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

[vsnet-grb-info 38116] EP250404a / GRB 250404A: Montarrenti Observatory optical observations
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40093 SUBJECT: EP250404a / GRB 250404A: Montarrenti Observatory optical observations DATE: 25/04/06 13:49:11 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini(a)iol.it> S. Leonini, A. Lorini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report: we observed the field of the X-ray transient EP250404a (Einstein Probe mission, Trigger ID 01709133918) probably associated with GRB 250404A (Fermi team, GCN 40050) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88). The observations were started at 2025-04-04 18:36:04 UT (approximately 4 hours after burst) ending at 2025-04-04 22:00:50 UT stacking a set of Rc-band CCD images. Observations were performed under thin cloud cover in the second part of the night. The optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al, GCN 40064; He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al, GCN 40073; Taguchi et al., GCN 40074; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085; Pankov et al., GCN 40086; Chu Chen et al., GCN 40088 and Chen et al., GCN 40089) was clearly detected at the following position: RA (J2000.0) 08h 20m 14.57s +/-0.06 Decl. (J2000.0) +35° 31' 42.0" +/-0.04 Preliminary photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-04-04 18:36:24 UT 4.27 50x40s Rc 19.60 +/-0.10 2025-04-04 19:11:30 UT 4.85 50x40s Rc 19.67 +/-0.10 2025-04-04 19:46:31 UT 5.43 50x40s Rc 19.81 +/-0.15 2025-04-04 20:21:33 UT 6.02 54x40s Rc 20.25 +/-0.20 2025-04-04 21:07:10 UT 6.78 78x40s Rc 20.16 +/-0.12 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Along the span of our observations and within our uncertainties, the afterglow evolves in agreement with a power-law decay with a rate alpha ~1.40. View this GCN Circular online at https://gcn.nasa.gov/circulars/40093. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38115] Fermi trigger No 765619921: Global MASTER-Net observations report
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40092 SUBJECT: Fermi trigger No 765619921: Global MASTER-Net observations report DATE: 25/04/06 13:46:45 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) started inspect of the Fermi GRB250406.34 (trigger No 765619921,16h 27m 07.92s , +59d 07m 01.2s, R=50) errorbox 915 sec after notice time and 949 sec after trigger time at 2025-04-06 08:27:46 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 49 deg. The sun altitude is -30.9 deg. MASTER-Tunka robotic telescope located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB250406.34 errorbox 18661 sec after notice time and 18696 sec after trigger time at 2025-04-06 13:23:33 UT, with upper limit up to 18.3 mag. Observations started at twilight. The observations began at zenith distance = 73 deg. The sun altitude is -14.9 deg. The galactic latitude b = 41 deg., longitude l = 89 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2834649 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 970 | 2025-04-06 08:27:46 | MASTER-OAFA | (15h 28m 20.65s , +13d 16m 46.0s) | C | 40 | 18.2 | 980 | 2025-04-06 08:27:46 | MASTER-OAFA | (15h 19m 00.28s , +12d 54m 07.9s) | C | 60 | 20.0 | 2262 | 2025-04-06 08:49:18 | MASTER-OAFA | (15h 28m 22.19s , +13d 17m 10.6s) | C | 40 | 18.3 | 2272 | 2025-04-06 08:49:18 | MASTER-OAFA | (15h 19m 02.07s , +12d 54m 31.6s) | C | 60 | 20.0 | 3654 | 2025-04-06 09:12:30 | MASTER-OAFA | (15h 28m 15.85s , +13d 17m 06.0s) | C | 40 | 18.3 | 3665 | 2025-04-06 09:12:31 | MASTER-OAFA | (15h 18m 56.28s , +12d 54m 26.8s) | C | 60 | 20.0 | 5045 | 2025-04-06 09:35:41 | MASTER-OAFA | (15h 28m 20.02s , +13d 18m 20.6s) | C | 40 | 18.2 | 5055 | 2025-04-06 09:35:41 | MASTER-OAFA | (15h 19m 00.70s , +12d 55m 40.3s) | C | 60 | 20.0 | 18727 | 2025-04-06 13:23:33 | MASTER-Tunka | (18h 23m 55.12s , +49d 33m 54.6s) | C | 60 | 18.2 | 18995 | 2025-04-06 13:28:01 | MASTER-Tunka | (18h 23m 53.09s , +49d 33m 24.0s) | C | 60 | 18.0 | 19206 | 2025-04-06 13:31:32 | MASTER-Tunka | (18h 23m 50.27s , +49d 34m 17.4s) | C | 60 | 18.2 | 19597 | 2025-04-06 13:38:03 | MASTER-Tunka | (18h 23m 50.38s , +49d 32m 59.3s) | C | 60 | 18.3 | 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/40092. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38114] Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40091 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB DATE: 25/04/06 13:13:13 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 765619921/250406342 at 08:11:56.54 UT on 06 April 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to an accidental trigger." View this GCN Circular online at https://gcn.nasa.gov/circulars/40091. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38113] GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40090 SUBJECT: GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit DATE: 25/04/06 13:05:06 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed GRB 250404A / EP250404a (Fermi GBM team, GCN 40050; Hu et al., GCN 40051; Frederiks et al., GCN 40087) with RC500 telescope of the INASAN-Kislovodsk observatory. The optical counterpart (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085; Pankov et al., GCN 40086; Chen et al., GCN 40088;) is not detected starting on 2025-04-04 (UT) 21:10:11. Preliminary upper limit of the stacked image is the following Date UT start t-T0 Filter Exp. OT Err. UL(3sigma) (mid, days) (s) 2025-04-04 21:10:11 0.33362 R 70*120 n/d n/d 20.1 The photometry is based on nearby USNO-B1.0 stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/40090. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38112] GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40089 SUBJECT: GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations DATE: 25/04/06 12:27:20 GMT FROM: Chen Liang-Jun at Guangxi University <chenlj(a)st.gxu.edu.cn> L. J. Chen(GXU), L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team: We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A (Fermi team, GCN 40050), with the GWAC-F50A and GWAC-F60 at Xinglong Observatory, China. F50 started observing at 2025-04-04T14:25:34 UTC and lasted until 2025-04-04T15:36:36 with 9 frames in R-band and 15 frames in I-band. F60A started observing at 2025-04-04T14:24:56 UTC and lasted until 2025-04-04T15:24:21 with 25 frames in R-band. F60B started observing at 2025-04-04T14:25:05 UTC and lasted until 2025-04-04T15:24:28 with 25 frames in R-band. The optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Pankov et al., GCN 40086), was clearly detected in our images. The afterglow shows a first brightening and then a single decay with a peak magnitude of R~14.3 mag, calibrated to the USNO B1.0 catalog, at about 1000 sec after the burst. Two 60cm GWAC-F60(A/B) are operated by Guangxi University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 19*19 arcmin. The 50cm telescope (F50A) is operated by Huaibei Normal University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 27*27 arcmin. View this GCN Circular online at https://gcn.nasa.gov/circulars/40089. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38111] EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40088 SUBJECT: EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope DATE: 25/04/06 12:26:24 GMT FROM: Chun Chen at Sun Yat-sen University, SYSU 80cm telescope team <chench386(a)mail2.sysu.edu.cn> Chun Chen, Xia Li, Zhong-Nan Dong, Jia-Qi Lin, Wei-Sen Huang, Jin-Ji Li, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Hao-Yuan Zheng, 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 EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB250404A (Fermi GBM team, GCN40050; Fermi GBM team, GCN40067), using the Sun Yat-sen University 80cm infrared telescope with 183 x 20 s exposures in J band. The calculated position is R.A. = 125.0575 deg, DEC = 35.5305 deg J2000, from EP/FXT observation. Our observations began at 2025-4-4 15:25:20 UTC, 1.09 hours after the EP trigger. We detected a counterpart at the position of the optical afterglow (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al. GCN 40063; Odeh et al., GCN 40064; Lipunov et al., GCN 40066; He et