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[vsnet-grb-info 42827] GRB 260523A: Fermi GBM Final Real-time Localization
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44698 SUBJECT: GRB 260523A: Fermi GBM Final Real-time Localization DATE: 26/05/23 16:16:46 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 16:06:10 UT on 23 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260523A (trigger 801245175.681708 / 260523671). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 315.6, Dec = -6.8 (J2000 degrees, equivalent to J2000 21h 02m, -6d 47'), with a statistical uncertainty of 5.5 degrees. The angle from the Fermi LAT boresight is 51.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260523671/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44698. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42826] GRB 260522A: Fermi GBM Observation
by GCN Circulars 23 May '26

23 May '26

TITLE: GCN CIRCULAR NUMBER: 44697 SUBJECT: GRB 260522A: Fermi GBM Observation DATE: 26/05/23 00:32:40 GMT FROM: Angus Jameson <abj0023(a)uah.edu> A. Jameson (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:15:08.78 UT on 22 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260522A (trigger 801108913/260522094), which was also detected by Fermi-LAT ( et al. 2026, GCN 44689). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 10 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 1.8 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.48 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 1010 +/- 70 keV. The event fluence (10-1000 keV) in this time interval is (8.1 +/- 0.7)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.51 s in the 10-1000 keV band is 3 +/- 1 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/44697. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42825] EP260518a (AT2026ndp): LCO observations and Gemini-South Redshift z = 2.28
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44695 SUBJECT: EP260518a (AT2026ndp): LCO observations and Gemini-South Redshift z = 2.28 DATE: 26/05/22 14:46:39 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. J. Levan (Radboud & Warwick), J. Chacón (PUC), F. E. Bauer (UTA/SSI), P. G. Jonker (Radboud), C. Rodriguez (Gemini), L. Magil (Gemini), report on behalf of a larger collaboration: We observed the optical transient AT2026ndp associated with the Einstein Probe sub-threshold event EP260518a (Liang et al., GCN 44690) using the LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with SINISTRO instruments. A series of 6x300s exposures were taken in both SDSS-r and SDSS-z bands. In both sequences the optical transient was clearly detected blended with the nearby Legacy Survey object. We carried out image subtraction against Legacy Survey images (DR 10) in both r and z band using PyZOGY (Guevel et al. 2021, Zackay et al. 2016) and obtained the following AB magnitudes, calibrated using nearby stars in the SkyMapper catalog and not corrected for Galactic extinction: r = 20.78 +/- 0.04 (midtime: 2026-05-22 09:54:14 UT, 3.84 days after trigger); z = 20.31 +/- 0.10 (midtime: 2026-05-22 09:15:40 UT, 3.81 days after trigger). We then observed the transient using the GMOS spectrograph equipped on Gemini–South. Our observations consisted of 2 x 600 s spectra taken using a 1" slit and the B480 grating, covering the wavelength range 4470-8500 Å. Observations started at 2026-05-22 09:54:13 UT (3.84 days after trigger). Continuum is detected over the entire wavelength range and a number of absorption features can be seen. We identify lines consistent with Fe II (1608, 2344, 