GRB 240112A

Chen-Wei Wang, Shao-Lin Xiong report on behalf of the GECAM team:
GECAM-B was triggered in-flight by a bright burst, tentatively named as GRB 240112A (see below),at 2024-01-12T05:41:25.850 UTC (denoted as T0).

GECAM-B localized this burst to the following position (J2000): 
Ra: 290.4 deg 
Dec: 18.4 deg
Err: 3.6 deg (1-sigma, statistical only)
We note that, although this in-flight location is very preliminary, it is generally consistent with SGR J1935+2154 within the error, therefore we suggest that it could be possibly from this magnetar. However, we cannot exclude the possibility of other origins at this moment.

According to the realtime alert data of GECAM-B, this burst mainly consists of two pulses
with a duration of about 3 s. The time-averaged spectrum from T0-0.2 to T0+3.8 s 
could be adequately fit by a power law with high energy exponential cutoff function 
with a fluence of about 5E-6 erg/cm^2 in 20-1000 keV.

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/240112_lc.png

We note that these results are based on realtime alert data and thus very preliminary. 
Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor
(GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B)
launched in Dec. 2020. As the third member of GECAM constellation, 
GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. 
GECAM mission is funded by the Chinese Academy of Sciences (CAS).

A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,

A. Ridnaia, D. Frederiks, D. Svinkin, A. Lysenko,
and T. Cline on behalf of the Konus-Wind team,

E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

and

W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:

The long-duration GRB 240112A
(GECAM-B detection: Wang and Xiong, GCN 35520
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 )
has been detected by Konus-Wind, INTEGRAL (SPI-ACS),
GECAM-B, and Mars-Odyssey (HEND), so far, 
at about 20482 s UT (05:41:22).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  289.407 (19h 17m 38s) +21.459 (+21d 27' 31")
 Corners:
  291.869 (19h 27m 29s) +20.713 (+20d 42' 47")
  287.138 (19h 08m 33s) +22.071 (+22d 04' 17")
  286.938 (19h 07m 45s) +22.067 (+22d 04' 02")
  291.666 (19h 26m 40s) +20.731 (+20d 43' 50")
 ---------------------------------------------
The error box area is 809 sq. arcmin, and its maximum
dimension is 4.8 deg (the minimum one is 3 arcmin).
The Sun distance was 42 deg.

The IPN localization is consistent with, but reduces
the area of, the GECAM-B localization (GCN 35520
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 ).
The position of SGR 1935+2154 is outside the box.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB240112_T20481/IPN

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

A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 240112A
(GECAM-B detection: Wang and Xiong, GCN 35520
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 ;
IPN triangulation: Kozyrev et al., GCN 35554
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 )
triggered Konus-Wind at T0=20481.732 s UT (05:41:21.732).

The burst light curve shows the main multi-peaked episode,
which starts at ~T0-0.2 s and has a total duration of ~2.8 s.
A fainter broad pulse is observed in the KW data from ~T0+113 s
to ~T0+120 s after the main pulse, whose association with
GRB 240112A is supported by the consistent KW ecliptic
latitude response. 

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240112_T20481/

As observed by Konus-Wind, the burst (main episode)
had a fluence of 7.58(-1.05,+1.13)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+1.376 s,
of 1.03(-0.19,+0.20)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The spectrum of the main episode
(measured from T0 to T0+8.448 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 = -1.04(-0.21,+0.23),
the high energy photon index beta = -2.67(-0.73,+0.26),
the peak energy Ep = 120(-15,+20) keV
(chi2 = 118/75 dof).

The spectrum of the fainter broad pulse
(measured from T0+106.752 to T0+123.136 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 = -1.67(-0.32,+0.53)
and Ep = 206(-195,+1360) keV (chi2 = 71/86 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.0
(chi2 = 71/85 dof).

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