GRB 250116A

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, bright GRB 250116A
(Fermi/GBM detection: Bissaldi et al., GCN 38962
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 ;
Fermi/LAT detection: Holzmann Airasca et al., GCN 38963
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 ;
INTEGRAL/SPI-ACS and PICsIT detection: Barria et al., GCN 38965
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 ;
GECAM-B detection: Wang et al., GCN 38967
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 )
triggered Konus-Wind at T0=45234.821 s UT (12:33:54.821).

The burst light curve shows a bright initial 
multipeaked emission episode which starts at ~T0-0.3 s and 
has a total duration of ~24.2 s, followed by a weaker
emission traced up to ~175 s.
The emission is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250116_T45234/

As observed by Konus-Wind, the initial emission episode
had a fluence of 1.05(-0.03,+0.03)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+15.344 s,
of 1.77(-0.14,+0.14)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the initial episode
(measured from T0 to T0+26.112 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 = -0.58(-0.04,+0.04),
the high energy photon index beta = -3.21(-0.28,+0.18),
the peak energy Ep = 382(-10,+11) keV
(chi2 = 111/98 dof).

A spectrum of the weaker emission tail
(measured from T0+26.112 to T0+181.760 s)
is best fit by a simple power-law (PL) function with
the PL index of -2.13(-0.17,+0.19), chi2 = 97/100 dof.
A 20 keV - 10 MeV fluence in this interval is estimated
to 1.25(-0.29,+0.39)x10^-5 erg/cm2.

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

Yue Wang, Shao-Lin Xiong, Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Cheng-Kui Li, Wen-Long Zhang, Yan-Qiu Zhang report on behalf of the GECAM team:

GECAM-B was triggered in-flight by a long burst, GRB 250116A, at 2025-01-16T12:33:59.550 UTC (T0), which was also observed by Fermi/GBM (GCN # 38962) and Fermi/LAT (GCN # 38963).

According to the GECAM-B light curves in about 20-1000 keV, this burst mainly consists of multiple pulses with a duration (T90) of about 15.5（+0.4,-0.6）s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250116A.png

GECAM location is consistent with the Fermi/LAT position within the error. 

We notice that the location is close to the Galactic plane and the light curve pattern is somewhat atypical for GRB but more similar to SGR, though the duration is much longer than SGR.

We note that these results are based on in-flight trigger 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 microsatellites (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).

Patrizia Barria(a,b), Giulia Gianfagna(a), James Craig Rodi(a), Aishwarya Linesh Thakur(a), Lorenzo Natalucci(a,b), Luigi Piro(a) report:

GRB 250116A was discovered by Fermi/GBM (GCN 38962
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 , seen also by Fermi/LAT GCN 38963
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 ) at time 2025-01-16T12:33:59.53 (UTC) with a duration of 16 s. We searched for any corresponding counterpart in the INTEGRAL/SPI-ACS and IBIS/PICsIT data.

In a SPI-ACS light curve above 80 keV, we find a pulse temporally coincident with the GBM detection having an approximate duration of ~ 15 sec. This pulse is also seen in the PICsIT lightcurve above 212 keV, with a similar duration. 

The approximate peak count rate in SPI/ACS is 80,000 cts/s for E>80 keV, over a median background rate of 65,000 cts/s.

After the GRB spike, we note that there is a second, stronger pulse in the light curves of both instruments. The association of this pulse to the GRB at this moment is unclear and is under investigation.

This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.

-----
(a) INAF/IAPS-Rome
(b) ICSC National Research Centre for High-Performance Computing

A. Holzmann Airasca (UniTrento and INFN Bari),  S. Lopez (CNRS / IN2P3), N. Di Lalla (Stanford University), T. Khalil (Johannesburg Univ) report on behalf of the Fermi-LAT Collaboration:

On January 16, 2025, Fermi-LAT detected high-energy emission from GRB 250116A, which was also detected by Fermi-GBM (trigger 758723644/ 250116524, GCN 38962
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 ).

The best LAT on-ground location is found to be:
RA, Dec = 266.64, -19.36 (J2000)

with an error radius of 0.13 deg (90 % containment, statistical error only). This was 53 deg from the LAT boresight at the time of the GBM trigger (T0 = 12:33:59.53 UT). 

The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1500 s after the GBM trigger is (4.0 ± 0.4) E-5 ph/cm2/s. The estimated photon index above 100 MeV is 2.3 ± 0.1. The highest-energy photon is a 3.9 GeV event which is observed 59 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is Chiara Bartolini (Chiara.Bartolini@ba.infn.it).

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

 E. Bissaldi (Politecnico and INFN Bari), A. Myers (NPP/GSFC), O.J. Roberts (USRA), and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 12:33:59.53 UT on 16 January 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250116A (trigger 758723644/250116524).

The angle from the Fermi LAT boresight is 55 degrees.

The GBM light curve consists of multiple peaks, with an  apparent duration (T90) of 15.9 s (50-300 keV). However, there is low energy emission that extends longer than the T90 out to at least several hundred seconds after the trigger time. The Sun emerges from Earth occultation midway during this burst, and thus due to the spacecraft motion during this time and the localization being relative close to the Sun position, it is currently unknown whether this is part of a long duration C-class Solar Flare or afterglow emission from the Burst. Analysis is ongoing. The time-averaged spectrum
from T0+0 to T0+21 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.71 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 462 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is
 (9.97 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+17 s in the 10-1000 keV band is 43.9 +/- 0.4 ph/s/cm^2. Multi-wavelength follow up of this Burst is strongly encouraged.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"