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EP250226a, GRB 250226A

GCN Circular 39796

Subject
EP250226a/GRB 250226A: KAIT optical observations
Date
2025-03-21T06:54:07Z (8 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and

Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, observed the field of EP250226a/GRB 250226A

(Fermi GBM team, GCN 39479; Jiang et al., GCN 39482; Jiang et al.,

GCN 39513; Zhang et al., GCN 39492; Thakur et al., GCN 39518;

Pathak et al., GCN 39530; Svinkin et al., GCN 39542; Ronchini

et al., GCN 39672) on Feb 26 at 09:27:20 (~2.88 hours after GBM

trigger) and lasted for 4 hours. A set of 160x60s images were

obtained in the clear (roughly R) filters. We detect the optical

afterglow (An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani

et. al, GCN 39488; Li et. al, GCN 39489; Aryan et. al, GCN 39509;

Zou et al., GCN 39511; Li et. al, GCN 39514; Jiang et al., GCN 39515;

Poidevin et al., GCN 39524; Tanasan et al., GCN 39554) in our single

images. We measure the OT brightness to be 19.6 +/- 0.1 mag (Vega)

at 2.88 hours after GBM trigger. We observed the OT again on the

following night with 60x60s exposures and detected the OT in the

coadd image with 22.2 +/- 0.2 mag (Vega) at a mid time of 1.17 days.

This gives a decay index of -1.04 between the two nights.

GCN Circular 39730

Subject
GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
Date
2025-03-15T07:21:33Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Novichonok (KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530; Pankov et. al, GCN 39539; Pankov et. al, GCN 39540; Svinkin et. al, GCN 39542; Tanasan et. al, GCN 39554) in the Rb filter with 1-meter Zeiss-1000 telescope of the Koshka Observatory (INASAN), and in the R-filter with 1.5-meter AZT-33IK telescope of Sayan Solar Observatory (Mondy). The observations began on 2025-02-28 23:27:51 UT, i.e. ~2.75 days since trigger at Koshka. We do not detect the optical counterpart in the stacked images from both telescopes. The preliminary upper limits are as follows:

Date       UT start  t-T0         Exp.    Filter  UL(3sigma)
                     (mid, days)  (s)
2025-02-28 23:27:51  2.75236      47*180  Rb      22.1
2025-03-01 20:06:19  3.60304      57*120  R       23.8

Ref. stars
USNO-B1.0
RA Dec R2
14:57:12.82 +20:57:33.04 15.73
14:57:12.66 +21:00:25.03 15.74
14:56:52.84 +21:00:58.82 14.86

The photometry is based on nearby stars from the USNO-B1.0 catalog (see above) and has not been corrected for the Galactic extinction.

GCN Circular 39672

Subject
GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
Date
2025-03-11T20:10:44Z (8 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form

Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:

Swift/BAT did not localize GRB 250226A onboard (T0: 2025-02-26T06:34:57.33 UTC, Fermi GCN 39479

Loading...
 
 
, GECAM GCN 39492, EP-WXT GCN 39482, INTEGRAL GCN 39518)

The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 23.9 in a 8.192 s analysis time bin, starting at T0.

Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)

The 90% credible area is 1,797 deg2 and the 50% credible area is 312 deg2. The integrated probability inside the coded field of view is <1%.

The joint NITRATES+GBM localization has a 90% credible area of 178 deg2 and a 50% credible area of 51 deg2, and is consistent with the external position by EP-WXT (GCN 39482

Loading...
 
 
)

A plot of the probability skymap can be viewed here:

skymap_plot

The probability skymap and joint skymap files can be downloaded from the links here

skymap_fits_file

joint_skymap_fits_file

Instructions on how to read and manipulate this map can be found here:

https://guano.swift.psu.edu/documentation

More details about this burst can be found on the trigger report page here:

https://guano.swift.psu.edu/trigger_report?id=762244532

GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.

