GRB 170511A

V. Sharma (IUCAA), V. Bhalerao (IIT-B), D. Bhattacharya (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration:

Analysis of Astrosat data showed the CZTI detection of a bright GRB 170511A which was also detected by MAXI/GSC (Takao et al., GCN 21137
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 ), CALET GBM (Yamaoka et al., GCN 21146
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 ) and Fermi GBM (E. Bissaldi et al., GCN 21161
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks emission with the strongest peak at 05:59:40.920 UT, ~30 s after the Fermi Trigger. The measured peak count rate is 515.9 cts/s above the background in combined data of four quadrants, with a total of 5191 cts. The local mean background count rate was 373 cts/s. Using cumulative rates, we measure a T90 of 36.6 s.

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.

E. Bissaldi (Politecnico & INFN Bari), O.J. Roberts (USRA/NASA)
and C. Meegan (UAH) report on behalf of the Fermi GBM Team:


"At 05:59:11.92 UT on 11 May 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170511A (trigger 516175156 / 170511249),
which was also detected by MAXI/GSC (Takao et al. 2017, GCN 21137
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 )
and by the CALET GBM (Yamaoka et al. 2017, GCN 21146
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 ).
The GBM on-ground location is consistent with the MAXI position.
The angle from the Fermi LAT boresight at the GBM trigger time is 85 degrees.

The GBM light curve consists of multiple peaks
with a duration (T90) of about 40 s (50-300 keV).
The time-averaged spectrum from T0 to T0+40 s is
best fit by a Band function with Epeak = 82 +/- 3 keV,
alpha = -0.90 +/- 0.03, and beta = -2.41 +/- 0.05.
The event fluence (10-1000 keV) in this time interval is
(2.80 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+34.5 s in the 10-1000 keV bandbis 30.1 +/- 0.5 ph/s/cm^2.


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

K. Yamaoka (Nagoya U), A. Yoshida, T. Sakamoto, Y. Kawakubo,
M. Moriyama, Y. Yamada, A. Tezuka, S. Matsukawa (AGU), S. Nakahira (RIKEN),
I. Takahashi (IPMU), Y. Asaoka, 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 170511A (Takao et al., GCN Circ. 21137
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 ;
Fermi-GBM trigger #516175156) was detected by the CALET
Gamma-ray Burst Monitor (CGBM).  The burst signal was only seen
by the SGM instrument.  Since the detection significance is less than
7 sigma in the CGBM data, no on-board trigger occurred for this event.

The light curve of the SGM shows two separated peaks.  The initial peak
starts at T+25 sec, peaks at T+28 sec and ends at T+33 sec (T is the trigger
time of Fermi-GBM).  The second peak starts at T+35 sec, peaks at T+38 sec
and ends at T+40 sec.  The T90 duration measured by the SGM data is
12.5 +- 1.0 sec (40-1000 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1178517128/

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

Y. Takao, M. Serino, S. Nakahira (RIKEN), S. Sugita (Tokyo Tech), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe (JAXA),
T. Mihara, M. Sugizaki, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN),
N. Kawai, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU),
H. Tsunemi, T. Yoneyama (Osaka U.),
M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.),
Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.),
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.),
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

At 2017-05-11T06:00 UT, the MAXI/GSC detected an uncatalogued X-ray
transient source.
The position reported to the MAXI new-transient mailing list was not accurate
due to an error of attitude determination.
With the corrected attitude information, we update the source
position assuming a constant source flux over the scan transit to be

 (R.A., Dec) = (300.633 deg, 33.315 deg) = (20 02 31, +33 18 53) (J2000)

with a statistical 90% C.L. elliptical error region
with long and short radii of 0.29 deg and 0.25 deg, respectively.
The roll angle of long axis from the north direction is 170.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The position and the time of the burst are consistent with a burst detected
by Fermi/GBM (trigger #516175156). Thus, we consider this event to be a GRB.
According to a quick-look light curve of Fermi/GBM, MAXI/GSC observed a tail 
part of the GRB.

The averaged X-ray flux was 228 +- 35 mCrab (4-10 keV). 
There were no significant excess fluxes at the previous
and followed scan transits at 2017/05/11 04:27 UT and 07:33 UT, 
respectively, with an upper limit of 20 mCrab for each.