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[vsnet-grb-info 38079] GRB 250331B Swift-BAT refined analysis
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40056 SUBJECT: GRB 250331B Swift-BAT refined analysis DATE: 25/04/04 16:16:25 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+842 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250331B (trigger #1299965) (Cenko, et al., GCN Circ. 39958). The BAT ground-calculated position is RA, Dec = 71.377, 43.794 deg which is RA(J2000) = 04h 45m 30.4s Dec(J2000) = +43d 47' 39.1" with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 55%. The mask-weighted light curve displays a single dim pulse. The T90 (15-350 keV) is 3.95 +- 0.77 sec (estimated error including systematics). The time-averaged spectrum from T-0.72 to T+3.76 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.61 +- 0.38. The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+1.28 sec in the 15-150 keV band is 0.9 +- 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/1299965 View this GCN Circular online at https://gcn.nasa.gov/circulars/40056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38078] GRB 250331B Swift-BAT refined analysis
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40056 SUBJECT: GRB 250331B Swift-BAT refined analysis DATE: 25/04/04 16:16:25 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+842 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250331B (trigger #1299965) (Cenko, et al., GCN Circ. 39958). The BAT ground-calculated position is RA, Dec = 71.377, 43.794 deg which is RA(J2000) = 04h 45m 30.4s Dec(J2000) = +43d 47' 39.1" with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 55%. The mask-weighted light curve displays a single dim pulse. The T90 (15-350 keV) is 3.95 +- 0.77 sec (estimated error including systematics). The time-averaged spectrum from T-0.72 to T+3.76 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.61 +- 0.38. The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+1.28 sec in the 15-150 keV band is 0.9 +- 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/1299965 View this GCN Circular online at https://gcn.nasa.gov/circulars/40056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38077] GRB 250403A: Swift/UVOT Detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40048 SUBJECT: GRB 250403A: Swift/UVOT Detection DATE: 25/04/04 13:28:59 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on behalf of the Swift UVOT team: Swift/UVOT observed the field of GRB 250403A detected by Fermi GBM (Fermi team, GCN Circ. 40025) and SVOM/ECLAIRs (Julakanti et al., GCN Circ. 40026), starting at 17:22:59 UT on 24/04/03, ~2.1 hours after the initial detections. An optical afterglow is initially detected in the U-band consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (Dichiara et al., GCN Circ. 40037) and the optical afterglow detected by various facilities (Starling et al., GCN Circ. 40028; Wu et al., GCN Circ. 40029; Du et al., GCN Circ. 40031; Li et al., GCN Circ. 40032; Ghosh et al., GCN Circ. 40039; Jiang et al., GCN Circ. 40041; Pérez-Fournon et al., GCN Circ. 40043; Xin et al., GCN Circ. 40045). At 00:02:02 UT on 25/04/04, ~6.7 hours later, the optical afterglow is no longer detected. The preliminary detection and 3-sigma upper limits calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial and subsequent exposures are: Filter T_start(h) Exp(s) Mag u 2.1 396 19.2 +/- 0.2 u 8.8 492 >20.3 b 8.8 386 >20.5 v 9.0 130 >19.0 w1 12.1 164 >19.3 m2 12.0 245 >19.7 w2 8.9 246 >19.8 The magnitudes given are calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) and are not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38076] GRB 250330A Swift-BAT refined analysis
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40055 SUBJECT: GRB 250330A Swift-BAT refined analysis DATE: 25/04/04 16:15:22 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> H. A. Krimm (NSF), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), R. Gupta (GSFC), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-137 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250330A (trigger #1299776) (Cenko, et al., GCN Circ. 39938). The BAT ground-calculated position is RA, Dec = 252.685, -86.875 deg which is RA(J2000) = 16h 50m 44.5s Dec(J2000) = -86d 52' 29.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 98%. The mask-weighted light curve shows a single well defined fast-rise exponential- decay pulse shape. the T90 (15-350 keV) is 11.27 +- 2.53 sec (estimated error including systematics). The time-averaged spectrum from T-0.16 to T+14.33 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.10. The fluence in the 15-150 keV band is 9.2 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+0.26 sec in the 15-150 keV band is 4.0 +- 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/1299776 View this GCN Circular online at https://gcn.nasa.gov/circulars/40055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38075] EP250321A: J band upper limit by SYSU 80cm telescope
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40054 SUBJECT: EP250321A: J band upper limit by SYSU 80cm telescope DATE: 25/04/04 15:32:10 GMT FROM: Yan Yu <yuyan35(a)mail2.sysu.edu.cn> Yan Yu, Jin-Ji Li, Jia-Qi Lin, Wei-Sen Huang, Zhong-Nan Dong, Pu Lin, Hao-Nan Yang, Hao-Ran Zhang, Chun Chen, P H Thomas Tam, Rong-Feng Shen, Bin Ma(Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team: We observed the field of EP250321A (EP GCN 39800; MASTER-OAFA GCN 39803; Zhu et al., GCNs 39809; Swift-XRT GCN 39811) using the Sun Yat-sen University 80cm infrared telescope with 90 x 20 s exposures in J band. The calculated position is RA. = 179.2625 deg, DEC = 17.3628 deg J2000, from EP observation. Our observations began at 2025-3-22 13:25:00 UTC, 31.25 hours after the EP trigger. We do not detect any counterpart at the position of the optical afterglow (Fu et al., GCN 39804; Perez-Garcia et al., GCNs 39805; Brivio et al., GCNs 39807; Becerra et al., GCNs 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831; Zheng et. al, GCN 39832; Pankov et al., GCN 39836; Bochenek et. al, GCN 7939837; Zhu et. al, GCN 39854), down to a 5-sigma depth of J~ 17.6 Vega magnitudes. View this GCN Circular online at https://gcn.nasa.gov/circulars/40054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38074] EP250404a: BOOTES-4/JGT optical afterglow detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40053 SUBJECT: EP250404a: BOOTES-4/JGT optical afterglow detection DATE: 25/04/04 15:31:24 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, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report: Following the detection of EP250404a by Einstein Probe (Hu et al. GCNC [40051](https://gcn.nasa.gov/circulars/40051)), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this X-ray transient starting on 2025-04-04 14:39:39UT (20 min after detection and 15 after notification). Series of images in clear filter were gathered and we detect and uncatalogud source constistent with position reported by Xu et al. (GCN [40052](https://gcn.nasa.gov/circulars/40052)). Using GaiaDR3 Gmag as reference we measure an initial magnitude of 14.8 +/- 0.03. Within 20 minutes, the source faded to magnitude 16.1. Further analysis of the additional images is ongoing. We thank the staff at Lijiang observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38073] EP250404a: Nanshan/HMT optical counterpart detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40052 SUBJECT: EP250404a: Nanshan/HMT optical counterpart detection DATE: 25/04/04 15:12:14 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> S.Q. Jiang, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of EP250404a detected by EP (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A detected by Fermi/GBM (GBM team, GCN 40050), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 14:24:59 UT on 2025-04-04, i.e., 300 s after the EP/WXT trigger time, and a series of unfiltered frames with different exposures were obtained. An uncatalogued and varying optical source is detected within the EP/FXT error circle at coordinates: R.A.(J2000) = 08:20:14.54 Dec.(J2000) = +35:31:41.57 with an uncertainty of ~0.5 arcsec. The source has R ~ 16.1 mag in the first image, calibrated with the nearby Pan-STARRS field and not corrected for Galactic extinction. Observations are still ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/40052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38072] EP250404a: Einstein Probe detection of an X-ray transient
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40051 SUBJECT: EP250404a: Einstein Probe detection of an X-ray transient DATE: 25/04/04 15:03:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. W. Hu (NAO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. L. Hua (PMO, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250404a. The transient triggered EP-WXT (ID: 01709133918) at 2025-04-04T14:19:59 (UTC). The WXT position of the source is R.A. = 125.064 deg, DEC = 35.511 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 125.0575 deg, DEC = 35.5305 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). It is noted that EP250404a is temporally and spatially coincident with GRB 250404A (Fermi team, GCN Circ. 40050). Further information will be updated when the telemetry data is received. 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/40051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38071] GRB 250404A: Fermi GBM Final Real-time Localization
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40050 SUBJECT: GRB 250404A: Fermi GBM Final Real-time Localization DATE: 25/04/04 14:30:25 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 14:19:46 UT on 4 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250404A (trigger 765469191.347644 / 250404597). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 123.4, Dec = 34.1 (J2000 degrees, equivalent to J2000 08h 13m, 34d 06'), with a statistical uncertainty of 1.2 degrees. The angle from the Fermi LAT boresight is 42.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250404597/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38070] GRB 250402A: Mondy optical observations
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40049 SUBJECT: GRB 250402A: Mondy optical observations DATE: 25/04/04 14:24:06 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> E. Mazaeva (IKI), E. Klunko (ISTP), N. Pankov (HSE), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed GRB 250402A (Chen et al. GCN 40014) with the AZT-33IK telescope starting on 2025-04-03 (UT) 18:11:28. We found the optical counterpart (Xin et al., GCN 40015; Pérez-Fournon et al., GCN 40020; Schneider et al., GCN 40022; Magnani et al., GCN 40023) at the position reported by Xin et al., GCN 40015. Preliminary photometry of the optical counterpart is the following Date UT start t-T0 Filter Exp. OT Err. UL(3sigma) (mid, days) (s) 2025-04-03 18:11:28 0.81567 R 29*120 21.9 0.2 22.3 The photometry is based on the nearby PS1 stars (R mag by Lupton transformations). View this GCN Circular online at https://gcn.nasa.gov/circulars/40049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38069] GRB 250403A: Swift/UVOT Upper Limits
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40048 SUBJECT: GRB 250403A: Swift/UVOT Upper Limits DATE: 25/04/04 13:28:59 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and S. R. Oates (Lancaster U.) report on behalf of the Swift UVOT team: Swift/UVOT observed the field of GRB 250403A detected by Fermi GBM (Fermi team, GCN Circ. 40025) and SVOM/ECLAIRs (Julakanti et al., GCN Circ. 40026) starting at 00:02:02 UT on 25/04/04, ~8.75 hours after the initial detections. No optical afterglow is detected consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (Dichiara et al., GCN Circ. 40037) or the optical afterglow detected by various facilities (Starling et al., GCN Circ. 40028; Wu et al., GCN Circ. 40029; Du et al., GCN Circ. 40031; Li et al., GCN Circ. 40032; Ghosh et al., GCN Circ. 40039; Jiang et al., GCN Circ. 40041; Pérez-Fournon et al., GCN Circ. 40043; Xin et al., GCN Circ. 40045). Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter Exp(s) Mag u 492 >20.3 b 386 >20.5 v 130 >19.0 w1 164 >19.3 m2 245 >19.7 w2 246 >19.8 The magnitudes in the table are not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38068] GRB 250402A: Swift/UVOT Upper Limits
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40047 SUBJECT: GRB 250402A: Swift/UVOT Upper Limits DATE: 25/04/04 12:51:00 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and S. R. Oates (Lancaster U.) report on behalf of the Swift UVOT team: Swift/UVOT observed the field of SVOM/ECLAIRs GRB 250402A (Chen et al. GCN Circ. 40014) for 2521 seconds in the U-band starting at 12:48:12 UT on 25/04/03, ~13 hours after the detection by SVOM/ECLAIRs. No optical afterglow is detected within a 5" radius of the position of the uncatalogued X-ray source detected by Swift/XRT (Dichiara et al., GCN Circ. 40027) and SVOM/MXT (Maggi et al., GCN circ. 40019) or the optical afterglow detected by SVOM/VT (Xin et al., GCN Circ. 40015), LCOGT (Pérez-Fournon et al., GCN Circ. 40020), and the SVOM/COLIBRÍ (Magnani et al., GCN Circ. 40023). The Swift/UVOT non-detection in the U-band has a preliminary 3-sigma upper limit of >21.1, calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373). View this GCN Circular online at https://gcn.nasa.gov/circulars/40047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38067] EP250402a: Optical upper limit with Kinder observations
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40046 SUBJECT: EP250402a: Optical upper limit with Kinder observations DATE: 25/04/04 12:01:23 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, Y.-H. Lee, T.-W. Chen, W.-J. Hou (all NCU), S. Brennan (OKC), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, H.-Y. Hsiao, C.-S. Lin, H.-C. Lin, C.-H. Lai, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250402a (Li et al., GCN 40017, GCN 40038) using the 40cm SLT telescope at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the r-band started at 14:18 UT on the 3rd of April 2025 (MJD = 60768.538), ~24.43 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. We did not detect any uncataloged optical counterpart candidate within the EP-WXT/EP-FXT localization error circle of radius 2.5 arcminutes/10 arcseconds. The field of FXT is only covered by SkyMapper. We further employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, 62) to perform PSF photometry on our stacked frames. The details of the observations and measured three sigma upper limits (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 60768.538 | 24.43 | 300 * 24 | >20.5 | 1".83 | 3.11 The presented upper limit was calibrated using the field stars from the SkyMapper catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.38 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/40046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38066] GRB 250403A: SVOM/VT optical observation
