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GRB 241228B

GCN Circular 38843

Subject
GRB 241228B: Fermi-LAT detection
Date
2025-01-07T18:46:55Z (9 months ago)
From
N. Di Lalla at Stanford University <niccolo.dilalla@stanford.edu>
Via
email
N. Di Lalla (Stanford University), A. Holzmann Airasca (UniTrento and INFN Bari), T. Khalil (Johannesburg Univ), S. Lopez (CNRS / IN2P3), D. Depalo (Politecnico and INFN Bari), C.C. Cheung (Naval Research Lab), C. Bartolini (UniTrento and INFN Bari) report on behalf of the Fermi-LAT Collaboration:

On December 28, 2024, Fermi-LAT detected high-energy emission from GRB 241228B, which was also detected by Fermi-GBM (trigger 757051990/241228176, GCN 38714), Swift-XRT (GCN 38713), Swift/BAT-GUANO (GCN 38700), GOTO24jmz (GCN 38684), TRT (GCN 38687), LCOGT (GCN 38692), GROWTH-India Telescope (GCN 38694), VLT/X-shooter (GCN 38704), LCO (GCN 38702), D50 (GCN 38715), SAO RAS (GCN 38733), 1.6m Mephisto (GCN 38739), 1.3m DFOT (GCN 38816).

The best LAT on-ground location is found to be:

RA, Dec = 127.8, 6.9 (J2000)

with an error radius of 0.1 deg (90 % containment, statistical error only).This was 56 deg from the LAT boresight at the time of the GBM trigger (T0 = 04:13:05.39 UT).

The data from the Fermi-LAT show 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 - 520 s after the GBM trigger is (1.2 +/- 0.3) E-5 ph/cm2/s. The estimated photon index above 100 MeV is 2.0 +/- 0.2. The highest-energy photon is a 16 GeV event which is observed about 31 seconds after the GBM trigger.

The Fermi-LAT point of contact for this burst is Francesco Longo (francesco.longo@ts.infn.it <mailto:francesco.longo@ts.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.

GCN Circular 38816

Subject
GRB 241228B: 1.3m DFOT Optical observations
Date
2025-01-04T05:44:27Z (9 months ago)
From
Amit Kumar Ror at ARIES <mitturor77894@gmail.com>
Via
email
Amit K. Ror, Anshika Gupta, Pranshu, Shashi B. Pandey, Kuntal Mishra
(ARIES) report:


We observed the field of GRB 241228B detected by the Fermi Gamma-ray Burst
Monitor (Fermi GBM team, GCN 38682), with the 1.3m Devasthal Fast Optical
Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta
Research Institute of Observational Sciences (ARIES), India. The
observations were started on 2024-12-30 at 17:50:12 UT, i.e., ~ 2.5 days
after the Fermi GBM trigger. We have taken multiple frames with an exposure
time of 300 s in the R filter. We stacked the images after the alignment.
We detected an optical emission in our stacked image at the position of the
optical counterpart candidate by GOTO collaboration (Amit et al. 2024, GCN
38684). We obtain the following preliminary magnitude in the stacked image:


Date Start_UT T_start-T0 (days) Filter  Exp time (s)  Magnitude

=========================================================

2024-12-30 17:50:12     ~2.56     R     300s*24     21.23 +/- 0.05


Our detection is consistent with Amit et al. 2024, GCN 38684; An et al.
2024, GCN 38687; Kumar et al. 2024, GCN 38691; Ortega-Casas et al. 2024,
GCN 38692; Ghosh et al. 2024, GCN 38702; An et al. 2024, GCN 38704; Volnova
et al. 2024, GCN 38709; Strobl et al. 2024, GCN 38715; Moskvitin et al.
2024, GCN 38733; Kumar et al. 2024, GCN 38739.


The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue. This circular may be cited.

