GRB 250221A
GCN Circular 39501
Subject
GRB 250221A: ATCA Detections and Upper Limits
Date
2025-02-26T21:23:21Z (8 months ago)
From
agul8829@uni.sydney.edu.au
Via
Web form
A. Gulati (USyd), G. E. Anderson (Curtin), Claire Morley (Curtin), S. Chastain (UNM), J. K. Leung (UofT/HUJI), A. J. van der Horst (GWU), and L. Rhodes (TSI/McGill) on behalf of the ATCA PanRadio GRB collaboration
We observed long GRB 250221A (Palmer et al., GCN 39396) as part of The Australia Telescope Compact Array (ATCA) "PanRadio GRB" Large Project C3542 (PI: G. Anderson) at 5.5 and 9 GHz on 2025-02-21 (starting 6 minutes post-burst, for 10 hours), and on 2025-02-23 (starting 2.2 days post burst for 4 hours).
No radio sources were detected near the Swift/XRT enhanced position (Beardmore et al., GCN 39404) in the first epoch, with a 3-sigma upper limit of 24 uJy at 9 GHz. We detect a radio counterpart in the second epoch at a position consistent with the Swift/XRT enhanced position, with a flux of 233 +/- 15 uJy at 9 GHz. This value significantly exceeds the 10 GHz VLA detection at 1.95 days (Ricci et al., GCN 39433), possibly due to strong interstellar scintillation near the typical 10 GHz transition frequency.
We thank the CSIRO Space and Astronomy staff for supporting these observations.
We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
GCN Circular 39491
Subject
GRB 250221A: EP-FXT detection of the X-ray afterglow
Date
2025-02-26T12:12:31Z (8 months ago)
From
Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it>
Via
Web form
E. Troja (U Rome), R. L. Becerra (U Rome), W. J. Zhang, T. Y. Lian, H. W. Pan (NAO, CAS), Y. Wang (PMO, CAS), and Y. -H. Yang (U Rome) report:
We performed a follow-up observation of GRB 250221A detected by Swift/BAT (Caputo et al., GCN 39396) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-02-23 05:16:58 (UTC), about ~ 2.1 days after the trigger, for a total exposure time of 5.2 ks.
At the position of the XRT counterpart (Beardmore et al., GCN 39404), an uncatalogued X-ray source is detected by both FXT-A and FXT-B. This position is also consistent with the optical (Watson et al., GCN 39397; Cotter et al., GCN 39413; Muenter et al., GCN 39417; Shilling et al. GCN 39409; Kumar et al. GCN 39412; Pozanenko et al., GCN 39422; Ghosh et al., GCN 39425; Iskandar et al., GCN 39446) and radio afterglow (Ricci et al., GCN 39433).
From a preliminary analysis we derive an observed flux of (1.7 +/- 0.2)*10^-13 erg/cm^2/s (0.3-10.0 keV), consistent with the latest Swift/XRT measurement (Salvaggio et al., GCN 39414) and indicative of a possible rebrightening (Pankov et al., GCN 39427).
Further observations are planned.
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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
GCN Circular 39471
Subject
GRB 250221A: Swift-BAT refined analysis
Date
2025-02-25T14:19:03Z (8 months ago)
From
Mike Moss at NASA GSFC <mikejmoss3@gmail.com>
Via
Web form
D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
R. Caputo (GSFC) R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
Using the data set from T-479 to T+600 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250221A (trigger #1290305)
(R. Caputo, et al., GCN Circ. 39396). The BAT ground-calculated position is
RA, Dec = 59.476, -15.137 deg which is
RA(J2000) = 03h 57m 54.4s
Dec(J2000) = -15d 08' 11.8"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 19%.
The mask-weighted light curve displays a single short pulse.
T90 (15-350 keV) is 1.80 +- 0.32 sec (estimated error including systematics).
The time-averaged spectrum from T-0.22 to T+1.84 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.43 +- 0.23. The fluence in the 15-150 keV band is 3.9 +- 0.6 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band
is 2.9 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1290305
GCN Circular 39446
Subject
GRB 250221A: TNOT detection of the optical counterpart
Date
2025-02-24T09:24:45Z (8 months ago)
Edited On
2025-02-24T14:15:51Z (8 months ago)
From
Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>
Via
Web form
A. Iskandar（XAO), H.-C. Zhu (THU)，X.-F. Wang（THU), L.-T. Wang (XAO), and Shengyu Yan(THU) report the optical detection of the afterglow of GRB 250221A (Francile et al., GCN 39395; Caputo et al., GCN 39396; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCNs 39422,39424,39426,39427; Ghosh et al., GCN 39425).
