GRB 240225B
GCN Circular 35859
Subject
GRB 240225B: Swift-XRT afterglow detection
Date
2024-03-04T13:18:03Z (2 years ago)
From
Chiara Salvaggio at INAF OABrera <chiara.salvaggio@inaf.it>
Via
email
C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), A. A. Breeveld (UCL-MSSL),
P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT
team:
Swift-XRT has performed further follow-up observations of the MAXI-detected
burst GRB 240225B (Nakajima et al., GCN Circ. 35796; Joshi et al., GCN
Circ. 35798; Kawakubo et al., GCN Circ. 35811; Frederiks et al., GCN Circ.
35835; Cheung et al., GCN Circ. 35848). The data were collected between
T0+461.7 ks and T0+508.9 ks, and are entirely in Photon Counting (PC) mode
for a total exposure time of 1.4 ks.
The uncatalogued X-ray source reported by D'Ai et al. ("Source 1"; GCN
Circ. 35810), is still detected at an average count rate of ~ 1.3e-2 ct/s
and shows signs of fading with >3-sigma significance, and is therefore
likely the GRB afterglow.
Using 1113 s of XRT Photon Counting mode data and 1 UVOT
image, we find an astrometrically corrected X-ray position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec =
128.36159, 27.07601 which is equivalent to:
RA (J2000): 08 33 26.78
Dec (J2000): +27 04 33.6
with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position
is consistent with the reported optical afterglow position (Gompertz et
el., GCN Circ. 35805; Liu et al., GCN Circ. 35812; Malesani et al., GCN
Circ. 35819; Wise et al., GCN Circ. 35820; Gompertz et el., GCN Circ.
35824; Pankov et al., GCN Circ. 35826; Moskvitin et al., GCN Circ. 35828;
Amit et al., GCN Circ. 35030; Sasada et al., GCN Circ. 35831; Moskvitin et
al., GCN Circ. 35839).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
The X-ray afterglow light curve can be modelled with a power-law with no
breaks and decay index alpha = 1.09 (+0.16, -0.13).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+0.8, -0.6). The
best-fitting absorption column is 1.0 (+2.0, -1.0) × 10^21 cm^-2, at a
redshift of 0.946 (Schneider et al., GCN Circ. 35832), in addition to the
Galactic value of 4.0 × 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 2.72 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/00021675.
This circular is an official product of the Swift-XRT team.
GCN Circular 35848
Subject
GRB 240225B: Glowbug gamma-ray detection
Date
2024-03-03T04:22:32Z (2 years ago)
From
C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil>
Via
Web form
C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2], operating on the International Space Station, reports the detection of GRB 240225B, which was also detected by MAXI/GSC (GCN 35796), AstroSat/CZTI (GCN 35798), CALET (GCN 35811), and Konus/Wind (GCN 35835).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-02-25 20:11:58.416 with a duration of 38.9 s and a total significance of ~89 sigma. The light curve comprises a multi-peaked structure with two primary peaks at ~T0+3s and ~T0+8s, and a fainter peak at ~T0+34s.
Using a standard power-law function with an exponential high-energy cutoff [3] to model the emission in two defined intervals from T0 to T0+22.5s and T0+22.5s to +38.9s resulted respectively in photon indices dN/dE~E^x of x=0.6 and x=0.7, and cutoff energies ("Epeak") of 324 keV and 262 keV. The respective modeled 10-10000 keV fluences are 9.7e-06 erg/cm^2 and 2.0e-06 erg/cm^2.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS. The detector comprises 12 large-area (15 cm x 15 cm) CsI:Tl panels covering the surface of a half cube, and two hexagonal (5-cm diameter, 10-cm length) CLLB scintillators, giving it a large field of view (instantaneous FoV ~2/3 sky) over a wide energy band of 50 keV to >2 MeV.
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 35839
Subject
GRB 240225B: further SAO RAS optical observations
Date
2024-02-29T18:48:28Z (2 years ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
legacy email
A. S. Moskvitin, O. I. Spiridonova (SAO RAS)
report on behalf of the GRB follow-up team.