GCN Circular 38739

Subject
GRB 241228B: Multiband optical monitoring with 1.6m Mephisto
Date
2024-12-31T09:02:12Z (9 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Brajesh Kumar, Yuan Fang, Jianhui Lian, Qinhao Shao, Bo Wu, Yu Pan, Xingzhu Zou, Xinlei Chen, Jinghua Zhang, Guowang Du, Yuanpei Yang, Yehao Cheng, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:

The 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory was triggered to perform monitoring of GRB 241228B discovered by (Fermi GBM team, GCN 38682, Scotton and Meegan, GCN 38714) and Swift (Evans, GCN 38688; Burrows et al., GCN 38713). Simultaneous uvgriz band observations were started at 15:38:16 UT 2024-12-28 (~11.4 hr after the trigger) at an altitude of ~32 deg in moderate sky conditions (seeing ~2”). The GOTO optical counterpart GOTO24jmz (Kumar et al., GCN 38684, GCN 38691; An et al. GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., GCN 38702; An et al., GCN 38704; Volnova et al., GCN 38709; Strobl and Jelinek, GCN 38715, Moskvitin et al., GCN 38733) is clearly detected in different bands in the stacked images. The monitoring of the GRB field was continued at different epochs between 2024-12-28 to 2024-12-30 each night and multiple sets of observations in vri bands were acquired. The preliminary photometry on the stacked i-band initial frames is 20.2 +/- 0.1 mag (15:53:03UT2024-12-28, ExpStart). Further analysis of our remaining data is in progress.

--------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m 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 38733

Subject
GRB 241228B: SAO RAS optical observations
Date
2024-12-30T21:08:56Z (9 months ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin, O. I. Spiridonova, Yu. V. Sotnikova (SAO RAS), 
A. Volnova, A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, 
University of Johannesburg), report on behalf of the GRB follow-up team.

We observed the field of GRB 241228B discovered by Fermi (Fermi GBM 
team, GCN 38682; Scotton and Meegan, GCN 38714), Swift (Evans, 
GCN 38688; Burrows et al., GCN 38713) with the 1-m telescope of SAO RAS
Zeiss-1000 equipped with the CCD-photometer on December 29, 21:49:11 -- 
22:57:57 UT (t_mid - T0 = 1.7573 days). We obtained 12 x 300 sec. 
images in Rc band.

The GOTO24jmz optical counterpart (Kumar et al., GCN 38684, GCN 38691; 
An et al. GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., 
GCN 38702; An et al., GCN 38704; Volnova et al., GCN 38709; 
Strobl and Jelinek, GCN 38715) is clearly detected in the stacked image 
with the brightness of R = 20.97 +/- 0.06. Based on photometry in R 
filter (this report and photometry by Volnova et al., GCN 38709) 
we found that the light curve of the afterglow of GRB 241228B/GOTO24jmz 
can be fitted with a simple power-law model 
with an power law index of -0.66.

The photometry is based on nearby SDSS stars used by Volnova et al., 
GCN 38709 (magnitudes were converted with Lupton 2005 equations).

GCN Circular 38715

Subject
GRB 241228B: D50 optical detection
Date
2024-12-29T22:35:20Z (10 months ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
J. Strobl and M. Jelinek (ASU CAS Ondrejov) report:

We observed the position of the Fermi/GBM-detected GRB 241228B (Fermi GBM team, GCN 38682) observed also by Swift/XRT (Evans, GCN 38688) with the D50 telescope of the Astronomical Institute in Ondřejov, near Prague, Czech Republic. Our observation started 16.4 h after the initial trigger and was performed with an SDSS r' filter.

We detect the optical counterpart (Kumar et al., GCNs 38684 and 38691; An et al., GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., GCN 38702; Xu et al., GCN 38704) in multiple combined 24x120 s frames obtained between 16.4 and 21.9 h after the trigger. Based on our observations, at 18 h after trigger the source had r' = 20.4 +/- 0.1 (AB).