2374, 2383, 2587), Si IV (1394, 1403), Si II 1527, C IV (1548, 1550), Al II (1670), Al III (1855, 1863), Mg I / Zn II 2026 at a redshift of z=2.28. Given the lack of detected fine structure lines or lyman alpha absorption, this redshift is strictly speaking a lower limit however we identify no other higher redshift systems and the lack of a Lyman alpha break in our spectrum sets an upper limit to the redshift of z < 2.75. We therefore conclude that z = 2.28 is likely the redshift for this event. The point-like source in the Legacy Survey noted in Liang et al. (GCN 44690) was also placed on the slit. Its spectrum is consistent with that of a Galactic M-dwarf. View this GCN Circular online at https://gcn.nasa.gov/circulars/44695. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42824] GRB 260522B: NuSTAR detection of prompt emission
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44696 SUBJECT: GRB 260522B: NuSTAR detection of prompt emission DATE: 26/05/22 17:46:34 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 260522B 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 2026-05-22T09:35:00.13 UTC, shows a detection of GRB 260522B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44694) and SVOM/GRM (Burst-ID sb26052201). The NuSTAR CsI shield data are recorded at 1 Hz. We detect two peaks lasting for a total of about 100-s, consistent with the GBM lightcurve. 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 44694) at RA = 278.65, Dec = -33.23 implies an offset from the NuSTAR boresight of 72-deg (i.e. from the side) and an offset from the geocenter of 142-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260522B 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/44696. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42823] EP260518a (AT2025ndp): LCO observations and Gemini-South Redshift z = 2.28
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44695 SUBJECT: EP260518a (AT2025ndp): LCO observations and Gemini-South Redshift z = 2.28 DATE: 26/05/22 14:46:39 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. J. Levan (Radboud & Warwick), J. Chacón (PUC), F. E. Bauer (UTA/SSI), P. G. Jonker (Radboud), C. Rodriguez (Gemini), report on behalf of a larger collaboration: We observed the optical transient AT2026ndp associated with the Einstein Probe sub-threshold event EP260518a (Liang et al., GCN 44690) using the LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with SINISTRO instruments. A series of 6x300s exposures were taken in both SDSS-r and SDSS-z bands. In both sequences the optical transient was clearly detected blended with the nearby Legacy Survey object. We carried out image subtraction against Legacy Survey images (DR 10) in both r and z band using PyZOGY (Guevel et al. 2021, Zackay et al. 2016) and obtained the following AB magnitudes, calibrated using nearby stars in the SkyMapper catalog and not corrected for Galactic extinction: r = 20.78 +/- 0.04 (midtime: 2026-05-22 09:54:14 UT, 3.84 days after trigger); z = 20.31 +/- 0.10 (midtime: 2026-05-22 09:15:40 UT, 3.81 days after trigger). We then observed the transient using the GMOS spectrograph equipped on Gemini–South. Our observations consisted of 2 x 600 s spectra taken using a 1" slit and the B480 grating, covering the wavelength range 4470-8500 Å. Observations started at 2026-05-22 09:54:13 UT (3.84 days after trigger). Continuum is detected over the entire wavelength range and a number of absorption features can be seen. We identify lines consistent with Fe II (1608, 2344, 2374, 2383, 2587), Si IV (1394, 1403), Si II 1527, C IV (1548, 