A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/

GCN Circular 39554

Subject
GRB 250226A: GRANDMA Optical Observations
Date
2025-03-03T04:48:59Z (8 months ago)
Edited On
2025-03-03T14:37:52Z (8 months ago)
From
Lydia Nyambane at UMN <nyamb021@umn.edu>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Lydia Nyambane at UMN <nyamb021@umn.edu>
Via
Web form
M. Tanasan (NARIT), L. Nyambane (UMN), H. Muenter (UMN), C. Andrade (UMN), Y. Rajabov (UBAI), F. Magnani (CPPM), M. Masek (FZU), S. Alshamsi (AUS), W. Corradi (LNA), T. Almeida (LNA), K. Noysena (NARIT), L. Fraga (LNA), N. Sasaki (LNA), A. Takey (NRIAG), Y. Hendy (NRIAG), M. Abdelkareem (NRIAG), E. Elhosseiny F. Navarete (NOIRLab/SOAR), S. Antier (OCA/IJCLAB), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), P-A. Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS) on behalf of the GRANDMA and Kilonova-Catcher collaborations:

The GRANDMA collaboration imaged the field of a fast X-ray transient GRB 250226A discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518).

GRANDMA observations were performed at RA = 224.2651, DEC = 20.9756 with the OPD/60cm, TRT-SBO, KAO, Lisnyky/AZT-8 and AbAO-T70 telescopes starting ~0.4 days post T0 in the R and i' bands.

We detect the optical afterglow and report some of the observations at the following magnitudes:

| T-start (UTC)       | Magnitude       | UL (5sigma)      | Filter     | Telescope      |
| 2025-02-26 17:19:21 | 21.5 +/- 0.2    | 21.5             | R (AB)     | TRT-SBO        |
| 2025-02-27 01:39:46 | 21.15+/-0.15    | 22.6             | i’ (AB)    | KAO            |
| 2025-02-27 05:28:50 | 22.0+/-0.25	| 21.8             | R (AB)     | OPD/60cm       |

Our findings were consistent with the MEPHISTO telescope (Zou et al., GCN 39511), the Xinglong Observatory ( Jiang et al., GCN 39515), and the Las Cumbres Observatory Global Telescope network (LCOGT) (Poidevin et al., GCN 39524). 

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 and PS1 catalog.

We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). 

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).

GCN Circular 39542

Subject
Konus-Wind detection of GRB 250226A
Date
2025-02-28T22:10:03Z (8 months ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 250226A
(Fermi-GBM detection: The Fermi GBM team, GCN 39479;
Pathak and Meegan, GCN 39530;
EP-WXT detection: Jiang et al., GCN 39482;
INTEGRAL SPI-ACS and PICsIT detection: Thakur et al., GCN 39518)
triggered Konus-Wind at T0=23700.486 s UT (06:35:00.486).

The burst light curve shows a single emission episode
which starts at ~T0-5 s and has a total duration of ~32 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250226_T23700/

As observed by Konus-Wind, the burst
had a fluence of 1.17(-0.21,+0.28)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.438 s,
of 3.45(-1.09,+1.18)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+24.832 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 = -0.16(-0.47,+0.68),
the high energy photon index beta = -2.25(-0.38,+0.24),
the peak energy Ep = 143(-28,+35) keV
(chi2 = 64/97 dof).

The spectrum near the maximum count rate
(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 = -0.60(-0.36,+0.54),
the high energy photon index beta = -2.00(-8,+0.17),
the peak energy Ep = 190(-53,+331) keV
(chi2 = 86/97 dof).

Assuming the redshift z=3.315 (Zhu et al. GCN 39487)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 2.80(-0.51,+0.67)x10^53 erg,
the peak luminosity L_iso is 3.56(-1.12,+1.22)x10^53 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is 616(-119,+151) keV and the spectrum near the maximum count rate
Ep,p,z is 822(-229,+1427) keV.

With the obtained estimates, GRB 250226A is inside 68% prediction bands for
both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long
KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB250226_T23700/GRB250226A_rest_frame.pdf

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

GCN Circular 39540

Subject
GRB 250226A: KAO Optical Upper Limit
Date
2025-02-28T20:48:07Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. M. Abdelaziz (NRIAG), M. Abdelkareem (NRIAG), E. Amin (NRIAG), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN:

We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530; Pankov et. al, GCN 39539) in the R filter with the 1.88-meter telescope of the Kottamia Astronomical Observatory (KAO). The observations started on (UT) 2025-02-28 00:30:36, i.e. ~1.78 days since trigger and consists of 39x150 sec exposures. We do not detect the optical counterpart in the stacked image. The preliminary upper limit is as follows:

Date       UT start  t-T0         Exp.    Filter  UL(3sigma)
                     (mid, days)  (s)
2025-02-28 00:30:36  1.78084      39*150  R        22.3

The photometry is based on nearby stars from the USNO-B1.0 catalog and has not been corrected for the Galactic extinction.