GCN Circular 38714

Subject
GRB 241228B: Fermi GBM Observation
Date
2024-12-29T21:37:56Z (10 months ago)
From
Lorenzo Scotton at UAH <lscottongcn@outlook.com>
Via
Web form
L. Scotton (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 04:13:05.39 UT on 28 December 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 241228B (trigger 757051990/241228176),
which was also detected by Swift/BAT-NITRATES (J. DeLaunay et al. 2024, GCN 38700).
The Fermi GBM on-ground location is consistent with the Swift/BAT-NITRATES position.

Follow-up observations report the detection of the potential afterglow 
(Kumar et al. GCN 38684 and GCN 38691; An et al. GCN 38687; Ortega-Casas et al. GCN 38692; 
Mohan et al. GCN 38694; Ghosh et al. GCN 38702, Burrows et al. GCN 38713) 
at a redshift z = 2.674 (An et al. GCN 38704).

The angle from the Fermi LAT boresight is 49 degrees.

The GBM light curve consists of two emission episodes, with a duration (T90)
of about 19.5 s (50-300 keV). The time-averaged spectrum
from T0-0.7 to T0+23.4 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.86 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 440 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is
(4.66 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.2 s in the 10-1000 keV band is 15.1 +/- 0.3 ph/s/cm^2.

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 38713

Subject
GRB 241228B: Swift-XRT afterglow detection
Date
2024-12-29T21:04:55Z (10 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), M. Ferro (INAF-OAB),
R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/GBM-detected burst GRB 241228B. We searched for X-ray sources in 
1.8 ks of Photon Counting (PC) mode data. The total exposure at the
position of the afterglow (see below) is 1.8 ks, obtained between
T0+40.0 ks and T0+41.8 ks.

An uncatalogued X-ray source is detected within the estimated 3-sigma
Fermi/GBM error region. Using 1809 s of PC mode data and 1 UVOT image,
we find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
127.77288, +6.84823 which is equivalent to:

RA (J2000): 08h 31m 05.49s
Dec(J2000): +06d 50' 53.6"

with an uncertainty of 3.2 arcsec (radius, 90% confidence). This
position is 0.6 arcsec from the optical source GOTO24jmz and is
believed to be the afterglow. The light curve is consistent with a
constant source of mean count rate 5.7e-02 ct/sec. A power-law fit
gives an index of -1.281 (+4.492, -0.030).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.4 (+0.5, -0.3). The
best-fitting absorption column is  3 (+15, -0) x 10^20 cm^-2,
consistent with the Galactic value of 2.9 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.8 x 10^-11 (5.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3 (+15, -0) x 10^20 cm^-2
Galactic foreground: 2.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.4 (+0.5, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021750.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021750.

This circular is an official product of the Swift-XRT team.

GCN Circular 38704

Subject
GRB 241228B: VLT/X-shooter redshift of z = 2.674
Date
2024-12-29T10:08:10Z (10 months ago)
Edited On
2024-12-30T14:08:27Z (10 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
J. An (NAOC), B. Schneider (LAM), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA/Irfu), D. Xu (NAOC), A. Kumar (RHUL/Warwick), A. J. Levan (Radboud Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), N. R. Tanvir (U. Leicester)  report on behalf of the Stargate collaboration:

We observed the field of the GRB 241228B triggered by Fermi (Fermi GBM team, GCN 38682) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 1200 s each. The observation was carried out with mid-time 06:35:08 UT on 2024 December 29 (~1.1 days after the trigger).

In the image taken with the acquisition camera, we detect the proposed optical afterglow (Kumar et al., GCN 38684 and GCN 38691; An et al. GCN 38687; Ortega-Casas et al., GCN 38692; Ghosh et al., GCN 38702), for which we measure an AB magnitude r = 20.7 +/- 0.1, calibrated against nearby stars from the Legacy Survey DR10 catalog.

In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From the detection of a broad Lya absorption at ~4470 AA and multiple absorption features, which interpreted as being due to NV, SII, SiII, OI, CII, SiIV, CIV, FeII, AlII, AlIII, NiII, CrII, ZnII, MgII, MgI, SiII*, OI*, CII*, FeII*, NiII*, we infer a common redshift of z = 2.674. The detection of fine-structure lines confirms the afterglow nature of the source, and we conclude this is the redshift of the burst. A strong Lyman alpha emission line is detected at a consistent redshift, which we interpret as being due to the GRB host galaxy.