1550), Al II (1670), Al III (1855, 1863), Mg I / Zn II 2026 at a redshift of z=2.28. Given the lack of detected fine structure lines or lyman alpha absorption, this redshift is strictly speaking a lower limit however we identify no other higher redshift systems and the lack of a Lyman alpha break in our spectrum sets an upper limit to the redshift of z < 2.75. We therefore conclude that z = 2.28 is likely the redshift for this event. The point-like source in the Legacy Survey noted in Liang et al. (GCN 44690) was also placed on the slit. Its spectrum is consistent with that of a Galactic M-dwarf. View this GCN Circular online at https://gcn.nasa.gov/circulars/44695. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42822] GRB 260522B: Fermi GBM Final Real-time Localization
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44694 SUBJECT: GRB 260522B: Fermi GBM Final Real-time Localization DATE: 26/05/22 12:01:10 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely LONG GRB "At 09:35:00.13 UT on 22 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260522B (trigger 801135305/260522399). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 278.65, Dec = -33.23 (J2000 degrees, equivalent to J2000 18h 34m, -33d 12'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 76 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260522399/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/44694. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42821] GRB 260522A: GOTO optical upper limit
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44693 SUBJECT: GRB 260522A: GOTO optical upper limit DATE: 26/05/22 11:34:14 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, G. Ramsay, A. Kumar, R. Starling, B. P. Gompertz, S. Belkin, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Fermi/GBM and LAT detected GRB 260522A (Fermi GBM team, GCN 44687; Bissaldi, E., GCN 44689). Observations covering the GBM localisation area began at 2026-05-22 03:16:58 UT (+1.03h post trigger) and continued through to 2026-05-22 04:54:51 UT (+2.66h post trigger). Observations covering the LAT position were taken at 2026-05-22 04:14:26 UT (+1.99h post trigger). Images consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks (Lyman et al. 2026). We found no new transients that could be credibly associated with 260522A within the LAT localisation down to a 5-sigma depth of L<19.8 AB mag. 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44693. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42820] Fermi trigger No 801135305: Global MASTER-Net observations report
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44692 SUBJECT: Fermi trigger No 801135305: Global MASTER-Net observations report DATE: 26/05/22 09:45:51 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB260522.40 (trigger No 801135305,18h 40m 52.08s , -25d 33m 00.0s, R=7.7) errorbox 88 sec after notice time and 124 sec after trigger time at 2026-05-22 09:37:04 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 57 deg. The sun altitude is -28.5 deg. The galactic latitude b = -10 deg., longitude l = 9 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3331401 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 134 | 2026-05-22 09:37:04 | MASTER-OAGH | (18h 37m 12.05s , -25d 49m 53.1s) | C | 20 | 17.7 | 169 | 2026-05-22 09:37:04 | MASTER-OAGH | (18h 37m 12.06s , -25d 49m 53.1s) | C | 90 | 18.0 | Coadd 170 | 2026-05-22 09:37:34 | MASTER-OAGH | (18h 37m 06.41s , -25d 50m 55.7s) | C | 30 | 17.9 | 215 | 2026-05-22 09:38:15 | MASTER-OAGH | (18h 37m 10.52s , -25d 50m 55.1s) | C | 40 | 17.6 | 270 | 2026-05-22 09:39:05 | MASTER-OAGH | (18h 37m 08.18s , -25d 49m 24.5s) | C | 50 | 18.0 | 270 | 2026-05-22 09:39:05 | MASTER-OAGH | (18h 45m 29.90s , -26d 25m 48.5s) | C | 50 | 18.4 | 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/44692. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42819] Fermi GRB 260522A: Global MASTER-Net observations report