al., GCN 40069; Perez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Ruocco, GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084) in the stacked images. The preliminary photometric magnitudes in J band are below: Start Time (UTC) |Band | Exp | Mag (Vega) --------------------|-----|-------|------------------ 2025/4/4 15:25:20 | J | 200s | 15.30+/-0.08 2025/4/4 15:28:40 | J | 200s | 15.28+/-0.09 2025/4/4 15:32:20 | J | 200s | 15.47+/-0.10 2025/4/4 15:35:40 | J | 200s | 15.76+/-0.11 2025/4/4 15:39:00 | J | 360s | 15.83+/-0.10 2025/4/4 15:50:20 | J | 400s | 16.05+/-0.12 2025/4/4 15:57:00 | J | 400s | 15.99+/-0.12 2025/4/4 16:03:40 | J | 400s | 15.99+/-0.12 2025/4/4 16:10:40 | J | 400s | 16.29+/-0.15 2025/4/4 16:17:40 | J | 1100s | 16.21+/-0.11 The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitudes are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40088. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38110] Konus-Wind detection of GRB 250404A / EP250404a
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40087 SUBJECT: Konus-Wind detection of GRB 250404A / EP250404a DATE: 25/04/06 12:08:53 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250404A (Fermi-GBM detection: The Fermi GBM team, GCN 40050; Mukherjee & Meegan, GCN 40067), coincident with the X-ray transient EP250404a (Hu et al., GCN 40051), triggered Konus-Wind (KW) at T0=51605.773 s UT (14:20:05.773). The burst light curve shows a multi-peaked structure which starts at ~T0-21 s and has a total duration of ~105 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250404_T51605/ As observed by Konus-Wind, the burst had a fluence of (2.83 ± 0.09)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.832 s, of (1.78 ± 0.22)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+81.186 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.38(-0.13,+0.14) and Ep = 56(-5,+4) keV (chi2 = 76/98 dof). Fitting this spectrum by a Band function yields the same values of alpha and Ep, and an upper limit on the high energy photon index beta of -3.5 (chi2 = 76/97 dof). The spectrum near the peak count rate(measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL with alpha = -1.16(-0.17,+0.19) and Ep = 68(-9,+8) keV (chi2 = 90/96 dof). Fitting this spectrum by a Band function yields the same values of alpha and Ep, and an upper limit on the high energy photon index beta of -4.2 (chi2 = 90/95 dof). Assuming the redshift z ~ 2.627 ( Li et al., GCN 40084) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (4.60 ± 0.14)x10^53 erg, the isotropic peak luminosity L_iso to (1.05 ± 0.13)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (203 ± 18) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (247 ± 30) keV. With the obtained estimates, GRB 250404A lies at the lower edge, but is consistent with 90% prediction bands of the 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250404_T51605/GRB250404A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40087. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38109] GRB 250404A / EP250404a: Mondy optical observations
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40086 SUBJECT: GRB 250404A / EP250404a: Mondy optical observations DATE: 25/04/06 11:27:55 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI GRB-FuN: We observed GRB 250404A / EP250404a (Fermi GBM team, GCN 40050; Hu et al., GCN 40051). The optical counterpart (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Yin et al., GCN 40085) is early detected on 2025-04-04 and was observed between (UT) 14:50:52 and 17:09:01. We obtained an upper limit on 2025-04-05. Preliminary photometry of some stacked images is the following Date UT start t-T0 Filter Exp. OT Err. UL(3sigma) (mid, days) (s) 2025-04-04 14:50:52 0.04244 R 40*90 16.53 0.02 22.4 2025-04-04 16:01:21 0.08999 R 28*120 17.96 0.03 22.2 2025-04-05 15:08:33 1.05611 R 42*90 n/d n/d 21.5 The photometry is based on nearby USNO-B1.0 stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/40086. