February 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 37546] EP250227a: Einstein Probe detected of a fast X-ray transient
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39532 SUBJECT: EP250227a: Einstein Probe detected of a fast X-ray transient DATE: 25/02/28 15:52:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> W.F. Wen (SZTU), J. H. Wu (GZHU), H. Z. Wu (HUST), B. -T. Wang (YNAO, CAS), Z. X. Ling(NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient EP250227a (trigger ID: 11916647689) at 2025-02-27 04:39:40 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The position of the source is R.A. = 204.133 deg, DEC = -13.820 deg (J2000) with an uncertainty of 2.7 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 40 seconds. The 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with nH fixed at 1.87 x 10^20 cm^-2 and a photon index of -0.07(+2.18/-1.22). The unabsorbed 0.5-4.0 keV flux is 2.1 (+2.6/-1.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. We performed a follow-up target of opportunity observation with EP-FXT. The observation began at 2025-02-27 15:19:07 (UTC) with an exposure time of 3020 seconds, about 10.7 hours after the detection by EP-WXT. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 204.1444 deg, DEC = -13.8216 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The X-ray spectrum can be fitted with an absorbed powerlaw with the nH fixed at the Galactic value and a photon index of 1.2 (-0.8, +0.8). The derived unabsorbed 0.5-10 keV flux is 2.4 (-1.4, +5.2) x 10^-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. 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/39532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37545] EP250228a: updates on the EP observations
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39531 SUBJECT: EP250228a: updates on the EP observations DATE: 25/02/28 15:49:46 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Y. Liu (NAO, CAS), J.Q. Peng (IHEP, CAS), W. F. Wen(SZTU), J. H. Wu (GZHU), C.C. Jin (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250228a (GCN 39525) triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2025-02-28T03:59:09 (UTC) and an autonomous observation was performed by the Follow-up X-ray Telescope (FXT) around 45 s later. The on-ground analysis of the FXT data shows that an uncatalogued source was detected at R.A. = 103.6059, DEC = -41.5710 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with that reported by the Swift XRT Team (GCN 39527). Given that the localisation of this source is well aligned with the position of Gaia DR3 5563280076339409920, EP250228a is likely a stellar flare associated with this star. The FXT spectrum can be well fitted by a 4T apec model with kT= 6.6(+3.4/-1.3), 1.4(+0.69/-0.35), 0.63(+0.16/-0.23), and 0.17(+0.04/-0.06) keV, respectively, and the derived flux is around 1.87 (+0.09/-0.09) x 10^-11 erg/s/cm^2 in 0.5-10 keV. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard 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/39531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37544] GRB 250226A: Fermi GBM Observation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39530 SUBJECT: GRB 250226A: Fermi GBM Observation DATE: 25/02/28 14:49:24 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> U. Pathak (IITB) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:34:57.33 UT on 26 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250226A (trigger 762244502/250226274) which was also detected by EP/WXT and EP/FXT (Jiang et al. 2024, GCN 39482). It was also detected by INTEGRAL SPI-ACS and PICsIT (Thakur et al. 2025, GCN 39518), GECAM-B (Zhang et al. 2025, GCN 39492). Optical follow-ups have been done with TRT (An et al. 2025, GCN 39486), COLIBRI/DDRAGO (Magnani et al. 2025, GCN 39488), GSP (Li et al. 2025, GCN 39489), Kinder (Aryan et al. 2025, GCN 39509), 1.6m Mephisto (Zhou et al. 2025, GCN 39511), SVOM/VT (Li et al. 2025, GCN 39514), Xinglong (Jin et al. 2025, GCN 39515). The spectroscopic redshift of the optical counterpart observed by VLT/X-shooter (Zhu et al. 2025, GCN 39487) is 3.315. The Fermi GBM on-ground location is consistent with the EP/FXT position. The angle from the Fermi LAT boresight is 108 degrees. The GBM light curve consists of multiple spikes from a single emission episode with a duration (T90) of about 61 s (50-300 keV). The time-averaged spectrum from T0-2.6 to T0+62.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.36 +/- 0.03, and the cutoff energy, parameterized as Epeak, is 4408 +/- 1160 keV. The event fluence (10-1000 keV) in this time interval is (1.96 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.4 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 2864 +/- 2100 keV, alpha = -1.35 +/- 0.04 and beta = -1.8 +/- 0.2. As the burst occurred near SAA entry, the spectral results of both fits to the data (especially Epeak) are likely to have some contamination and thus may not reflect the burst's true spectral nature. 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/39530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37543] EP250225a: EP-FXT follow-up observation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39529 SUBJECT: EP250225a: EP-FXT follow-up observation DATE: 25/02/28 14:11:40 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang, T. Zhao (NAO, CAS), B.-T. Wang (YNAO, CAS), H. Z. Wu (HUST), Y. J. Song, Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team: We performed one follow-up observation of the X-ray transient EP250225a (Jiang et al., GCN 39475) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-02-26 11:53:56 (UTC), about 23.67 hours after the WXT detection, with an exposure of ~3 ks. No source was detected within the WXT error circle. The 0.5-10 keV upper limit at the NOT candidate position (Malesani et al., GCN 39516) is about 7e-14 erg/s/cm^2 (90% C. L.). 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/39529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37542] EP250223a: J band upper limit by SYSU 80cm telescope
