GRB 170826B

S. Poolakkil (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 19:38:56.48 UT on 26 August 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170826B (trigger 525469141/ 170826819).

The on-ground calculated location, using the GBM trigger
data, is RA = 327.7, DEC = -31.8, with an uncertainty
of 1 degree (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 fluence
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 to
the GBM ground best location is 110 degrees.

The GBM light curve shows multiple overlapping pulses
with a duration (T90) of about 11 s (50-300 keV).
The time-averaged spectrum from T0-2.0 to T0+20.5 s is
best fit by a Band function with Epeak = 385 +/- 24 keV,
alpha = -0.98 +/- 0.02, and beta = -2.24 +/- 0.10.

The event fluence (10-1000 keV) in this time interval is
(3.592 +/- 0.052)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.0 s in the 10-1000 keV band
is 25.4 +/- 0.5 ph/s/cm^2.

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

-- 
Suraj Poolakkil
Fermi GBM Graduate Research Assistant
Dept. of Space Science
University of Alabama in Huntsville

Z. W. Li, J. Y. Liao, C. K. Li, X. B. Li, S. L. Xiong, C. Z. Liu, 
X. F. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang,
C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU),
F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP),
report on behalf of the Insight-HXMT team:


During the commissioning phase, at 2017-08-26T19:38:58.00 (T0),
Insight-HXMT detected GRB 170826B (trigger ID: HEB170826818)
in a routine search of the data, which was also observed by
Fermi/GBM (Poolakkil et al, GCN Circ.21717
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 ).


The Insight-HXMT light curve consists of multiple pulses
with a duration (T90) of 10.12 s measured from T0-0.46s.
The 500-ms peak rate, measured from T0-0.46 s, is 2948.6 cnts/sec.
The total counts from this burst is 23373.3 counts.


URL_LC: http://www.hxmt.org/images/GRB/HEB170826818_lc.jpg


All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (record energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the telescope.


The time-averaged spectrum from T0-1.00 to T0+9.00 s is
adequately fit by a Power Law model with spectral index = -2.03 +/- 0.04 . 
The energy fluence is (1.46 +/- 0.06)E-05 erg/cm^2 in 200 - 5000 keV in 
this time interval.


The analysis results presented above are preliminary;
final results will be published elsewhere.


Insight-HXMT is the first Chinese space X-ray telescope, which was funded
jointly by the China National Space Administration (CNSA) and the Chinese
Academy of Sciences (CAS). More information about it could be found at:
http://www.hxmt.org/index.php/enhome.




--

Sincerely Yours,
Zhengwei Li,
Key Laboratory of Particle Astrophysics,
Institute of High Energy Physics, 
Chinese Academy of Sciences, Beijing China
TEL:15210983070 E-mail:lizw@ihep.ac.cn

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,

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 long-duration GRB 170826B (Poolakkil et al., GCN 21717
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 ) was detected
by Fermi (GBM trigger 525469141), Konus-Wind, INTEGRAL (SPI-ACS),
Insight (HXMT, Li et al., GCN 21739
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 ), Mars-Odyssey (HEND),
and Swift (BAT) at about 70736 s UT (19:38:56).
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:
   331.259 (22h 05m 02s) -33.916 (-33d 54' 58")
  Corners:
   329.379 (21h 57m 31s) -34.070 (-34d 04' 13")
   329.998 (21h 59m 59s) -34.318 (-34d 19' 05")
   333.019 (22h 12m 04s) -33.643 (-33d 38' 34")
   332.435 (22h 09m 44s) -33.458 (-33d 27' 30")
  ---------------------------------------------
The error box area is 3108 sq. arcmin, and its maximum
dimension is 3.1 deg (the minimum one is 20 arcmin).
The Sun distance was 155 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170826_T70742/IPN

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

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

The long-duration GRB 170826B (Fermi GBM observation: Poolakkil
et al., GCN 21717
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 ; Insight-HXMT detection: Li et al., GCN 21739
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 ;
IPN Triangulation: Hurley et al., GCN 21753
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 )
triggered Konus-Wind at T0=70742.555 s UT (19:39:02.555).

The burst light curve shows a multipeaked structure
which starts at ~T0-3.9 s and has a total duration of ~23.6 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 5.70(-0.53,+0.53)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.728 s,
of 1.62(-0.29,+0.30)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+14.592 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.73(-0.14,+0.15),
the high energy photon index beta = -2.12(-0.14,+0.10),
the peak energy Ep = 261(-32,+46) keV
(chi2 = 87/83 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+6.400 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.54(-0.19,+0.20),
the high energy photon index beta = -2.05(-0.13,+0.09),
the peak energy Ep = 259(-36,+53) keV
(chi2 = 99/83 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170826_T70742/

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