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38108] EP250404a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40085 SUBJECT: EP250404a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/04/06 09:45:07 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (NJU), J. W. Hu (NAO, CAS), Y. L. Hua (PMO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP250404a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 40051), and followed up by several telescopes (Jiang et al, GCN 40052, Perez-Garcia et al, GCN 40053, Du et al, GCN 40058, Zhu et al, GCN 40061, Konno et al, GCN 40063, Odeh et al, GCN 40064, Lipunov et al, GCN 40066, He et al, GCN 40069, Pérez-Fournon et al, GCN 40071, Jelinek et al, GCN 40072, Rakotondrainibe et al, GCN 40073, Taguchi et al, GCN 40074, Brivio et al, GCN 40075, Ruocco et al, GCN 70076, Martin-Carrillo et al, GCN 40080, Pavoni et al, GCN 40083, Li et al, GCN 40084), with an optical counterpart detected at a redshift of 2.63 (Zhu et al, GCN 40061, Li et al, GCN 40084). Refined analysis of the WXT data shows that the event started at T0=2025-04-04T14:19:45 (UTC) and lasted for about 16 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.41 (-0.28/+0.26). The absorption is fixed at the best-fit values from FXT spectral fitting with a Galactic hydrogen column density of 6.00 x 10^20 cm^-2 and an intrinsic hydrogen column density of 4.89 x 10^22 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 5.9 (-1.6/+2.2) x 10^(-8) erg/s/cm^2. The data recovered from the slew process shows that the transient event lasted for about 300 seconds. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 1 min after T0, starting at 2025-04-04T14:20:46 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 125.0601, DEC = -35.5284 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is also consistent with the position of the optical counterpart. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 6.00 x 10^20 cm^-2 and an intrinsic hydrogen column density of 4.89 (-0.45/+0.33) x 10^22 cm^-2. The photon index is 2.18 (-0.03/+0.03). The derived average unabsorbed 0.5-10 keV flux is 9.00 (-0.25/+0.19) x 10^(-10) erg/s/cm^2. 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/40085. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38107] GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
by GCN Circulars 06 Apr '25

06 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40084 SUBJECT: GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627 DATE: 25/04/06 03:57:18 GMT FROM: Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi(a)ynao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report: GRB 250404A / EP250404a was detected by Fermi GBM (Fermi GBM team, GCN 40050) and by EP/WXT (Hu et al., GCN 40051). We observed the optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083). The spectroscopic observation was conducted using the GMG-2.4m telescope with Grism #14, which provides a wavelength coverage of 3600–7460 AA. A single 1800s spectrum was obtained, with exposure beginning at 2025-04-04T15:18:24, about 0.98 hours after the Fermi/GBM and EP/WXT trigger (Fermi GBM team, GCN 40050; Hu et al., GCN 40051). Two absorption systems were identified in the spectrum. For the first absorption system, we detected multiple metal absorption features, including Si II at 1527 AA, Al II at 1671 AA, Al III at 1855 AA and 1863 AA, Zn II/Cr II at 2026 AA and 2062 AA, and Fe II at 2344 AA, 2374 AA, and 2383 AA. These features consistently indicate a redshift of z ~ 1.881. For the second absorption system, the spectrum shows multiple metal absorption lines from Si II/S II at 1260 AA, O I/Si II at 1303 AA, C II at 1335 AA, Si IV at 1394 AA, Si II at 1527 AA, Fe II at 1608 AA, and Al III at 1863 AA. These absorption features correspond to a redshift of z ~ 2.627. These results support a redshift of z ~ 2.627 for the transient, consistent with the measurement reported by Xinglong-2.16m (Zhu et al., GCN 40061). We thank the staff at the Lijiang Observatory for their support in conducting the observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/40084. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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