We also note the presence of additional absorption features likely due to multiple intervening systems at z = 2.000 and z = 1.824.

We acknowledge expert support from the ESO staff in Paranal, in particular Marcela Espinoza and Boris Haeussler.

GCN Circular 38702

Subject
GRB 241228B: LCO optical observation
Date
2024-12-29T03:35:55Z (10 months ago)
Edited On
2024-12-30T14:09:51Z (10 months ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
Web form
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
 
We observed the field of the GRB 241228B triggered by Fermi (Fermi GBM team, GCN 38682) in B  filter of  the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring New South Wales, Australia. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on December 28, 2024, starting from 10.97 hours after the GRB trigger.

We clearly detect the optical transient (OT) reported by GCNs (Kumar et al., GCN 38684 and GCN 38691, An et al. GCN 38687)  in our B band image. 

Date		UTstart	 	JD		 		t-T0 (hours)	Exp (sec)	Filter		Magnitude       
2024-12-28	15:11:37.24	2460673.13307			10.97		1 x 1200 	B		B = 21.35 +/- 0.03

The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.

GCN Circular 38700

Subject
GRB 241228B: Swift/BAT-GUANO localization skymap of a burst
Date
2024-12-29T03:18:26Z (10 months ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form

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

Swift/BAT did not localize GRB 241228B onboard (T0: 2024-12-28T04:13:05.39 UTC, Fermi trig 757051990)

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 55.7 in a 16.384 s analysis time bin, starting at T0 + 0.0 s.

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 411 deg2 and the 50% credible area is 113 deg2. The integrated probability inside the coded field of view is <1%.

The NITRATES skymap is consistent with the Fermi localization reported in the final position notice (GCN 38682

Loading...
 
 
). The combined Fermi/GBM+NITRATES 90% credible area is 145 deg2 and the 50% credible area is 38 deg2.

The NITRATES skymap is consistent with the position of the candidate optical afterglow GOTO24jmz (GCN 38684

Loading...
 
 
), with the position lying on the 0.33 credible region contour of the NITRATES skymap and on the 0.77 credible region contour of the combined Fermi/GBM+NITRATES skymap.

A plot of the probability skymap can be viewed here:

skymap_plot

The probability skymap file can be downloaded from the link here

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=757052020

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 38696

Subject
Fermi GRB 241228B: Global MASTER-Net observations report
Date
2024-12-28T21:30:39Z (10 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-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 241228B ( Fermi GBM team, GCN 38682) errorbox  55483 sec after notice time and 55523 sec after trigger time at 2024-12-28 19:38:28 UT, with upper limit up to  19.0 mag. The observations began at zenith distance = 78 deg. The sun  altitude  is -19.7 deg. 

The galactic latitude b = 24 deg., longitude l = 209 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2724467

We obtain a following upper limits.  