GCN Circular 39539

Subject
GRB 250226A: AbAO AS-32 Optical Upper Limit
Date
2025-02-28T20:42:33Z (8 months ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 250226A (The Fermi GBM team, GCN 39479; V.Lipunov et. al, GCN 39481; Jiang et. al, GCN 39482; An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Li et. al, GCN 39492; Aryan et. al, GCN 39509; Zou et. al, GCN 39511; Jiang et. al, GCN 39513; Li et. al, GCN 39514; Junjie-Jin et. al, GCN 39515; Thakur et. al, GCN 39518; Poidevin et. al, GCN 39524; Pathak et. al, GCN 39530) in the R filter with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory. The observations started on (UT) 2025-02-28 00:25:49, i.e. ~1.76 days since trigger and consists of 70*60 sec exposures. We do not detect the optical counterpart in the stacked image. The preliminary upper limit is as follows:

Date       UT start  t-T0         Exp.    Filter  UL(3sigma)
                     (mid, days)  (s)
2025-02-28 00:25:49  1.76796      70*60   R       21.4

The photometry is based on nearby stars from the USNO-B1.0 catalog and has not been corrected for the Galactic extinction.

GCN Circular 39530

Subject
GRB 250226A: Fermi GBM Observation
Date
2025-02-28T14:49:24Z (8 months ago)
From
Utkarsh Pathak at IIT Bombay <utkarshpathak.07@gmail.com>
Via
Web form
U. Pathak (IITB) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 06:34:57.33 UT on 26 February 2025, the Fermi Gamma-ray Burst 
Monitor (GBM) triggered and located GRB 250226A (trigger 762244502/250226274)
which was also detected by EP/WXT and EP/FXT (Jiang et al. 2024, GCN 39482).
It was also detected by INTEGRAL SPI-ACS and PICsIT (Thakur et al. 2025, GCN 39518),
GECAM-B (Zhang et al. 2025, GCN 39492). Optical follow-ups have been done with 
TRT (An et al. 2025, GCN 39486), COLIBRI/DDRAGO (Magnani et al. 2025, GCN 39488),
GSP (Li et al. 2025, GCN 39489), Kinder (Aryan et al. 2025, GCN 39509),
1.6m Mephisto (Zhou et al. 2025, GCN 39511), SVOM/VT (Li et al. 2025, GCN 39514),
Xinglong (Jin et al. 2025, GCN 39515). The spectroscopic redshift of the optical
counterpart observed by VLT/X-shooter (Zhu et al. 2025, GCN 39487) is 3.315.
The Fermi GBM on-ground location is consistent with the EP/FXT position.

The angle from the Fermi LAT boresight is 108 degrees.

The GBM light curve consists of multiple spikes from a single emission
episode with a duration (T90) of about 61 s (50-300 keV). The 
time-averaged spectrum from T0-2.6 to T0+62.0 s is best fit by a 
power law function with an exponential high-energy cutoff. The power law
index is -1.36 +/- 0.03, and the cutoff energy, parameterized 
as Epeak, is 4408 +/- 1160 keV.

The event fluence (10-1000 keV) in this time interval is
(1.96 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.4 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 2864 +/- 2100
keV, alpha = -1.35 +/- 0.04 and beta = -1.8 +/- 0.2.

As the burst occurred near SAA entry, the spectral results of both fits
to the data (especially Epeak) are likely to have some contamination and
thus may not reflect the burst's true spectral nature.

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/"

GCN Circular 39524

Subject
GRB 250226A / EP250226a: LCO detection of the afterglow
Date
2025-02-27T23:22:56Z (8 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
F. Poidevin, I. Pérez-Fournon (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)

We observed the location of the long-duration GRB 250226A / EP250226a discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518) with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). Simultaneous 300-sec exposures were obtained in the SDSS i' and r' filters starting at about 18.89 hr after the Fermi trigger. We detect the optical afterglow  at the location reported by An et al. (GCN circ. 39486) and with optical detections by other groups (Zhu et al., GCN circ. 39487; Magnani et al., GCN circ. 39488; Li et al.,  GCN circ. 39489; Aryan et al., GCN circ. 39509; Zou et al., GCN circ. 39511; Li et al., GCN circ. 39514; and Junjie-Jin et al., GCN circ. 39515). A redshift of z = 3.315 has been reported by Zhu et al. (GCN circ. 39487). 