We observed the field of GRB 240225B (Nakajima et al., GCN 35796;
Evans, GCN 35797; Joshi et al., GCN 35798; D'Ai et al., GCN 35810;
Kawakubo et al., GCN 35811; Frederiks et al., GCN 35835)
with the SAO RAS 1m telescope Zeiss-1000 equipped with CCD-photometer.
We obtained 8 x 300 sec frames in the Rc band on Feb. 29,
17:11:52--18:03:46 UT (t_mid - T0 = 3.8903 days).
The OT (Gompertz et al., GCN 35805; Liu et al., GCN 35812;
Malesani et al., GCN 35819; Wise et al., GCN 35820;
Gompertz & Malesani, GCN 35824; Pankov et al., GCN 35826;
Ror et al., GCN 35830; Sasada et al., GCN 35831; Schneider et al.,
GCN 35832) is clearly detected in our stacked frame
with the brightness of R = 21.11 +/- 0.04.
The photometry is based on nearby SDSS stars (magnitudes converted
with Lupton 2005 equations).
GCN Circular 35836
Subject
GRB 240225B: Swift ToO observations
Date
2024-02-29T15:26:30Z (2 years 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 MAXI GRB 240225B.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021682
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 MAXI 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 35835
Subject
Konus-Wind detection of GRB 240225B (long)
Date
2024-02-29T14:46:36Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
legacy email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
GRB 240225B (MAXI/GCS detection: Nakajima et al., GCN 35796;
AstroSat CZTI detection: Joshi al., GCN 35798)
triggered Konus-Wind (KW) at T0=72727.251 s UT (20:12:07.251),
i.e., ~3.5 min before the MAXI trigger.
The burst light curve shows a multi-peaked emission
pulse, which starts at ~T0 - 2 s, peaks around ~T0 + 6 s,
and has a total duration of ~35 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/GRB240225_T72727/
As observed by Konus-Wind, the burst had
a fluence of (2.16 ± 0.35)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 6.144 s,
of (2.87 ± 0.41)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
A time-averaged spectrum (measured from T0 to T0+41.216 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.37 (-0.14,+0.15),
the high energy photon index beta = -2.74 (-7.26,+0.43),
the peak energy Ep = 270 (-43,+64) keV,
chi2 = 107/97 dof.
A spectrum near the peak count rate (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.85 (-0.110,+0.10),
the high energy photon index beta = -2.43 (-0.55,+0.24),
the peak energy Ep = 287 (-47,+59) keV,
chi2 = 75/79 dof.
Assuming the redshift z=0.946 (Schneider et al., GCN 35832)
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 burst isotropic energy release E_iso to (5.38 ± 0.95)x10^52 erg,
the isotropic peak luminosity L_iso to (1.87 ± 0.27)x10^52 erg/s,
the rest-frame peak energy of the time-integrated spectrum Ep,i,z to ~525 keV,
and the rest-frame peak energy at the peak of the emission Ep,p,z to ~558 keV.
With the obtained estimates, GRB 240225B is inside 68% prediction bands for
both 'Amati' and '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/GRB240225_T72727/GRB240225B_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 35832
Subject
GRB 240225B: VLT/X-shooter redshift
Date
2024-02-29T10:36:12Z (2 years ago)
From
Andrea Rossi at INAF <andrea.rossi@inaf.it>
Via
Web form
B. Schneider (MIT), G. Pugliese (API), A. Rossi (INAF/OAS), J. Palmerio (GEPI/Obs. de Paris & IAP), D. B. Malesani (DAWN/NBI and Radboud Univ.), Z. Zhu (NAOC), D. Xu (NAOC), B. P. Gompertz (Birmingham), A. Saccardi (GEPI/Obs. de Paris) report on behalf of the Stargate collaboration:
We observed the field of the MAXI/GSC GRB 240225B (Nakajima et al., GCN 35796; see also Joshi et al. 2024, GCN 35798; Kawakubo et al., GCN 35811) 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 mid-time is 02:29:56 UT on 2024 Feb 29 (~3.3 days after the MAXI trigger).