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

   55553 | 2024-12-28 19:38:28 |         MASTER-SAAO | (07h 54m 54.88s , +12d 40m 09.5s) |   C |    60 | 18.1 |        
   56070 | 2024-12-28 19:47:05 |         MASTER-SAAO | (08h 03m 04.96s , +12d 39m 30.2s) |   C |    60 | 16.7 |        
   56692 | 2024-12-28 19:57:27 |         MASTER-SAAO | (07h 54m 52.81s , +12d 39m 26.0s) |   C |    60 | 18.0 |        
   56772 | 2024-12-28 19:58:46 |         MASTER-SAAO | (08h 03m 04.32s , +12d 40m 43.1s) |   C |    60 | 16.5 |        
   58004 | 2024-12-28 20:19:19 |         MASTER-SAAO | (07h 54m 54.92s , +12d 40m 11.9s) |   C |    60 | 18.3 |        
   58084 | 2024-12-28 20:20:39 |         MASTER-SAAO | (08h 03m 07.28s , +12d 39m 10.9s) |   C |    60 | 17.8 |        
   58882 | 2024-12-28 20:33:57 |         MASTER-SAAO | (07h 54m 51.05s , +12d 39m 25.5s) |   C |    60 | 18.5 |        
   58961 | 2024-12-28 20:35:16 |         MASTER-SAAO | (08h 03m 04.08s , +12d 40m 44.1s) |   C |    60 | 18.3 |        
   59580 | 2024-12-28 20:45:35 |         MASTER-SAAO | (07h 54m 50.78s , +12d 40m 28.4s) |   C |    60 | 18.5 |        
   59660 | 2024-12-28 20:46:55 |         MASTER-SAAO | (08h 03m 10.24s , +12d 39m 46.4s) |   C |    60 | 18.8 |        
   60280 | 2024-12-28 20:57:15 |         MASTER-SAAO | (07h 54m 57.16s , +12d 39m 31.6s) |   C |    60 | 18.8 |        
   60359 | 2024-12-28 20:58:34 |         MASTER-SAAO | (08h 03m 02.92s , +12d 38m 48.5s) |   C |    60 | 18.8 |        
   60438 | 2024-12-28 20:59:53 |         MASTER-SAAO | (07h 58m 43.86s , +14d 32m 58.5s) |   C |    60 | 18.9 |        
   60523 | 2024-12-28 21:01:18 |         MASTER-SAAO | (08h 07m 02.39s , +14d 34m 55.5s) |   C |    60 | 18.8 |        
   60604 | 2024-12-28 21:02:39 |         MASTER-SAAO | (08h 03m 12.94s , +16d 27m 55.2s) |   C |    60 | 18.8 |        
   60683 | 2024-12-28 21:03:58 |         MASTER-SAAO | (08h 11m 26.65s , +16d 27m 10.6s) |   C |    60 | 18.7 |        
   60762 | 2024-12-28 21:05:17 |         MASTER-SAAO | (08h 10m 29.63s , +12d 39m 19.4s) |   C |    60 | 18.9 |        
   60841 | 2024-12-28 21:06:36 |         MASTER-SAAO | (08h 18m 45.35s , +12d 40m 59.7s) |   C |    60 | 18.8 |        
   60921 | 2024-12-28 21:07:56 |         MASTER-SAAO | (08h 14m 28.98s , +14d 34m 17.4s) |   C |    60 | 18.7 |        
   61000 | 2024-12-28 21:09:15 |         MASTER-SAAO | (08h 22m 39.46s , +14d 33m 30.7s) |   C |    60 | 18.8 |        
   61079 | 2024-12-28 21:10:34 |         MASTER-SAAO | (07h 58m 46.86s , +14d 33m 13.5s) |   C |    60 | 18.9 |        
   61159 | 2024-12-28 21:11:53 |         MASTER-SAAO | (08h 06m 59.82s , +14d 34m 45.5s) |   C |    60 | 18.9 |        
   61238 | 2024-12-28 21:13:13 |         MASTER-SAAO | (08h 03m 09.07s , +16d 27m 01.5s) |   C |    60 | 18.9 |        
   61317 | 2024-12-28 21:14:32 |         MASTER-SAAO | (08h 11m 31.76s , +16d 29m 13.2s) |   C |    60 | 18.9 |        
   61397 | 2024-12-28 21:15:52 |         MASTER-SAAO | (08h 10m 27.01s , +12d 40m 12.9s) |   C |    60 | 19.0 |        
Filter C is a clear (unfiltred) band. 


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

GCN Circular 38694

Subject
GRB241228B: GROWTH-India Telescope optical observations
Date
2024-12-28T19:49:02Z (10 months ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form

T. Mohan, V. Swain, A. P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of GRB241228B (Fermi GRB, GCN 38682

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) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2024-12-28 17:37:04 UT, i.e., 13.39 hours after the Fermi trigger. We obtained multiple exposures in r' filter. We detected the optical afterglow in our stacked image at position reported by Kumar et al., GCN 38684. The photometry result follows as:

MJD (mid)FilterTotal Exposure Time (sec)Magnitude (AB)
60672.73893r'84020.05 +/- 0.1

Our magnitude is consistent with other optical observations (Kumar et al., GCN 38684

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, An et al., GCN 38687, Kumar et al., GCN 38691, Ortega-Casas et al., GCN 38692).

