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[vsnet-grb-info 42377] The EP-WXT trigger 01709259790 is likely a flaring star
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44256 SUBJECT: The EP-WXT trigger 01709259790 is likely a flaring star DATE: 26/04/10 15:22:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> G. L. Huang, Z. X. Li, J. Y. Cao (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259790 at the time of 2026-04-10T11:27:58 (UTC), is likely a stellar flare associated with Gaia DR3 782359908221356544. The estimated flux of the flare is around 6 x 10^(-11) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 6x 10^31 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/44256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42376] GRB 260410B: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44255 SUBJECT: GRB 260410B: Fermi GBM Final Real-time Localization DATE: 26/04/10 15:01:29 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 SHORT GRB At 12:22:26 UT on 10 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260410B (trigger 797516551.925452 / 260410516). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 4.2, Dec = 37.7 (J2000 degrees, equivalent to J2000 00h 16m, 37d 42'), with a statistical uncertainty of 5.6 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410516/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44255. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42375] EP-WXT01709259790: Xinglong optical upper limit
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44254 SUBJECT: EP-WXT01709259790: Xinglong optical upper limit DATE: 26/04/10 14:18:44 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Min-He (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP-WXT01709259790, we observed the field of EP-WXT01709259790 using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s clear-band frames with a median time of 2026-04-10T12:16:23, 52 minutes after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (WXT01709259790), down to 3-sigma limiting magnitudes of 22.18 mag for 2.16-m, 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/44254. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42374] GRB 260410A: Fermi-LAT detection
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44253 SUBJECT: GRB 260410A: Fermi-LAT detection DATE: 26/04/10 14:03:21 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (Univ. Trento and INFN Bari), D. Depalo (Politecnico and INFN Bari), S. Lopez (CNRS / IN2P3), R. Gupta (NASA / GSFC) and F. Longo (Univ. and INFN Trieste) report on behalf of the Fermi-LAT team the detection of a likely SHORT GRB: At 07:03:57.00 UT on April 10th, 2026, Fermi-LAT detected high-energy emission from GRB 260410A, which was also detected by Fermi-GBM (trigger 797497442 / 260410294, GCN #44252). The best LAT on-ground location is found to be RA, Dec = 110.67, -20.94 (J2000) with an error radius of 0.17 deg (90 % containment, statistical error only). This was 49 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 0 - 2 s after the GBM trigger is (1.23 ± 0.38)E-3 ph/cm2/s. The estimated photon index above 100 MeV is -1.84 ± 0.24. The highest-energy photon is a 6.1 GeV event, which is observed 0.37 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini(a)pg.infn.it) 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/44253. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42373] GRB 260410A: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44252 SUBJECT: GRB 260410A: Fermi GBM Final Real-time Localization DATE: 26/04/10 07:14:31 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 SHORT GRB At 07:03:56 UT on 10 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260410A (trigger 797497441.997288 / 260410294). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 108.3, Dec = -28.9 (J2000 degrees, equivalent to J2000 07h 13m, -28d 53'), with a statistical uncertainty of 8.2 degrees. The angle from the Fermi LAT boresight is 41.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410294/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410294/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260410294/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44252. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42372] EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
by GCN Circulars 10 Apr '26

10 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44251 SUBJECT: EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations DATE: 26/04/10 06:06:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), S. Q. Jiang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260409a was detected by the Wide-field X-ray Telescople (WXT) on board the Einstein Probe (EP) mission (Jiang et al., GCN 44240). The refined analysis of the WXT data shows that the event started at T0=2026-04-09T00:16:43 (UTC). WXT coverage of the transient lasted for approximately 100 seconds after trigger, and was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.74 × 10^(20) cm^-2, and a photon index of 0.6 +/- 0.7. The derived average unabsorbed 0.5-4 keV flux is 3.2 (-1.2, +1.7) × 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP autonomously observed this source a few minutes after the on board trigger. The FXT observation started at 2026-04-09T00:22:08 (UTC, T0+325 s). The effective exposure time of the observation is around 2 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 172.9096, DEC = -9.3457 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed Galactic hydrogen column density of 2.74 × 10^(20) cm^-2, and a photon index of 1.9 +/- 0.4. The derived average unabsorbed 0.5-10 keV flux is 6.4 (-1.8, +2.8) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. The optical follow-up observations were performed by Lipunov et al. (GCN 44241), Noémie Globus et al. (GCN 44243), Li et al. (GCN 44244). 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/44251. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42371] EP260321a: Chandra X-ray Non-detection
by GCN Circulars 09 Apr '26

