May 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 38610] GRB 250527D: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 30 May '25

30 May '25

TITLE: GCN CIRCULAR NUMBER: 40575 SUBJECT: GRB 250527D: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/30 03:02:08 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Akaike (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, 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 250527D (Swift/BAT-GUANO localization skymap: DeLaunay et al., GCN Circ. 40573) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 23:38:44.85 UTC on 27 May 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1432424119). The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.1 sec, peaks at T+5.1 sec, and ends at T+5.6 sec. The T90 and T50 durations measured by the SGM data are 3.1 +/- 0.2 sec and 1.7 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1432424119 The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/40575. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38609] GRB 250527C: Swift/UVOT Upper Limits
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40574 SUBJECT: GRB 250527C: Swift/UVOT Upper Limits DATE: 25/05/29 21:29:30 GMT FROM: noelklin(a)umbc.edu N. Klingler (UMBC / NASA-GSFC / CRESST II) reports on behalf of the Swift/UVOT team: Swift/UVOT has performed observations of GRB 250527C centered on the BAT position, RA, Dec = 21h 18m 31.92s, +52d 44' 13.2" (= 319.633, 52.737 deg; 90% uncertainty of 5 arcmin) (DeLaunay et al.; GCN 40563). UVOT collected 4536 s of data between 96 ks and 113 ks post-trigger, using the White filter. No uncatalogued/transient sources are detected, with an approximate 3 sigma upper limit > 22.56 (AB) in the 90% BAT localization region. For the X-ray sources detected by XRT (https://www.swift.ac.uk/ToO_GRBs/00021843/): sources 3, 4, and 6 fall outside the UVOT field of view. XRT source 2 is not detected. XRT source 1 is a star: TYC 3953-1190-2. XRT 5 has an optical counterpart (AB mag 17.99 +/- 0.07), but it is seen in archival DSS images and thus does not appear to be a transient. No correction has been made for the expected Galactic extinction due to the reddening of E(B-V) = 3.43 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40574. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38608] GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40573 SUBJECT: GRB 250527D: Swift/BAT-GUANO localization skymap of a burst DATE: 25/05/29 13:56:28 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report: Swift/BAT did not localize GRB 250527D onboard (T0: 2025-05-27T23:38:44.84 UTC, CALET trig 1432424119) The CALET 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 90 seconds of BAT event-mode data from [-45,+45] 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 20.4 in a 2.048 s analysis time bin, starting at T0 + 3.584 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 4,958 deg2 and the 50% credible area is 912 deg2. The integrated probability inside the coded field of view is <1%. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=770081960/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/770081960/0_n_PROBMAP) 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=770081960 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/ View this GCN Circular online at https://gcn.nasa.gov/circulars/40573. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38607] EP J1350.0-8622: EP-FXT follow-up observation
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40572 SUBJECT: EP J1350.0-8622: EP-FXT follow-up observation DATE: 25/05/29 13:35:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. H. Zhao, M. J. Liu (NAO, CAS), Y. Wang (PMO, CAS),W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the X-ray transient candidate EP J1350.0-8622 (Liu et al., GCN 40548, I. Perez-Garcia et al., GCN 40549), a follow-up observation was performed by EP-FXT at 2025-05-26T23:17:23 (UTC), about 24 hours after the detection, with an exposure time of 1.85 ks. An X-ray source is detected at R.A., Dec. = 207.5779, -86.3934 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors), which is likely associated with the 1eRASS J135031.1-862323. The unabsorbed 0.5-10 keV flux is estimated to be 1.9 (+1.2, -0.9) x 10^-13 erg/cm^2/s, derived using an absorbed power law model with the hydrogen column density fixed to the Galactic value of 8.2 x 10^20 cm^-2 and the photon index fixed at 2.0, due to the limited photon statistics. All uncertainties quoted above are at the 90% confidence level. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/40572. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38606] GRB 250529B: Fermi GBM Final Real-time Localization
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40571 SUBJECT: GRB 250529B: Fermi GBM Final Real-time Localization DATE: 25/05/29 11:08:59 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 10:58:24 UT on 29 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250529B (trigger 770209109.316756 / 250529457). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 149.1, Dec = 71.6 (J2000 degrees, equivalent to J2000 09h 56m, 71d 35'), with a statistical uncertainty of 2.9 degrees. The angle from the Fermi LAT boresight is 121.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529457/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40571. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38605] GRB 250527B: Swift-XRT observations
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40570 SUBJECT: GRB 250527B: Swift-XRT observations DATE: 25/05/29 09:30:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 250527B in a series of observations tiled on the sky. The total exposure time is 3.5 ks, distributed over 12 tiles; the maximum exposure at a single sky location in the tiling was 620 s. The data were collected between T0+57.5 ks and T0+65.2 ks, and are entirely in Photon Counting (PC) mode. No X-ray sources have been detected. The 3-sigma upper limit in the field (not including the regions where the tiles overlap) ranges from ~0.02 to ~0.05 ct s^-1, corresponding to a 0.3-10 keV observed flux of 9.2e-13 to 2.0e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum). The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00136. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38604] EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40569 SUBJECT: EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6 DATE: 25/05/29 04:32:53 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, G. Garcia-Segura and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of trigger 01709177124 by EP-WXT (Hu et al. GCNC [40568](https://gcn.nasa.gov/circulars/40568)), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to the alert on May. 28, 17:17 UT (i.e. 2 min after detection and 32 min after notification). Within the reported EP-FXT error circle we find the star Gaia DR3 5778356748440163840 decreasing in brightness from 14.0 to 16.0 mag in clear filter and using Gaia DR3 Gmag magnitude as reference, during a ~3 hour time interval, confirming as due to a stellar flare. We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40569. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38603] The EP-WXT trigger 01709177124 is likely a flaring star
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40568 SUBJECT: The EP-WXT trigger 01709177124 is likely a flaring star DATE: 25/05/29 04:00:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. F. Hu (PMO, CAS), S. Q. Jiang, W. X. Wang, Y. J. Song, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709177124 at the time of 2025-05-28T16:45:02, is likely a stellar flare associated with Gaia DR3 5778356748440163840. The estimated flux of the flare is around 1.4 x 10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 2.5 x 10^(31) erg/s. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/40568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38602] GRB 250529A: Fermi GBM Final Real-time Localization
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40567 SUBJECT: GRB 250529A: Fermi GBM Final Real-time Localization DATE: 25/05/29 03:56:55 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 03:46:16 UT on 29 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250529A (trigger 770183181.316048 / 250529157). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 7.1, Dec = 54.7 (J2000 degrees, equivalent to J2000 00h 28m, 54d 42'), with a statistical uncertainty of 4.2 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529157/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529157/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250529157/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40567. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38601] GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
by GCN Circulars 29 May '25