We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:

Date       |  UT start | t_mid - t0 (hours)   | mag | error | filter |
----------------------------------------------------------------------
2025-02-27   01:28:39         18.94            21.22  0.29     i'
2025-02-27   01:28:40         18.94            21.44  0.36     r'


This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).

GCN Circular 39518

Subject
EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection
Date
2025-02-27T14:31:11Z (8 months ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
Aishwarya Linesh Thakur(a), James Craig Rodi(a), Patrizia Barria(a,b), Giulia Gianfagna(a), Luigi Piro(a), Lorenzo Natalucci(a,b) report:

EP250226a/GRB 250226A was discovered by Fermi/GBM (GCN 39479) and EP-WXT (GCN 39482) at 2025-02-26T06:34:57 (UTC) and has also been detected by GECAM-B (GCN 39492)

In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM and EP-WXT detections, having an approximate duration of ~ 15 sec. The signal consists of a single pulse over this duration. This signal is also detected marginally in the IBIS/PICsIT data. 

The approximate peak count rate in SPI-ACS is 74,000 cts/s for E>80 keV, over a median background rate of 67,600 cts/s. 

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

GCN Circular 39515

Subject
EP250226a/GRB 250226A:Xinglong optical follow-up observations
Date
2025-02-27T12:36:12Z (8 months ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Sen-Liu (NAOC), JinLei-Zhang (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: 
We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN #39482; The Fermi team, GCN #39479) using the the Xinglong 2.16-m telescope located at Xinglong, Hebei, China. We obtained 3600 s R and I-band with the time of 2025-02-26T17:04:55 . The optical object reported by An et al. (GCN #39486) is detected in our image. We measure a preliminary magnitude of R = 21.19 +/- 0.07 and I = 21.68 +/- 0.05 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog.
We summarize our observation results as follows:
Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name

1 | 2025-02-26T17:04:55 | 3600 s | R |21.19 +/- 0.07| Xinglong 2.16-cm Telescope

2 | 2025-02-26T18:05:21 | 3600 s | I | 21.68 +/- 0.0 | Xinglong 2.16-m Telescope

GCN Circular 39514

Subject
EP250226a / GRB 250226A: SVOM/VT optical observations
Date
2025-02-27T11:48:14Z (8 months ago)
From
Xuhui Han at NAOC/SVOM <hxh@nao.cas.cn>
Via
Web form
R. Z. Li (YNAO), Z. Q. Wang (GXU), W. K. Zheng (UCB), X. H. Han, L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, H. B. Cai, J. Wang, Y. Xu, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM team:

The SVOM/VT conducted a ToO follow-up observation of the EP250226a/GRB 250226A (Jiang et al., GCN 39482; Fermi GBM team, GCN 39479; Zhang et al., GCN 39492; INTEGRAL/SPI-ACS (triNum #11070)) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously with an exposure time of 18*100 seconds. 

The afterglow (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509; Zou et al., GCN 39511; Zhu et al., GCN 39487) was detected with a brightness of 22.58+/-0.14 mag (AB) in VT_B and 21.56+/-0.10 mag (AB) in VT_R, at the mid-time of 20.45 hours post the burst.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.

GCN Circular 39513

Subject
EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
Date
2025-02-27T09:18:11Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
S. Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), T. Zhao, Y. J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team:

The X-ray transient EP250226a/GRB 250226A triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 39482), which is also detected by Fermi/GBM (Fermi GBM team, GCN 39479), GECAM-B (Zhang et al., GCN 39492) and INTEGRAL/SPI-ACS (triNum #11070), and followed by several optical telescopes (An et al., GCN 39486, Magnani et al., GCN 39488, Li et al., GCN 39489, Aryan et al., GCN 39509, Zou et al., GCN 39511) at the redshift of 3.315 (Zhu et al., GCN 39487). The refined analysis of the WXT data shows that the event started at 2025-02-26T06:34:54 (UTC) and lasted for 22 s with the peak flux of 9.8 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. 