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40045 SUBJECT: GRB 250403A: SVOM/VT optical observation DATE: 25/04/04 11:49:37 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, Y. L. Qiu, C. Wu, H. L. Li, J . Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, Y. N. Yi, J. Y. Wei (NAOC), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM team: SVOM performed a Target of Opportunity observation of GRB 250403A detected by Fermi/GBM (Fermi GBM team, GCN 40025) and SVOM/ECLAIRs (Julakanti et al., GCN 40026) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical afterglow (Starling et al., GCN. 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041, Pérez-Fournon et al., GCN 40043, Brivio et al., GCN 40044) was detected with a brightness of VT_R=21.26 +/- 0.07 (AB) mag and VT_B=21.78 +/- 0.07 (AB) at the mid time of 14.26 hours after the burst. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38065] GRB 250403A: REM NIR afterglow detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40044 SUBJECT: GRB 250403A: REM NIR afterglow detection DATE: 25/04/04 10:49:24 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> 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 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 03 at 23:27:03 UT (i.e. 8.2 hr after the burst), and lasted for about 1 hour. From preliminary photometry, we detect the NIR counterpart at the position of the optical afterglow (Starling et al., GCN. 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041, Pérez-Fournon et al., GCN 40043) with the following magnitude: H = 16.3 +/- 0.3 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 8.6 hours after the trigger. The afterglow is not detected in our r-band observations down to the following 3sigma limit: r > 20.7 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 8.7 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38064] GRB 250403A: LCO optical counterpart detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40043 SUBJECT: GRB 250403A: LCO optical counterpart detection DATE: 25/04/04 10:34:53 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report on Las Cumbres Observatory Global Telescope network (LCOGT) observations of GRB 250403A, detected by Fermi GBM (Fermi GBM team, GCN circ. 40025), SVOM/ECLAIRs (Julakanti et al., GCN circ. 40026), and Swift XRT (Dichiara et al., GCN circ. 40037) We observed the field of GRB 250403A with two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa) in the SDSS r, i, g, and u filters, starting at 2025-04-03 22:00:46 UTC, about 6.76 hours after the Fermi and SVOM triggers. A source is clearly detected in the four filters at the position of the optical counterpart first reported by GOTO (Starling et al., GCN circ. 40028) and detected also by WU et al. (GCN circ. 40029), Du et al. (GCN circ. 40031), Li et al. (GCN circ. 40032), Julakanti et al. (GCN circ. 40034), Ghosh et al. (GCN circ. 40039), and Jiang et al. (GCN circ. 40041). The r, i, and g images were calibrated against Pan-STARRS DR2 stars and the u image was calibrated against stars from the Gaia DR3 synthetic photometry catalog generated from the Gaia BP/RP mean spectra (Gaia Collaboration, 2022). We measure the following preliminary magnitudes, that are not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) --------------------------------------------------------------------- 2025-04-03 22:00:46 20.34 0.08 r 300 2025-04-03 23:00:56 20.39 0.08 i 300 2025-04-03 23:08:52 20.97 0.08 g 300 2025-04-04 00:14:01 21.44 0.16 u 600 We note that a faint source, morphologically classified as point-like, is detected in the Legacy Surveys (LS) DR10 images at the position of the optical counterpart of GRB 250403A, with coordinates RA, Dec (J2000) = 194.6157, -24.3795, and magnitudes in the LS DR10 catalog of g = 24.16, r = 24.17, i = 23.88, and z = 24.34. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38063] IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40042 SUBJECT: IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect DATE: 25/04/04 10:05:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> K. Labzina, K.Zhirkov, V.Lipunov, E.Gorbovskoy, A.Kuznetsov, G.Antipov, D.Vlasenko, A.Kuznetsov, N.Tyurina, P.Balanutsa, A.Chasovnikov, V.Topolev, Ya.Kechin, V.Senik (Lomonosov MSU), O.Gress, N.Budnev, O.Ershova (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), D.Buckley (SAAO), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the IC250330A alert(IceCube GCN# 39943, trigger No 49427574, 20h 29m 18.48s, +10d 58m 33.6s, R=0.51deg) errorbox 91 sec after notice time (148 sec after trigger time) at 2025-03-30 08:33:34 UT, with upper limit up to 19.2m (Lipunov et al.GCN# 39942) MASTER cover map: https://master.sai.msu.ru/site/master2/observ.php?id=2828042 We analyzed MASTER archive images since 2010 of possible sources, that can be related with this event. There is blazar PKS 2032+107 inside 3 sigma https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=&-out.add=_r&-out.add=… We detected the blazar in a dim state with m=15.4m 4 minutes after the alarm, and 3 minutes later, it brightened to 14.6m. After it an hour later, blazar returned to its original state. MASTER archive light curve from 2010 year is available at http://observ.pereplet.ru/IC/MASTER_IC250330.jpg This, we report observation of an Zhirkov effect, discovered earlier (The Astrophysic Jornal Letters, 896, L19, 2020 https://ui.adsabs.harvard.edu/abs/2020ApJ...896L..19L/abstract ). View this GCN Circular online at https://gcn.nasa.gov/circulars/40042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38062] GRB 250403A: JinShan optical observations
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40041 SUBJECT: GRB 250403A: JinShan optical observations DATE: 25/04/04 09:10:46 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, D. Xu (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 18:03:34.11 UT on 2025-04-03, i.e., 2.80 hr after the SVOM/ECLAIRs trigger, and a series of 600 s frames were obtained in the Sloan r- and i- bands. The optical afterglow (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039) of GRB 250403A is clearly detected in our stacked images. Preliminary photometry results are as follows: T_mid(hr) Filter Mag(AB) MagErr 4.06 r 19.77 0.05 4.73 i 20.11 0.06 calibrated with nearby Legacy Survey stars and not corrected for Galactic extinction. We acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38061] GRB 250402A: EP-FXT afterglow detection
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40040 SUBJECT: GRB 250402A: EP-FXT afterglow detection DATE: 25/04/04 09:08:48 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> D. Turpin, B. Cordier (CEA), H. Q. Cheng (NAO, CAS), R.-Z. Li (YNAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS), W. Yuan (NAO, CAS) on behalf of the SVOM and Einstein Probe teams We performed a follow-up observation of GRB 250402A (Chen et al., GCN 40014) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-04-03 20:30:51 (T-TGRB ~ 21.4 hr) for about 4.6ks of exposure in total. A bright uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000) RA, DEC = 213.4094, -5.9295 (error=10", 90% C.L.), 2.1 arcminute away from the SVOM/ECLAIRs position (Chen et al., GCN 40014). This position is consistent with the x-ray and optical afterglow positions reported by SVOM/VT (Xin et al., GCN 40015), SVOM/MXT (Maggi et al., GCN 40019), the LCO telescope (Pérez-Fournon et al., GCN 40020), VLT/X-shooter (Schneider et al., GCN 40022), SVOM/COLIBRI (FM-GFT, Magnani et al., GCN 40023) and Swift/XRT (Dichiara et al., GCN 40027). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.2 x 10^21 cm^-2 and a photon index of 2.16 (-0.22/+0.25). The derived average observed 0.5-10 keV flux is 1.31 (-0.12/+0.16) x 10^(-12) erg/s/cm^2. 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/40040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38060] GRB 250403A: Optical counterpart detection by LCO.
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40039 SUBJECT: GRB 250403A: Optical counterpart detection by LCO. DATE: 25/04/04 08:44:09 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> 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 250403A triggered by Fermi (Fermi GBM team, GCN 40025) in the V, r filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Teide Observatory, Tenerife, Canary Islands, Spain. 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 March 29, 2025, starting 1.49 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Julakanti et al. 2025, GCN 40026, Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032, Julakanti et al. 2025, GCN 40034) in our r band image. ------------------------------------------------------------------------------------------------- |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| -------------------------------------------------------------------------------------------------- 2025-04-04 00:11:21.696 8.93 1 x 900 r r = 20.83 +/- 0.07 -------------------------------------------------------------------------------------------------- The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38059] EP250402a: EP-FXT follow-up observations
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40038 SUBJECT: EP250402a: EP-FXT follow-up observations DATE: 25/04/04 08:39:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), H. Q. Cheng (NAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250402a was detected by EP-WXT (Li et al., GCN 40017). Two follow-up observations were conducted by EP-FXT. The first follow-up observation was performed at 2025-04-03T07:25:06 (UTC), about 18.93 hours after the trigger, with an exposure time of 1 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source at the coordinates (J2000): R.A., Dec. = 172.1798, -47.2954 deg, with an uncertainty of about 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). This source lies within the EP-WXT error circle (Li et al., GCN 40017). The 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the column density nH fixed at the Galactic value of 1.43e21 cm^-2, and a photon index of 2.9 (+1.2, -1.0). The unabsorbed 0.5-10 keV flux is 1.9 (+1.2, -0.7) e-13 erg/s/cm^2. The second follow-up observation was performed at 2025-04-03T17:11:45 (UTC), about 28.71 hours after the trigger, with an exposure time of 4.4 ks. The 0.5-10 keV spectrum can also be fitted with an absorbed power-law model, with nH fixed at the Galactic value of 1.43e21 cm^-2, and a photon index fixed at 2.9. The unabsorbed 0.5-10 keV flux is 9.1 (+5.0, -3.5) e-14 erg/s/cm^2. 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/40038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38058] GRB 250403A: Swift-XRT observations
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40037 SUBJECT: GRB 250403A: Swift-XRT observations DATE: 25/04/04 03:32:07 GMT FROM: Simone Dichiara at Pennsylvania State University <sbd5667(a)psu.edu> S. Dichiara (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB), K.L. Page and P.A. Evans (U.Leicester) reports on behalf of the Swift-XRT team: We have analysed 401 s of XRT data for the GRB 250402A detected by Fermi GBM (Fermi team, GCN circ. 40025) and SVOM/ECLAIRs (SVOM trigger sb25040305; Julakanti et al., GCN circ. 40026), from T0+7.62 ks to T0+8.02 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source 3.1 sigma above the RASS limit, consistent with the reported optical counterpart (Starling et al., GCN 40028, Chao et al., GCN 40029, Guowang et al., GCN 40031, Li et al., GCN 40032). Details of this source are given below: Source 1: RA (J2000.0): 194.6162 = 12:58:27.90 Dec (J2000.0): -24.3800 = -24:22:47.9 Error: 3.7 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.29 (±0.07) ct s-1 Flux: 1.2 (±0.3) ×10-11 erg cm-2 s-1 (observed, 0.3-10 keV) This XRT position is 2.5 arcsec away from the optical position (Starling et al., GCN 40028). 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/SVOM/SVOM_FIELD00010/. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38057] GRB 250322A: 10 GHz VLA radio upper limits
by GCN Circulars 04 Apr '25

04 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40036 SUBJECT: GRB 250322A: 10 GHz VLA radio upper limits DATE: 25/04/04 01:52:21 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), T. Laskar (Utah), W. Fong, J. Rastinejad (Northwestern) report: We observed the position of the short GRB 250322A (Gupta et al., GCN 39835; Tembhurnikar et al., GCN 39849; Ridnaia et al., GCN 39873) with the Karl G. Jansky Very Large Array (VLA) under program 25A-063 (PI Schroeder) beginning on 2025 March 25 at 22:07 UT (3.25 days post-burst) for 1 hour at a mean frequency of 10 GHz. Based on preliminary analysis, we do not detect any radio emission at or near the position of the XRT afterglow (Perri et al., GCN 39855), to a 3 sigma limit of 20 microJy. We additionally do not detect the putative host galaxy in our image (Martin-Carrillo et al., GCN 39842; Becerra et al., GCN 39844; 39845l; Kilpatrick & Fong, GCN 39846; Fong et al., GCN 39852, Schneider et al., GCN 39863). Assuming a redshift of z = 0.42 (Fong et al., GCN 39852; Yang et al. GCN 39859), these observations imply a limit on the radio-inferred star formation rate of < 18 M_sol/year (following the formalism of Greiner et al. 2016). Using the putative host redshift, the lack of radio afterglow detection implies a radio luminosity of < 1.3e29 erg/Hz/s, which is a factor of >~4 lower than the median radio luminosity of radio-detected short GRBs at a similar epoch and rest frame time (Laskar et. al. 2022). Overall, this limit places GRB 250322A in the bottom 25% of radio-observed short GRBs with redshift determinations, in terms of radio luminosity. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38056] Fermi GRB 250403A: Global MASTER-Net observations report
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40035 SUBJECT: Fermi GRB 250403A: Global MASTER-Net observations report DATE: 25/04/03 21:47:38 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250403A ( Fermi GBM team, GCN 40025) errorbox 22256 sec after notice time and 22291 sec after trigger time at 2025-04-03 21:26:53 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 27 deg. The sun altitude is -58.3 deg. The galactic latitude b = 36 deg., longitude l = 316 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2832003 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22321 | 2025-04-03 21:26:53 | MASTER-SAAO | (13h 38m 33.90s , -25d 30m 56.0s) | C | 60 | 18.5 | 22400 | 2025-04-03 21:28:13 | MASTER-SAAO | (13h 47m 18.63s , -25d 31m 56.8s) | C | 60 | 18.4 | 22559 | 2025-04-03 21:30:51 | MASTER-SAAO | (13h 34m 56.63s , -27d 26m 34.6s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38055] GRB 250403A: GOTO optical counterpart follow-up observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40034 SUBJECT: GRB 250403A: GOTO optical counterpart follow-up observations DATE: 25/04/03 19:34:36 GMT FROM: Yashaswi Julakanti at University of Leicester <skyj1(a)leicester.ac.uk> Y. Julakanti, A. Kumar, B. P. Gompertz, D. O'Neill, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on further observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) on GRB 250403A (Julakanti et al. 2025, GCN 40026; Fermi GBM team, GCN 40025). Images were processed immediately after acquisition using the GOTO pipeline. Observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). We continue to detect the optical counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032) with the following AB magnitudes: +-------------------------------------------------------------------+ | Observation time (UT) | t-t0 | filter | mag (AB) | +-------------------------------------------------------------------+ | 2025-04-03 16:20:24 | +1.08h | L | 18.99 ± 0.07 | | 2025-04-03 16:27:28 | +1.2h | L | 19.10 ± 0.07 | | 2025-04-03 16:34:48 | +1.32h | L | 19.30 ± 0.08 | | 2025-04-03 17:41:22 | +2.44h | L | 19.35 ± 0.08 | | 2025-04-03 17:51:00 | +2.60h | L | 19.47 ± 0.12 | +-------------------------------------------------------------------+ Our observations can be fit with a broken power-law model with slopes of t^-0.90 and t^-0.44 on either side of a break at 1.32 hours. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/40034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38054] GRB 250402A: NUTTelA-TAO Early Optical Limits
