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

[vsnet-grb-info 42433] GRB 260415A: Insight-HXMT/HE detection
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44311 SUBJECT: GRB 260415A: Insight-HXMT/HE detection DATE: 26/04/16 12:39:40 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng (IHEP) report on behalf of the Insight-HXMT team: At 2026-04-15T04:44:27.200 (T0), Insight-HXMT/HE detected a long burst, GRB 260415A, which is also detected by Fermi/GBM (Fermi GBM team, GCN #44299). The Insight-HXMT/HE light curve mainly consists of multi-pulses with T90 of 39 +3/-2 s. The 1s peak rate, measured from T0+0.75 s, is 2212 cnts/sec. Insight-HXMT/HE detected a total of 27305 counts from this burst. The Insight-HXMT /HE light curve can be found here: https://www.bursthub.cn/admin/static/hxmtgrb260415A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/ View this GCN Circular online at https://gcn.nasa.gov/circulars/44311. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42432] EP260416a: COLIBRÍ optical counterpart candidate
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44310 SUBJECT: EP260416a: COLIBRÍ optical counterpart candidate DATE: 26/04/16 09:22:19 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260416a (Hu et al., GCN Circ. 44307) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-16 05:36:04 to 06:51:03 UTC (from 0.11 to 1.36 hours after the trigger) and obtained 60 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with both the COLIBRÍ and COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In r band, we detect a source revealed by image subtraction using Legacy Survey as template and consistent with the FXT 20 arcsec error circle (Hu et al., GCN Circ. 44307) at: RA(J2000) = 13:15:20.49 = 198.8354 degrees Dec(J2000) = +31:35:49.4 = 31.5971 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: r = 23.4 +/- 0.2 z > 22.8 (3 sigma-limit) The position of the source is coincident with a galaxy in the Legacy Survey catalog (Dey et al. 2019) with a photometry of g = 24.01 +/- 0.17 r = 24.05 +/- 0.30 z = 23.35 +/- 0.34. In our observations, we find evidence for brighter emission in the r band relative to the catalog value, suggesting tentative excess emission relative to the cataloged galaxy flux. However, the non-detection in the z band, combined with the lack of clear evidence for variability, prevents a firm confirmation . We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44310. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42431] COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44309 SUBJECT: COLIBRI optical observations of the transient GOTO26djh/AT2026jpw DATE: 26/04/16 06:26:13 GMT FROM: enriquemm(a)astro.unam.mx GOTO26djh/AT2026jpw: COLIBRÍ optical observations. Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the orphan afterglow candidate GOTO26djh/AT2026jpw reported by O'Neill et al., (GCN Circ. 44301) and also observed by Corcoran et al. (GCN Circ. 44303), Moskvitin et al. (GCN Circ. 44304), Xu et al. (GCN Circ. 44305), and Sosnovskij et al. (GCN Circ. 44306) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-16 03:47:39 to 04:44:41 (from 52.50 to 53.45 hours after the trigger) and obtained 15/15/15/45 minutes of simultaneous exposure in the g/r/i/z filters. The data were reduced and coadded with the ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by D. O'Neill et al., GCN Circ. 44301 at preliminary magnitudes of: g = 22.51 +/- 0.06 r = 22.10 +/- 0.06 i = 21.87 +/- 0.08 z = 21.55 +/- 0.07 Comparing our values with the reported by NOT (Corcoran et al. GCN Circ. 44303), we estimate an optical decay alpha 1.6. Moreover, the detection in the four filters suggests a photo-z < 2.7 using typical IGM absorption. Further observations and analysis are ongoing. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44309. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42430] EP260416a: Global MASTER-Net observations report