In grz images taken with the acquisition camera on Feb 29 01:37:53 UT, we clearly detect the optical afterglow (Gompertz et al., GCN 35805; Liu et al., GCN 35812; Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz et al., GCN 35824; Pankov et al., GCN 35826; Moskvitin et al., GCN 35828; Mo et al., GCN 35829; Ror et al., GCN 35830; Sasada et al., GCN 35831), for which we measure a preliminary AB magnitude r ~ 21 (the absolute calibration is uncertain due to the low number of Pan-STARRS calibrators in our small FoV).
In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From detection of multiple absorption features, which we interpret as being due to Fe II, Mg II, AlIII, Ca II, and Fe II*, we infer a common redshift of z = 0.946. We conclude this is the redshift of the burst. We also detect emission lines ([O II] and [O III] doublets, and H_alpha) at a consistent redshift, which we interpret as being due to the GRB host galaxy. As noted by Gompertz & Malesani (GCN 35824), the host galaxy is also detected in the Legacy Survey with r ~ 24.2 and a photometric redshift z ~ 0.9, which is consistent with the value we measured.
We acknowledge expert support from the ESO staff in Paranal, in particular Francesca Lucertini, Israel Blanchard and Thomas Rivinius.
GCN Circular 35831
Subject
GRB 240225B : MITSuME Akeno optical afterglow candidate detection
Date
2024-02-29T10:30:01Z (2 years ago)
From
Mahito Sasada at Tokyo Institute of Technology <sasada@hp.phys.titech.ac.jp>
Via
Web form
M. Sasada, I. Takahashi, M. Niwano, S. Sato, N. Higuchi, S. Hayatsu, H. Takei, H. Seki, Y. Yatsu and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 240225B (Nakajima et al. GCN 35796) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno.
The observation with a series of 60 sec exposures started at 2024-02-27 09:49:24 UT (1.565 days after the MAXI trigger). We stacked the images in good conditions. Here we report the g’- and Rc-band magnitudes of the optical candidate and upper limits by the aperture photometry.
T0+[days] | MID-UT | T-EXP[sec] | candidate magnitude and 5-sigma limits
----------------------------------------------------------------------------------------------------------------
1.638 | 2024-02-27 11:35:11 | 9480 | g’=19.78+/-0.13, Rc=19.53+/-0.10, Ic>19.7
----------------------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time
The position of the optical candidate is consistent with Gompertz et al., GCN 35805. The obtained magnitudes are broadly consistent with Gompertz et al., GCN 35805; Liu et al., GCN 35812; Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz et al., GCN 35824; Pankov et al., GCN 35826; Moskvitin et al., GCN 35828; and Geoffrey et al., GCN 35829; and Ror et al., GCN 35830.
We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g'-, Rc- and Ic-band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).
GCN Circular 35830
Subject
GRB 240225B: 3.6m DOT observation
Date
2024-02-29T06:15:59Z (2 years ago)
From
Amit Kumar Ror at ARIES <mitturor77894@gmail.com>
Via
email
Amit K. Ror, Shashi B. Pandey, Rahul Gupta, and Amar Aryan, Shivangi Pandey
(ARIES) report:
We observed the field of GRB 240225B detected by MAXI (Nakajima et al.
2024, GCN 35796), Swift (Evans 2024, GCN 35797), and AstroSat (Joshi et al.
2024, GCN 35798) using the 3.6m Devasthal Optical Telescope of ARIES
Nainital. The observations were started on 2024-02-28 at 01:04:01.085 UT,
i.e., 2.2 days after the MAXI trigger. We have taken multiple frames with a
60-second exposure time in the r, i, and z filters. We detected the OT at
the position of the GOTO afterglow candidate reported by Gompertz et al.
(2024, GCN 35805) in each observed image in the i and z bands and the
stacked image of the r band, indicating a redder nature. The preliminary
magnitude measurements are as follows:
Date Start_UT T_start-T0 (days) Filter Exp time (s) Limiting magnitude
=========================================================
2024-02-28 01:04:01.085 2.2 i 60s 19.96 +/- 0.04
Our i-band observation, combined with the observation of Wise et al. (2024,
GCN 35820), yielded a decay index of ~ 0.8 in the i-band.
The magnitude quoted is not corrected for the host and Galactic extinction
in the direction of the burst. Photometric calibration is performed using
the standard stars from the Pan-STARRS catalog.