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40033 SUBJECT: GRB 250402A: NUTTelA-TAO Early Optical Limits DATE: 25/04/03 19:02:42 GMT FROM: Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh(a)nu.edu.kz> T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), D. Berdikhan (NU), B. Grossan (UCB, NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB250402A on receipt of an automated GCN / SVOM position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We started observations at 23:10:30 UT on 2025-04-02, 154 seconds after the SVOM/ECLAIRs trigger (X. Chen et al., GCN 40014). Observations were made in partially cloudy conditions. No source consistent with the SVOM/VT (L. P. Xin et al., GCN 40015) was detected. We report the following results: start time t-t0(s) end time UL g' UL r' exposure_time (s) -------------------------------------------------------------- 23:10:30 154 23:11:30 18.01 18.35 60 23:12:13 257 23:22:13 18.58 18.67 600 t is the middle time, t0 is the SVOM/ECLAIRs trigger time, t-t0 is given in seconds. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images of the given exposure time. Calibration was done with 4 Pan-STARRS catalog stars on our images. No color or other corrections were applied to the values above. ---------------------------------- NU = Nazarbayev University, Astana, Kazakhstan UCB = University of California, Berkeley, USA FAI = Fesenkov Astrophysical Institute, Kazakhstan This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan. View this GCN Circular online at https://gcn.nasa.gov/circulars/40033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38053] GRB 250403A: GMG Optical Observation
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40032 SUBJECT: GRB 250403A: GMG Optical Observation DATE: 25/04/03 17:52:32 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi(a)ynao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report: We observed the field of GRB 250403A (Fermi/GBM team, GCN 40025, T0 at 2025-04-03T15:15:22; Julakanti et al., GCN 40026) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-04-03 17:24:07, about 2.15 hours after the trigger. The optical counterpart of GRB 250403A (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031) was clearly detected in the r-band image with an exposure of 600 s. The preliminary analysis results are shown as follows: +---------------+------------+----------+--------------+----------------+ | Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma U.L. | +===============+============+==========+==============+================+ | 2.23 | 600 | r | 19.23 ± 0.03 | 21.6 | +---------------+------------+----------+--------------+----------------+ The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.1110 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/40032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38052] GRB 250403A: 1.6m Mephisto multi-band optical detection
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40031 SUBJECT: GRB 250403A: 1.6m Mephisto multi-band optical detection DATE: 25/04/03 17:46:43 GMT FROM: Chenxu Liu at Mephisto Team <cxliu(a)ynu.edu.cn> Guowang Du (SWIFAR, YNU), Ziwei Li (SWIFAR, YNU), Dezi Liu (SWIFAR, YNU), Yaosong Yu (SWIFAR, YNU), Chenxi Shang (SWIFAR, YNU), Chenxu Liu (SWIFAR, YNU), Jinghua Zhang (SWIFAR, YNU), Yuan Fang (SWIFAR, YNU), Xufeng Zhu (SWIFAR, YNU), Tao Wang (SWIFAR, YNU), Xinlei Chen (SWIFAR, YNU), Xingzhu Zou (SWIFAR, YNU), Xuhui Han (NAOC), Pinpin Zhang (NAOC), Liping Xin (NAOC), Chao Wu (NAOC), Yu Pan (SWIFAR, YNU), Brajesh Kumar (SWIFAR, YNU), Yuanpei Yang (SWIFAR, YNU), Xiangkun Liu (SWIFAR, YNU), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We performed simultaneous multi-band photometric observations of GRB 250403A (SVOM burst-id sb25040305) detected by SVOM/ECLAIRs (Y. Julakanti et. al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 15:17:48UTC 2025-04-03 (i.e., 148s after the Swift/BAT trigger) and are still ongoing at the time of this report. Multiple frames were obtained in uvgriz- bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is listed below: UT start |Band | Exp | Mag (AB) ---------------------------|-------|---------------- 2025/04/03T15:25:37 | u |180s |17.92 +/- 0.12 2025/04/03T15:17:48 | v |180s |16.51 +/- 0.03 2025/04/03T15:25:38 | g | 50s |17.16 +/- 0.05 2025/04/03T15:17:49 | r | 50s |15.64 +/- 0.01 2025/04/03T15:25:38 | i | 79s |16.68 +/- 0.04 2025/04/03T15:17:49 | z | 79s |15.27 +/- 0.02 Our results are consistent with the previously reported circulars (R. Starling et al., GCN 40028; Wu et al., GCN 40029). Further analysis of the additional images is ongoing. ---------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m 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. ---------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38051] GRB 250402A: Fermi GBM Observation
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40030 SUBJECT: GRB 250402A: Fermi GBM Observation DATE: 25/04/03 17:29:10 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Jacob Smith (UAH), Utkarsh Pathak(IIT Bombay), and Matt Godwin (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:08:09.09 UT on 02 April 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250402A (trigger 765328094/250402964). which was also detected by SVOM (Chen et al. 2025, GCN 40014). The Fermi GBM on-ground location is consistent with the SVOM position. The angle from the Fermi LAT boresight is 57 degrees. The GBM light curve consists of a double peak with a duration (T90) of about 44 s (50-300 keV). The time-averaged spectrum from T0-5.1 to T0+45.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 115 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (4.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+23 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 60 +/- 10 keV, alpha = -0.4 +/- 0.3 and beta = -2.1 +/- 0.1. 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/40030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38050] GRB 250403A: SVOM/C-GFT optical observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40029 SUBJECT: GRB 250403A: SVOM/C-GFT optical observations DATE: 25/04/03 17:08:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Liping Xin(NAOC), Zhe Kang (CHO), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250403A detected by FERMI/GBM(FERMI team: GCN 40025) and SVOM/ECLAIRs/GRM (sb25040305, Julakanti et al., GCN 40026)with C-GFT. Our observations were started on 2025-04-03T15:16:17 UTC, ~57s after the trigger. The optical counterpart (reported by Starling et al., GCN 40028) was clearly detected in our images. Its brightness is 15.60 +/- 0.13 mag in i band at 62 sec after the burst. The photometry was calibrated with nearby Pan-STARRS1 stars. Further observation and analysis is on-going. We thank the observation assistants Shuai lui and Guangsheng Zhang at Jilin observatory for their excellent support. Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope. View this GCN Circular online at https://gcn.nasa.gov/circulars/40029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38049] GRB 250403A: GOTO detection of the optical afterglow
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40028 SUBJECT: GRB 250403A: GOTO detection of the optical afterglow DATE: 25/04/03 16:26:51 GMT FROM: Rhaana Starling at U of Leicester <rlcs1(a)leicester.ac.uk> R. Starling, Y. Julakanti, A. Kumar, D. O'Neill, B. P. Gompertz, J. Lyman, G. Ramsay, M. Kennedy, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250403A detected by SVOM (Julakanti et al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025). Targeted observations were performed using the GOTO-South starting at 15:25:31 UT on 2025-04-03 (10.12 minutes after the SVOM ECLAIRs trigger) to to 15:30:27 UT on 2025-04-03 (15.10 minutes after the SVOM ECLAIRs trigger). The images are 90s exposures in the GOTO L-band (400-700 nm). A new optical source within the SVOM localisation region (Julakanti et al., GCN 40026) is identified at the position: RA, Dec: 194.61570 -24.37950 deg. We report four epochs of observations, showing a clear power-law-like decay with t^-1.1. +------------------------------------------------------------------------------------------------+ | Observation time (UT) | t-t0 (min) | Mag (AB) | +------------------------------------------------------------------------------------------------+ | 2025-04-03 15:25:31.182 | 10.12 | 17.02 ± 0.02 | | 2025-04-03 15:27:09.645 | 11.82 | 17.16 ± 0.03 | | 2025-04-03 15:28:48.308 | 13.47 | 17.35 ± 0.03 | | 2025-04-03 15:30:26.677 | 15.10 | 17.50 ± 0.03 | +------------------------------------------------------------------------------------------------+ 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/40028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38048] GRB 250402A: Swift-XRT observations
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40027 SUBJECT: GRB 250402A: Swift-XRT observations DATE: 25/04/03 16:01:19 GMT FROM: Simone Dichiara at Pennsylvania State University <sbd5667(a)psu.edu> S. Dichiara (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB), K.L. Page and P.A. Evans (U.Leicester) reports on behalf of the Swift-XRT team: We have analysed 2.4 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250402A (SVOM trigger sb25040203; Chen et al., GCN circ. 40014), from T0+49.2 ks to T0+51.5 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source consistent with the X-ray counterpart identified by SVOM/MXT (Maggi et al., GCN circ. 40019) and the optical counterpart (Xin et al., GCN 40015, Pérez-Fournon et al., GCN 40020, Schneider et al., GCN 40022, Magnani et al., GCN 40023). We note that the source is fading compared to the flux reported by previous MXT observations (Maggi et al., GCN circ. 40019). Details of this source are given below: Source 1: RA (J2000.0): 213.4089 = 14:13:38.13 Dec (J2000.0): -5.9302 = -05:55:48.5 Error: 3.4 arcsec (radius, 90% conf. [Enhanced position]) Count-rate:0.045 (±0.012) ct s-1 Flux: 1.9 (±0.5) ×10-12 erg cm-2 s-1 (observed, 0.3-10 keV) This XRT position is 1.07 arcsec away from the optical position. 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/SVOM/SVOM_FIELD00009/. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38047] GRB 250403A : SVOM detection of a burst
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40026 SUBJECT: GRB 250403A : SVOM detection of a burst DATE: 25/04/03 15:58:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne, D. Turpin (CEA), M. Brunet (IRAP) report: SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250403A (SVOM burst-id sb25040305) starting at 2025-04-03T15:15:20 UTC (Tb), also detected by Fermi (GCN 40025). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT) which produced a sequence of 19 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 42.11 in the 8-120 keV energy band over a time window of 20.40 seconds starting at Tb. The downloaded light curve shows a single broad structure of duration of about 20 seconds. The localization of the best alert is R.A., Dec 194.5927, -24.3762 degrees: RA (J2000) = 12h58m22.24s Dec (J2000) = -24d22m34.36s with a 90% C.L. radius of 2.71 arcmin (including systematic error of 2 arcmin added in quadrature). The burst was also detected by GRM as SVOM burst-id sb25040306. No immediate slew was performed on this burst. A SVOM ToO has been programmed for follow-up. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is Y. Julakanti (skyj1(a)leicester.ac.uk). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38046] GRB 250403A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40025 SUBJECT: GRB 250403A: Fermi GBM Final Real-time Localization DATE: 25/04/03 15:26:06 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 15:15:22 UT on 3 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250403A (trigger 765386127.830438 / 250403636). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 204.2, Dec = -25.4 (J2000 degrees, equivalent to J2000 13h 36m, -25d 23'), with a statistical uncertainty of 5.1 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250403636/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250403636/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250403636/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38045] GRB 250225B: VLT host galaxy redshift z = 0.950
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40024 SUBJECT: GRB 250225B: VLT host galaxy redshift z = 0.950 DATE: 25/04/03 14:50:19 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), G. Corcoran (UCD), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick) report on behalf of the Stargate collaboration: We observed with the ESO VLT UT3 (Melipal) the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (Schneider et al., GCN 39494; Yang et al., GCN 39495, 39521; Rayson et al., GCN 39535; Yang et al., GCN 39544) of GRB 250225B (Williams et al., GCN 39473; Zhang et al., GCN 39493; Ridnaia et al., GCN 39498; Godwin et al., GCN 39502; Thakur et al., GCN 39517; Finneran et al., GCN 39541; Liu et al., GCN 39830). Due to its spatial coincidence, this is the likely GRB host galaxy. We obtained two spectra of 1000 s each with the X-shooter instrument, starting at 07:08:05 UT on 2025 April 3, i.e. about 36.5 days after the Swift trigger. The observations were obtained under good conditions, with a measured seeing of 0.5". Emission lines are detected in the visible and near-infrared arms, which we identify as H-alpha, [O III] 5007 and the [O II] 3726,3729 doublet at a common redshift of z = 0.950. This value is consistent with the photometric solution z_phot = 1.12 +/- 0.18 from the Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764). The absolute magnitude of the galaxy is M_B ~ -21, which is at the bright end of the distribution of long-duration (collapsar) GRB hosts. Our redshift measurement rules out an association between the object in the Legacy Survey and ESO 340-26 at z = 0.018. Considering the low chance association probability (Schneider et al., GCN 39494; Yang et al., GCN 39495), we consider this to be the likely redshift of GRB 250225B. We acknowledge the excellent support from the ESO staff in Paranal, in particular Matias Jones, Rob van Holstein, and Rodrigo Palominos. View this GCN Circular online at https://gcn.nasa.gov/circulars/40024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38044] GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40023 SUBJECT: GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart DATE: 25/04/03 10:48:39 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Camila Angulo (UNAM), Damien Dornic (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), William H. Lee (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), , Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and X. Chen (YNU) report: We imaged the field of the SVOM/ECLAIRs GRB 250402A (sb25040203, Chen et al. GCN 40014) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-04-03 04:37 to 06:49 UTC (between 5.49 and 7.69 hours after the trigger) and obtained 43 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. At the position of the previously reported optical afterglow (Xin et al., GCN 40015; Pérez-Fournon et al. GCN 40020; Schneider et al. GCN 40022), we detect a source with a magnitude of i = 21.22 +/- 0.11 Further observations are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40023. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38043] GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40022 SUBJECT: GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823 DATE: 25/04/03 09:52:28 GMT FROM: luca.izzo(a)inaf.it B. Schneider (LAM), A. Saccardi (CEA/Irfu), A. de Ugarte Postigo (LAM), L. Izzo (INAF-OACn and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester), A. Martin-Carrillo (UCD) report on behalf of the Stargate collaboration: We observed the afterglow of the SVOM/ECLAIRs GRB 250402A (Chen et al., GCN 40014; Xin et al., GCN 40015, Maggi et al., GCN 40019; Pérez-Fournon et al., GCN 40020) using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. Observations started on April 3 at 05:54:45 UT (6.78 hr after the SVOM trigger). Four exposures of 600 s were obtained. From a 60 s acquisition image obtained on April 3 at 05:43:17 UT (6.59 hr after the SVOM trigger), we measure r ~ 21.1 +/- 0.2 (AB). From a preliminary reduction of the 300V spectrum, a trough due to Lya absorption is visible at 4645 AA. From the detection of multiple absorption features, which we interpret as due to Si II, O I, C II, Si IV, Si II*, C IV, Fe II, and Al II, we infer a redshift of z = 2.823. Additionally, we note the presence of an intervening absorber at z = 1.409 with multiple Fe II absorption lines. We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/40022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38042] GRB 250402A: REM optical/NIR upper limits