We obtained the r-band images (about 2.40 days after the burst) with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy Observatory, starting on 2025-02-23 (UT) 13:05:49. The afterglow is clearly detected on the stacked images, with the following magnitude:
r = 20.46 +- 0.17 mag (MJD =60698.5457)
The above photometric result is calibrated against the Pan-STARRS catalog without a correction for the Galactic extinction.
GCN Circular 39433
Subject
GRB 250221A: VLA radio detection
Date
2025-02-23T18:32:23Z (8 months ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
R. Ricci (U Rome), E. Troja (U Rome) report on behalf of a larger collaboration:
We observed the GRB 250221A discovered by Swift/BAT (Caputo et al. GCN 39396) with
the Very Large Array at the centre frequency of 10 GHz (X-band) with a bandwidth of 4 GHz
at a mid time of 1.95 days after the trigger.
A weak source is detected at the target position with a flux density of 63 +/- 9 microJy.
Further observations are planned to assess its variability.
We thank the VLA staff for promptly executing the observations.
GCN Circular 39427
Subject
GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
Date
2025-02-23T11:51:11Z (8 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), V. Kim (FAI), M. Krugov (FAI), Y. Aimuratov (FAI),
A. Volnova(IKI), A. Pozanenko (IKI) report on behalf of IKI GRB FuN:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et
al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo
et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418;
Pankov et al., GCNs 39422,39424; Ghosh et al., GCN 39425) of the Swift GRB
250221A (Caputo et al., GCN 39396) with AZT-20 telescope of Assy-Turgen
observatory starting on 2025-02-22 (UT) 15:01:45 in r' filter.
The afterglow is clearly detected. Preliminary photometry of the afterglow
in the stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
2025-02-22 15:01:45 1.49280 45x60 r' 20.50 0.05 22.7
The photometry is based on nearby PS1 stars.
Compared to our previous observations (Pankov et al., GCNs 39422, 39424,
39426) we can confirm the afterglow brightening. We can estimate the time
of the maximum earlier than 2025-02-22 (UT) 12:29:44
GCN Circular 39426
Subject
GRB 250221A: continued Mondy optical observations, brightening afterglow
Date
2025-02-23T11:47:30Z (8 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunlo (ISZF), A. Volnova
(IKI) report on behalf of IKI GRB FuN:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et
al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo
et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418;
Pankov et al., GCNs 39422,39424; Ghosh et al., GCN 39425) of the Swift GRB
250221A (Caputo et al., GCN 39396) with AZT-33IK telescope of Mondy
observatory starting on 2025-02-22 (UT) 12:29:44 in R filter.
The afterglow is clearly detected. Preliminary photometry of the afterglow
in the stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
2025-02-22 12:29:44 1.38790 18x120 R 19.95 0.05 21.6
The photometry is based on nearby USNO-B1.0 (R2) stars.
Compared to our previous observations (Pankov et al., GCNs 39422,39424) the
afterglow has apparently become brighter.
GCN Circular 39425
Subject
GRB 250221A: Optical counterpart detection by LCO.
Date
2025-02-22T15:06:17Z (8 months ago)
From
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 250221A triggered by Swift (Caputo et al., GCN 39396) in B, r filters of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. 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 February 21, 2025, starting 22.46 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs ( Francile et al., GCN 39395; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCN 39422; Pankov et al., GCN 39424) in our B, r band image.
|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
----------------------------------------------------------------------------------------------------
2025-02-22 02:02:15.36 22.46 1 x 1200 B B = 21.91 +/- 0.06
2025-02-22 02:10:02.78 22.59 1 x 900 r r = 20.85 +/- 0.06
----------------------------------------------------------------------------------------------------
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 39424
Subject
GRB 250221A: Mondy optical observations
Date
2025-02-22T12:25:53Z (8 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunlo (ISTP), A. Volnova
(IKI) report on behalf of IKI GRB FuN:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et
al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo
et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418;
Pankov et al., GCN 39422) of the Swift GRB 250221A (Caputo et al., GCN
39396) with AZT-33IK telescope of Mondy observatory starting on 2025-02-21
(UT) 12:25:52 in R filter.
The afterglow is clearly detected. Preliminary photometry of the afterglow
in the stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
2025-02-21 12:25:52 0.38490 23x60 R 20.30 0.05 22.5
The photometry is based on nearby USNO-B1.0 (R2) stars.