The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.

GCN Circular 38692

Subject
GRB 241228B: LCOGT photometry of the likely optical counterpart GOTO24jmz
Date
2024-12-28T18:26:47Z (10 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form

I. Ortega-Casas, B. Armas-Chinea, F. Dobrindt, P. Escudero-Coca, G. Fernández-Rodríguez, Á. García Lozano, A. Huertas Ferrer, C. Méndez-Lapido, M. Torreiro Martínez, G. Villa (ULL), S.R. Berlanas, F. Poidevin, and I. Pérez-Fournon (IAC and ULL)

We report on multi-band optical imaging of the GOTO optical counterpart candidate GOTO24jmz (Kumar et al., GCN 38684 and GCN 38691) of GRB 241228B detected by Fermi (Fermi GBM team, GCN 38682) with Las Cumbres Observatory global telescope network (LCOGT) telescopes. We used first the two 40-cm telescopes of the LCOGT node at Haleakala Observatory (Maui, Hawaii). The observations (600 sec in the SDSS r', i', and g' filters and in the PanSTARRS zs filter) started at 09:33:19 UT on 2024-12-28, i.e. 5.33 hr after the Fermi GBM trigger. We used also one of the LCOGT 1-m telescopes located at the LCOGT node at Siding Spring Observatory (Australia) to obtain a 180-sec SDSS r' image starting at 14:09:01 on 2024-12-28, i.e. 9.93 hr after the Fermi GBM trigger. The likely optical counterpart of GRB 241228B is clearly detected in all the LCOGT observations at the position reported by Kumar et al. (GCN 38684 and GCN 38691). This source has also been detected by An et al. (GCN 38687).

 
We measure the following magnitudes, calibrated against PanSTARRS and not corrected for Galactic extinction:

r' = 18.62 +/- 0.06, on 2024-12-28 09:38:19 UT

i' = 18.31 +/- 0.09, on 2024-12-28 10:07:03 UT
 
g' = 19.40 +/- 0.06, on 2024-12-28 10:18:46 UT

zs = 18.25 +/- 0.28, on 2024-12-28 10:49:38 UT

r' = 19.62 +/- 0.05, on 2024-12-28 14:10:31 UT

These results are based on observations made with the Las Cumbres Observatory’s education network 
telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation 
and are part of a course on Astrophysical Techniques of the Master in Astrophysics of the Universidad de La Laguna, Tenerife, Spain (LCOGT observing programme IAC2024B-010, ULL-ASTRO-MASTER).

This work makes use of observations from the Las Cumbres Observatory global telescope network (1-m telescopes, LCOGT observing programme IAC2024B-004, SGLF).

GCN Circular 38691

Subject
GRB 241228B: GOTO24jmz optical follow-up observations
Date
2024-12-28T17:51:08Z (10 months ago)
From
Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, G. Ramsay, B. P. Gompertz, S. Belkin, D. O'Neill, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:

We report on updated observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) on GRB 241228B (Fermi GBM Team, GCN 38682). Follow-up observations of the GOTO optical counterpart candidate GOTO24jmz (Kumar et al. GCN 38684) were performed by GOTO-South at 2024-12-28 13:00:42 UT  (t0+8.79h post-trigger). The observation consisted of 4x90s exposure in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings.

GOTO24jmz (RA = 08:31:05.46 and Dec = +06:50:54.07) was detected at an L-band magnitude of 19.73 ± 0.10 at t0+8.79h post-trigger. These updated observations align well with the previously reported decay rate of t^−1.45 (Kumar et al., GCN 38684) and are also consistent with the magnitude reported by An et al. (GCN 38687).

We encourage further deeper follow-up observations.

Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).

