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[vsnet-grb-info 42155] EP260316a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 17 Mar '26

17 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44034 SUBJECT: EP260316a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/03/17 08:21:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B. Zhang, J. P. Feng (USTC), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260316a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 44027). The transient was detected immediately when WXT observation started at T0=2026-03-16 12:32:52. The WXT observation lasted for approximately 22 seconds, and was interrupted due to the autonomous follow-up observation. The WXT light curve exhibits a double-peaked structure, which is also observed in the Fermi/GBM data (Ravasio et al., GCN 44029). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 2.4 (-1.1/+1.4) × 10^22 cm^-2 and a photon index of 2.9 (-1.4/+1.6). The derived average unabsorbed 0.5-4 keV flux is 3.1 (-2.1/+9.1) × 10^(-8) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-16 12:35:40 (UTC, T0+168 s). The exposure time of this observation is 5.4 ks. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 226.9819, 27.4455 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 7.01 (-0.55/+0.57) × 10^21 cm^-2 and a photon index of 2.39 (-0.10/+0.11). The derived average unabsorbed 0.5-10 keV flux is 9.51 (-0.41/+0.47) × 10^(-12) erg/s/cm^2. A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data are 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/44034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42154] IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44033 SUBJECT: IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/03/16 17:57:13 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(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-260315A (https://gcn.nasa.gov/circulars/44017) in a time range of 1000 seconds centered on the alert event time (2026-03-15 02:10:46.630 UTC to 2026-03-15 02:27:26.630 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-260315A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260315A 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 3e+02 GeV and 2e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-03-14 02:19:06.630 UTC to 2026-03-16 02:19:06.630 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260315A 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/44033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42153] EP260316a: Xinglong optical upper limit
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44032 SUBJECT: EP260316a: Xinglong optical upper limit DATE: 26/03/16 17:46:14 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junbo-Zhang (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Jie-Zheng (NAOC), Dong-Xu (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260316a by EP-WXT (Jiang et al., GCN 44027), we observed the field of EP260316a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 6x300s clear-band frames with a median time of 2026-03-16 16:18:40 (UT), 3.76 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Jiang et al., GCN 44027), down to 3-sigma limiting magnitudes of g ~22.00 mag, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. We also detected no optical transient candidate with a median time of 2026-03-16T16:37:50.536 (UT) with the 0.8-m Telescope in Xinglong, Hebei, China. The upper limit is ～19.9 mag in the g-band. View this GCN Circular online at https://gcn.nasa.gov/circulars/44032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42152] GRB 260316A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44031 SUBJECT: GRB 260316A: Fermi GBM Final Real-time Localization DATE: 26/03/16 17:23:26 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 17:12:52 UT on 16 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260316A (trigger 795373977.681026 / 260316717). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 305.5, Dec = -79.3 (J2000 degrees, equivalent to J2000 20h 22m, -79d 17'), with a statistical uncertainty of 3.2 degrees. The angle from the Fermi LAT boresight is 81.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42151] EP260316a: optical upper limit with Kinder observations
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44030 SUBJECT: EP260316a: optical upper limit with Kinder observations DATE: 26/03/16 17:12:28 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, 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 EP260316a (Jiang et al., GCN 44027) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 14:11 UTC on 16th of March 2026 (MJD 61115.591), 1.63 hr after the EP-WXT detection. 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 utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of a new or uncatalogued source within the EP-FXT localization circle (20"). Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing | Med. Airmass LOT | g | 61115.591 | 1.63 | 300 * 12 | >23.2 | 1".52 | 1.94 The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.12 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42150] EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44029 SUBJECT: EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection DATE: 26/03/16 17:06:07 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA), and P. Veres (UAH) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260316a detected by EP-WXT (EP Team GCN 44027). There was no Fermi-GBM onboard trigger around the corrected EP starting time at T0 = 2026-03-16T12:33:13 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from T0, seeking signals between 64 ms and 32.768 s in duration. A faint transient signal was found most significantly at ~T0-3.6 s on a 4 s timescale, with a false alarm rate of 6.5e-05 Hz, although there is evidence of an earlier start of the emission at T0-20 s. The localisation is consistent with the EP one, with a spatial association probability of 98.8%. Among the three spectral templates tested, the transient was best-fit with a“soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42149] GRB 260314A: Glowbug gamma-ray detection
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44028 SUBJECT: GRB 260314A: Glowbug gamma-ray detection DATE: 26/03/16 16:43:10 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260314A, which was also detected by Fermi/GBM (GCN 43997) and GECAM-B (GCN 44008). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-03-14 00:58:49.312 with a duration of 6.1 s and a total significance of about 16.5 sigma. The detection occurred during a time of high background. The light curve comprises a single peak at ~T0+3s. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42148] The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44027 SUBJECT: The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up DATE: 26/03/16 14:23:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang (NAO, CAS), B. Zhang, J. P. Feng (USTC), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The trigger time reported in the notice for EP-WXT alert 00199258890 is incorrect. The correct trigger time is 2026-03-16T12:33:13.451 (UTC), rather than 2026-03-16T20:33:13.451 (UTC). The X-ray transient was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260316a. The transient triggered EP-WXT (ID: 00199258890) at 2026-03-16T12:33:13.451 (UTC). The WXT position of the source is R.A. = 226.983 deg, DEC = 27.466 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. = 226.9840 deg, DEC = 27.4447 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/44027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42147] IceCube-260315A: COLIBRÍ optical observations
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44026 SUBJECT: IceCube-260315A: COLIBRÍ optical observations DATE: 26/03/16 13:05:38 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> IceCube 260315A: COLIBRÍ optical observations Francis Fortin (IRAP), Leonardo García García (UNAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), 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 IceCube 260315A (The IceCube Collaboration, GCN Circ. 44017) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-16 06:23:48 to 09:13:24 UTC (from 28 to 30.9 hours after the trigger) and obtained 63 minutes of exposure in the g, r filters, and 126 minutes in the z filter. The data were reduced, coadded and analyzed with the COLIBRÍ 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 candidate AT 2026fpm reported by Segura et al., GCN Circ. 44023, at a preliminary magnitude of: g = 19.94 +/- 0.01 r = 19.69 +/- 0.01 z = 19.66 +/- 0.01 The optical counterpart candidate lies on top of a catalogued source in the Legacy Survey with magnitudes of: g = 21.04 r = 20.59 z = 20.48 However, this LS source is flagged as variable. We also note that it is found in PS1 at a much fainter level. This would indicate that AT 2026 fpm is a known variable source. 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/44026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42146] EP260314a: Xinglong optical upper limit
by GCN Circulars 16 Mar '26

16 Mar '26

TITLE: GCN CIRCULAR NUMBER: 44025 SUBJECT: EP260314a: Xinglong optical upper limit DATE: 26/03/16 13:00:42 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junbo-Zhang (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Jie-Zheng(NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260314a by EP-WXT (Zhao et al., GCN 44010; Wu et al., GCN 44016), we observed the field of EP260314a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x600s clear-band frames with a median time of 2026-03-15 17:58:07 (UT), 19.11 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Zhao et al., GCN 44010; Wu et al., GCN 44016), down to 3-sigma limiting magnitudes of g ~21.5, 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/44025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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