GRB 170626B

C. Z. Liu, X. Ma, J. Y. Liao, X. F. Li, Z. W. 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), X. B. Li, S. L. Xiong, C. K. Li, Y. Huang, Y. P. Chen,
M. Y. Ge, M. Gao (IHEP), T. P. Li (IHEP/THU), G. Li, M. S. Li, H. W. Liu,
F. J. Lu, L. M. Song, W. H. Tao, H. Y. Wang, Y. H. Wang, X. Y. Wen,
M. Wu, H. Xu, Y. P. Xu, C. M. Zhang, F. Zhang, J. Zhang, T. Zhang,
S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:

The Insight-HXMT (Hard X-ray Modulation Telescope) satellite,
was launched successfully on June 15, 2017. As one of the three
instruments onboard the Insight-HXMT, the High Energy x-ray telescope (HE)
consists of 18 detector modules with a total area of about 5000 cm2.
Each HE module is made of a NaI(Tl)/CsI(Na) PHOSWICH detector.
The CsI detectors can work as a GRB monitor in the energy range of 40 keV
to ~1000 keV in the normal operation mode, or 200 keV to ~3 MeV in the
GRB operation mode, with a large effective area up to about 2000 cm2
on average and a FoV covering nearly the whole sky unblocked by the Earth.

During the commissioning phase, at 2017-06-26T00:57:55.800 (T0),
Insight-HXMT detected the GRB 170626B (trig ID: HEB170626040)
in a routine search of the data, which was also observed by the CALET
(trig# 1182473374) and the Konus-Wind (trig time: 2017-06-26T00:58:02.21).

After comparing the measurements with CALET and Konus-Wind,
we conclude that this is the first confirmed GRB discovered by
the Insight-HXMT Telescope!

The Insight-HXMT light curve mainly consists of two pulses
with a duration (T90) of 6.5 s measured from T0+1.26 s.
The 1-second peak rate, measured from T0+5.0 s, is 4624.5 cnts/sec.
The total counts from this burst is 13919 counts.
All measurements above are made with the CsI detectors in the energy range
of about 80-840 keV. Please note that this is the deposited energy,
rather than the incident photon energy.

URL_LC: http://www.hxmt.org/images/GRB/HEB170626040_lc.jpg

The Insight localization of this GRB gives (J2000):
RA:     241.69   [deg]
DEC:    -54.13   [deg]
Err:     10	 [deg]

The statistical error is about 2 deg, however, the systematic error should
dominate at the commissioning phase since the calibration is sill ongoing.
We estimate the total error of location is about 10 deg, as indicated with
the red circle in the following location map.

URL_LOC: http://www.hxmt.org/images/GRB/HEB170626040_loc.jpg

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 this telescope could be found at:
http://www.hxmt.org/index.php/enhome .

[GCN OPS NOTE(27jun17):  Per author's request, this is a revised version
of the original GCN 21265
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  circular.  The "localization" and "statistical error"
paragraphs were added.]

///////////////////////////Original Distribution///////////////////////
TITLE:   GCN CIRCULAR
NUMBER:  21265
SUBJECT: GRB 170626B: The first GRB detected by the Insight-HXMT X-ray Telescope
DATE:    17/06/26 16:16:06 GMT
FROM:    Shaolin Xiong at IHEP  <xiongsl@ihep.ac.cn>

C. Z. Liu, X. Ma, J. Y. Liao, X. F. Li, Z. W. 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), X. B. Li, S. L. Xiong, C. K. Li, Y. Huang, Y. P. Chen,
M. Y. Ge, M. Gao (IHEP), T. P. Li (IHEP/THU), G. Li, M. S. Li, H. W. Liu,
F. J. Lu, L. M. Song, W. H. Tao, H. Y. Wang, Y. H. Wang, X. Y. Wen,
M. Wu, H. Xu, Y. P. Xu, C. M. Zhang, F. Zhang, J. Zhang, T. Zhang,
S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:

The Insight-HXMT (Hard X-ray Modulation Telescope) satellite,
was launched successfully on June 15, 2017. As one of the three
instruments onboard the Insight-HXMT, the High Energy x-ray telescope (HE)
consists of 18 detector modules with a total area of about 5000 cm2.
Each HE module is made of a NaI(Tl)/CsI(Na) PHOSWICH detector.
The CsI detectors can work as a GRB monitor in the energy range of 40 keV
to ~1000 keV in the normal operation mode, or 200 keV to ~3 MeV in the
GRB operation mode, with a large effective area up to about 2000 cm2
on average and a FoV covering nearly the whole sky unblocked by the Earth.