Our detection is consistent with Gompertz et al. 2024, GCN 35805; Liu et
al. 2024, GCN 35812; Malesani et al. 2024, GCN 35819; Wise et al. 2024, GCN
35820; Gompertz et al. 2024, GCN 35824; Pankov et al. 2024, GCN 35826;
Moskvitin et al. 2024, GCN 35828; and Geoffrey et al. 2024, GCN 35829.
This circular may be cited. 3.6m Devasthal Optical Telescope (DOT) is a
recently commissioned facility in the Northern Himalayan region of India
(long:79 41 04E, lat:29 21 40N, alt:2540m) owned and operated by the
Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (
https://www.aries.res.in). Authors of this GCN circular thankfully
acknowledge consistent support from the staff members to run and maintain
the 3.6m DOT.
GCN Circular 35829
Subject
GRB 240225B: WINTER near-IR observations and upper limits
Date
2024-02-29T01:10:22Z (2 years ago)
From
Geoffrey Mo at MIT <gmo@mit.edu>
Via
Web form
Geoffrey Mo (MIT), Viraj Karambelkar (Caltech), Danielle Frostig (MIT), Robert Stein (Caltech), Nathan Lourie (MIT), Tomas Ahumada (Caltech), Robert Simcoe (MIT), Mansi Kasliwal (Caltech) report:
We observed the field of GRB 240225B (Nakajima et al., GCN 35796; Evans, GCN 35797; Joshi et al., GCN 35798; D'Ai et al., GCN 35810; Kawakubo et al., GCN 35811) using the Palomar 1-m telescope equipped with the 1-square degree infrared WINTER camera (Lourie et al., 2020) in the Y and J bands. Observations began at 2024-02-28T05:55:09 UTC (~2.4 days after the GRB) and consisted of 8 x 120 s exposures in each filter.
The images were processed using the WINTER data reduction pipeline (https://github.com/winter-telescope/mirar), with J-band image subtraction performed against reference images from the UKIRT Hemisphere Survey (Dye et al., 2017).
We do not detect the GOTO-discovered counterpart (Gompertz et al., GCN 35805; Liu et al., GCN 35812; Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz & Malesani, GCN 35824; Pankov et al., GCN 35826; Moskvitin et al., GCN 35828), setting the following upper limits (AB): Y = 18.3 mag and J = 18.8 mag.
GCN Circular 35828
Subject
GRB 240225B: SAO RAS optical observations
Date
2024-02-28T22:16:52Z (2 years ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
legacy email
A. S. Moskvitin, O. I. Spiridonova (SAO RAS)
report on behalf of the GRB follow-up team.
We observed the field of GRB 240225B (Nakajima et al., GCN 35796;
Evans, GCN 35797; Joshi et al., GCN 35798; D'Ai et al., GCN 35810;
Kawakubo et al., GCN 35811) with the SAO RAS 1m telescope Zeiss-1000
equipped with CCD-photometer. We obtained 8 x 300 sec frames in the Rc
band on Feb. 28, 18:20:36--19:11:22 UT (t_mid - T0 = 2.9307 days).
The OT (Gompertz et al., GCN 35805; Liu et al., GCN 35812;
Malesani et al., GCN 35819; Wise et al., GCN 35820;
Gompertz & Malesani, GCN 35824; Pankov et al., GCN 35826)
is clearly detected in our stacked frame with the brightness of
R = 20.51 +/- 0.02.
The photometry is based on nearby SDSS stars (magnitudes converted
with Lupton 2005 equations).
GCN Circular 35826
Subject
GRB 240225B: Mondy afterglow observations
Date
2024-02-28T07:44:44Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
Via
legacy email
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI, HSE)
report on behalf of IKI-GRB-FuN:
We observed the field of GRB 240225B (Nakajima et al., GCN 35796; Evans, GCN 35797,
Joshi et al., GCN 35798; D'Ai et al., GCN 35810; Kawakubo et al., GCN 35811) with
AZT-33IK telescope of Sayan observatory (Mondy) equipped with CMOS-photometer
ANDOR NEO. We took 60x120 sec frames in the R-filter starting on 2024-02-26 (UT)
12:30:03. The optical afterglow (Gompertz et al., GCN 35805; Liu et al., GCN 35812;
Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz & Malesani, GCN 35824)
is well detected in the stacked frame with a total exposure of 59x120 sec. Photometry
of the optical afterglow is following:
Date UT-start t-T0 Exp Filter OT Err UL FWHM
(UT) (mid.) (nxT) (3sigma) (arcsec)
2024-02-27 13:01:23 1.71919 59x120 R 19.16 0.09 22.8 2.1
The magnitudes were calibrated using nearby USNO-B1.0 stars (R2 magnitudes).