The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed about 44 minutes later as blocked by the Earth. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 224.2641, DEC = 20.9754 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic equivalent hydrogen column density of 3.7 x 10^20 cm^-2 and a photon index of 2.07 (-/+0.06). The derived average unabsorbed 0.5-10 keV flux is 2.89 (-/+0.08) x 10^(-11) erg/s/cm^2. Further FXT observation performed at about 11.9 hours after the trigger showed an average unabsorbed 0.5-10 keV flux is 1.83 (-/+0.18) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).

GCN Circular 39511

Subject
EP250226a/GRB 250226A: 1.6m Mephisto observations
Date
2025-02-27T08:51:56Z (8 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Xingzhu Zou, Brajesh Kumar, Wenqiang Fan, Tao Wang, Jiayu Qi, Yuan Fang, Guowang Du, Jinghua Zhang, Helong Guo, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:

The field of EP250226a/GRB 250226A (Jiang et al., GCN 39482; The Fermi team, GCN 39479) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Three exposures of 300s each in the MEPHISTO u, v, g, and r bands were simultaneously (ug, vr) obtained starting from 2025-02-26T17:59:42 (~ 11.5h after the trigger). In our stacked g and r band images, we detect a source at the position of the optical candidate (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509) but not in u, v bands. The preliminary magnitudes and the 3-sigma upper limits are below:

Start_Time(UT)      | Band | Exp(s) | Mag/LimMag(AB)
--------------------|------|--------|---------------
2025-02-26T17:59:42 | u    | 300*3  |  > 22.6
2025-02-26T18:17:11 | v    | 300*3  |  > 23.0
2025-02-26T17:59:42 | g    | 300*3  |  22.2 +/- 0.2
2025-02-26T18:17:11 | r    | 300*3  |  21.2 +/- 0.1

-------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
-------------------------------------------------------------------------------------------------

GCN Circular 39509

Subject
EP250226a/GRB 250226A: Kinder optical follow-up observations
Date
2025-02-27T05:20:39Z (8 months ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, M.-H. Lee, H.-C. Lin, C.-H. Lai, C.-S. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
 
We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN 39482; The Fermi team, GCN 39479) using the  Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first LOT epoch of observations in the g band started at 19:34 UT on the 26th of February 2025 (MJD = 60732.815), ~12.98 hrs after the EP trigger; while the first LOT epoch of observations in the r band started at 19:59 UT on the 26th of February 2025 (MJD = 60732.826), ~13.25 hrs after the EP trigger.
 
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked r-band image, we marginally detected the optical counterpart candidate proposed by An et al. (GCN 39486) and confirmed by several other observations (e.g., Zhu et al., GCN 39487; Magnani et al., GCN 39488; and Li et al., GCN 39489). 
 
We employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured photometry (in the AB system) are as follows:  

Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass   
LOT | g | 60732.815 | 12.98 | 300 * 3 | >21.1 | 0".92 | 1.02   
LOT | r | 60732.826 | 13.25 | 300 * 3 | 21.73  +/- 0.17 | 0".91 | 1.01   

The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of  A_g = 0.16 mag and A_r = 0.11 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011).

GCN Circular 39492

Subject
GRB 250226A: GECAM-B detection
Date
2025-02-26T14:05:27Z (8 months ago)
From
yqzhang_cl@163.com
Via
Web form
GRB 250226A: GECAM-B detection

Yan-Qiu Zhang (IHEP), Shao-Lin Xiong (IHEP), Chen-Wei Wang (IHEP) report on behalf of the GECAM team:

GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 250226A, at 2025-02-26T06:34:56.000 UTC (T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #39479), EP/WXT (EP250226a/GRB 250226A, S.Q. Jiang et al., GCN #39482) and INTEGRAL/SPI-ACS (triNum #11070).

According to the GECAM-B light curves in about 5-2000 keV, this burst mainly consists of multiple pulses with a duration (T90) of about 63.5 +/- 11.7 s.

The GECAM light curve could be found here:
https://www.bursthub.cn//admin/static/gecamgrb250226A.png

We note that these results are 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).

GCN Circular 39489

Subject
EP250226a/GRB 250226A: GSP detects optical counterpart
Date
2025-02-26T10:57:41Z (8 months ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
Web form
W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report:
Following the detection of the fast X-ray transient EP250226a/GRB 250226A by the Einstein Probe (Jiang et al., GCN 39482), we initiated observations of the fast X-ray transient location starting on Feb 26 at 9:23 UT (~3 hours after the EP/WXT trigger) in the i and z bands. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at the Cerro Tololo Inter-American Observatory in Chile.
The optical counterpart (An et al., GCN 39486; Magnani et al., GCN 39488) was detected in the co-added images with i ~19.0 and z~19.3 mag.
These observations were taken as part of the Global Supernova Project.