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40021 SUBJECT: GRB 250402A: REM optical/NIR upper limits DATE: 25/04/03 09:46:37 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> 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 the SVOM/ECLAIRs GRB 250402A (Chen et al., GCN 40014) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 03 at 00:50:28 UT (i.e. 1.7 hr after the burst), and lasted for about 2 hours. From preliminary inspection, we do not find any counterpart at the position of the reported optical afterglow candidate (Xin et al., GCN. 40015; Pérez-Fournon et al., GCN 40020) down to the following 3sigma limits: r > 20.3 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 2.8 hours after the trigger, H > 16.1 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 2.2 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38041] GRB 250402A: LCO optical counterpart detection
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40020 SUBJECT: GRB 250402A: LCO optical counterpart detection DATE: 25/04/03 09:09:55 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of the SVOM GRB 250402A (Chen et al., GCN circ. 40014; Maggi et al., GCN circ. 40019). We observed the field of GRB 250402A with the three LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Cerro Tololo Inter-American Observatory (Chile) in the SDSS r, g, and i filters, starting at 2025-04-03 02:58:50 UTC, about 3.85 hours after the SVOM trigger. An uncatalogued source is clearly detected in the three filters at the position of the optical counterpart detected by SVOM/VT (Xin et al., GCN circ. 40015). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) --------------------------------------------------------------------- 2025-04-03 02:58:50 21.01 0.14 r 300 2025-04-03 03:15:44 21.91 0.17 g 300 2025-04-03 03:21:06 20.80 0.13 i 300 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38040] GRB 250402A: LCO optical counterpart detection
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40020 SUBJECT: GRB 250402A: LCO optical counterpart detection DATE: 25/04/03 09:09:55 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of the SVOM GRB 250402A (Chen et al., GCN circ. 40014; Maggi et al., GCN circ. 40019). We observed the field of GRB 250402A with the three LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Cerro Tololo Inter-American Observatory (Chile) in the SDSS r, g, and i filters, starting at 2025-04-03 02:58:50 UTC, about 3.85 hours after the SVOM trigger. An uncatalogued source is clearly detected in the three filters at the position of the optical counterpart detected by SVOM/VT (Xin et al., GCN circ. 40015). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) --------------------------------------------------------------------- 2025-04-03 02:58:50 21.01 0.14 r 300 2025-04-03 03:15:44 21.91 0.17 g 300 2025-04-03 03:21:06 20.80 0.13 i 300 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38039] GRB 250402A: refined SVOM/MXT data analysis
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40019 SUBJECT: GRB 250402A: refined SVOM/MXT data analysis DATE: 25/04/03 07:20:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 250402A (Chen et al. GCN 40014) was observed by SVOM/MXT after an automatic SVOM slew starting at T0 = 2025-04-02T23:10:59.278 (183s after trigger time Tb). MXT observed for 4.3 ks effective exposure. Using the full X band dataset, we find a rapidly fading uncatalogued source with a light curve temporal index of -0.75+/-0.02. At times T0>500s the source is no longer detected and hence we restricted the analysis to the first 500s of data. Its position is RA=213.4051, Dec=-5.94374 RA (J2000) = 14h13m37s Dec (J2000) = -05d56m37s with a statistical 90% C.L. radius of 38". The position is 51" away from, but consistent with, the one reported for the SVOM/VT afterglow candidate (Xin et al. GCN 40015) when including a 35" systematic uncertainty. The X-ray spectrum (t<T0+500s) can be fit by an absorbed power law model with a photon index of 3.2 (-0.8, +1.3) and an NH value of 0.21 (-0.1, +0.2) x 1e22 /cm2 (90% C.L. uncertainties). The absorbed X-ray flux in the 0.3-10 keV range is 8.4e-11 (+/-0.5e-11) erg/cm2/s. Follow-up observations at other wavelengths are encouraged. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this burst is: X. Chen: xlchen(a)stu.ynu.edu.cn View this GCN Circular online at https://gcn.nasa.gov/circulars/40019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38038] The EP-WXT trigger 01709133862 is a flaring star
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40018 SUBJECT: The EP-WXT trigger 01709133862 is a flaring star DATE: 25/04/03 07:02:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), H. Q. Cheng (NAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: The EP-WXT triggered event 01709133862 at the time of 2025-04-02 17:38:19, which is a stellar flare associated with the Rotating Variable star ASAS J145837-3915.1. The estimated flux of the flare is around 1.0 x 10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.6 x 10^32 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/40018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38037] EP250402a: Einstein Probe detected of a fast X-ray transient
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40017 SUBJECT: EP250402a: Einstein Probe detected of a fast X-ray transient DATE: 25/04/03 06:33:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), H. Q. Cheng (NAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient EP250402a (trigger ID: 01709133860) at 2025-04-02T12:29:06.850 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A., DEC. = 172.168, -47.290 deg (J2000) with an uncertainty of 2.5 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 80 seconds, with a peak 0.5-4 keV flux of 5.7 x 10^-9 erg/s/cm^2. The 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with the column density nH fixed at the Galactic value of 1.43 x 10^21 cm^-2 and a photon index of 1.3 (+0.7/-0.7). The unabsorbed 0.5-4.0 keV flux is 1.2 (+0.6, -0.4) x10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT are prepared. 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/40017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38036] GRB 250402B: AstroSat CZTI detection of a short burst
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40016 SUBJECT: GRB 250402B: AstroSat CZTI detection of a short burst DATE: 25/04/03 04:52:18 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (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 short duration GRB 250402B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-02 09:13:57.65 UTC. The measured peak count rate associated with the burst is 288 (+164, -12) counts/s above the background in the combined data of three quadrants (out of four), with a total of 218 (+50, -53) counts. The local mean background count rate was 292 (+10, -12) counts/s. Using cumulative rates, we measure a T90 of 0.93 (+0.11, -0.23) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The measured peak count rate associated with the burst is 360 (+65, -74) counts/s above the background in the combined data of all the four quadrants with a total of 457 (+202, -244) counts. The local mean background rate was 1317 (+8, -7) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it. 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/40016. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38035] GRB 250402A: SVOM/VT optical counterpart
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40015 SUBJECT: GRB 250402A: SVOM/VT optical counterpart DATE: 25/04/03 00:26:36 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, Y. L. Qiu, C. Wu, H. L. Li, J . Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, Y. N. Yi, J. Y. Wei (NAOC), J. T. Palmerio(CEA/Irfu), T. Sadibekova(CEA) report on behalf of the SVOM team: SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Chen et al., GCN 40014). SVOM/VT began observing the field automatically with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With VHF downlinked data, a bright uncatalogued source was found in both channels in the first sequence, and brightening with about 0.2 mag in the second sequence, compared to DESI catalog. The coordinates are RA, Dec = 213.40915, -5.93013 which is equivalent to: R.A.(J2000) = 14:13:38.20, DEC.(J2000)= -05:55:48.5 Error=0.5 arcseconds. The brightness are VT_B ~21.53 mag(AB) and VT_R ~20.61 mag(AB) in the first sequence with the mid time of 443 seconds after the burst. We proposed that this is the optical counterpart of the burst. Given the VT color, it is likely a low/medium redshift burst. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40015. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38034] GRB 250402A: SVOM detection of a burst
by GCN Circulars 03 Apr '25

03 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40014 SUBJECT: GRB 250402A: SVOM detection of a burst DATE: 25/04/03 00:15:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> X. Chen(YNU), Y. Hu(GXU), H. Yang(IRAP), B. Cordier (CEA), L. Zhang(IHEP), P. Maggi (ObAS) on behalf of the SVOM mission team. At 2025-04-02T23:07:56 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250402A (SVOM burst-id sb25040203). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 15 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 27.79 in the [8-120] keV energy band over a time window of 40.96 seconds starting at Tb. The light curve showed a long GRB with a T90 duration of about 35 (+/-3) s. The localization of the best alert is R.A., Dec 213.3783, -5.9457 degrees (J2000) with a 90% C.L. radius of 3.42 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. MXT began observing the field at 2025-04-02T23:10:58 UTC, 183 seconds after Tb. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec 213.3893, -5.9468 degrees: RA (J2000) = 14h13m33.44s DEC (J2000) = -5d56m48.59s with a 90% C.L. radius of 45 arcseconds(including 25 arcseconds systematic error added in quadrature). This location is 0.66 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is X. Chen: xlchen(a)stu.ynu.edu.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40014. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38033] GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40013 SUBJECT: GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit DATE: 25/04/02 20:48:13 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We imaged the field of GRB 250331C detected by Swift Burst Alert Telescope (BAT) (Cenko et al. GCN 39959), with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-03-31 20:59 UT (approximately 16.37 hours after burst) stacking a set of unfiltered CCD image. The observations were made with modest sky conditions and the target low on the horizon. We co-added 30 exposures of 60 sec each. Start T0+ End T0+ CR lim 16.37 hour 16.92 hour 18.7 We did not found any optical counterpart in the error box of the XRTcandidate. Evans GCN 39960 Magnitudes were estimated with the PanSTARRS cat. and are not corrected for galactic dust extinction. Our observations are consistent with other already reported Dornic et al. (GCN 39963), Lipunov et al. (GCN 39981), Siegel et al. (GCN 40003). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38032] GRB 250314A: ALMA detection
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40012 SUBJECT: GRB 250314A: ALMA detection DATE: 25/04/02 20:20:24 GMT FROM: Tanmoy Laskar at U of Utah <tanmoylaskar(a)gmail.com> T. Laskar (University of Utah), R. Margutti, R. Chornock, Nayana A. J. (UC Berkeley), K. D. Alexander (University of Arizona), and H. Sears (Rutgers University) report: “We observed the high-redshift (z ~ 7.3; Malesani et al., GCN 39732; Rakotondrainibe et al., GCN 39743) SVOM/ECLAIRs GRB 250314A (Wang et al., GCN 39719) with the Atacama Large Millimeter/Submillimeter Array (ALMA) beginning on 2025 March 26 02:55 UTC (11.6 days after the burst) at multiple frequencies. Preliminary analysis reveals a mm source with flux density of ~ 40 microJy at 42 GHz at position: RA (J2000) = 13:25:12.14 Dec (J2000) = -05:16:55.29 with an uncertainty of 0.18" in each coordinate. This is consistent with the optical position (Malesani et al., GCN 39727) and radio position (Nayana A. J. et al., GCN 39954). We note that GRBs 250314A and 090423 (z ~ 8.2; Tanvir et al., Nature, 461, 7268, 1254; Castro Tirado et al., GCN 9273; de Ugarte Postigo et al., A&A, 538, A44, 2012) are the highest-redshift GRBs with mm-band detections so far. Further ALMA observations are planned. We thank the ALMA Director for rapidly granting our DDT request and the JAO staff, AoD, P2G, and the entire ALMA team for their help with these observations." View this GCN Circular online at https://gcn.nasa.gov/circulars/40012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38031] GRB 250329B: Swift/UVOT Upper Limit
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40011 SUBJECT: GRB 250329B: Swift/UVOT Upper Limit DATE: 25/04/02 15:39:59 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) and R. Caputo (GSFC) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250329B 7.4 ks after the SVOM trigger sb25032902 (Xie et al., GCN Circ. 39925). We do not detect an afterglow at the position of the XRT counterpart (Beardmore et al., GCN Circ. 39939). Preliminary detections and 3-sigma upper limits for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 7392 8531 1121 >21.00 u 92986 110466 2225 >20.80 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.01 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40011. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38030] GRB 250329A: Swift/UVOT Upper Limit
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40010 SUBJECT: GRB 250329A: Swift/UVOT Upper Limit DATE: 25/04/02 15:12:53 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) and R. Caputo (GSFC) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250329A 6.8ks after the SVOM trigger sb25032901 (Wang et al., GCN Circ. 39916). We do not detect an afterglow at the position of the XRT counterpart (Dichiara et al., GCN Circ. 39924) or optical-infrared counterparts (Watson et al., GCN Circ. 39915; Want et al., GCN Circ. 39917; Ghosh et al., GCN Circ. 39922). The lack of detection in the u-band for this bright burst would be consistent with the redshift of z=2.9 reported by Schneider et al. (GCN Circ. 39918). Preliminary detections and 3-sigma upper limits for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 6812 13135 1551 >20.95 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.021 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38029] GRB 250327B: Swift/UVOT Detection
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40009 SUBJECT: GRB 250327B: Swift/UVOT Detection DATE: 25/04/02 13:32:05 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M.H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250327B 1753 s after the SVOM trigger sb25032706 (GCN Circ. 39888). A fading source consistent with the XRT position (Page et al., GCN Circ. 39895) and the optical counterpart (Moskvitin et al., GCN Circ. 39889; Xin et al., GCN Circ. 39890; O’Neill et al., GCN Circ. 39891; Lian et al., GCN Circ. 39894; Shrestha et al., GCN Circ. 39896; Ducoin et al., GCN Circ. 39897; Perley & Bochenek; GCN Circ. 39902; Kumar et al., GCN Circ. 39904; Dennefeld et al., GCN circ. 39905; Pankov et al., GCN circ. 39906) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 1753 2505 740 19.78+/-0.18 u 91894 113326 2601 >21.28 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38028] GRB 250327A: Swift/UVOT Upper Limits