GCN Circular 35824
Subject
GRB 240225B: Liverpool Telescope afterglow observations
Date
2024-02-28T00:26:44Z (2 years ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud Univ.) report:
We observed the position of the optical afterglow (Gompertz et al., GCN 35805; Liu et al., GCN 35812; Malesani et al., GCN 35819; Wise et al., GCN 35820) of GRB 240225B (Nakajima et al., GCN 35796; Joshi et al., GCN 35798; Kawakubo et al., GCN 35811) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 21:37:18 on 2024-02-27, 2.06 days after trigger, and consisted of 15x120 s exposures in the SDSS r filter.
We detect the afterglow with an AB magnitude of r = 20.04 +/- 0.05, calibrated against nearby SDSS stars and not corrected for foreground extinction. Between this epoch and the initial detection by GOTO (Gompertz et al., GCN 35805), the afterglow is well described by a power-law decay with an index of 0.8, which is consistent with the magnitudes reported by NOT (Malesani et al., GCN 35819) and LT (Wise et al., GCN 35820), though under-predicts those reported by Nanshan/HMT (Liu et al., GCN 35812), potentially suggestive of flaring behaviour at the time of their observation. The steepening in the light curve noted in GCN 35819 may be thus due to local variability, rather than a break in the power-law evolution.
We note the presence of a faint underlying source at the afterglow position in Legacy Survey archival imaging, which may be the host galaxy of GRB 240225B.
GCN Circular 35820
Subject
GRB 240225B: Liverpool Telescope optical afterglow observations
Date
2024-02-27T16:49:48Z (2 years ago)
From
Jacob Wise at Liverpool John Moores University <J.L.Wise@2022.ljmu.ac.uk>
Via
Web form
J. Wise, A. Bochenek, D. A. Perley (LJMU) report:
We report observations the optical afterglow GOTO24tz/AT2024dgu (Gompertz et al, GCN 35805; D'Ai et al, GCN 35810; Xu, D., GCN 35812; Malesani et al, GCN 35819) associated with GRB 240225B (Nakajima et al, GCN 35796; Joshi et al, GCN 35798; Kawakubo et al, GCN 35811) using the IO:O optical camera on the 2-meter Liverpool Telescope. Observations commenced at 2024-02-27 00:20:06.433 UTC, approximately 28.1 hours after the burst. 2x75s exposures were taken using the SDSS g, r, i, and z filters, with Pan-STARRS foreground stars used for calibration. Conditions were generally favourable throughout.
The transient was well detected in all 4 filters, with magnitudes listed in the following table. Times since burst for each filter were calculated using the strongest peak found with the AstroSat CsI anticoincidence (Veto) detector as reference (Joshi et al, GCN 35798).
MJD Time since burst (hours) Filter Mag. (AB)
60367.01396 28.135 g 19.97 ± 0.12
60367.01624 28.189 r 19.51 ± 0.15
60367.01848 28.243 i 19.44 ± 0.10
60367.02073 28.297 z 19.28 ± 0.14
Magnitudes are not corrected for foreground extinction.
GCN Circular 35819
Subject
GRB 240225B: NOT optical observations
Date
2024-02-27T12:24:03Z (2 years ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud Univ.), B. P. Gompertz (Birmingham), Z.-P. Zhu, D. Xu (NAOC), L. Izzo (INAF/OACN and DARK/NBI), on behalf of a larger collaboration, and R. Forsberg (Lund), S. Bijavara Seshashayana (Malmo univ.), report:
We observed the optical afterglow (Gompertz et al., GCN 35805; D'Ai et al., GCN 35810) of GRB 240225B (Nakajima et al., GCN 35796; Joshi et al., GCN 35798; Kawakubo et al., GCN 35811). We used the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started on 2024 Feb 26.934 UT (1.09 days after the MAXI trigger time).
