TITLE: GCN CIRCULAR
NUMBER: 40612
SUBJECT: GRB 250602A: Fermi GBM Observation
DATE: 25/06/03 01:47:35 GMT
FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu>
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
At 03:04:31.31 UT on 02 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250602A (trigger 770526276/250602128).
which was also detected by Fermi-LAT (A. Holzmann Airasca, et al. 2025, GCN 40611).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.
The angle from the Fermi LAT boresight is 111 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 14.6 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+8.768 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.9 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 120 +/- 10 keV.
The event fluence (10-1000 keV) in this time interval is
(1.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band is 5.8 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 102 +/- 22 keV, alpha = -0.7 +/- 0.3 and beta = -2.2 +/- 0.2.
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/
View this GCN Circular online at https://gcn.nasa.gov/circulars/40612.
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TITLE: GCN CIRCULAR
NUMBER: 40611
SUBJECT: GRB 250602A: Fermi-LAT detection
DATE: 25/06/02 20:13:59 GMT
FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov>
A. Holzmann Airasca (UniTrento and INFN Bari), S. Lopez (CNRS / IN2P3), R. Gupta (NASA GSFC), F. Longo (University and INFN, Trieste), N. Di Lalla (Stanford Univ.), and J. Racusin (NASA GSFC) report on behalf of the Fermi-LAT Collaboration:
On June 02, 2025, Fermi-LAT detected high-energy emission from GRB 250602A, which was also detected by Fermi-GBM (trigger 770526276 / 250602128, GCN 40602).
The best LAT on-ground location is found to be:
RA, Dec = 111.9, 56.9 (J2000)
with an error radius of 0.4 deg (90 % containment, statistical error only). This was 111 deg from the LAT boresight at the time of the GBM trigger (T0 = 03:04:31.31 UT).
The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 3000 - 8000 s after the GBM trigger is (8.2 ± 3.2) E-7 ph/cm2/s. The estimated photon index above 100 MeV is -2.17 ± 0.33.
The highest-energy photon is a 1.6 GeV event which is observed ~ 4800 seconds after the GBM trigger.
The Fermi-LAT point of contact for this burst is Rahul Gupta (rahul.gupta(a)nasa.gov).
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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40611.
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TITLE: GCN CIRCULAR
NUMBER: 40610
SUBJECT: GRB 250602A: DDOTI Optical Upper Limit
DATE: 25/06/02 19:56:39 GMT
FROM: sahil.atri(a)students.uniroma2.eu
Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of GRB 250602A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40602) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-06-02 UTC.
DDOTI observed the Fermi/GBM error region, covering about 88% of the statistical
error region (Fermi GBM Team, GCN Circ. 40602). DDOTI observed the field of GRB 250602A from 04:05 UTC to 06:05 UTC (from T+1.01 h to T+ 3.02 h after the trigger) and obtained a total exposure of 50 minutes, alternating with other scientific programs.
Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we
detect no uncatalogued fading sources within the observed field down to a 10-sigma limiting AB magnitude of:
w > 20.0
This value is not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40610.
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TITLE: GCN CIRCULAR
NUMBER: 40609
SUBJECT: GRB 250530C: Swift-BAT refined analysis
DATE: 25/06/02 19:11:33 GMT
FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com>
D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC),
R. Caputo (NASA/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), D. M. Palmer (LANL),
T. Parsotan (GSFC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+885 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250530C (trigger #1319125)
(Caputo, et al., GCN Circ. 40585). The BAT ground-calculated position is
RA, Dec = 55.146, -22.457 deg which is
RA(J2000) = 03h 40m 35.1s
Dec(J2000) = -22d 27' 26.1"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
The mask-weighted light curve displays a complex structure with multiple dim pulses.
The T90 (15-350 keV) is 42.86 +- 6.04 sec (estimated error including systematics).
The time-averaged spectrum from T-29.77 to T+21.26 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.32 +- 0.17. The fluence in the 15-150 keV band is 8.5 +- 0.9 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.28 sec in the 15-150 keV band
is 0.8 +- 0.2 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/1319125
View this GCN Circular online at https://gcn.nasa.gov/circulars/40609.