GCN Circular 39423
Subject
Konus-Wind detection of GRB 250221A
Date
2025-02-22T12:13:42Z (8 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova,
M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report
GRB 250221A (Swift detection: Caputo et al., GCN 39396)
was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a ~12 sigma count-rate increase in the interval
from T0-1.5 s to T0+4.4 s where T0 = T0(BAT) = 03:34:37 UT.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB250221A/
Modeling the time-integrated spectrum of the burst
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.05 (-0.12, + 0.12) and Ep = 242(-22,+26) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (1.67 ± 0.09)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (2.97 ± 0.17)x10^-7 erg/cm^2/s.
Assuming the redshift z=0.768 (Palmerio et al., GCN 39418)
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 (2.8 ± 0.2)x10^51 erg,
the isotropic peak luminosity L_iso to (8.6 ± 0.5)x10^50 erg/s, and
the rest-frame peak spectral energy Ep,z to (428 ± 44) keV.
With the obtained estimates, GRB 250221A is a hard-spectrum outlier
(lies outside 90% prediction bands) of both 'Amati' and 'Yonetoku' relations 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/GRB250221A/GRB250221A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 39422
Subject
GRB 250221A: Assy optical observations
Date
2025-02-22T11:10:50Z (8 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), V. Kim (FAI), M. Krugov (FAI), Y. Aimuratov (FAI),
A. Volnova(IKI), A. Pozanenko (IKI) report on behalf of IKI GRB FuN:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et
al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo
et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418)
of the Swift GRB 250221A (Caputo et al., GCN 39396) with AZT-20 telescope
of Assy-Turgen observatory starting on 2025-02-21 (UT) 15:25:09.55 in r'
filter.
The afterglow is clearly detected. Preliminary photometry of the OT in the
stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
2025-02-21 15:25:09 0.50385 30x60 r' 20.90 0.05 22.8
The photometry is based on nearby PS1 stars.
GCN Circular 39418
Subject
GRB 250221A: VLT/X-shooter redshift z = 0.768
Date
2025-02-22T04:24:41Z (8 months ago)
Edited On
2025-02-24T14:55:30Z (8 months ago)
From
J. T. Palmerio at CEA-Saclay <jesse.palmerio@obspm.fr>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of J. T. Palmerio at CEA-Saclay <jesse.palmerio@obspm.fr>
Via
Web form
J. T. Palmerio (CEA/Irfu), A. Saccardi (CEA/Irfu), B. Rayson (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. J. Levan (Radboud and Warwick), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration:
We observed the optical afterglow (Francile et al., GCN 39395; Caputo et al., GCN 39396; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Cotter et al. GCN 39413) of GRB 250221A (Caputo et al., GCN 39396) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4x600 s exposures. The slit’s position angle was set to cover the afterglow position as well as the nearby object to the NW (Watson et al., GCN 39397; Cotter et al. GCN 39413). The observation mid time was 2025 Feb 22.08 UT (~22.5 hr after the GRB).
In a preliminary reduction of the spectra, we detect two blended traces, corresponding to the afterglow and to the NW object. Spatially consistent with the afterglow position, we detect emission lines of H alpha, [O III] 5007, [O III] 4959, H beta, [O II] 3726/3729 at a common redshift of z = 0.768.
In the UBV arm, the trace is dominated by the afterglow continuum. Absorption features are detected corresponding to Mg II and Fe II, at a consistent redshift, which we suggest is the redshift of the burst.
We should note the presence of a possible, weak emission feature at 16,855 AA at the position of the afterglow trace. We are not able to identify this feature presently and a full reduction of the data is required to ascertain its reality.
At the position of the NW object, a faint, red continuum is detected in the VIS and NIR arms. No clear emission or absorption features are detected, and at the moment we can not provide a redshift determination for this object.
We thank Alan Watson (UNAM) for providing us with accurate coordinates of the afterglow. We acknowledge expert support from the ESO staff in Paranal, in particular Francesca Lucertini and Rodrigo Palominos.
GCN Circular 39417
Subject
GRB 250221A: GRANDMA/TAROT Detection
Date
2025-02-22T03:00:44Z (8 months ago)
From
Heather N. Muenter at UMN <hmuenter000@gmail.com>
Via
Web form
H. Muenter (UMN), F. Magnani (CPPM), S. Antier (OCA/IJCLAB), Y. Rajabov (UBAI), C. Andrade (UMN), A. Klotz (IRAP), C. Limonta, Q. Andre, A. Durroux (OCA), 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 collaboration:
We imaged the field of GRB 250221A detected by SWIFT (GCN 39396) with the TAROT robotic telescope located at the European Southern Observatory, La Silla observatory, Chile.