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40008 SUBJECT: GRB 250327A: Swift/UVOT Upper Limits DATE: 25/04/02 13:08:08 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250327A 13.8 ks after the BAT trigger (Parsotan et al., GCN Circ. 39877). No optical afterglow consistent with the XRT position (Burrows et al., GCN Circ. 39892) GCN Circ. 39977) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag B 25500 43748 1714 >20.88 UVM2 47869 48769 885 >20.28 U 14704 42891 1711 >20.58 V 21282 21402 117 >18.30 UVW1 13797 49176 1885 >20.62 UVW2 20376 21275 885 >20.31 WHITE 26413 27065 633 >20.81 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.053 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38027] GRB 250331E: SVOM/GRM observation
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40007 SUBJECT: GRB 250331E: SVOM/GRM observation DATE: 25/04/02 08:09:11 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP), Frédéric Piron (LUPM), Nicolas Dagoneau (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250331E (SVOM trigger reference: sb25033103) at 2025-03-31T22:46:35.000 (T0). This burst was also detected by Fermi/GBM (Fermi GBM Team, GCN 39988). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of single main pulse with a T90 of 12.0 +1.0/-2.0 s in the 15-5000 keV band. In addition, ECLAIRs was taking data and did not trigger, since the position of this burst, as determined by Fermi/GBM (GCN 39988, RA: 196.6 deg, DEC: -27.7 deg, Error: 14.0 deg), is located at about 60.7 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250331E.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38026] GRB 250327B: Kilonova-Catcher Observations
by GCN Circulars 02 Apr '25

02 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40006 SUBJECT: GRB 250327B: Kilonova-Catcher Observations DATE: 25/04/02 01:27:54 GMT FROM: Cristina Andrade at UMN <andra104(a)umn.edu> E. Broens, F. Dubois, M. Freeberg, A. Lekic, G. Parent, M. Serrau (KNC), C. Andrade (UMN), E. de Bruin (UMN), D. Turpin (CEA-Saclay/Irfu), S. Antier (OCA), M. Coughlin (UMN),S. Karpov (FZU), I. Tosta e Melo (UniCT-DFA), P. Hello (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250327B (Bouchet et al., GCN 39888) detected by SVOM/ECLAIRs with the citizen science project, Kilonova-Catcher (KNC). These observations were performed by our members using the following telescopes: T-BRO, ODK16 f/6.8, Quatro F4, T180, a Newton telescope T200 and using the Telescope Live Network. In our stacked frames, we detected an optical afterglow at the position reported by SAO/RAS (Moskvitin et al., GCN 39889, Pankov et al. GCN 39906), SVOM/VT (Xin et al., GCN 39890), GOTO (O’Neill et al. GCN 39891), the NOT (Malesani et al., GCN 39893), Mephisto (Lian et al, GCN 39894), the LCOGT (Shrestha et al. GCN 39896, Kumar et al. GCN 39904, Pérez-Fournon et al. GCN 39912), SVOM/COLIBRI (F-GFT) (Ducoin et al., GCN 39897, 39930), the Liverpool telescope (Perley et al., GCN 39902), the OHP/T193 telescope (Dennefeld et al. GCN 39905) and MASTER (Tarasenkov et al., GCN 39913). We report some of our detections and upper limits (5 sigma) in the following table: --------------------------------------------------------------------------------------------- | Tstart-TGRB (hr) | Exposure | Mag | UL (5σ) | Filter | Telescope | --------------------------------------------------------------------------------------------- | 1.62 | 180s | 16.87 ± 0.06 | | Rc (Vega) | T-BRO | | 1.67 | 180s | 17.48 ± 0.10 | | V (Vega) | T-BRO | | 3.29 | 10x60s | 18.98 ± 0.09 | | V (Vega) | ODK16 f/6.8 | | 3.52 | 180s | | 17.8 | V (Vega) | Quatro F4 | | 3.56 | 2x300s | 19.78 ± 0.11 | | g’ (AB) | ODK16 f/6.8 | | 3.58 | 180s | | 17.6 | R (Vega) | Quatro F4 | | 3.81 | 3x300s | 18.93 ± 0.17 | | r’ (AB) | ODK16 f/6.8 | | 4.24 |10x180s | 19.73 ± 0.21 | | V (Vega) | T-BRO | | 6.49 |10x180s | | 20.6 | g’ (AB) | T180 | | 6.51 |15x180s | 20.16 ± 0.36 | | Rc (Vega) | T-BRO | | 6.74 |10x180s | 19.87 ± 0.24 | | r’ (AB) | T180 | | 29.07 |100x40s | | 20.3 | r’ (AB) | Newton T200 | | 76.42 | 59x80s | | 20.5 | V (Vega) | Telescope Live T200 | --------------------------------------------------------------------------------------------- All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022, 2025). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog. Images obtained with sloan filters were calibrated using the PanSTARRS DR1 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/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38025] GCN Announcement: Circulars over Kafka Event Name Backfill
by GCN Announcements 01 Apr '25

01 Apr '25

In preparation for new search and sort features in the GCN Circulars archive, on April 7, 2025 the GCN team will be backfilling the automatically assigned event name (e.g. "eventId": "GRB 250331C") derived from each GCN Circular subject. Event names have been included in all JSON versions of Circulars starting with GCN Circular 37912. The backfill of all prior Circulars will result in the following behavior that may impact some users: - The entire archive of ~40k Circulars will be distributed over Kafka with the new event names. - Revised Circulars will not be redistributed over email. For more details on this new feature and an archive of GCN news and announcements, see https://gcn.nasa.gov/news. For questions, issues, or bug reports, please contact us via: - Contact form: https://gcn.nasa.gov/contact - GitHub issue tracker: https://github.com/nasa-gcn/gcn.nasa.gov/issues --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38024] GRB250331D: AbAO optical observations
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40005 SUBJECT: GRB250331D: AbAO optical observations DATE: 25/04/01 14:15:27 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed the entire localisation region of BAT-GUANO/Swift of GRB250331D (Ronchini et al., GCN 39979), initially detected by GBM/Fermi (Fermi GBM team, GCN 39961) with AS-32 telescope of AbAO starting on 2025-03-31 (UT) 18:56:37. We report the results of optical transient searches in five XRT/Swift localisations reported in https://www.swift.ac.uk/ToO_GRBs/00021825/ and (Melandri et al., GCN 39998). Details of the preliminary photometry of the stacked image and the sources detected so far are given below. Date UT start t-T0 Filter Exp. UL(3sigma) Telescope (mid, d) (s) 2025-03-31 18:56:37 0.56447 R 61x60 20.8 AS-32 XRT #1 ------ RA = 48.26026d Dec = 62.30756d Err90 = 5.1" Inside the XRT error circle the single source is detected: RA = 48.25957d +/- 0.05" Dec = 62.30756 +/- 0.02" R(AbAO) = 13.24 +/- 0.05 USNO-B1.0 R2 = 13.39 XRT #2 ------ RA = 48.65718d Dec = 62.28326d Err90 = 3.5" Inside the XRT error circle the single source is detected: RA = 48.66142d +/- 0.14" Dec = 62.28324d +/- 0.07" R(AbAO) = 18.72 +/- 0.07 USNO-B1.0 R2 = 18.97 XRT #3 ------ RA = 48.86152d Dec = 62.34017d Err90 = 7.0" Inside the XRT error circle the single source is detected: RA = 48.85897d +/- 0.12" Dec = 48.85897d +/- 0.06" R(AbAO) = 18.64 +/- 0.07 USNO-B1.0 R2 = 18.93 XRT #4 ------ RA = 48.77053d Dec = 62.37337d Err90 = 5.9" Inside the XRT error circle the single source is detected: RA = 48.76831d +/- 0.3" Dec = 62.37292d +/- 0.3" R(AbAO) = 19.68 +/- 0.26 USNO-B1.0 R2 = 19.94 XRT #5 ------ RA = 48.3703896d Dec = 62.10607d Err90 = 6.9" Inside the XRT error circle the single source is detected: RA = 48.37039d +/- 0.3" Dec = 62.10664d +/- 0.3" R(AbAO) ~ 21.0 PS1 r = 21.17 +/- 0.15, i = 20.21 +/- 0.06 We did not identify any variable sources in any of the XRT localisations ( https://www.swift.ac.uk/ToO_GRBs/00021825/). View this GCN Circular online at https://gcn.nasa.gov/circulars/40005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38023] GRB 250331D: Fermi GBM observation
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40004 SUBJECT: GRB 250331D: Fermi GBM observation DATE: 25/04/01 13:33:45 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> E. Bissaldi (Politecnico and INFN Bari), C. Meegan (UAH) and A. Holzmann Airasca (Univ. Trento and INFN Bari) report on behalf of the Fermi GBM Team: "At 05:49:17.01 UT on 31 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 250331D (trigger 765092962 / 250331243), which was also detected by the Swift/BAT-GUANO (Ronchini et al. 2025, GCN 39979). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 27 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 9 s (50-300 keV). The time-averaged spectrum from T0-2.5 s to T0+6.4 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.12 +/- 0.27 and the cutoff energy, parameterized as Epeak, is 91 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (6.1 +/- 0.8)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.64 s in the 10-1000 keV band is 2.2 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/40004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38022] GRB 250331C: Swift/UVOT Upper Limits
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40003 SUBJECT: GRB 250331C: Swift/UVOT Upper Limits DATE: 25/04/01 13:06:09 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250331C 140 s after the BAT trigger (Cenko et al., GCN Circ. 39959). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 39977) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 140 289 147 >21.1 u_FC 297 547 246 >19.9 white 140 1717 411 >22.3 v 628 1767 136 >19.1 b 553 1863 133 >20.1 u 297 1841 363 >20.1 w1 676 1817 136 >19.1 m2 652 1792 136 >19.8 w2 603 1743 136 >20.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.921 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38021] GRB 250331B: Swift/UVOT Upper Limits
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40002 SUBJECT: GRB 250331B: Swift/UVOT Upper Limits DATE: 25/04/01 13:04:29 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250331B 317 s after the BAT trigger (Cenko et al., GCN Circ. 39958). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 39974) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 317 467 147 >19.5 white 317 1020 334 >19.9 v 474 1070 78 >18.3 b 572 764 39 >18.3 u 547 1144 58 >18.6 w1 523 1120 58 >18.0 m2 670 690 19 >17.7 w2 621 1046 58 >18.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.979 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38020] GRB 250328A: AbAO AS-32 Optical Observations
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40001 SUBJECT: GRB 250328A: AbAO AS-32 Optical Observations DATE: 25/04/01 13:02:02 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250328A (Brunet et. al, GCN 39910; Osborne et. al, GCN 39967) with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations started on (UT) 2025-03-28 20:21:40, i.e. about 0.17 days since trigger. The series of frames in the R-filter was obtained. We marginally detect the optical afterglow (Schneider et. al, GCN 39919; Schneider et. al, GCN 39920; Li et. al, GCN 39923; Li et. al, GCN 39936; Kumar et. al, GCN 39946; Klingler et. al, GCN 39968) in the stacked image. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL (mid, days) (s) (3sigma) 2025-03-28 20:21:40 0.17064 82*60 R 22.2 S/N=1.7 21.6 The photometry is based on nearby stars of USNO-B1.0 and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38019] GRB 250219A: NOT candidate host galaxy detection
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40000 SUBJECT: GRB 250219A: NOT candidate host galaxy detection DATE: 25/04/01 09:28:18 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Benjamin Schneider (LAM), Gregory Corcoran (UCD), A. Martin-Carrillo (UCD), and Nikko Pyykkinen (NOT and Turku) report on behalf of a larger collaboration: We observed the field of GRB 250219A (Daigne et al., GCN 39376) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations were carried out with the r-band filter and started on 2025 March 26 at 02:18 UT (34.4 days after the GRB), for a total of 50 min on source. Seeing and Moon conditions were favorable. Consistent with the position of the optical afterglow (Xin et al., GCN 39380; Magnani et al., GCN 39382; Fu et al., GCN 39383), we detect a faint object with AB magnitude r = 25.2 +- 0.3, calibrated against nearby objects from Pan-STARRS. While we note a slight offset (~0.9") compared to the afterglow position (Fu et al., GCN 39383), we suggest the above object to be a candidate host galaxy of GRB 250219A. We thank Liping Xin, Francis Fortin and Susanna Vergani for helpful discussion. View this GCN Circular online at https://gcn.nasa.gov/circulars/40000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38018] GRB 250322B: GRBAlpha detection
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39999 SUBJECT: GRB 250322B: GRBAlpha detection DATE: 25/04/01 09:27:19 GMT FROM: Martin Kolář at Masaryk University <mkolar(a)physics.muni.cz> M. Kolar, M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, L. Szakszonova, M. Duriskova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250322B (AstroSat/CZTI: GCN Circular 39848, NuSTAR: GCN Circular 39857) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-03-22 20:08:19 UTC . The T90 duration measured by GRBAlpha is 77.5 s and the overall significance during T90 reaches 132 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250322B_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/39999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38017] GRB 250331D: Swift-XRT observations
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39998 SUBJECT: GRB 250331D: Swift-XRT observations DATE: 25/04/01 08:59:42 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) 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 250331D, collecting 5.3 ks of Photon Counting (PC) mode data between T0+45.2 ks and T0+68.1 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): 48.6572 = 03:14:37.72 Dec (J2000.0): +62.2833 = +62:16:59.7 Error: 3.5 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (7.4 [+1.6, -1.4])e-3 ct s^-1 Distance: 235 arcsec from Swift/BAT position. Flux: (3.18 [+0.67, -0.61])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 4: RA (J2000.0): 48.7705 = 03:15:4.93 Dec (J2000.0): +62.3734 = +62:22:24.1 Error: 5.9 arcsec (radius, 90% conf.) Count-rate: (1.77 [+0.95, -0.72])e-3 ct s^-1 Distance: 476 arcsec from Swift/BAT position. Flux: (1.19 [+0.64, -0.49])e-10 erg cm^-2 s^-1 (observed, 0.3-10 keV) A catalogued source was also detected within the estimated 3-sigma Swift/BAT error region (493 arcsec). Two uncatalogued sources were also detected too far from the GRB position to be likely afterglow candidates. 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/00021825. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38016] GRB 250331C: Swift-XRT refined Analysis
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39997 SUBJECT: GRB 250331C: Swift-XRT refined Analysis DATE: 25/04/01 07:45:44 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> 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), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 3.9 ks of XRT data for GRB 250331C, from 137 s to 62.7 ks after the BAT trigger. The data comprise 95 s in Windowed Timing (WT) mode 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=2.81 (+0.11, -0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.11 (+0.11, -0.08). The best-fitting absorption column is consistent with the Galactic value of 6.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.65 (+0.32, -0.30) and a best-fitting absorption column of 9.0 (+3.4, -2.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.9 x 10^-11 (8.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.0 (+3.4, -2.5) x 10^21 cm^-2 Galactic foreground: 6.5 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.65 (+0.32, -0.30) If the light curve continues to decay with a power-law decay index of 2.81, the count rate at T+24 hours will be 3.2 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x 10^-17 (2.8 x 10^-17) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01299967. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38015] GRB 250331B: Swift-XRT refined Analysis