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39528 SUBJECT: EP250223a: J band upper limit by SYSU 80cm telescope DATE: 25/02/28 11:41:02 GMT FROM: Wei-Sen Huang at SYSU <huangws5(a)mail2.sysu.edu.cn> Wei-Sen Huang, Jin-Ji Li, Chun Chen, Zhong-Nan Dong, Jia-Qi Lin, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Si-Yuan Zhu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team: We observed the field of EP250223a (Lian et al., GCN 39429; Kennea et al., GCN 39437; Wang et al., GCN 39448) using the Sun Yat-sen University 80cm infrared telescope in J band. The calculated position is R.A. = 98.2712, DEC = -22.4449 (J2000), from EP/FXT observation. Our first observations began at 2025-02-24 12:10:00 UTC, 21.09 hours after the EP trigger, with 180 x 20 s exposures. The second observations began at 2025-02-25 12:54:00 UTC, 45.82 hours after the EP trigger, with 90 x 20 s exposures. We do not detect any counterpart in the stacked images at the position of the optical afterglow(Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445; Guo et al., GCN 39447; An et al., GCN 39449; Ducoin et al., GCN 39453; O’Neill et al., GCN 39455; Aryan et al., GCN 39464; Saikia et al., GCN 39472; Wang et al., GCN 39476; Mazaeva et al., GCN39496), down to a 5-sigma depth of J~17.2 Vega magnitudes on 2025-02-24 and J~17.0 Vega magnitudes on 2025-02-25. View this GCN Circular online at https://gcn.nasa.gov/circulars/39528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37541] EP250228a: Swift/XRT localisation
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39527 SUBJECT: EP250228a: Swift/XRT localisation DATE: 25/02/28 10:52:50 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, P.A. Evans (U.Leicester) and J. DeLaunay (PSU) report on behalf of the Swift XRT Team: On 2025 February 28, at 05:53 UT, Swift obtained an Target of Opportunity observation of EP250228a (GCN Circ. 39525), collecting ~340 s of data around 1.9 hr after the Einstein Probe trigger. The XRT data show an uncatalogued X-ray source, consistent with the FXT source reported by the EP team, at a position of RA, Dec = 103.60631, -41.57160, which is equivalent to RA (J2000): 06h 54m 25.51s Dec (J2000): -41d 34′ 17.8″ with an uncertainty of 4.4 arcsec (radius, 90% confidence). The flux of this source was (5.4 +/- 0.9) x 10^-12 erg cm^-2 s^-1 (0.3 - 10 keV). View this GCN Circular online at https://gcn.nasa.gov/circulars/39527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37540] EP250228a: Global MASTER-Net observations report
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39526 SUBJECT: EP250228a: Global MASTER-Net observations report DATE: 25/02/28 08:18:36 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250228a ( EP Team et al., GCN 39525) errorbox 229 sec after notice time and 12029 sec after trigger time at 2025-02-28 07:19:38 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 74 deg. The sun altitude is -36.6 deg. The galactic latitude b = -17 deg., longitude l = 252 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2794721 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12059 | 2025-02-28 07:19:38 | MASTER-OAFA | (06h 55m 12.36s , -41d 21m 41.5s) | C | 60 | 19.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37539] EP250228a: Einstein Probe detection of an X-ray transient
by GCN Circulars 28 Feb '25

28 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39525 SUBJECT: EP250228a: Einstein Probe detection of an X-ray transient DATE: 25/02/28 07:09:00 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Y. Liu (NAO, CAS), J.Q. Peng (IHEP, CAS), W. F. Wen(SZTU), J. H. Wu (GZHU), C.C. Jin (NAO, CAS) report on behalf of the Einstein Probe 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 EP250228a. The transient triggered EP-WXT (ID: 01709132122) at 2025-02-28T03:59:09 (UTC). The WXT position of the source is R.A. = 103.607 deg, DEC = -41.581 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 cirlce, an uncatalogued X-ray source was detected at R.A. = 103.6021 deg, DEC = -41.5715 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/39525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37538] GRB 250226A / EP250226a: LCO detection of the afterglow
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39524 SUBJECT: GRB 250226A / EP250226a: LCO detection of the afterglow DATE: 25/02/27 23:22:56 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> F. Poidevin, I. Pérez-Fournon (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL) We observed the location of the long-duration GRB 250226A / EP250226a discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518) with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). Simultaneous 300-sec exposures were obtained in the SDSS i' and r' filters starting at about 18.89 hr after the Fermi trigger. We detect the optical afterglow at the location reported by An et al. (GCN circ. 39486) and with optical detections by other groups (Zhu et al., GCN circ. 39487; Magnani et al., GCN circ. 39488; Li et al., GCN circ. 39489; Aryan et al., GCN circ. 39509; Zou et al., GCN circ. 39511; Li et al., GCN circ. 39514; and Junjie-Jin et al., GCN circ. 39515). A redshift of z = 3.315 has been reported by Zhu et al. (GCN circ. 39487). We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | t_mid - t0 (hours) | mag | error | filter | ---------------------------------------------------------------------- 2025-02-27 01:28:39 18.94 21.22 0.29 i' 2025-02-27 01:28:40 18.94 21.44 0.36 r' This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/39524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37537] LIGO/Virgo/KAGRA S250227e: Updated Sky localization
by GCN Circulars 27 Feb '25

27 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39523 SUBJECT: LIGO/Virgo/KAGRA S250227e: Updated Sky localization DATE: 25/02/27 17:40:48 GMT FROM: ethan.payne(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250227e (GCN Circular 39506). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250227e For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 280 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(19h19m, +06d18m, 14.62d, 6.11d, 101.52d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2004 +/- 527 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. (2023) arXiv:2307.13380 View this GCN Circular online at https://gcn.nasa.gov/circulars/39523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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