GCN Circular 38688

Subject
GRB 241228B: Swift ToO observations
Date
2024-12-28T15:17:34Z (10 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the Fermi/GBM GRB 241228B. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021750

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/GBM event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

GCN Circular 38687

Subject
GRB 241228B: TRT optical counterpart confirmation
Date
2024-12-28T14:25:42Z (10 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu, S.Q. Jiang, X. Liu, Z.P. Zhu, S.Y. Gao, D. Xu (NAOC) report on behalf of a large collaboration:

We observed the GOTO optical counterpart candidate (Kumar et al., GCN 38684) of GRB 241228B detected by Fermi (Fermi GBM team, GCN 38682), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia. Observations started at 12:52:57 UTC on 2024-12-28, i.e., 8.7 hr after the Fermi/GBM trigger, and we obtained 4 x 300 s frames in the R filter.

The optical candidate is clearly detected in our stacked image and has decayed to R = 19.20 +/- 0.04 (AB), calibrated with PanSTARRS stars in the field and not corrected for Galactic extinction.

GCN Circular 38684

Subject
GRB 241228B: GOTO possible optical counterpart candidate
Date
2024-12-28T08:40:34Z (10 months ago)
Edited On
2024-12-30T14:17:14Z (10 months ago)
From
Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, S. Belkin, B. P. Gompertz, D. O'Neill, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022; Dyer et al. 2024) in response to the Fermi/GBM detected GRB 241228B (alert GBM757051990; Fermi GBM Team, GCN 38682). Targeted imaging obtained with GOTO-North covered the Fermi localisation region from 2024-12-28 04:26:19 UT (+0.22h post trigger) to 2024-12-28 06:05:06 UT (+1.87h post trigger). In total, 88 images were taken, across 10 unique pointings, covering 205.5 square degrees within the 90% localisation contour. ~87.4% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.4 mag. The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.

A new optical source, GOTO24jmz, is identified. It is located on the 94.5% probability contour, formally outside of the GBM 90% localisation region. The source is initially detected at a magnitude of L = 14.54 ± 0.01 at 04:32:24 (t0+19 minutes post-trigger) before decaying to L = 16.99 ± 0.04 mag at 05:43:42 (t0+90 minutes post-trigger). This fading of 2.3 mags in 71 minutes is equivalent to a decay rate of t^-1.45 from the time of the GBM trigger, consistent with GRB afterglows. 

+------------------------------------------------------------------------------------+
|  Internal name |  RA (J2000) | Dec (J2000) | Time (UT) | t-t0 (minutes) |  Mag  |
+------------------------------------------------------------------------------------+

|  GOTO24jmz  | 08:31:05.46 | +06:50:54.07 | 2024-12-28 04:32:24 | 19 | 14.54 ± 0.01 | 
                                           | 2024-12-28 05:43:42 | 90 | 16.99 ± 0.04 |

We find no evidence of the source to a 3-sigma limiting magnitude of L > 20.3 mag prior to the GRB trigger time in previous GOTO observations taken at 17:47:09 UT on 2024-12-27 (t-t0 = -10.43h pre-trigger). In addition, we find no evidence of this source prior to the GRB trigger time in the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). There is a faint, ambiguous underlying source at the position of GOTO24jmz visible in DESI legacy survey images that we cannot definitively identify as a star or galaxy.


Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).

GCN Circular 38682

Subject
GRB 241228B: Fermi GBM Final Real-time Localization
Date
2024-12-28T04:23:41Z (10 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 04:13:05 UT on 28 Dec 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 241228B (trigger 757051990.391412 / 241228176).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 122.2, Dec = 14.0 (J2000 degrees, equivalent to J2000 08h 08m, 14d 00'), with a statistical uncertainty of 1.7 degrees.

The angle from the Fermi LAT boresight is 49.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn241228176/quicklook/glg_skymap_all_bn241228176.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn241228176/quicklook/glg_healpix_all_bn241228176.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn241228176/quicklook/glg_lc_medres34_bn241228176.gif
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