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TITLE: GCN CIRCULAR
NUMBER: 40608
SUBJECT: GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
DATE: 25/06/02 16:07:14 GMT
FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie>
A. Martin-Carrillo (UCD), B. Schneider (LAM), L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), G. Corcoran (UCD), B. Gompertz (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud), R. H. Rasmussen (NOT and Aarhus Univ.), report on behalf of a larger collaboration.
We carried out spectroscopic observations of AT2025mgj (Andreoni et al., GCN 40566), a candidate optical counterpart to GRB 250521C (Fermi GBM team, GCN 40515), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 4x900 s exposures starting at 21:16 UT on 2025-05-31 (10.3 days after the Fermi trigger) with a wavelength coverage of 3800-9500 AA.
The spectrum shows a blue, featureless continuum, peaking at around 4500 AA. Redward of the peak, the continuum is consistent with a power law F_lambda propto lambda^-2.7. The overall shape does not resemble a power-law spectrum, which would be typical of GRB afterglows, nor a SN spectrum, given the lack of any features. Although the spectrum does not fully resemble those of dwarf novae in outbursts, the spectral energy distribution is overall consistent with previous examples (e.g. Aviles et al. 2018, doi:10.14482/INDES.30.1.303.661).
In summary, our spectroscopic observations confirm that AT2025mgj is not associated with GRB250521C, as already suggested by Busmann et al. (GCN 40597) and Gillanders et al. (GCN 40605) based on photometric observations.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40608.
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TITLE: GCN CIRCULAR
NUMBER: 40607
SUBJECT: GRB 250601A: EP-FXT follow-up observation and afterglow candidates
DATE: 25/06/02 15:46:51 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
Q. C. Liu (THU), X. Y. Zhou (PRIC), H. L. Peng (NNU), B. B. Zhang (BNU) and Y. Liu (NAO,CAS) report on behalf of the Einstein Probe (EP) team :
We performed a follow-up observation of GRB 250601A (detected through on-broad trigger of Fermi/GBM, Fermi, GCN #40596, and localized by Swift/BAT, DeLaunay, GCN #40600; followed by Swift/XRT, Page et al., GCN #40604), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-06-02T02:10:26 (T-TGRB ~ 8.7 hrs) with an exposure time of about 5.8 ks.
Two uncatalogued sources were detected by FXT-A and FXT-B in the 3-sigma Swift/BAT error circle with a radius of 493 arcsecond centered at RA, DEC = 90.0709 deg, -57.2892 deg, as listed below (the FXT flux is taken from FXT-B module). EP J060023.3-571631 has a separation of 11.6 arcsecond from the XRT source 3, and EP J060048.7-571413 has a separation of 4.8 arcsecond from the XRT source 2.
Source name | RA | DEC | Estimated Flux | SNR | Dist from Swift/BAT |
| deg | deg | (erg/s/cm^2) | | offset (in arcmin) |
EP J060023.3-571631 | 90.0971 | -57.2752 | 3.2(+/-1.2) x 10^-14 | 4.1 | 1.19 |
EP J060048.7-571413 * | 90.2037 | -57.2368 | 1.0(+/-0.2) x 10^-13 | 9.4 | 5.33 |
Note: * EP J060048.7-571413 was also detected by Swift/XRT (GCN #40604) in a ~4.6 ks observation conducted at T-TGRB ~ 4.8 hrs, with a flux of ~ 4e-13 erg/s/cm^2. The source thus exhibits a decreasing trend in the X-ray flux within the two epochs.
The above observation was made with the EP-FXT instrument. 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.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40607.
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TITLE: GCN CIRCULAR
NUMBER: 40606
SUBJECT: GRB 250601A: Swift/XRT candidate afterglow
DATE: 25/06/02 15:13:44 GMT
FROM: Chiara Salvaggio at INAF OABrera <chiara.salvaggio(a)inaf.it>
C. Salvaggio (INAF-OAB), S. B. Cenko (GSFC), B. Sbarufatti (INAF-OAB)
report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/GBM,
Swift/BAT-GUANO detected burst GRB 250601A (GCN 40596, 40600).