The first image was taken 45 s post T0 and without filter is trailed (see the description in Klotz et al., 2006, A&A 451, L39). We detect the UVOT optical transient at r-mag 17 +/- 0.1 mag, 1.95 min post T0. We continuously detected the source for the first 30 min.
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 39414
Subject
GRB 250221A: Swift-XRT refined Analysis
Date
2025-02-22T00:09:17Z (8 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), M. A. Williams (PSU), S.
Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio
(INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.0 ks of XRT data for GRB 250221A, from 107 s to 66.9
ks after the BAT trigger. The data comprise 9 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.06 (+/-0.06).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.09 (+0.24, -0.23). The
best-fitting absorption column is 1.4 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 3.7 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 3.3 x 10^-11 (4.4 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.4 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: 2.7 sigma
Photon index: 2.09 (+0.24, -0.23)
If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 2.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x
10^-14 (1.1 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01290305.
This circular is an official product of the Swift-XRT team.
GCN Circular 39413
Subject
GRB 250221A: NOT optical observations
Date
2025-02-22T00:06:03Z (8 months ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. Palmerio (CEA/Irfu), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), report on behalf of a larger collaboration:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412) of the Swift GRB 250221A (Caputo et al., GCN 39396), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the griz filters. The afterglow is well detected in all filters.
In a single r-band observation with mid-time 2025 Feb 21.86 UT (17.07 hr after the trigger), we measure for the afterglow r = 22.0 +- 0.15 AB, calibrated against nearby Pan-STARRS objects. Our measurement is affected by the presence of a nearby object about 1" to the NW, visible in the Legacy Survey (Watson et al., GCN 39397). More accurate photometry can be attained via template subtraction.
The nearby object has a photometric redshift z = 0.34 +- 0.08 (Zhou et al. 2021, doi:10.1093/mnras/staa3764). The relationship between this object and the GRB is unclear at the moment.
We thank Alan Watson (UNAM) for providing us with accurate coordinates of the afterglow. We also thank the observers at the NOT for securing our data, in particular Linda Lombardo, Annika Schichtel, Clara Peter, Diego Mederos Leber, Svenja Heil, and Nina Caviziel (all Goethe University Frankfurt).
GCN Circular 39412
Subject
GRB 250221A: 1.6m Mephisto optical detection
Date
2025-02-21T18:35:37Z (8 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Helong Guo, Guowang Du, Xinlei Chen, Xiaotong Chen, Yiheng Xie, Brajesh Kumar, Yuan Fang, Xingzhu Zou, Yu Pan (all SWIFAR, YNU), Xuhui Han, Pinpin Zhang, Liping Xin, Chao Wu (all NAOC), Yuanpei Yang, Jinghua Zhang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of Mephisto Team:
Simultaneous multi-band photometric observations of the Swift GRB 250221A (Caputo et al., GCN 39396; Beardmore et al., GCN 39404) was performed with 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were started from 11:55:52 2025-02-21 UT (~8.35 hr after the trigger) and several frames with different exposure time were obtained in uvgr bands. The afterglow candidate (Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409) is clearly detected in the stacked images of g and r band but not in u and v bands. The preliminary magnitudes and 3-sigma upper limits are below:
Start_Time(UT) Filter Exp(sec) Mag/LimMag(AB)
2025-02-21T11:55:53 u 120*4, 300*3 >22.20
2025-02-21T12:05:54 v 120*3, 300*3 >22.61
2025-02-21T11:55:52 g 120*4, 300*3 21.57 +/- 0.26
2025-02-21T12:05:54 r 120*3, 300*3 20.87 +/- 0.13
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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.
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GCN Circular 39410
Subject
GRB 250221A: AKO Optical Upper Limit
Date
2025-02-21T16:45:15Z (8 months ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Via
email
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International Astronomical Center in Abu Dhabi, UAE), and Shaikha Alshamsi, Nuha Manal Pattani, and Nidhal Guessoum (American University of Sharjah, UAE), report:
We observed the field of GRB 240221A (Swift BAT and XRT team, Caputo et al. GCN 39396, Beardmore et al., GCN 39404; Shilling et al., GCN 39409; COLIBRÍ/DDRAGO, Watson et al. GCN 39397; REM, Melandri et al. GCN 39406) with our 0.36m f/7.7 robotic telescope. The observation was performed on 21 February 2025 at 15:53: 37 UTC (mid-time), 12.32 hours after the trigger.