During the commissioning phase, at 2017-06-26T00:57:55.816 (T0),
Insight-HXMT detected the GRB 170626B (trig ID: HEB170626040)
in a routine search of the data, which was also observed by the CALET
(trig# 1182473374) and the Konus-Wind (trig time: 2017-06-26T00:58:02.21).

After comparing the measurements with CALET and Konus-Wind,
we conclude that this is the first confirmed GRB discovered by
the Insight-HXMT Telescope!

The Insight-HXMT light curve mainly consists of two pulses
with a duration (T90) of 6.3 s measured from T0+2.51 s.
The 1-second peak rate, measured from T0+6.5 s, is 4426.9 cnts/sec.
The total counts from this burst is 13784 counts.
All measurements above are made with the CsI detectors in the energy range
of about 80-840 keV. Please note that this is the deposited energy,
rather than the incident photon energy.

URL_LC: http://newshxmt.ihep.ac.cn/images/GRB/HEB170626040_lc.jpg

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 this telescope could be found at:
http://newshxmt.ihep.ac.cn/index.php/enhome .

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

K. Hurley, on behalf of the IPN,

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

The long-duration GRB 170626B was detected by Insight (HXMT),
Konus-Wind, CALET (CGBM), and Swift (BAT) at about 3482 s UT (00:58:02).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a Konus-BAT annulus centered at
RA(2000)=289.789 deg (19h 19m 09s)  Dec(2000)=-19.171 deg (-19d 10' 15"),
whose radius is 4.975 �� 4.975 deg (3 sigma).

This annulus is inconsistent with the HXMT position reported
by Liu et al. (GCN 21265
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 ); also, the KW ecliptic latitude response
implies the source position close to the ecliptic plane, which
is ~30 deg from the HXMT localization.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB170626_T03482/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 170626B
(Insight-HXMT observation: Liu et al., GCN 21265
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 ;
IPN triangulation: Kozlova et al., GCN 21279
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 )
triggered Konus-Wind at T0=3482.215 s UT (00:58:02.215).

The burst light curve shows a multipeaked structure
started at ~T0-6.1 s with a total duration of ~16.8 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.12(-0.20,+0.22)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.256 s,
of 1.03(-0.18,+0.18)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 a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.59(-0.13,+0.14)
and Ep = 423(-38,+45) keV (chi2 = 87/99 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 = 87/98 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 a power law with exponential cutoff model
with  alpha = -0.45(-0.11,+0.12)
and Ep = 429(-30,+35) keV (chi2 = 91/92 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.8
(chi2 = 91/91 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170626_T03482/

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

Y. Asaoka (Waseda U), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama,
Y. Yamada, A. Tezuka, S. Matsukawa (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (RIKEN), I. Takahashi (IPMU), S. Ozawa, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration GRB 170626B (Liu et al., GCN Circ. 21265
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 ; Konus-Wind
trigger time on 00:58:02.21 UT) triggered the CALET Gamma-ray Burst
Monitor (CGBM) at 00:57:56.28 on 26 June 2017.  The burst signal was
seen by the all CGBM instruments.

The light curve of the SGM shows two overlapping peaks.  The emission
starts at T+1 sec, peaks at T+2.5 sec (the first peak) and T+5.5 sec
(the second peak), and ends at T+10 sec.  The T90 duration measured by
the SGM data is 5.0 +- 0.4 sec (40-1000 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1182473374/

The CALET data used in this analysis are provided by the Waseda
CALET Operation Center located at the Waseda University.