29 May '25

TITLE: GCN CIRCULAR NUMBER: 40566 SUBJECT: GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart DATE: 25/05/29 02:45:22 GMT FROM: Igor Andreoni at JSI/UMD/NASA <igor.andreoni(a)gmail.com> Igor Andreoni (UNC), Anna Ho (Cornell), Vishwajeet Swain (IITB), Michael Coughlin (UMN), on behalf of the ZTF Collaboration The optical transient ZTF25aarhkyn / AT2025mgj was first detected by the Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) on 2025-05-23 03:42 UT at a magnitude r = 17.61 +- 0.07 (AB) during the regular survey. The previous non-detection at the transient location was on 2025-05-09 05:23. AT2025mgj was identified as a rapidly evolving transient by the ''ZTF Realtime Search and Triggering'' project (ZTFReST; Andreoni & Coughlin et al., 2021) and by a custom filter for fast transient discovery (Ho et al., 2022) within the ZTF Collaboration. A fading rate of ~0.4 mag/day was observed in r-band in the first two days after the initial detection. This was followed by a slower evolution. The latest photometric data point, r~18.7 mag, was taken on 2025-05-27 04:07 UT. Only r-band data points are available, so we do not have color information. The rapidly fading transient AT2025mgj is spatially and temporally consistent with the “likely short” gamma-ray burst GRB 250521C detected by the Fermi GBM instrument on 2025-05-21 13:31:01.20 UT (Fermi GBM team, GCN Circular 40515). The GRB location was reported with a statistical uncertainty of 16.05 deg, the angular separation between AT2025mgj and the center of the GBM localization is 11.05 deg. Archival ZTF and Legacy Survey images do not reveal high S/N detections. A faint (r=24.21 mag) source may be present near the transient location in Legacy Survey DR10, which is classified as a likely galaxy according to Tractor modeling, although classification is challenging at such faint magnitudes. We caution that, with the data in hand, we cannot exclude that AT2025mgj is a Galactic source. The transient was found at a relatively low Galactic latitude (l, b = 161.329994, 21.4 deg) and the light curve behavior may resemble a CV. Follow-up observations are strongly encouraged to determine the nature of this optical transient and its possible association with GRB 250521C. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. View this GCN Circular online at https://gcn.nasa.gov/circulars/40566. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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