We obtained 11x180s images using Ic filter at the position given by Swift/XRT:
RA (J2000): 03h 57m 51.09s
Dec (J2000): -15d 08' 00.6"
We did not detect an afterglow candidate at the above position down to a magnitude of Ic = 19.7 for the stacked images. The magnitude was estimated using the Atlas catalogue as a reference. The magnitude is not corrected for galactic extinction.
GCN Circular 39409
Subject
GRB 250221A: Swift/UVOT Detection
Date
2025-02-21T15:27:39Z (8 months ago)
From
Sam Shilling at Lancaster University <shilling.sam@gmail.com>
Via
Web form
S.P.R. Shilling (Lancaster U.), A.A. Breeveld (UCL-MSSL)
and R. Caputo (NASA/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250221A
107 s after the BAT trigger (Caputo et al., GCN Circ. 39396).
A source consistent with the enhanced XRT position
(Beardmore et al., GCN Circ. 39404) is detected in the initial UVOT exposures
and appears to be fading. An optical candidate in this field is
also detected by Watson et al., (GCN Circ. 39397) and by
Melandri et al., (GCN Circ. 39406).
Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 127 277 147 17.52 +/- 0.04
white 620 639 19 18.41 +/- 0.17
v 107 118 10 17.10 +/- 0.32
v 4484 4683 197 >18.8
b 595 615 19 >18.7
u 340 590 245 17.78 +/- 0.07
w1 4894 5041 144 >19.0
m2 4689 4889 197 >18.6
w2 4279 4479 197 >18.7
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.332 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 39406
Subject
GRB 250221A: REM optical/NIR afterglow detection
Date
2025-02-21T13:50:48Z (8 months ago)
Edited On
2025-02-21T15:07:50Z (8 months ago)
From
Andrea Melandri at INAF-OAR <andrea.melandri@inaf.it>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Andrea Melandri at INAF-OAR <andrea.melandri@inaf.it>
Via
Web form
A. Melandri (INAF-OAR), R. Brivio, M. Ferro, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250221A detected by Swift (Caputo et al., GCN 39396; Beardmore et al., GCN 39404) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2025 February 21 at 03:35:39 UT (i.e. ~60 s after the Swift trigger), and lasting for about 2 hours.
From preliminary photometry we detect the counterpart in the optical and NIR images at the position of the optical afterglow (Francile et al., GCN 39395; Watson et al., GCN 39397) with the following early-time magnitudes:
r = 16.5 +/- 0.2 (AB; calibrated against the Pan-STARRS catalogue)
at a mid-time of t - t0 = 70 s after the trigger.
H = 14.8 +/- 0.3 (Vega; calibrated against the 2MASS catalogue)
at a mid-time t - t0 = 87 s after the trigger.
GCN Circular 39404
Subject
GRB 250221A: Enhanced Swift-XRT position
Date
2025-02-21T10:38:49Z (8 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1504 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 250221A, 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 = 59.46290, -15.13349 which is equivalent
to:
RA (J2000): 03h 57m 51.09s
Dec (J2000): -15d 08' 00.6"
with an uncertainty of 2.5 arcsec (radius, 90% confidence).
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).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 39397
Subject
GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
Date
2025-02-21T04:03:03Z (8 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Camila Angulo (UNAM), William H. Lee (UNAM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of Swift/BAT GRB 250221A (Caputo et al., GCN Circ. 39396) 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 started observing at 2025-02-21 03:35:56 UTC (80 seconds after the trigger). The data were coadded with custom software 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 first two 60 second exposure, we detect a source with
i = 17.04 +/- 0.01
There is a much fainter source visible in the Pan-STARRS DR2 at this position. This might be the host galaxy.
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 39396
Subject
GRB 250221A: Swift detection of a burst with an optical counterpart
Date
2025-02-21T03:53:15Z (8 months ago)
From
David Palmer at LANL <palmer@lanl.gov>
Via
email
R. Caputo (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. M. Parsotan (GSFC)
and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 03:34:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250221A (trigger=1290305). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 59.477, -15.139 which is
RA(J2000) = 03h 57m 54s
Dec(J2000) = -15d 08' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peak
structure with a duration of about 5 sec. The peak count rate
was ~2200 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 03:36:39.9 UT, 122.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 59.46251, -15.13379
which is equivalent to:
RA(J2000) = 03h 57m 51.00s
Dec(J2000) = -15d 08' 01.6"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 53 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.73 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.1
(+2.63/-2.31) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 250 seconds with the U filter starting
340 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 03:57:51.06 = 59.46274
DEC(J2000) = -15:07:59.2 = -15.13311
with a 90%-confidence error radius of about 0.76 arc sec. This position is 2.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.82 with a 1-sigma error of about 0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.046.
Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)