GCN Circular 39488

Subject
EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
Date
2025-02-26T10:37:22Z (8 months ago)
From
Francesco <francesco.magnani.work@gmail.com>
Via
Web form
Francesco Magnani (CPPM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report:

We observed the field of EP250226a (Jiang et al., GCN Circ. 39482), consistent with the likely long GRB 250226A detected by Fermi/GBM (Fermi GCN Circ. 39479), with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.

We observed from 2025-02-26 07:56:43 to 09:14:20 UTC (82 minutes to 164 minutes after the trigger) and obtained 50 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.

In our stacked image we detect a source at the position of the optical candidate reported by An et. al. (GCN Circ. 39486) and Zhu et. al. (GCN Circ. 39487) with magnitude:

	i = 19.05 +/- 0.03

We encourage continued monitoring of this source.

We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.

GCN Circular 39487

Subject
EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
Date
2025-02-26T10:21:06Z (8 months ago)
From
Zipei Zhu at NAOC <zpzhu@nao.cas.cn>
Via
Web form
Z. P. Zhu (NAOC), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Izzo (INAF-OACn and DARK/NBI), J. T. Palmerio (CEA/Irfu), D. Xu (NAOC), N. R. Tanvir (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Pugliese (API-UvA), A. J. Levan (Radboud and Warwick), S. D. Vergani (CNRS, Obs. Paris/LUX) report on behalf of the Stargate collaboration:

We observed the optical afterglow (An et al., GCN 39486) of EP250226a / GRB 250226A (Fermi GBM team, GCN 39479; Jiang et al., GCN 39482) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 2x600 s. The observation mid-time was 2025 Feb. 26 at 08:43:57 (2.15 hr after the GBM trigger).

In a 15 s image taken with the acquisition camera on Feb. 26 at 08:27:06 UT, we detect the optical afterglow, for which we measure a magnitude r =19.17 +/- 0.03 AB (calibrated against nearby stars from the Pan-STARRS catalogue).

In a preliminary reduction of the spectra, we clearly detect a continuum down to 4000 AA. From the detection of a broad Lya absorption at ~5230 AA and multiple narrow absorption features, including O I, O I*, Si II, Si II*, C II, C II*, C IV, Si IV, Al II, Fe II, Fe II*, Al III, Ni II, Ni II*, Zn II, Cr II, Mg II, Mg I, Ca II we infer the redshift of the GRB to be z = 3.315.

We acknowledge expert support from the ESO staff in Paranal, in particular Diego Parraguez and Marco Berton.

GCN Circular 39486

Subject
EP250226a / GRB 250226A: TRT optical counterpart observation
Date
2025-02-26T08:35:09Z (8 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
J. An, S.Q. Jiang, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:

We observed the field of EP250226a detected by EP/WXT (Jiang et al., GCN 39482), which is very likely the same event of GRB 250226A detected by Fermi/GBM (Fermi GBM team, GCN 39479), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. We obtained several 300 s frames in the Sloan-r filter.

An uncatalogued and decaying optical source is detected within the EP/FXT error circle (Jiang et al., GCN 39482) at coordinates 

R.A. (J2000) = 14:57:03.63
Dec. (J2000) = +20:58:32.31

with an uncertainty of about 1.0 arcsec. The source has r ~ 17.7 mag at 21.8 min after the EP trigger, calibrated with PanSTARRS DR2 stars and not corrected for Galactic extinction.

We think that the source is the optical counterpart of EP250226a / GRB 250226A.

GCN Circular 39484

Subject
EP250226a: Global MASTER-Net observations report
Date
2025-02-26T08:09:29Z (8 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250226a ( EP Team et al., GCN 39482) errorbox  460 sec after notice time and 3834 sec after trigger time at 2025-02-26 07:39:10 UT, with upper limit up to  20.4 mag. The observations began at zenith distance = 56 deg. The sun  altitude  is -32.9 deg. 