09 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44250 SUBJECT: EP260321a: Chandra X-ray Non-detection DATE: 26/04/09 22:11:06 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Brendan O'Connor (CMU) and Eleonora Troja (U Rome) on behalf of a larger collaboration: We observed the position of EP260321a (Huang et al., GCN 44068) with the Chandra X-ray Observatory (CXO) under GO program 27400339 (PI: O'Connor). Observations were carried out with ACIS-S starting on 2026-04-05 at 22:00 UT, corresponding to ~15.4 d after the EP trigger, for a total of 19.81 ks. We do not detect any coincident X-ray source at this time. With the exception of GW170817, this observation is capable of excluding all known GRB X-ray afterglows from the Swift era, including GRB 060218 which is also located at ~150 Mpc. Further observations are planned. We thank the staff of the Chandra X-ray Observatory, including Pat Slane, Dan Schwartz, Jack Steiner, and Vinay Kashyap, for rapidly scheduling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44250. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42370] GRB 260409A: Fermi GBM Final Real-time Localization
by GCN Circulars 09 Apr '26

09 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44249 SUBJECT: GRB 260409A: Fermi GBM Final Real-time Localization DATE: 26/04/09 17:43:22 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 17:32:45 UT on 9 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260409A (trigger 797448770.671026 / 260409731). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 298.8, Dec = 61.6 (J2000 degrees, equivalent to J2000 19h 55m, 61d 36'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 121.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260409731/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260409731/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260409731/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44249. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42369] GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
by GCN Circulars 09 Apr '26

09 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44248 SUBJECT: GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification DATE: 26/04/09 13:57:11 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg, M. Serrau (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We have continued to observe the field of GRB 260310A detected by Fermi/GBM (Fermi GBM team, GCN 43951) and AstroSat CZTI (Salunke et al., GCN 43958) with the GRANDMA citizen science project Kilonova-catcher (KNC) over the past days mainly in Rc and sdssr filters. Our last night observations were performed with a TEC180FL telescope operated by M. Freeberg. Our observations started at TGRB+29.9 days and were taken with Rc filters. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we still detect the optical counterpart at Rc = 20.39+/-0.18 at a midtime T-TGRB = 29.97 days. Despite the moderate Signal-to-Noise ratio (SNR) in our image series, we tentatively identified the supernova peak brightness at Rc = 19.9+/-0.1 around T-TGRB = 21.8 days. At z = 0.153 (de Ugarte Postigo et al., GCN 43984), such a brightness and peak time seem in good agreement with the expected peak brightness and time of the redshifted canonical GRB/SNe SN 1998bw. The KNC members will keep monitoring the source as long as it stays detectable. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-Cousins filters were calibrated using the GAIA DR3 Synphot 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/44248. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42368] The EP-WXT trigger 01709259773 is likely a flaring star
by GCN Circulars 09 Apr '26

09 Apr '26

TITLE: GCN CIRCULAR NUMBER: 44247 SUBJECT: The EP-WXT trigger 01709259773 is likely a flaring star DATE: 26/04/09 12:34:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Q. Jiang (NAO, CAS), G. L. Huang, Z. X. Li, J. Y. Cao (IHEP, CAS), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709259773 at the time of 2026-04-09T11:45:11, is likely a stellar flare associated with 1RXS J121842.8-060921. The estimated flux of the flare is around 1.4 × 10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 8.6 × 10^30 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/44247. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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