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44691 SUBJECT: Fermi GRB 260522A: Global MASTER-Net observations report DATE: 26/05/22 09:15:54 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260522A ( Fermi GBM team, GCN 44687) errorbox 20242 sec after notice time and 20291 sec after trigger time at 2026-05-22 07:53:20 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 81 deg. The sun altitude is -37.9 deg. The galactic latitude b = -40 deg., longitude l = 86 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3330735 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 20321 | 2026-05-22 07:53:20 | MASTER-OAGH | (22h 29m 21.04s , +17d 30m 10.0s) | C | 60 | 17.6 | 20736 | 2026-05-22 08:00:14 | MASTER-OAGH | (22h 31m 10.56s , +15d 35m 11.4s) | C | 60 | 17.8 | 20961 | 2026-05-22 08:04:00 | MASTER-OAGH | (22h 44m 59.44s , +19d 24m 13.9s) | C | 60 | 17.6 | 21293 | 2026-05-22 08:09:31 | MASTER-OAGH | (22h 37m 34.70s , +18d 07m 52.6s) | C | 60 | 18.5 | 21293 | 2026-05-22 08:09:31 | MASTER-OAGH | (22h 45m 20.15s , +17d 30m 06.7s) | C | 60 | 17.7 | 21552 | 2026-05-22 08:13:50 | MASTER-OAGH | (22h 47m 01.86s , +15d 35m 01.0s) | C | 60 | 17.6 | 21552 | 2026-05-22 08:13:50 | MASTER-OAGH | (22h 39m 21.07s , +16d 12m 47.8s) | C | 60 | 18.5 | 21807 | 2026-05-22 08:18:05 | MASTER-OAGH | (22h 31m 54.37s , +12d 23m 27.9s) | C | 60 | 18.2 | 21807 | 2026-05-22 08:18:05 | MASTER-OAGH | (22h 39m 27.63s , +11d 45m 47.0s) | C | 60 | 17.9 | 21879 | 2026-05-22 08:19:17 | MASTER-OAGH | (22h 27m 00.97s , +14d 18m 45.6s) | C | 60 | 18.8 | 21879 | 2026-05-22 08:19:17 | MASTER-OAGH | (22h 34m 37.36s , +13d 41m 11.6s) | C | 60 | 18.3 | 21965 | 2026-05-22 08:20:43 | MASTER-OAGH | (22h 42m 42.24s , +14d 19m 33.9s) | C | 60 | 18.5 | 21965 | 2026-05-22 08:20:43 | MASTER-OAGH | (22h 50m 18.96s , +13d 41m 45.4s) | C | 60 | 17.5 | 22042 | 2026-05-22 08:22:00 | MASTER-OAGH | (22h 53m 22.36s , +20d 01m 39.3s) | C | 60 | 18.4 | 22042 | 2026-05-22 08:22:00 | MASTER-OAGH | (23h 01m 12.71s , +19d 23m 51.7s) | C | 60 | 17.6 | 22189 | 2026-05-22 08:24:27 | MASTER-OAGH | (22h 53m 34.68s , +18d 06m 41.9s) | C | 60 | 18.5 | 22189 | 2026-05-22 08:24:27 | MASTER-OAGH | (23h 01m 19.97s , +17d 28m 52.6s) | C | 60 | 17.6 | 22410 | 2026-05-22 08:28:08 | MASTER-OAGH | (22h 38m 08.15s , +10d 29m 27.1s) | C | 60 | 18.7 | 22410 | 2026-05-22 08:28:08 | MASTER-OAGH | (22h 45m 38.44s , +09d 51m 42.6s) | C | 60 | 18.1 | 22633 | 2026-05-22 08:31:52 | MASTER-OAGH | (22h 47m 29.08s , +12d 24m 15.1s) | C | 60 | 18.6 | 22634 | 2026-05-22 08:31:52 | MASTER-OAGH | (22h 55m 02.26s , +11d 46m 29.2s) | C | 60 | 17.6 | 22713 | 2026-05-22 08:33:12 | MASTER-OAGH | (22h 55m 14.36s , +16d 11m 27.2s) | C | 60 | 18.3 | 22713 | 2026-05-22 08:33:12 | MASTER-OAGH | (23h 02m 54.91s , +15d 33m 41.2s) | C | 60 | 17.8 | 22938 | 2026-05-22 08:36:56 | MASTER-OAGH | (23h 09m 34.33s , +20d 00m 02.3s) | C | 60 | 18.6 | 23357 | 2026-05-22 08:43:56 | MASTER-OAGH | (22h 58m 25.81s , +14d 18m 37.0s) | C | 60 | 18.5 | 23357 | 2026-05-22 08:43:56 | MASTER-OAGH | (23h 06m 02.72s , +13d 40m 58.6s) | C | 60 | 17.9 | 23430 | 2026-05-22 08:45:08 | MASTER-OAGH | (23h 01m 03.75s , +09d 52m 16.5s) | C | 60 | 17.9 | 23430 | 2026-05-22 08:45:08 | MASTER-OAGH | (22h 53m 