The galactic latitude b = 60 deg., longitude l = 28 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2792303

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

    3865 | 2025-02-26 07:39:10 |         MASTER-OAFA | (14h 57m 01.08s , +20d 57m 34.1s) |   C |    60 | 20.4 |        
    4736 | 2025-02-26 07:53:41 |         MASTER-OAFA | (14h 57m 24.39s , +21d 12m 59.9s) |   C |    60 | 20.4 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

GCN Circular 39482

Subject
EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
Date
2025-02-26T07:30:36Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
S. Q. Jiang (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), T. Zhao, Y.J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team:

We report on the detection of an X-ray transient EP250226a at 2025-02-26 06:35:16 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The WXT position of the source is R.A. = 224.273 deg, DEC = 20.973 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The trigger time and the position are generally consistent with the likely long GRB 250226A detected by Fermi (GCN 39479).

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 224.2668 deg, DEC = 20.9743 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).

GCN Circular 39481

Subject
Fermi GRB 250226A: Global MASTER-Net observations report
Date
2025-02-26T07:19:05Z (8 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250226A ( Fermi GBM team, GCN 39479) errorbox  24 sec after notice time and 42 sec after trigger time at 2025-02-26 06:35:39 UT, with upper limit up to  20.6 mag. The observations began at zenith distance = 68 deg. The sun  altitude  is -42.6 deg. 

The galactic latitude b = 63 deg., longitude l = 32 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2792277