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44308 SUBJECT: EP260416a: Global MASTER-Net observations report DATE: 26/04/16 06:18:42 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260416a ( EP Team et al., GCN 44307) errorbox 436 sec after trigger time at 2026-04-16 05:36:48 UT, with upper limit up to 20.7 mag. The observations began at zenith distance = 66 deg. The sun altitude is -64.5 deg. The galactic latitude b = 83 deg., longitude l = 71 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3254155 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 482 | 2026-04-16 05:36:48 | MASTER-OAFA | (13h 14m 35.21s , +31d 29m 47.4s) | C | 90 | 20.1 | 602 | 2026-04-16 05:36:48 | MASTER-OAFA | (13h 14m 35.21s , +31d 29m 47.4s) | C | 330 | 20.7 | Coadd 588 | 2026-04-16 05:38:25 | MASTER-OAFA | (13h 14m 34.93s , +31d 29m 48.7s) | C | 110 | 20.2 | 714 | 2026-04-16 05:40:21 | MASTER-OAFA | (13h 14m 34.60s , +31d 29m 49.8s) | C | 130 | 20.2 | 865 | 2026-04-16 05:42:37 | MASTER-OAFA | (13h 14m 34.22s , +31d 29m 50.9s) | C | 160 | 20.2 | 925 | 2026-04-16 05:42:37 | MASTER-OAFA | (13h 14m 34.22s , +31d 29m 50.8s) | C | 280 | 20.4 | Coadd 981 | 2026-04-16 05:45:23 | MASTER-OAFA | (13h 14m 33.92s , +31d 29m 51.3s) | C | 60 | 20.0 | 1047 | 2026-04-16 05:46:28 | MASTER-OAFA | (13h 14m 33.76s , +31d 29m 51.3s) | C | 60 | 20.0 | 1112 | 2026-04-16 05:47:34 | MASTER-OAFA | (13h 14m 33.59s , +31d 29m 51.5s) | C | 60 | 20.0 | 1172 | 2026-04-16 05:47:34 | MASTER-OAFA | (13h 14m 33.59s , +31d 29m 51.5s) | C | 180 | 20.3 | Coadd 1178 | 2026-04-16 05:48:40 | MASTER-OAFA | (13h 14m 33.42s , +31d 29m 51.9s) | C | 60 | 20.0 | 1244 | 2026-04-16 05:49:45 | MASTER-OAFA | (13h 14m 33.23s , +31d 29m 52.2s) | C | 60 | 20.0 | 1309 | 2026-04-16 05:50:51 | MASTER-OAFA | (13h 14m 33.04s , +31d 29m 52.8s) | C | 60 | 20.0 | 1369 | 2026-04-16 05:50:51 | MASTER-OAFA | (13h 14m 33.04s , +31d 29m 52.8s) | C | 180 | 20.3 | Coadd 1375 | 2026-04-16 05:51:57 | MASTER-OAFA | (13h 14m 32.87s , +31d 29m 52.7s) | C | 60 | 20.0 | 1441 | 2026-04-16 05:53:02 | MASTER-OAFA | (13h 14m 32.72s , +31d 29m 52.6s) | C | 60 | 20.0 | 1506 | 2026-04-16 05:54:08 | MASTER-OAFA | (13h 14m 32.54s , +31d 29m 52.7s) | C | 60 | 20.0 | 1566 | 2026-04-16 05:54:08 | MASTER-OAFA | (13h 14m 32.54s , +31d 29m 52.7s) | C | 180 | 20.4 | Coadd 1573 | 2026-04-16 05:55:15 | MASTER-OAFA | (13h 14m 32.35s , +31d 29m 52.6s) | C | 60 | 20.0 | 1639 | 2026-04-16 05:56:20 | MASTER-OAFA | (13h 14m 32.16s , +31d 29m 52.8s) | C | 60 | 20.0 | 1704 | 2026-04-16 05:57:26 | MASTER-OAFA | (13h 14m 32.01s , +31d 29m 52.6s) | C | 60 | 20.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44308. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42429] EP260416a: Einstein Probe detection of an X-ray transient
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44307 SUBJECT: EP260416a: Einstein Probe detection of an X-ray transient DATE: 26/04/16 06:15:34 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. F. Hu (PMO, CAS), J. Yang (ZZU), M. J. Liu, 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 EP260416a. The transient triggered EP-WXT (ID: 01709260236) at 2026-04-16T05:29:32 (UTC). The WXT position of the source is R.A. = 198.836 deg, DEC = 31.590 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. = 198.8353 deg, DEC = 31.5986 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). 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/44307. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42428] GOTO26djh/AT2026jpw : MASTER OT observation
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44306 SUBJECT: GOTO26djh/AT2026jpw : MASTER OT observation DATE: 26/04/16 01:58:03 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> A.Sosnovskij, V.Lipunov, A.Kuznetsov, E.Gorbovskoy, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina, V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko, A.Sankovich, I.Gorbunov (Lomonosov MSU), M.J. Segura, C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), N.Budnev, O.Gress (ISU), D.Buckley (SAAO), A. Gabovich (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, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tavrida robotic telescope of MASTER Global Robotic Net [1-4] started GOTO26djh/AT2026jpw (discovered by GOTO O'Neill et al., GCN 44301, also observed by NOT (Corcoran et al., GCN 44303) and Zeiss-1000 at SAO RAS (Moskvitin et al. GCN 44304) observations at 2026-04-15 23:10:27UT. There is optical transient at summary MASTER image (2520s exposition, mlim=22.2m) with unfiltered m_OT~21.5+-0.6m , calibrated by Pan-STARRs stars in our field. MASTER images are available on request. Observation and reduction will continue. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44306. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42427] GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44305 SUBJECT: GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection DATE: 26/04/16 01:54:19 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> D. Xu (NAOC), B. P. Gompertz (U. Birmingham), S.Q. Jiang (NAOC) report on behalf of a large group: We performed a ToO observation at the location of GOTO26djh/AT2026jpw, a candidate orphan GRB afterglow (O'Neill et al., GCN 44301) with the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe (EP) mission. The observation started at 18:49:01 on 2026-04-15 UT with a total exposure time of ~3000 s. An uncatalogued X-ray source, with a flux of ~ 1.7 x 10^-13 erg/cm^2/s (0.5-10 keV; observed), is detected at coordinates R.A.(J2000) = 13:22:13.34 Dec.(J2000) = +37:02:26.88 with an uncertainty of 15 arcsec, being consistent with the location of GOTO26djh/AT2026jpw, confirming it's the soft X-ray counterpart of GOTO26djh/AT2026jpw. The X-ray counterpart detection at ~ 3 days since the event happening favors its nature of an afterglow of a high-energy burst. Further EP-FXT observations are scheduled. View this GCN Circular online at https://gcn.nasa.gov/circulars/44305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42426] GOTO26djh/AT2026jpw transient: SAO RAS optical observations
by GCN Circulars 16 Apr '26

16 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44304 SUBJECT: GOTO26djh/AT2026jpw transient: SAO RAS optical observations DATE: 26/04/16 00:39:58 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin and O. I. Spiridonova (SAO RAS) report on behalf of GRB follow-up team. We observed the field of the fast-fading transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) with the Zeiss-1000 1m telescope of the SAO RAS on April 15/16 night. We obtained two series of images in Rc band. The OT (O'Neill et al., GCN 44301; Corcoran et al., GCN 44303) is clearly detected in the stacked images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2026-04-15T19:30:44 1.87945 8*300 Rc 21.6 +/- 0.1 23.3 2026-04-15T22:01:13 1.97747 13*300 Rc 22.0 +/- 0.1 23.8 This preliminary photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42425] NOT r-band observations of the transient GOTO26djh/AT2026jpw
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44303 SUBJECT: NOT r-band observations of the transient GOTO26djh/AT2026jpw DATE: 26/04/15 23:26:03 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> G. Corcoran (UCD), A. de Ugarte Postigo (LAM), L. Cotter (UCD), A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), N. Pyykkinen (NOT and UTU), report on behalf of a larger collaboration: We observed the field of the transient GOTO26djh/AT2026jpw (O'Neill et al., GCN 44301) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument. Observations consisted of 3x500 s in the SDSS-r band starting at 21:01:12 UT on the 15th of April 2026 (45.73 hr after the GOTO discovery). In our stacked image, the transient is well detected. The calculated AB magnitude was found to be r = 21.85 +/- 0.05 (AB), calculated against the Pan-STARRS catalog, and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42424] GRB 260415B: NuSTAR detection of long prompt emission
by GCN Circulars 15 Apr '26

15 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44302 SUBJECT: GRB 260415B: NuSTAR detection of long prompt emission DATE: 26/04/15 22:13:57 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260415B in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-04-15T02:28:55.54 UTC, shows a detection of GRB 260415B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44300) and CALET/GBM (Trigger 1460255329). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~30-s burst followed by a ~20-s burst after a ~20-s gap, consistent with CALET/GBM and the broad bright Fermi/GBM peak at ~200 s post-trigger. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44300) at RA = 229.43, Dec = 24.94 implies an offset from the NuSTAR boresight of 71-deg (i.e. from the side of the instrument) and an offset from the geocenter of 107-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260415B Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/44302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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