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39996 SUBJECT: GRB 250331B: Swift-XRT refined Analysis DATE: 25/04/01 07:45:13 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.5 ks of XRT data for GRB 250331B, from 321 s to 35.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.11 (+0.17, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.9, -0.8). The best-fitting absorption column is 2.1 (+1.5, -1.1) x 10^22 cm^-2, in excess of the Galactic value of 6.6 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.7 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+1.5, -1.1) x 10^22 cm^-2 Galactic foreground: 6.6 x 10^21 cm^-2 Excess significance: 2.2 sigma Photon index: 2.2 (+0.9, -0.8) If the light curve continues to decay with a power-law decay index of 1.11, the count rate at T+24 hours will be 7.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-14 (1.2 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/01299965. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38014] GRB 250331B: Swift-XRT refined Analysis
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39995 SUBJECT: GRB 250331B: Swift-XRT refined Analysis DATE: 25/04/01 07:45:10 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.5 ks of XRT data for GRB 250331B, from 321 s to 35.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.11 (+0.17, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+0.9, -0.8). The best-fitting absorption column is 2.1 (+1.5, -1.1) x 10^22 cm^-2, in excess of the Galactic value of 6.6 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.7 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+1.5, -1.1) x 10^22 cm^-2 Galactic foreground: 6.6 x 10^21 cm^-2 Excess significance: 2.2 sigma Photon index: 2.2 (+0.9, -0.8) If the light curve continues to decay with a power-law decay index of 1.11, the count rate at T+24 hours will be 7.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x 10^-14 (1.2 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/01299965. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38013] GRB 250322B possible detection by the AstroSat Satellite
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39994 SUBJECT: GRB 250322B possible detection by the AstroSat Satellite DATE: 25/04/01 05:55:08 GMT FROM: Tilak Katoch at TIFR <tilak(a)tifr.res.in> Tilak Katoch, H. M. Antia and Parag Shah from TIFR, Mumbai, India report for the LAXPC onboard AstroSat. AstroSat LAXPC data analysis revealed the presence of a strong long duration multiple peaks complex GRB 250322B. The GRB burst profile shows that it was triggered at T0 = 20h 08m 05s UT on 22 Mar 2025, when the satellite was in a normal operating mode and well before and after the SAA region. This multiple peak complex burst profile has been recorded by both LAXPC instruments (LAXPC10 and LAXPC20) in their respective lightcurves. The burst profile observed in these lightcurves lasted for T90 ~ 97 sec. The strongest peak measured has a count rate 526 +/- 28 count/sec in LAXPC10 above the background and 1110 +/- 36 count/sec in LAXPC20 at T0+12 sec. A precursor peak is observed by both LAXPC10 and LAXPC20 at T0-50 sec. LAXPC20 has a nominal energy range of 3-100 keV, but due to the lower gain in LAXPC10, the energy range is approximately 15-400 keV. The background subtracted lightcurves of the LAXPC instruments with 1 sec time bin is available at the website: https://www.tifr.res.in/~astrosat_laxpc/grb250322b.jpg LAXPC was built by TIFR in collaboration with the Indian Space Research Organisation. The Indian Space Research Organisation funded, managed and facilitated the project. View this GCN Circular online at https://gcn.nasa.gov/circulars/39994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38012] GRB 250330B: SVOM/GRM observation of a short burst
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39993 SUBJECT: GRB 250330B: SVOM/GRM observation of a short burst DATE: 25/04/01 04:33:43 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Jia-Cong Liu, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: O. Godet, Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250330B (SVOM trigger reference: sb25033007) at 2025-03-30T21:52:22.100 (T0). This burst was also detected by Fermi/GBM (Fermi GBM Team, GCN 39951). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of single main pulse with a T90 of 0.48 +0.32/-0.11 s in the 15-5000 keV band. In addition, ECLAlRs was taking data and did not trigger, since the position of this burst, as determined by Fermi/GBM (GCN 39951, RA: 114.1 deg, DEC: 13.3 deg, Error: 3.1 deg), is located at about 96.2 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250330B.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38011] LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39992 SUBJECT: LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2) DATE: 25/04/01 01:35:09 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> S. MacBride (UZH), I. McMahon (UZH), M. Soares-Santos (UZH), K. Herner (Fermilab), S. Kaur (UZH), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team: At 01:46 UTC, March 30th, the Dark Energy Camera (DECam) began the second epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). We observed eight fields centered on the following ICRS coordinates: | RA | DEC | | ---------- | ---------- | | 145.286221 | 10.615360 | | 145.996500 | 12.108130 | | 143.786221 | 10.715360 | | 144.496500 | 12.208130 | | 144.069167 | 9.115670 | | 143.344621 | 7.609550 | | 145.900667 | 13.593470 | | 142.620092 | 6.103430 | These pointings are identical to the first epoch observations from March 29th, 2025 (GCN 39934). All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~22.8 in r-band, ~22.5 in i-band, and ~21.9 in z-band. We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts, requiring an autoscan score of at least 0.7 on both nights of observations. We also match our candidates against the ALLWISE, Milliquas, Quaia, and LQAC-6 AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024, Souchay et al 2024) within the LVK localization volume. After candidate selection, we report 25 high confidence candidates listed below. After vetting and identification, 15 candidates are classified as nuclear candidates (likely active galactic nuclei) and 10 candidates as possible supernovae. No candidates from the second epoch of observations match known AGNs within 1 arcsecond. 12 of the 20 candidates in the first epoch are listed here, while the candidates which do not appear did not have a confident detection in the second epoch. We also do not recover any of the X-ray source candidates reported by Swift XRT (GCN 39972) within their reported error bounds. | TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | | -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- | | SN_LIKE | 2290036 | AT2025gek | 145.199481 | 10.828527 | 20.77 | 0.04 | 20.62 | 0.03 | 20.69 | 0.1 | | SN_LIKE | 2290467 | AT2020woa | 144.388798 | 10.255536 | 19.87 | 0.02 | N/A | N/A | 20.1 | 0.04 | | SN_LIKE | 2292782 | AT2025geo | 144.928578 | 10.349243 | 20.92 | 0.04 | 21.07 | 0.04 | N/A | N/A | | SN_LIKE | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 | | SN_LIKE | 2290334 | AT2025geq | 145.235616 | 12.469694 | 20.22 | 0.02 | 20.57 | 0.03 | 21.11 | 0.11 | | AGN_LIKE | 2290623 | AT2025gen | 144.112464 | 11.641817 | 21.4 | 0.04 | 21.3 | 0.08 | 21.37 | 0.12 | | AGN_LIKE | 2291223 | N/A | 146.389563 | 13.131801 | 20.56 | 0.02 | 20.64 | 0.04 | 20.52 | 0.05 | | SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | N/A | N/A | 21.22 | 0.1 | | SN_LIKE | 2293190 | AT2025cvb | 144.191297 | 10.828462 | 20.86 | 0.03 | 20.87 | 0.03 | N/A | N/A | | SN_LIKE | 2290143 | AT2025ggv | 146.033906 | 11.088812 | 21.26 | 0.05 | 21.46 | 0.07 | 21.47 | 0.13 | | AGN_LIKE | 2292003 | N/A | 144.007084 | 9.336975 | 21.18 | 0.03 | 21.16 | 0.05 | 21.6 | 0.11 | | SN_LIKE | 2292854 | AT2025ggw | 142.67125 | 6.637349 | N/A | N/A | 20.75 | 0.04 | 20.72 | 0.06 | | AGN_LIKE | 2290453 | N/A | 146.299999 | 13.629839 | 21.7 | 0.06 | 21.89 | 0.11 | 22.14 | 0.19 | | AGN_LIKE | 2292040 | AT2025ges | 144.438216 | 9.885617 | 21.72 | 0.07 | 21.75 | 0.11 | 21.93 | 0.17 | | AGN_LIKE | 2290059 | N/A | 144.679961 | 10.018211 | N/A | N/A | 20.26 | 0.03 | 21.11 | 0.12 | | AGN_LIKE | 2290970 | AT2025ger | 142.543835 | 6.090899 | 21.71 | 0.05 | 21.43 | 0.06 | 21.28 | 0.09 | | AGN_LIKE | 2294074 | AT2025gew | 144.291829 | 8.349302 | 22.23 | 0.1 | 21.85 | 0.11 | 22.28 | 0.15 | | AGN_LIKE | 2292786 | N/A | 144.037664 | 10.810454 | 22.27 | 0.08 | 22.12 | 0.11 | 22.89 | 0.25 | | AGN_LIKE | 2293517 | AT2025geu | 145.956024 | 12.381673 | 21.73 | 0.08 | 21.65 | 0.07 | 21.51 | 0.14 | | AGN_LIKE | 2295862 | N/A | 145.361115 | 12.521385 | 22.44 | 0.11 | 23.33 | 0.36 | 23.47 | 0.46 | | AGN_LIKE | 2290563 | N/A | 145.149074 | 11.756403 | 23.41 | 0.33 | 22.11 | 0.11 | 22.3 | 0.24 | | AGN_LIKE | 2290298 | N/A | 144.167668 | 10.985136 | 21.59 | 0.05 | 21.99 | 0.12 | 21.1 | 0.1 | | SN_LIKE | 2289995 | AT2025ggx | 144.57373 | 10.274445 | 22.62 | 0.19 | 22.31 | 0.14 | 21.7 | 0.22 | | AGN_LIKE | 2291169 | N/A | 145.423743 | 11.834742 | 22.57 | 0.14 | 23.44 | 0.34 | 22.8 | 0.46 | | AGN_LIKE | 2293519 | N/A | 143.751725 | 9.714206 | 22.75 | 0.15 | 22.23 | 0.14 | 21.63 | 0.12 | We encourage followup of the 25 candidates identified herein. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38010] Fermi GRB 250331E: Global MASTER-Net observations report
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39991 SUBJECT: Fermi GRB 250331E: Global MASTER-Net observations report DATE: 25/04/01 01:16:06 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250331E ( Fermi GBM team, GCN 39988) errorbox 4 sec after trigger time at 2025-03-31 22:46:37 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 12 deg. The sun altitude is -62.4 deg. The galactic latitude b = 35 deg., longitude l = 308 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2829592 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 35 | 2025-03-31 22:46:37 | MASTER-SAAO | (12h 57m 48.00s , -20d 04m 42.7s) | C | 60 | 19.0 | 114 | 2025-03-31 22:47:56 | MASTER-SAAO | (13h 06m 14.94s , -20d 06m 25.5s) | C | 60 | 19.1 | 1229 | 2025-03-31 23:06:32 | MASTER-SAAO | (13h 25m 08.68s , -32d 04m 39.4s) | C | 60 | 19.0 | 1388 | 2025-03-31 23:09:10 | MASTER-SAAO | (13h 34m 31.38s , -32d 07m 08.5s) | C | 60 | 19.2 | 2434 | 2025-03-31 23:26:37 | MASTER-SAAO | (13h 25m 13.32s , -32d 05m 29.0s) | C | 60 | 19.2 | 2593 | 2025-03-31 23:29:15 | MASTER-SAAO | (14h 07m 32.41s , -36d 55m 59.7s) | C | 60 | 19.3 | 3468 | 2025-03-31 23:43:50 | MASTER-SAAO | (14h 07m 42.96s , -36d 54m 45.6s) | C | 60 | 19.1 | 4282 | 2025-03-31 23:57:24 | MASTER-SAAO | (14h 07m 44.51s , -36d 53m 28.5s) | C | 60 | 19.1 | 5764 | 2025-04-01 00:22:06 | MASTER-SAAO | (14h 07m 53.30s , -36d 53m 01.5s) | C | 60 | 19.1 | 6499 | 2025-04-01 00:34:21 | MASTER-SAAO | (14h 07m 57.57s , -36d 54m 12.1s) | C | 60 | 19.2 | 7157 | 2025-04-01 00:45:19 | MASTER-SAAO | (14h 07m 59.18s , -36d 53m 44.9s) | C | 60 | 19.1 | 7236 | 2025-04-01 00:46:38 | MASTER-SAAO | (13h 35m 38.73s , -27d 21m 54.8s) | C | 60 | 19.1 | 7315 | 2025-04-01 00:47:58 | MASTER-SAAO | (13h 44m 37.58s , -27d 21m 15.5s) | C | 60 | 19.3 | 7474 | 2025-04-01 00:50:36 | MASTER-SAAO | (13h 22m 32.82s , -25d 27m 53.6s) | C | 60 | 19.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38009] Fermi GRB 250331D: Global MASTER-Net observations report
by GCN Circulars 01 Apr '25

01 Apr '25

TITLE: GCN CIRCULAR NUMBER: 39990 SUBJECT: Fermi GRB 250331D: Global MASTER-Net observations report DATE: 25/04/01 00:03:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250331D ( Fermi GBM team, GCN 39961) errorbox 62486 sec after notice time and 62523 sec after trigger time at 2025-03-31 23:11:20 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 71 deg. The sun altitude is -35.8 deg. The galactic latitude b = -7 deg., longitude l = 128 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2829033 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 62554 | 2025-03-31 23:11:20 | MASTER-Kislovodsk | (02h 54m 34.96s , +65d 33m 33.8s) | C | 60 | 17.7 | 63431 | 2025-03-31 23:25:58 | MASTER-Kislovodsk | (02h 54m 36.68s , +65d 33m 23.8s) | C | 60 | 17.9 | 64508 | 2025-03-31 23:43:54 | MASTER-Kislovodsk | (02h 53m 45.13s , +65d 44m 21.5s) | C | 60 | 17.7 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39990. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38008] GRB 250330B: EIRSAT-1 GMOD Detection
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39989 SUBJECT: GRB 250330B: EIRSAT-1 GMOD Detection DATE: 25/03/31 23:14:24 GMT FROM: David Murphy at University College Dublin <david.murphy(a)ucd.ie> D. Murphy, J. Fisher, C. de Barra, P. McDermott, C. McKenna, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the short gamma-ray burst GRB 250330B by the Gamma-ray Module (GMOD) instrument, which was also detected by Fermi GBM (GCN [39951](https://gcn.nasa.gov/circulars/39951)). The GMOD detection was made starting at 2025-03-30 21:52:22.4 UTC. The GMOD light curve for GRB250330B, with 1.2s binning, shows a single peak, consistent with the detection by Fermi GBM. The spacecraft location at time of detection was 1.704 S, 7.769 E and an altitude of 407.7 km. The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250330B/250330B_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite ([Doyle et al. Proceedings of the 4th SSEA, 2022](https://researchrepository.ucd.ie/bitstreams/2f3fdccb-6e36-4ac1-88cd-4e80feecf446/download)). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector ([Murphy et al, Experimental Astronomy, 53, 961–990, 2022](https://link.springer.com/article/10.1007/s10686-022-09842-z)). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023. View this GCN Circular online at https://gcn.nasa.gov/circulars/39989. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38007] GRB 250331E: Fermi GBM Final Real-time Localization
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39988 SUBJECT: GRB 250331E: Fermi GBM Final Real-time Localization DATE: 25/03/31 22:57:04 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 22:46:32 UT on 31 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250331E (trigger 765153997.78765 / 250331949). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 196.6, Dec = -27.7 (J2000 degrees, equivalent to J2000 13h 06m, -27d 41'), with a statistical uncertainty of 14.0 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331949/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38006] GRB 250327A Swift-BAT refined analysis
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39987 SUBJECT: GRB 250327A Swift-BAT refined analysis DATE: 25/03/31 21:38:12 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> S. D. Barthelmy (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), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+843 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250327A (trigger #1299088) (Parsotan, et al., GCN Circ. 39877). The BAT ground-calculated position is RA, Dec = 248.209, 61.610 deg which is RA(J2000) = 16h 32m 50.1s Dec(J2000) = +61d 36' 35.4" with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 10%. The mask-weighted light curve shows a single main pulse lasting ~60 sec composed of several shorter pulses. The remainder of the burst emission is included in a dim tail. The T90 (15-350 keV) is 91.008 +- 12.21 sec (estimated error including systematics). The time-averaged spectrum from T+1.67 to T+109.928 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.28 +- 0.12. The fluence in the 15-150 keV band is 7.6 +- 0.5 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+24.49 sec in the 15-150 keV band is 2.1 +- 0.7 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/1299088 View this GCN Circular online at https://gcn.nasa.gov/circulars/39987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38005] LIGO/Virgo/KAGRA S250331o: Updated Sky localization