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      47 | 2025-02-26 06:35:39 |         MASTER-OAFA | (14h 37m 17.00s , +28d 44m 10.7s) |   C |    10 | 17.3 |        
      62 | 2025-02-26 06:35:39 |         MASTER-OAFA | (14h 37m 17.01s , +28d 44m 10.7s) |   C |    40 | 18.0 |  Coadd 
      48 | 2025-02-26 06:35:40 |         MASTER-OAFA | (14h 47m 34.56s , +29d 06m 42.6s) |   C |    10 | 18.8 |        
      73 | 2025-02-26 06:35:40 |         MASTER-OAFA | (14h 47m 34.57s , +29d 06m 42.7s) |   C |    60 | 19.9 |  Coadd 
     133 | 2025-02-26 06:35:40 |         MASTER-OAFA | (14h 47m 34.56s , +29d 06m 42.7s) |   C |   180 | 20.5 |  Coadd 
      97 | 2025-02-26 06:36:24 |         MASTER-OAFA | (14h 37m 16.85s , +28d 44m 13.0s) |   C |    20 | 17.7 |        
      98 | 2025-02-26 06:36:25 |         MASTER-OAFA | (14h 47m 34.39s , +29d 06m 43.3s) |   C |    20 | 19.2 |        
     132 | 2025-02-26 06:37:04 |         MASTER-OAFA | (14h 37m 16.73s , +28d 44m 14.3s) |   C |    10 | 17.3 |        
     143 | 2025-02-26 06:37:04 |         MASTER-OAFA | (14h 47m 34.22s , +29d 06m 43.3s) |   C |    30 | 19.5 |        
     168 | 2025-02-26 06:37:40 |         MASTER-OAFA | (14h 37m 16.62s , +28d 44m 15.1s) |   C |    10 | 17.2 |        
     193 | 2025-02-26 06:37:40 |         MASTER-OAFA | (14h 37m 16.64s , +28d 44m 15.1s) |   C |    60 | 18.5 |  Coadd 
     178 | 2025-02-26 06:37:40 |         MASTER-OAFA | (14h 47m 34.11s , +29d 06m 43.3s) |   C |    30 | 19.6 |        
     223 | 2025-02-26 06:37:40 |         MASTER-OAFA | (14h 47m 34.28s , +29d 06m 43.1s) |   C |   120 | 20.0 |  Coadd 
     209 | 2025-02-26 06:38:16 |         MASTER-OAFA | (14h 37m 16.46s , +28d 44m 15.8s) |   C |    20 | 17.8 |        
     219 | 2025-02-26 06:38:16 |         MASTER-OAFA | (14h 47m 33.97s , +29d 06m 42.9s) |   C |    40 | 19.7 |        
     260 | 2025-02-26 06:39:02 |         MASTER-OAFA | (14h 37m 16.25s , +28d 44m 16.5s) |   C |    30 | 18.0 |        
     270 | 2025-02-26 06:39:02 |         MASTER-OAFA | (14h 47m 33.77s , +29d 06m 42.4s) |   C |    50 | 19.9 |        
     321 | 2025-02-26 06:39:58 |         MASTER-OAFA | (14h 37m 15.96s , +28d 44m 16.6s) |   C |    40 | 18.3 |        
     331 | 2025-02-26 06:39:58 |         MASTER-OAFA | (14h 47m 33.52s , +29d 06m 41.8s) |   C |    60 | 19.9 |        
     439 | 2025-02-26 06:41:46 |         MASTER-OAFA | (14h 38m 47.22s , +23d 27m 51.0s) |   C |    60 | 18.4 |        
     529 | 2025-02-26 06:41:46 |         MASTER-OAFA | (14h 38m 47.22s , +23d 27m 51.0s) |   C |   240 | 19.5 |  Coadd 
     449 | 2025-02-26 06:41:46 |         MASTER-OAFA | (14h 48m 37.68s , +23d 50m 29.6s) |   C |    80 | 20.2 |        
     559 | 2025-02-26 06:41:46 |         MASTER-OAFA | (14h 48m 37.68s , +23d 50m 29.7s) |   C |   300 | 20.6 |  Coadd 
     535 | 2025-02-26 06:43:12 |         MASTER-OAFA | (14h 38m 46.84s , +23d 27m 50.2s) |   C |    80 | 18.6 |        
     545 | 2025-02-26 06:43:12 |         MASTER-OAFA | (14h 48m 37.34s , +23d 50m 28.1s) |   C |   100 | 20.2 |        
     652 | 2025-02-26 06:44:59 |         MASTER-OAFA | (14h 38m 46.33s , +23d 27m 48.1s) |   C |   100 | 18.8 |        
     662 | 2025-02-26 06:44:59 |         MASTER-OAFA | (14h 48m 36.92s , +23d 50m 26.1s) |   C |   120 | 20.2 |        
     793 | 2025-02-26 06:47:04 |         MASTER-OAFA | (14h 38m 45.75s , +23d 27m 45.8s) |   C |   130 | 18.7 |        
     953 | 2025-02-26 06:47:04 |         MASTER-OAFA | (14h 38m 45.75s , +23d 27m 45.8s) |   C |   450 | 19.7 |  Coadd 
     803 | 2025-02-26 06:47:05 |         MASTER-OAFA | (14h 48m 36.39s , +23d 50m 23.4s) |   C |   150 | 20.2 |        
     973 | 2025-02-26 06:49:50 |         MASTER-OAFA | (14h 38m 45.03s , +23d 27m 41.9s) |   C |   160 | 18.8 |        
     983 | 2025-02-26 06:49:50 |         MASTER-OAFA | (14h 49m 41.16s , +23d 48m 31.7s) |   C |   180 | 20.2 |        
    1163 | 2025-02-26 06:49:50 |         MASTER-OAFA | (14h 49m 41.16s , +23d 48m 31.8s) |   C |   540 | 20.6 |  Coadd 
    1167 | 2025-02-26 06:53:04 |         MASTER-OAFA | (14h 38m 44.30s , +23d 27m 37.0s) |   C |   160 | 18.7 |        
    1177 | 2025-02-26 06:53:04 |         MASTER-OAFA | (14h 49m 40.51s , +23d 48m 27.3s) |   C |   180 | 20.1 |        
    1362 | 2025-02-26 06:56:19 |         MASTER-OAFA | (14h 38m 43.40s , +23d 27m 31.4s) |   C |   160 | 18.6 |        
    1372 | 2025-02-26 06:56:19 |         MASTER-OAFA | (14h 49m 39.69s , +23d 48m 22.0s) |   C |   180 | 20.1 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

GCN Circular 39479

Subject
GRB 250226A: Fermi GBM Final Real-time Localization
Date
2025-02-26T06:42:51Z (8 months ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB

At 06:34:57 UT on 26 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226A (trigger 762244502.334384 / 250226274).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 222.1, Dec = 23.8 (J2000 degrees, equivalent to J2000 14h 48m, 23d 48'), with a statistical uncertainty of 3.9 degrees.

The angle from the Fermi LAT boresight is 111.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/quicklook/glg_skymap_all_bn250226274.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/quicklook/glg_healpix_all_bn250226274.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250226274/quicklook/glg_lc_medres34_bn250226274.gif
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