M. Hui (NASA/MSFC), C. Meegan (UAH)
and A. von Kienlin (MPE) report on behalf of the Fermi GBM Team:

At 11:31:02.37 UT on 27 May 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170527A (trigger 517577467 / 170527480).

The on-ground calculated location, using the GBM trigger
data, is RA = 195.19 , DEC = +0.94  (J2000 degrees,
equivalent to 13h 00m, +0d 54.0'), with an uncertainty
of 1.00 degrees (radius, 1-sigma containment, statistical only; 
there is additionally a systematic error which we have characterized 
as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error 
and a small tail suffering a larger than 10 deg systematic error 
[Connaughton et al. 2015, ApJS, 216, 32] ).

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed 
to the GBM in-flight location. The initial angle from the 
Fermi LAT boresight is 37.00 degrees.

The GBM light curve shows a sharp peak with multiple sub-structures
with a duration (T90) of about 49.2 s (50-300 keV).
The time-averaged spectrum from T0+1.1 s to T0+50.3 s is 
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.03 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 1001.00 +/- 33.50 keV

The event fluence (10-1000 keV) in this time interval is
(8.430 +/- 0.003)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.8 s in the 10-1000 keV band is 
22.19 +/- 0.36 ph/s/cm^2.

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

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,

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, on behalf of the Fermi GBM 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 170527A (Stanbro et al.,GCN 21157)
was detected by Fermi(GBM), Konus-Wind, and
Mars-Odyssey(HEND), at about 41467 s UT (11:31:07).

We have triangulated it to a preliminary, 3 sigma error box whose
coordinates are:
 ---------------------------------------------
  RA(2000), deg       Dec(2000), deg
 ---------------------------------------------
 Center:
   192.3245             -1.4883
 Corners:
   192.3882             -1.5179
   197.2538             +8.1347
   196.7137             +7.4412
   192.2608             -1.4588
   188.2675            -10.5805
   188.0687            -11.4344
 ---------------------------------------------
The error box area is 2.9 sq. deg, and its maximum
dimension is 21.6 deg (the minimum one is 8.4 arcmin).
The Sun distance was about 125 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170527_T41466/IPN/

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

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 GRB 170527A (IPN localization: Hurley et al., GCN 21164
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triggered Konus-Wind at T0=41466.714 s UT (11:31:06.714).

The KW light curve shows a multi-peaked emission with a total duration
of ~57 s. The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst had a fluence of
(8.9 �� 0.6)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+0.640, of (1.79 �� 0.13)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+48.128 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.71(-0.09,+0.09),
and the peak energy Ep = 571(-47,+55) keV,
chi2 = 103/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep and an upper limit on beta of -2.5,
chi2 = 102/97 dof.

The spectrum near the peak count rate (measured from T0 to T0+7.168 s)
is best fit in the 20 keV - 15 MeV range by the CPL function
with the following model parameters:
the photon index alpha = -0.23(-0.10,+0.10),
and the peak energy Ep = 714(-44,+48) keV,
chi2 = 113/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -3.9,
chi2 = 113/97 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170527_T41466/

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