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39986 SUBJECT: LIGO/Virgo/KAGRA S250331o: Updated Sky localization DATE: 25/03/31 19:50:46 GMT FROM: Michael J. Williams at University of Portsmouth <michael.williams(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250331o (GCN Circular 39953). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250331o For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 18 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(02h07m, +31d03m, 3.98d, 1.46d, 114.57d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 657 +/- 91 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/39986. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38004] GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39985 SUBJECT: GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits DATE: 25/03/31 19:48:32 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), A. S. Moskvitin (SAO RAS), O. I. Spiridonova (SAO RAS), Yu. V. Sotnikova (SAO RAS), A. Ghosh (CAPP, University of Johannesburg), S. Razzaque (CAPP, University of Johannesburg) and IKI GRB-FuN report We observed the field of GRB 250329A (Wang et al., GCN 39916; Dichiara et al., GCN 39924) in the R filter with the 0.7-meter AS-32 telescope of the Abastumani Observatory (AbAO), in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy) and in the Rc filter with the 1-meter Zeiss-1000 of SAO RAS. We do not detect the OT (Watson et al., GCN 39915; Wang et al., GCN 39917; Schneider et al., GCN 39918; Ghosh et al., GCN 39922; Ferro et al., GCN 39927) down to the following limits. Date UT start t-T0 Filter Exp. UL(3sigma) Telescope (mid, d) (s) 2025-03-29 17:07:10 0.56824 R 98 x 60 21.7 AS-32 2025-03-29 19:11:57 0.64726 R 38 x 120 22.7 AZT-33IK 2025-03-29 20:00:02 0.66837 Rc 7 x 300 22.3 Zeiss-1000 Photometry is based on nearby USNO-B1.0 stars and is not corrected for Galactic extinction RA Dec R2 197.4269 9.4669 15.26 197.4732 9.4981 13.49 197.4408 9.5091 15.64 View this GCN Circular online at https://gcn.nasa.gov/circulars/39985. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38003] Fermi trigger No 765078057: Global MASTER-Net observations report
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39984 SUBJECT: Fermi trigger No 765078057: Global MASTER-Net observations report DATE: 25/03/31 19:31:03 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250331.07 (trigger No 765078057,06h 45m 38.40s , -32d 23m 24.0s, R=9.26) errorbox 56780 sec after notice time and 62879 sec after trigger time at 2025-03-31 19:08:51 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 30 deg. The sun altitude is -32.9 deg. The galactic latitude b = -15 deg., longitude l = 242 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828891 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 62909 | 2025-03-31 19:08:51 | MASTER-SAAO | (06h 42m 35.05s , -35d 00m 33.0s) | C | 60 | 19.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39984. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38002] GRB 250329B: CAHA 2.2m telescope optical limit
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39983 SUBJECT: GRB 250329B: CAHA 2.2m telescope optical limit DATE: 25/03/31 18:52:11 GMT FROM: Youdong HU at INAF-OAB <huyoudong072(a)hotmail.com> A. J. Castro-Tirado, E. Fernandez-Garcia, I. Perez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), and A. Fernandez-Martin, J. F. Agui Fernandez (CAHA) on behalf of a larger collaboration, report: Following the detection of GRB 250329B by SVOM/ECLAIRs (Xie et al. GCNC 39925), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered starting on Mar. 30 01:33:35 UT (i.e. ~13.4 hours after trigger) in Sloan-riz and clear bands for the error region. On the co-added z band image (90 x 10 s), no optical transient detected, includeing the afterglow detected by Swift/XRT (Beardmore et al. GCNC 39939, P. Evans GCNC 39971), which down to 22.5 mag. This non-detection is consistent with the reports from GWAC-F50A (Xin et al. GCNC 39926), Mephisto (Chen et al. GCNC 39929), SVOM/VT (Xin et al. GCNC 39931), SVOM/C-GFT (Wu et al. GCNC 39935), SVOM/F-GFT (Rakotondrainibe et al. GCNC 39945). We thank the staff at Calar Alto observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39983. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38001] GRB 250331D: Swift ToO observations
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39982 SUBJECT: GRB 250331D: Swift ToO observations DATE: 25/03/31 18:37:26 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT-detected event GRB 250331D. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021825 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 Swift/BAT 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/39982. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38000] Swift GRB 250331C: Global MASTER-Net observations report
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39981 SUBJECT: Swift GRB 250331C: Global MASTER-Net observations report DATE: 25/03/31 18:16:57 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 250331C ( S. B. Cenko et al., GCN 39959) errorbox 48174 sec after notice time and 48531 sec after trigger time at 2025-03-31 18:06:32 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 75 deg. The sun altitude is -20.0 deg. The galactic latitude b = -1 deg., longitude l = 174 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828956 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 48622 | MASTER-SAAO | C | 180 | 17.9 | 48821 | MASTER-SAAO | C | 180 | 18.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37999] Swift GRB 250331B: Global MASTER-Net observations report
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39980 SUBJECT: Swift GRB 250331B: Global MASTER-Net observations report DATE: 25/03/31 17:47:41 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 250331B ( S. B. Cenko et al., GCN 39958) errorbox 47556 sec after notice time and 47612 sec after trigger time at 2025-03-31 17:33:15 UT, with upper limit up to 16.9 mag. Observations started at twilight. The observations began at zenith distance = 85 deg. The sun altitude is -13.0 deg. The galactic latitude b = -1 deg., longitude l = 161 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2828939 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 47702 | MASTER-SAAO | C | 180 | 16.5 | 47902 | MASTER-SAAO | C | 180 | 16.7 | 48101 | MASTER-SAAO | C | 180 | 16.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39980. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37998] GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39979 SUBJECT: GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew DATE: 25/03/31 17:36:04 GMT FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu> Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: Swift/BAT did not localize GRB 250331D onboard (T0: 2025-03-31T05:49:17 UTC, Fermi GCN 39961). The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The burst occurred during a Swift slew. The imaging is performed using BatAnalysis tools (Parsotan et al. 2025 [https://arxiv.org/abs/2502.00278](https://arxiv.org/abs/2502.00278)). A confident location is found for the burst with SNR of 11.6 The BAT position is RA, Dec = 48.52543, 62.30596 deg which is RA(J2000) = 03h 14m 06.10s Dec(J2000) = +62d 18’ 21.5″ with an estimated uncertainty of 5 arcmin. This position is consistent with the Ferm/GBM localization (GCN 39961). XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. 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/39979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37997] Konus-Wind detection of GRB 250327B
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39978 SUBJECT: Konus-Wind detection of GRB 250327B DATE: 25/03/31 16:40:41 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250327B (SVOM-ECLAIRs detection: Bouchet et al., GCN 39888) was detected by Konus-Wind (KW) in the waiting mode at T0 = T0(ECLAIRs) = 76287 s UT (21:11:27). A Bayesian block analysis of the KW waiting mode data in the 20-1200 keV band reveals a ~20 sigma count rate increase in the interval from ~T0-12 s to ~T0+424 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250327B/ The total burst fluence is 2.31(-0.22,+0.26)x10^-5 erg/cm^2, and the 2.944 s peak energy flux, measured from T0+85 s, is 2.43(-0.52,+0.55)x10^-7 erg/cm^2. (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst, measured from T0-12 s to T0+424 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.11(-0.17,+0.21) and Ep = 212(-38,+48) keV. The spectrum near the peak count rate, measured from T0+76 s to T0+91 s, can be described by a CPL model with alpha = -0.82(-0.31,+0.43) and Ep = 203(-49,+64) keV. Assuming the redshift z=3.035 (Malesani et al., GCN 39893) 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 following rest-frame parameters: the isotropic energy release E_iso is 4.78(-0.45,+0.54)x10^53 erg, the peak luminosity L_iso is 2.03(-0.44,+0.46)x10^52 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 856(-152,+195) keV and the spectrum near the maximum count rate Ep,p,z is 818(-198,+257) keV. With the obtained estimates, GRB 250327B is inside 68% prediction band for the 'Amati' and 90% prediction band for the '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/GRB250327B/GRB250327B_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/39978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37996] GRB 250331C: Enhanced Swift-XRT position
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39977 SUBJECT: GRB 250331C: Enhanced Swift-XRT position DATE: 25/03/31 16:38:10 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1624 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250331C, 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 = 80.95619, +33.06347 which is equivalent to: RA (J2000): 05h 23m 49.49s Dec (J2000): +33d 03' 48.5" with an uncertainty of 2.2 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/39977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37995] IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39976 SUBJECT: IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/03/31 16:15:15 GMT FROM: Jessie Thwaites at IceCube/U Wisc-Madison <thwaites(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250330A (https://gcn.nasa.gov/circulars/39943) in a time range of 1000 seconds centered on the alert event time (2025-03-30 08:22:46.320 UTC to 2025-03-30 08:39:26.320 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250330A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250330A is 1.3e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-03-29 08:31:06.320 UTC to 2025-03-31 08:31:06.320 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250330A is 1.5e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/39976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37994] LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39975 SUBJECT: LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume DATE: 25/03/31 15:48:32 GMT FROM: David Cook at Caltech/IPAC-NED <dcook(a)ipac.caltech.edu> David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC) On behalf of the NASA/IPAC Extragalactic Database (NED) Team. We spatially cross-matched the LVK S250331o-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 582 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links: Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250331o/3 Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250331o/3/20 The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume. | objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1| |-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------| |WISEA J020352.96+300418.6| 30.97068| 30.07186| G| 450.96| null| null| null| 13.417| 0.135| 10.147| 0.006|2.21e-06| 3.99e-08| |WISEA J020524.84+300356.4| 31.35354| 30.06568| G| 653.76| null| null| null| 13.537| 0.143| 12.061| 0.009|1.69e-06| 1.10e-08| | 3C 059 NED01| 31.75919| 29.51278| G| 510.64| 2.89| 18.553| 0.047| 12.531| 0.068| 11.452| 0.006|1.47e-06| 1.02e-08| |WISEA J020815.86+330236.7| 32.06612| 33.04354| G| 528.82| null| null| null| 12.409| 0.098| 12.307| 0.010|1.99e-06| 6.80e-09| |WISEA J020728.78+301402.8| 31.86992| 30.23411| G| 488.46| null| 22.228| 0.345| 12.899| 0.118| 12.205| 0.008|2.12e-06| 6.76e-09| |WISEA J021035.33+303608.5| 32.64721| 30.60238| G| 569.79| null| null| null| 12.895| 0.117| 12.315| 0.013|1.64e-06| 6.45e-09| |WISEA J020735.81+301139.9| 31.89924| 30.19442| G| 697.62| null| null| null| 13.258| 0.120| 12.206| 0.008|9.86e-07| 6.42e-09| |WISEA J020447.91+305422.6| 31.19964| 30.90630| G| 421.78| null| null| null| 12.281| 0.097| 11.835| 0.007|1.92e-06| 6.41e-09| |WISEA J021036.53+303612.4| 32.65223| 30.60347| G| 607.46| null| null| null| 13.762| 0.178| 12.435| 0.008|1.55e-06| 6.19e-09| |WISEA J020031.78+285022.0| 30.13243| 28.83945| G| 548.45| null| null| null| 13.274| 0.142| 12.152| 0.008|1.32e-06| 5.57e-09| |WISEA J020247.16+295941.4| 30.69650| 29.99484| G| 557.31| null| 20.629| 0.118| 13.505| 0.133| 12.951| 0.014|2.62e-06| 5.47e-09| |WISEA J020311.55+300127.5| 30.79816| 30.02432| G| 512.31| 0.08| null| null| 13.071| 0.101| 12.808| 0.010|2.61e-06| 5.24e-09| |WISEA J021613.00+340524.3| 34.05421| 34.09010| G| 677.00| null| null| null| 13.485| 0.160| 11.789| 0.007|5.73e-07| 5.16e-09| |WISEA J020959.78+325524.0| 32.49910| 32.92334| G| 589.92| 0.10| 21.761| 0.336| 13.738| 0.179| 13.027| 0.012|2.33e-06| 5.10e-09| |WISEA J020619.97+294730.7| 31.58324| 29.79188| G| 507.55| 0.07| null| null| 12.533| 0.104| 12.599| 0.020|2.12e-06| 5.09e-09| |WISEA J020633.75+303828.7| 31.64066| 30.64131| G| 429.37| null| null| null| 12.181| 0.101| 12.041| 0.008|1.73e-06| 4.95e-09| | VI Zw 139| 30.40470| 30.82735| G| 509.90| 0.06| null| null| 13.148| 0.120| 12.551| 0.009|1.91e-06| 4.80e-09| |WISEA J020659.62+303130.8| 31.74842| 30.52523| G| 462.52| null| 21.179| 0.192| 13.405| 0.144| 12.477| 0.009|2.02e-06| 4.49e-09| |WISEA J020919.83+314709.5| 32.33265| 31.78598| G| 656.06| 0.12| null| null| 14.209| 0.268| 13.409| 0.016|2.34e-06| 4.46e-09| |WISEA J020626.94+302913.7| 31.61227| 30.48715| G| 672.91| 0.08| null| null| 13.829| 0.091| 13.152| 0.013|1.69e-06| 4.27e-09| Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250331o sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). View this GCN Circular online at https://gcn.nasa.gov/circulars/39975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37993] GRB 250331B: Enhanced Swift-XRT position
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39974 SUBJECT: GRB 250331B: Enhanced Swift-XRT position DATE: 25/03/31 15:22:51 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 824 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250331B, 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 = 71.37215, +43.81257 which is equivalent to: RA (J2000): 04h 45m 29.32s Dec (J2000): +43d 48' 45.2" with an uncertainty of 3.6 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/39974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37992] GRB 250320C : SVOM detection of a burst through offline search