In a single 300-s exposure in the r band, we measure r = 19.53 +- 0.03 (AB), calibrated against nearby Pan-STARRS stars.
This confirms the decay of the GOTO candidate noted by Liu et al. (GCN 35812). Assuming an unbroken power law decay (F propto t^-alpha) between their observation and ours, the inferred decay slope is alpha = 1.8 +- 0.3, suggesting a faster decay then indicated in Liu et al. (GCN 35812).
GCN Circular 35812
Subject
GRB 240225B: Nanshan/HMT optical afterglow detection
Date
2024-02-26T23:18:55Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
email
X. Liu,, J. An, S.Y. Fu, S.Q. Jiang, Z.P. Zhu, T.H. Lu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of GRB 240225B detected by MAXI (Nakajima et al., GCN 35796) and AstroSat (Joshi et al., GCN 35798) using the HMT-0.5m telescope with big FOV (~1 deg^2) located at Nanshan, Xinjiang, China. Photometry was carried out twice in the same night without any filter..
A slowly decaying uncatalogued optical transient is detected at coordinates
R.A. = 08:33:26.80 (J2000)
Dec. = +27:04:32.77 (J2000)
with an uncertainty of radius ~ 0.3 arcsec, with r ~ 18.9 +/- 0.1 mag (AB) at a median time of 18.90 hr post-burst, calibrated with the nearby PanSTAR field. This OT is positionally at the border of the error circle of Swift/XRT "Source 1" (D'Ai et al., GCN 35810), and is also consistent with and thus confirming the GOTO candidate (Gompertz et al., GCN 35805).
We thus think the OT is the optical afterglow of GRB 240225B.
GCN Circular 35811
Subject
GRB 240225B: CALET Gamma-Ray Burst Monitor detection
Date
2024-02-26T22:35:56Z (2 years ago)
From
Yuta Kawakubo at Louisiana State University <kawakubo1@lsu.edu>
Via
Web form
Y. Kawakubo (LSU), A. Yoshida, T. Sakamoto, S. Sugita (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The long GRB 240225B (MAXI/GSC detection: Nakajima et al.,
GCN Circ. 35796; AstroSat CZTI detection: Joshi et al., 35798)
was detected in the ground analysis of the CALET Gamma-ray
Burst Monitor (CGBM) data around 20:12:08.50 on 25 February
2024 (referenced to the AstroSat detection: GCN Circ. 35798)
(http://cgbm.calet.jp/cgbm_trigger/flight/1392926875/index.html).
The main episode that AstroSat CZTI detected was seen by all CGBM
detectors. Also, a hint of emission that MAXI/GSC detected was seen
in the HXM data around T+230 s.
The burst light curve of the main episode shows a multi-peaked
structure that starts at T-7.6 sec, and ends at T+31.1 sec. The T90
and T50 durations measured by the SGM data are 33.0 +/- 0.9 sec
and 17.1 +/- 1.3 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
http://cgbm.calet.jp/cgbm_trigger/ground/1392926875/index.html
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 35810
Subject
GRB 240225B: Swift-XRT observations
Date
2024-02-26T22:22:37Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans (U.
Leicester) and A. A. Breeveld (UCL-MSSL) reports on behalf of the
Swift-XRT and the Swift-UVOT team:
Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 240225B in a series of observations tiled on the sky. The
total exposure time is 1.8 ks, distributed over 7 tiles; the maximum
exposure at a single sky location was 693 s. The data were collected
between T0+29.1 ks and T0+30.9 ks, and are entirely in Photon Counting
(PC) mode.
Two uncatalogued X-ray sources are detected, of which one ("Source 1")
is above the RASS 3-sigma upper limit at this position. The position of
this source is RA, Dec=128.3629, +27.0746 which is equivalent to:
RA (J2000): 08:33:27.11
Dec(J2000): +27:04:28.5
with an uncertainty of 4.4 arcsec (radius, 90% confidence). This
position is 25.3 arcmin from the MAXI position. At the present time the
light curve of Source 1 shows no signs of fading and we can not
confirm this source as the GRB afterglow.