Two XRT sources have been previously reported in GCN 40604. One of the two
sources (source 2) has an eROSITA counterpart, while XRT source 3 is a new
transient. Therefore we consider source 3 a candidate afterglow for GRB
250601A.
Source 3:
RA (J2000.0): 90.0936 = 06:00:22.47
Dec (J2000.0): -57.2778 = -57:16:40.0
Error: 5.7 arcsec (radius, 90% conf.)
Count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1
Distance: 60 arcsec from Swift/BAT position.
Flux: (1.00 [+0.45, -0.35])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
More Swift/XRT observations are planned to (un)confirm the afterglow
detection.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021844.
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40606.
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TITLE: GCN CIRCULAR
NUMBER: 40605
SUBJECT: GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
DATE: 25/06/02 15:01:40 GMT
FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com>
J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii).
We observed the fast-fading transient AT2025mgj (Andreoni et al., GCN 40566), tentatively associated with the short-GRB 250521C (Fermi GBM Team, GCN 40515) using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJDs 60825.26 and 60827.26 (approximately 8.7 and 10.7 days post-GRB, respectively). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters.
Our observations consisted of 120s (MJD 60825.26) and 200s exposures (MJD 60827.26) in grizy-bands. All images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target images (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4).
From these difference images, we recover the following photometry measurements:
MJD Filter AB mag
60825.26 g 18.97 +/- 0.06
60825.26 r 19.18 +/- 0.08
60825.26 i 19.29 +/- 0.08
60825.26 z 19.5 +/- 0.2
60827.26 g 19.29 +/- 0.05
60827.26 r 19.39 +/- 0.06
60827.26 i 19.62 +/- 0.06
60827.26 z 19.57 +/- 0.08
From our multi-band Pan-STARRS photometry, we estimate a fade rate of ~0.1 mag/day in r-band. Our rate of fading across our photometric bands match those reported previously by Martin-Carrillo et al. (GCN 40584), Becerra et al. (GCN 40590), and Busmann et al. (GCN 40597).
The rate of fading and persistent blue colour, with some indication of cooling, are all reminiscent of typical CV behaviour. While the connection to GRB 250521C cannot be definitively ruled out, the data match the lightcurve behaviour of CVs. Late-time, deep imaging is required to unambiguously uncover the nature of AT2025mgj. A point source would confirm AT2025mgj is indeed a CV, whereas an extended source in its vicinity would indicate that it was the afterglow of GRB 250521C.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40605.
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TITLE: GCN CIRCULAR
NUMBER: 40604
SUBJECT: GRB 250601A: Swift-XRT observations
DATE: 25/06/02 08:18:00 GMT
FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk>
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio
(INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara
(PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 250601A, collecting 4.6 ks of Photon
Counting (PC) mode data between T0+17.2 ks and T0+35.3 ks.
Two uncatalogued X-ray sources have been detected within the estimated
3-sigma Swift/BAT error region (493 arcsec), however none of them is
above the RASS limit or shows definitive signs of fading. Therefore, at
the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:
Source 2:
RA (J2000.0): 90.2023 = 06:00:48.56
Dec (J2000.0): -57.2379 = -57:14:16.6
Error: 7.3 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: (7.8 +/- 1.9)e-3 ct s^-1
Distance: 315 arcsec from Swift/BAT position.
Flux: (4.2 +/- 1.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Source 3:
RA (J2000.0): 90.0936 = 06:00:22.47
Dec (J2000.0): -57.2778 = -57:16:40.0
Error: 5.7 arcsec (radius, 90% conf.)
Count-rate: (3.6 [+1.6, -1.3])e-3 ct s^-1
Distance: 60 arcsec from Swift/BAT position.
Flux: (1.00 [+0.45, -0.35])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Another uncatalogued source was also detected, however this was too far
from the GRB position to be the afterglow.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021844.
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/40604.
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