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39973 SUBJECT: GRB 250320C : SVOM detection of a burst through offline search DATE: 25/03/31 14:25:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), S. Schanne (CEA), J. Atteia (IRAP), C. W. Wang, Y. Huang (IHEP), O. Godet (IRAP), D. Turpin (CEA) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 250320C, starting at 2025-03-20T17:39:40.0 UTC (Tb), through an offline search with the event-by-event data downloaded through the X-band ground station. The burst was detected by several methods and within several energy ranges and timescales. The best detection is obtained by the image trigger with a signal-to-noise ratio of 7.7 within 4-120 keV over a time window of 40.96 seconds starting at 2025-03-20T17:40:39.4 UTC. The lightcurve shows a first episode, starting at Tb, composed of a single peak that lasted around 5s and a second episode 1 minute later composed of multiple peaks, that lasted around 40s. The localization of the source is RA, Dec = 170.930, 40.677 (J2000). The uncertainty on this position is 11.6 arcminutes at 90% C.L. We notice the presence of several quasars in this error box, among which the closest is SDSS J112340.66+404052.0 located at 0.5 arcmin. However the lightcurve is more suggestive of a GRB. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM point of contact for this event is: Marius Brunet (IRAP) marius.brunet(a)irap.omp.eu. Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37991] LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39972 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources DATE: 25/03/31 14:04:07 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team: Swift has carried out 97 observations of the LVK error region for the GW trigger S250328ae convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9), using the 'BAYESTAR' GW localisation map. As this is a 3D skymap, galaxy distances were taken into account in selecting which ones to observe. The observations currently span from 3.0 ks to 38 ks after the LVK trigger, and the XRT has covered 5.3 deg^2 on the sky (corrected for overlaps). This covers 68% of the probability in the 'ligo-skymap-from-samples' skymap, and 72% after convolving with the 2MPZ galaxy catalogue, as described by Evans et al. (2016, MNRAS, 462, 1591). We have detected 34 X-ray sources. Each source is assigned a rank of 1-4 which describes how likely it is to be related to the GW trigger, with 1 being the most likely and 4 being the least likely. The ranks are described at https://www.swift.ac.uk/ranks.php. We have found: * 0 sources of rank 1 * 0 sources of rank 2 * 34 sources of rank 3 * 0 sources of rank 4 RANK 3 sources ============== These are uncatalogued X-ray sources, however they are not brighter than previous upper limits, so do not stand out as likely counterparts to the GW trigger. | Source ID | RA | Dec | Err90 | Detection Flag | | S250328ae_X1 | 09h 37m 34.26s | +11d 00' 47.1" | 8.3" | POOR | | S250328ae_X2 | 09h 37m 40.59s | +11d 15' 09.3" | 5.4" | REASONABLE | | S250328ae_X3 | 09h 38m 01.16s | +11d 14' 02.6" | 6.5" | POOR | | S250328ae_X5 | 09h 38m 05.54s | +11d 24' 32.5" | 6.5" | POOR | | S250328ae_X6 | 09h 37m 57.28s | +11d 18' 05.4" | 6.5" | POOR | | S250328ae_X8 | 09h 38m 05.52s | +11d 19' 00.3" | 9.1" | POOR | | S250328ae_X9 | 09h 38m 34.55s | +11d 14' 28.5" | 6.4" | POOR | | S250328ae_X10 | 09h 38m 37.34s | +11d 16' 12.5" | 9.9" | POOR | | S250328ae_X11 | 09h 38m 13.89s | +11d 16' 52.4" | 9.5" | POOR | | S250328ae_X12 | 09h 37m 35.17s | +10d 47' 58.5" | 6.6" | POOR | | S250328ae_X13 | 09h 39m 29.53s | +11d 47' 43.2" | 6.0" | POOR | | S250328ae_X14 | 09h 39m 57.31s | +12d 06' 58.4" | 8.7" | POOR | | S250328ae_X15 | 09h 39m 31.81s | +12d 06' 34.6" | 7.9" | POOR | | S250328ae_X16 | 09h 40m 10.28s | +11d 53' 17.1" | 6.7" | POOR | | S250328ae_X17 | 09h 39m 48.52s | +11d 55' 48.6" | 7.4" | POOR | | S250328ae_X18 | 09h 39m 45.99s | +11d 54' 42.0" | 7.5" | POOR | | S250328ae_X19 | 09h 39m 39.79s | +11d 54' 32.3" | 6.6" | POOR | | S250328ae_X20 | 09h 39m 23.21s | +11d 57' 42.7" | 6.6" | POOR | | S250328ae_X21 | 09h 39m 41.64s | +11d 53' 24.9" | 13.1" | POOR | | S250328ae_X22 | 09h 39m 45.64s | +11d 51' 32.9" | 9.1" | POOR | | S250328ae_X23 | 09h 39m 28.69s | +11d 59' 35.2" | 8.2" | POOR | | S250328ae_X24 | 09h 39m 51.34s | +11d 52' 24.6" | 6.2" | POOR | | S250328ae_X25 | 09h 40m 08.46s | +11d 55' 52.5" | 8.9" | POOR | | S250328ae_X26 | 09h 39m 51.33s | +11d 55' 00.9" | 6.6" | POOR | | S250328ae_X27 | 09h 39m 34.55s | +12d 01' 50.9" | 7.2" | POOR | | S250328ae_X28 | 09h 40m 17.23s | +11d 54' 47.3" | 9.7" | POOR | | S250328ae_X29 | 09h 39m 31.19s | +11d 54' 35.1" | 8.4" | POOR | | S250328ae_X30 | 09h 39m 39.91s | +12d 04' 29.3" | 15.4" | POOR | | S250328ae_X31 | 09h 38m 40.15s | +11d 14' 00.3" | 5.7" | POOR | | S250328ae_X32 | 09h 38m 17.68s | +11d 19' 25.6" | 13.5" | POOR | | S250328ae_X33 | 09h 39m 18.34s | +11d 59' 40.6" | 8.9" | POOR | | S250328ae_X34 | 09h 39m 52.80s | +11d 54' 16.5" | 8.0" | POOR | | S250328ae_X35 | 09h 39m 34.91s | +12d 05' 56.6" | 9.0" | POOR | | S250328ae_X36 | 09h 39m 29.20s | +12d 02' 51.1" | 10.7" | POOR | For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7, unless otherwise stated. The results of the XRT automated analysis, including details of the sources listed above, are online at https://www.swift.ac.uk/LVC/S250328ae This circular is an official product of the Swift XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37990] GRB 250329B: Swift-XRT confirmation of fading
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39971 SUBJECT: GRB 250329B: Swift-XRT confirmation of fading DATE: 25/03/31 12:43:42 GMT FROM: P.A. Evans at U. Leicester <pae9(a)leicester.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has carried out a second observation of GRB 250329B. The X-ray source reported by Beardmore et al. (GCN Circ. 39939) has faded, with a decay index of 1.19 (+0.47, -0.28). We therefore confirm that it is the afterglow of this GRB. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37989] GRB 250330A: VLT/FORS2 Afterglow Detection
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39970 SUBJECT: GRB 250330A: VLT/FORS2 Afterglow Detection DATE: 25/03/31 12:35:19 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Rome), Yu-Han Yang (U Rome), Simone Dichiara (PSU), Muskan Yadav (U Rome), Eleonora Troja (U Rome), Lei Hu (CMU) and Roberto Ricci (U Rome) report on behalf of the ERC BHianca team: We reobserved the field of GRB 250330A (Cenko et al., GCN 39938) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began at T+19.8 hours after the trigger and were carried out in the R filter at an average seeing of 1.0" and airmass about 2.5. A comparison to our first epoch (Becerra et al., GCN 39941) reveals a fading source within the XRT enhanced position (Evans et al., GCN 39947), located at RA, Dec (J2000) = 16:51:47.01, -86:52:51.85. We estimate a preliminary magnitude of R~23.2 AB mag at 1.25 h post-trigger, calibrated using nearby stars from the SkyMapper Southern Survey (SMSS) Fourth Data Release (DR4) catalog (Onken et al., 2024) and not corrected for Galactic extinction. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37988] GRB20250327B: 45th Parallel Observatory upper limit
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39969 SUBJECT: GRB20250327B: 45th Parallel Observatory upper limit DATE: 25/03/31 12:21:20 GMT FROM: Vincenzo Della Vecchia <v.dellavecchia(a)uai.it> Vincenzo della Vecchia (45th Parallel Observatory, Italy) Member of: AAVSO - American Association of Variable Star Observers UAI - Unione Astrofili Italiani - Gamma Ray Burst Section In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), report: We imaged the field of GRB 250327B detected by SVOM (burst-id sb25032706, GCN Circular 39888) and Swift XRT (GCN circ. 39895) with the 0.25-m f/5.6 Ritchey-Chrétien telescope of the 45th Parallel Observatory (IAU code D43). The observation started 22.33 hours after the GRB trigger, with acceptable sky transparency and seeing. A series of 10 sec observations has been added for a total integration time of approximately 30 minutes. Start T0+ End T0+ CR lim 22.33 hour 22.83 hour 19.5 CR as unfiltered with R zero point. No optical counterpart has been detected at the position expected for the GRB. Limit magnitudes are estimated with the Pan-STARSS DR1 catalogue and are not corrected for galactic dust extinction. I am grateful to Ulisse Quadri (Bassano Bresciano Astronomical Observatory) for his support. This message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39969. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37987] GRB 250328A: Swift/UVOT Detection
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39968 SUBJECT: GRB 250328A: Swift/UVOT Detection DATE: 25/03/31 10:23:48 GMT FROM: noelklin(a)umbc.edu N. Klingler (NASA-GSFC / UMBC / CRESST II), M.H. Siegel (PSU), and P.A. Evans (U. Leicester), report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250328A 3254 s after the SVOM trigger sb25032803 (GCN Circ. 39910). A source consistent with the XRT position (Evans et al., GCN Circ. 39967) is detected in the initial UVOT exposures and appears to be fading. Preliminary detections and 3-sigma upper limits for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag(AB) u 3254 4993 1711 21.93 +/- 0.30 u 8758 8994 232 >21.01 u 177580 190264 970 >21.88 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998). This is an official data product of the Swift/UVOT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39968. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37986] GRB 250328A: Swift-XRT refined Analysis
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39967 SUBJECT: GRB 250328A: Swift-XRT refined Analysis DATE: 25/03/31 09:33:00 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 4.5 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250328A (SVOM trigger sb25032803), from 3.2 ks to 190.2 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. We find an uncatalogued fading X-ray source. Using 1975 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 215.95979, +25.93224 which is equivalent to: RA (J2000): 14h 23m 50.35s Dec(J2000): +25d 55' 56.1" with an uncertainty of 4.4 arcsec (radius, 90% confidence). This position is 3.1 arcmin from the SVOM/ECLAIRs position and 1.6 arcsec from the IR/optical afterglow candidate (Schneider et al., GCN 39919; Schneider et al., GCN 39920; Li et al., GCN 39923; Li et al, GCN 39936; Kumar et al., GCN 39946). The light curve can be modelled with a power-law decay with a decay index of alpha=0.67 (+0.24, -0.18). The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019661. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39967. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37985] Fermi-LAT gamma-ray observations of IceCube-250330A
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39966 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250330A DATE: 25/03/31 07:12:49 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), C. Bartolini (INFN Bari), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250330A neutrino event (GCN 39943) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-03-30 08:31:06.33 UTC (T0) with J2000 position RA = 307.53 (+0.57, -0.47) deg, Decl. = 11.07 (+0.45, -0.47) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250330A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5 sigma) new excess emission (> 100 MeV) within the IC250330A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is <3.06e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <1.85e-08(<1.06e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). 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/39966. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37984] SVOM/sb25033102 is a false trigger
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39965 SUBJECT: SVOM/sb25033102 is a false trigger DATE: 25/03/31 07:00:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo MA, Chao WU, Donghua ZHAO, Wenjin XIE (NAOC), Hatsune GOTO (CEA, Kanazawa Univ) on behalf of the SVOM mission team. The SVOM trigger sb25033102 (GCN Circular 39955) on 2025-03-31T02:04:18 UTC (Tb) is a false trigger, caused by the nearby known bright source SCO X-1, and does not correspond to a real transient. We apologize for any confusion and inconvenience caused by this mistake. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. View this GCN Circular online at https://gcn.nasa.gov/circulars/39965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37983] GRB 250330A: Fermi GBM Observation
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39964 SUBJECT: GRB 250330A: Fermi GBM Observation DATE: 25/03/31 06:48:11 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB), R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:07:38.42 UT on 30 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250330A (trigger 765007663/250330255). which was also detected by Swift-BAT (Cenko et al. 2025, GCN 39938). The afterglow has been detected by Swift-XRT (Osborne et al. 2025, GCN 39947). The Fermi GBM Final Localization (GCN 39944) is consistent with the Swift-BAT and Swift-XRT positions (Page et al. 2025, GCN 39940). The angle from the Fermi LAT boresight is 46 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 4.8 s (50-300 keV). The time-averaged spectrum from T0-0.6 to T0+6.53 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 95 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (1.50 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.26 s in the 10-1000 keV band is 6.5 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 86 +/- 10 keV, alpha = -0.8 +/- 0.2 and beta = -2.7 +/- 0.4. 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/39964. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37982] GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39963 SUBJECT: GRB 250331C: COLIBRÍ/DDRAGO optical upper limit DATE: 25/03/31 06:24:32 GMT FROM: damien dornic <damiendornic(a)gmail.com> Damien Dornic (CPPM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Ny Avo Rakotondrainibe (LAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of Swift/BAT GRB 250331C (Cenko et al., GCN Circ. 39959) 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 2025-03-31 04:43:50 UTC (370 s after the trigger) and obtained a total of 720 s of exposure time in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), 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. At the XRT localization (Evans et al. 39960), we do not find any optical counterpart to a 3-sigma limiting magnitude of: i > 22.26 We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37981] GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39962 SUBJECT: GRB 250331B: COLIBRÍ/DDRAGO optical upper limit DATE: 25/03/31 06:21:34 GMT FROM: damien dornic <damiendornic(a)gmail.com> Damien Dornic (CPPM), Margarita Pereyra (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Ny Avo Rakotondrainibe (LAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of Swift/BAT GRB 250331B (Cenko et al., GCN Circ. 39958) 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 2025-03-31 04:21:10 UTC (87 s after the trigger) and obtained a total of 100 s exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), 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. At the XRT localization, we do not find any optical counterpart to a 3-sigma limiting magnitude of: i > 20.96 We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37980] GRB 250331D: Fermi GBM Final Real-time Localization
by GCN Circulars 31 Mar '25

31 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39961 SUBJECT: GRB 250331D: Fermi GBM Final Real-time Localization DATE: 25/03/31 05:59:53 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 05:49:17 UT on 31 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250331D (trigger 765092962.014718 / 250331243). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 21.1, Dec = 55.7 (J2000 degrees, equivalent to J2000 01h 24m, 55d 42'), with a statistical uncertainty of 13.9 degrees. The angle from the Fermi LAT boresight is 12.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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