The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00124.
Source 1 was out of the field of view for UVOT so we can't say anything
about optical properties.
This circular is an official product of the Swift team.
GCN Circular 35805
Subject
GRB 240225B: GOTO detection of a candidate optical afterglow
Date
2024-02-26T20:45:40Z (2 years ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, R. L. C. Starling, M. Kennedy, G. Ramsay, D. B. Malesani, B. Godson, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, A. Kumar, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration:
We report on observations of the MAXI-discovered GRB 240225B (Nakajima et al, GCN 35796) with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022). GOTO-North serendipitously tiled the MAXI localisation at 21:45:51 UT on 2024-02-25, 1.5 hours after trigger. The observation consisted of 4x45 s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks.
We identify a new optical source (GOTO24tz/AT2024dgu) with a magnitude of L = 17.12 +/- 0.04 at RA 08:33:26.67, Dec +27:04:32.71 (J2000). The optical source is close to the probable X-ray afterglow identified in tiled Swift observations (Evans, GCN 35797), offset by 7.2”, whilst formally outside the 4.4” 90% confidence contour of the X-ray localisation. This source was not present in the previous GOTO epoch, taken one day prior at 22:05:36 UT on 2024-02-24, to a limiting magnitude of L > 18.7. Given the tight pre-burst limit and close proximity with a new X-ray source, we propose this as a strong candidate afterglow of GRB 240225B.
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 35798
Subject
GRB 240225B: AstroSat CZTI detection
Date
2024-02-26T09:04:31Z (2 years ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar24@gmail.com>
Via
Web form
J. Joshi (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 240225B which was also detected by MAXI/GSC (M. Nakajima et al., GCN Circ. 35796). Inspection of INTEGRAL/SPI-ACS data also showed the detection of the burst. We note that the INTEGRAL/SPI-ACS detection time is consistent with our time which is about 3 min offset from the time reported in the MAXI/GSC detection (GCN 35796).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-02-25 20:12:08.50 UTC. The measured peak count rate associated with the burst is 185 (+40, -22) counts/s above the background in the combined data of all quadrants, with a total of 1617 (+331, -224) counts. The local mean background count rate was 346 (+1, -5) counts/s. Using cumulative rates, we measure a T90 of 19 (+10, -5) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2024-02-25 20:12:01.80 UTC. The measured peak count rate associated with the burst is 570 (+72, -69) counts/s above the background in the combined data of all quadrants, with a total of 5119 (+490, -666) counts. The local mean background count rate was 1539 (+7, -6) counts/s. We measure a T90 of 23 (+3, -4) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 35797
Subject
GRB 240225B: Tiled Swift observations
Date
2024-02-26T04:13:59Z (2 years 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 series of observations, tiled on the sky, of the
MAXI GRB 240225B. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00124
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: 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 35796
Subject
GRB 240225B: MAXI/GSC detection
Date
2024-02-26T03:37:58Z (2 years ago)
From
Yuta Kawakubo at Louisiana State University <kawakubo1@lsu.edu>
Via
Web form
M. Nakajima, H. Negoro (Nihon U.), Y. Kawakubo (LSU),
K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU),
Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto, E.Goto (Chuo U.),
M. Shidatsu (Ehime U.),
I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA),
Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani, Y. Okada (Kyoto U.),
M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (NAOC),
W. Iwakiri (Chiba U.)
report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source
at 20:15:46 UT on February 25, 2024.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (128.458 deg, 27.487 deg) = (08 33 49, +27 29 13) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.13 deg and 0.11 deg, respectively.
The roll angle of long axis from the north direction is 67.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 874 +- 86 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (127.906, 26.756) deg = (08 31 37, +26 45 21) (J2000)
(R.A., Dec) = (128.157, 26.654) deg = (08 32 37, +26 39 14) (J2000)
(R.A., Dec) = (128.895, 28.075) deg = (08 35 34, +28 04 29) (J2000)
(R.A., Dec) = (128.642, 28.179) deg = (08 34 34, +28 10 44) (J2000)
There was no significant excess flux in the previous transit at 18:43 UT
and in the next transit at 21:48 UT with an upper limit of 20 mCrab for each.