April 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42296] GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44175 SUBJECT: GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454) DATE: 26/04/01 12:11:04 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 796733611 at 10:53:26 on 01 April 2026 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 220.7 deg Decl.(2000.0) = -16.9 deg The 1 sigma statistical error radius is 1.3 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260401454/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260401454/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260401454/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42295] GRB 260401A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44174 SUBJECT: GRB 260401A: Fermi GBM Final Real-time Localization DATE: 26/04/01 11:02:02 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 10:53:26 UT on 1 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260401A (trigger 796733611.002678 / 260401454). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.5, Dec = -17.4 (J2000 degrees, equivalent to J2000 14h 37m, -17d 23'), with a statistical uncertainty of 1.6 degrees. The angle from the Fermi LAT boresight is 60.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260401454/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44174. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42294] EP260329b: Mondy and Assy-Turgen optical upper limits
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44173 SUBJECT: EP260329b: Mondy and Assy-Turgen optical upper limits DATE: 26/04/01 09:25:28 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), D. Anarbek (FAI), M. Krugov (FAI), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142; EP Team, GCN 44155) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 40-second expositions in R-band, and with the AZT-20 telescope of Assy-Turgen observatory taking several 30-second exposures in r' filter on Mar. 29. In the stacked frames we do not detect the optical counterpart reported previously (Li et al., GCN 44139; Zhu et al., GCN 44140; Eyles-Ferris et al., GCN 44144; Aryan et al., GCN 44147; Lipunov et al., GCN 44150; Mo et al., GCN 44163; O'Neill et al., GCN 44169). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-03-29 15:24:19 0.22110 90*40 R n/d n/d 21.1 Mondy/AZT-33IK 2026-03-29 19:57:04 0.40444 80*30 r n/d n/d 21.6 Assy-Turgen/AZT-20 The photometry is based on several nearby stars from the SDSS-DR16 catalogue (Lupton transformations were used for the R-band values) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42293] GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44172 SUBJECT: GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng DATE: 26/04/01 07:07:05 GMT FROM: Y.C. Kang at Peking University <yckang(a)stu.pku.edu.cn> Zhuokai Liu, Zexuan Wu, Chenxi Bao, Yacheng Kang (PKU) report on behalf of the Interestar Collaboration and the PKU HiTF (High-energy Transients Follow-up) group: We observed the field of GRB 260310A, detected by Fermi/GBM (GCN 43951; T0 = 2026-03-10T04:57:10.81) and AstroSat/CZTI (Salunke et al., GCN 43958), using a 28cm optical telescope located in Daocheng, Sichuan, China. Observations began on 2026 Mar 17, approximately ~ 7.4 days after the GRB trigger, and spanned six epochs in the Luminance filter. In the stacked Luminance-band images, we detect the optical counterpart at a position consistent with AT2026fgk, the reported GRB afterglow candidate at z = 0.153 (O'Neill et al. 2026, TNS Discovery Report 294132; Hinds et al., AstroNote 2026-65; Konno et al., GCN 43974; Hinds et al., GCN 43977), later found to show Type Ic-BL SN features (de Ugarte Postigo et al., GCN 44124; Guelfand et al., GCN 44125; O'Connor et al., GCN 44137). Preliminary photometry was calibrated using nearby catalogued field stars and is reported as approximate AB-equivalent magnitudes, without correction for Galactic extinction. Our measurements show that the optical counterpart continues to fade, from ~ 19.0 mag to ~ 19.8 mag between 7.4 and 14.3 days after the GRB trigger. The observation log is summarized below: | Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | Magnitude (AB) | | :--------: | :------: | :---------------: | :-------: | :----------: | :------------: | | 2026-03-17 | 13:28:40 | 7.40 | Luminance | 7400 | 19.02 +/- 0.04 | | 2026-03-18 | 13:52:51 | 8.42 | Luminance | 7600 | 19.10 +/- 0.04 | | 2026-03-19 | 14:14:50 | 9.42 | Luminance | 6000 | 19.18 +/- 0.04 | | 2026-03-20 | 12:37:02 | 10.36 | Luminance | 7400 | 19.39 +/- 0.04 | | 2026-03-21 | 12:39:41 | 11.35 | Luminance | 5000 | 19.65 +/- 0.05 | | 2026-03-24 | 12:33:31 | 14.33 | Luminance | 2200 | 19.84 +/- 0.08 | Further analysis and follow-up observations are ongoing. The 28cm optical telescope is located in Daocheng, Sichuan, China, and is operated by the Interestar Collaboration. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients. View this GCN Circular online at https://gcn.nasa.gov/circulars/44172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42292] EP260321a :Xinglong optical observations
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44171 SUBJECT: EP260321a :Xinglong optical observations DATE: 26/04/01 05:05:57 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yu-Zhang(NAOC), Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Yuguang-Sun(NAOC), Pengliang-Du (NAOC), Jie-Zheng(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration: We performed optical observations of the field of a fast X-Ray transient EP260321a(Q.J. Huang et al., GCN 44068) in the g, r and i filter using Tsinghua-NAOC 0.8-m telescope (TNT) located at Xinglong, Hebei, China. A series of 300-s exposures were obtained on three epochs (March 25, 26, and 27, 2026), with the first observation at 2026-03-25T14:37:57, approximately 4 days after the EP FXT trigger (2026-03-21T12:30:18). We measure a preliminary magnitude calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name 1 | 2026-03-25T14:37:57 | 300 s | g |17.70 +/- 0.24| Tsinghua-NAOC 0.8-m telescope (TNT) 2 | 2026-03-25T14:53:18 | 300 s | r |17.69 +/- 0.20| Tsinghua-NAOC 0.8-m telescope (TNT) 3 | 2026-03-25T15:08:39 | 300 s | i |17.42 +/- 0.25| Tsinghua-NAOC 0.8-m telescope (TNT) 4 | 2026-03-26T16:00:16 | 300 s | g |17.17 +/- 0.24| Tsinghua-NAOC 0.8-m telescope (TNT) 5 | 2026-03-26T16:15:37 | 300 s | r |17.30 +/- 0.23| Tsinghua-NAOC 0.8-m telescope (TNT) 6 | 2026-03-26T16:40:01 | 300 s | i |17.38 +/- 0.30| Tsinghua-NAOC 0.8-m telescope (TNT) 7 | 2026-03-27T13:25:21 | 300 s | g |16.61 +/- 0.01| Tsinghua-NAOC 0.8-m telescope (TNT) 8 | 2026-03-27T13:40:42 | 300 s | r |16.53 +/- 0.01| Tsinghua-NAOC 0.8-m telescope (TNT) 9 | 2026-03-27T13:56:03 | 300 s | i |16.43 +/- 0.02| Tsinghua-NAOC 0.8-m telescope (TNT) View this GCN Circular online at https://gcn.nasa.gov/circulars/44171. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42291] EP260327a: Xinglong optical upper limit
by GCN Circulars 01 Apr '26

01 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44170 SUBJECT: EP260327a: Xinglong optical upper limit DATE: 26/04/01 04:32:23 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yu-Zhang(NAOC), Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Junjun-Jia(NAOC), Jie-Zheng(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration: Following the detection of EP260327a by EP-WXT (C. Y. Dai, GCN 44126), we observed the field of EP260327a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 6x300s clear-band frames with a median time of 2026-03-27T14:06:25 i.e., 8.2 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (C. Y. Dai, GCN 44126), down to 3-sigma limiting magnitudes of clear ~ 20.87 mag, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/44170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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