GRB 210123A

W. C. Xue, C. Cai, J. C. Liu, Q. Luo, S. Xiao, 
Q. B. Yi, Y. Q. Zhang, C. Zheng, Y. Huang, C. K. Li, 
G. Li, X. B. Li, J. Y. Liao, X. Y. Song, S. L. Xiong, C. Z. Liu, 
X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, 
X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), 
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2021-01-23T07:19:10.350 (T0), Insight-HXMT/HE detected 
GRB 210123A (trigger ID: HEB210123304) in a routine search of the data, 
which also triggered INTEGRAL and IPN.

The Insight-HXMT/HE light curve mainly consists of multiple
pulses with a duration (T90) of 6.56 s measured from T0-0.52 s. 
The 1-ms peak rate, measured from T0+1.95 s, is 1825 cnts/sec. 
The total counts from this burst is 5536 counts. 
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB210123304_lc.jpg

All measurements above are made with the CsI detectors operating in the 
GRB mode with the energy range of about 80-800 keV (deposited 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. 

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.

The Fermi GBM team reports the detection of a likely long GRB.

"At 07:19:03.07 UT on 23 January 2021, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 210123A (trigger 633079148 / 210123305).

This burst was also independently detected by INTEGRAL SPI-ACS and
the Insight-HXMT/HE (Xue et al. 2019, GCN 29349
Loading...
 
 )

The on-ground calculated location, using the GBM trigger
data, is RA = 345.1, DEC = -56.9 (J2000 degrees,
equivalent to 23h 00m, -56d 53'), with a statistical uncertainty
of 1.1 degrees.

The angle from the Fermi LAT boresight is 110 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210123305/quicklook/glg_skymap_all_bn210123305.png

The HEALPix FITS file, including the estimated localization systematic, can
be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210123305/quicklook/glg_healpix_all_bn210123305.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210123305/quicklook/glg_lc_medres34_bn210123305.gif

D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta 
(IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), 
A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the 
AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 
2020, arxiv:2011.07067) showed detection of a long GRB 210123A, which 
was also detected by Insight-HXMT/HE (GCN #29349
Loading...
 
 ) and Fermi-GBM (GCN 
#29351
Loading...
 
 ).

The source was detected in the 20-200 keV energy range. The light curve 
showed a single peak of emission at 2021-01-23 07:19:08.5 UT. Quadrant A 
was noisy, and we exclude it from further analysis. The measured peak 
count rate associated with the burst is 205 (+40, -38) cts/s above the 
background in the combined data of three quadrants (out of four), with a 
total of 996 (+259, -237) cts. The local mean background count rate was 
394 (+3, -3) cts/s. Using cumulative rates, we measure a T90 of 14 (+5, 
-4) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve showed multiple peaks 
of emission with the strongest peak at 2021-01-23 07:19:09.1 UT in all 
four quadrants. The measured peak count rate is 1710 (+95, -102) cts/s 
above the background in the combined Veto data of four quadrants, with a 
total of 8982 (+648, -679) cts. The local mean background count rate was 
1817 (+5, -7) cts/s. We measure a T90 of 14 (+5, -1) s from the 
cumulative Veto light curve.

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.