33.23s , +10d 29m 56.5s) | C | 60 | 18.4 | 23607 | 2026-05-22 08:48:05 | MASTER-OAGH | (23h 03m 00.46s , +12d 23m 19.5s) | C | 60 | 18.2 | 23607 | 2026-05-22 08:48:05 | MASTER-OAGH | (23h 10m 33.91s , +11d 45m 40.8s) | C | 60 | 17.8 | 23679 | 2026-05-22 08:49:17 | MASTER-OAGH | (23h 11m 07.56s , +16d 12m 42.7s) | C | 60 | 18.2 | 23679 | 2026-05-22 08:49:17 | MASTER-OAGH | (23h 18m 48.36s , +15d 35m 03.0s) | C | 60 | 17.5 | 23760 | 2026-05-22 08:50:39 | MASTER-OAGH | (22h 45m 45.40s , +08d 34m 28.4s) | C | 60 | 18.5 | 23760 | 2026-05-22 08:50:39 | MASTER-OAGH | (22h 53m 13.26s , +07d 57m 00.4s) | C | 60 | 18.5 | 24000 | 2026-05-22 08:54:38 | MASTER-OAGH | (23h 14m 05.04s , +14d 17m 27.5s) | C | 60 | 18.1 | 24073 | 2026-05-22 08:55:51 | MASTER-OAGH | (23h 09m 34.28s , +18d 06m 37.0s) | C | 60 | 18.6 | 24073 | 2026-05-22 08:55:51 | MASTER-OAGH | (23h 17m 19.72s , +17d 29m 07.5s) | C | 60 | 18.1 | 24253 | 2026-05-22 08:58:51 | MASTER-OAGH | (23h 09m 06.45s , +10d 28m 56.4s) | C | 60 | 18.7 | 24253 | 2026-05-22 08:58:51 | MASTER-OAGH | (23h 16m 37.32s , +09d 51m 15.3s) | C | 60 | 18.4 | 24325 | 2026-05-22 09:00:04 | MASTER-OAGH | (23h 01m 10.70s , +08d 36m 20.3s) | C | 60 | 18.6 | 24325 | 2026-05-22 09:00:04 | MASTER-OAGH | (23h 08m 39.11s , +07d 58m 43.5s) | C | 60 | 18.2 | 24618 | 2026-05-22 09:04:56 | MASTER-OAGH | (23h 18m 37.97s , +12d 23m 55.7s) | C | 60 | 18.5 | 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/44691. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42818] EP260518a: Einstein Probe detection of an sub-threshold X-ray transient with counterpart AT 2026ndp
by GCN Circulars 22 May '26

22 May '26

TITLE: GCN CIRCULAR NUMBER: 44690 SUBJECT: EP260518a: Einstein Probe detection of an sub-threshold X-ray transient with counterpart AT 2026ndp DATE: 26/05/22 08:38:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, W. X. Li, D. Y. Li, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report the detection of a sub-threshold X-ray transient, EP260518a, associated with the optical transient AT 2026ndp. EP260518a was detected by the Wide-field X-ray Telescope (WXT) aboard the Einstein Probe (EP) mission at R.A. = 299.034 deg, Dec. = -48.618 deg (J2000), with an uncertainty radius of 3 arcmin, at 2026-05-18 13:44:21 UTC. The measured 0.5–4 keV flux was approximately 2.5 x 10^-11 erg cm^-2 s^-1. Due to the low signal-to-noise ratio, no significant flare-like feature is apparent in the X-ray light curve. A candidate optical counterpart, AT 2026ndp, was identified through real-time cross-matching. The transient was discovered by ATLAS at 2026-05-19 07:44:02.400 UTC, approximately 17 hours after the WXT detection, with a c-band magnitude of 18.73 +/- 0.10. There is a faint point-like source in Legacy Survey dr10, which is 1.8 arcsec away. Follow-up observations were performed with the Follow-up X-ray Telescope (FXT) aboard EP, starting at 2026-05-21 08:23:08 UTC (~66 hr after the WXT detection). An uncatalogued X-ray source was detected within the WXT error region at R.A. = 299.0407 deg, Dec. = -48.6362 deg (J2000), with an uncertainty of 10 arcsec. The FXT position is offset by 4.7 arcsec from the optical counterpart. The FXT spectrum can be fitted with an absorbed power-law model with a photon index of 2.5 (+0.8/-0.7) and hydrogen column density of 2.3 (+2.0/-1.7) x 10^21 cm^-2. The estimated average 0.3–10 keV flux is around 4.6 (+1.9/-1.2) x 10^-13 erg cm^-2 s^-1. 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/44690. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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