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[vsnet-grb-info 38255] GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40228 SUBJECT: GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310 DATE: 25/04/24 09:42:20 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Corcoran (UCD), S. Covino (INAF/OAB), N. Habeeb (Leicester), L. Izzo (INAF/OACN and DARK/NBI), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), G. Pugliese (API), B. Schneider (LAM), N. R. Tanvir (Leicester), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), report on behalf of the Stargate collaboration: We observed the optical and NIR afterglow of GRB 250424A (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations started on 2025 Apr 24.322 UT (0.87 hr after the Swift/BAT trigger) and consisted of a sequence of increasing exposure times (175, 300, 600, 1200, 1920 s). In the acquisition image (taken at a mid time of 0.851 hr after the Swift/BAT trigger), the counterpart is well detected with a magnitude r = 19.09 +- 0.02, calibrated against nearby stars from the SkyMapper catalog (Wolf et al. 2018, doi:10.4225/41/593620ad5b574). We detect a bright continuum over the wavelength range 3100 to 24,500 AA. Many absorption features are visible which we interpret as Mn II, Fe II, Mg II, Mg I, Ti II, Ca II, Na I, including a number of fine-structure transitions from Fe II*, all at a common redshift z = 0.310. At a consistent redshift, we also detect several emission lines, due to [O II], [O III], [S II], [N II], and the Balmer lines from the GRB host galaxy (Perez-Fournon et al., GCN 40227). We note that our redshift is consistent with the photometric determination z = 0.33 +/- 0.12 of the host redshift from the Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764). We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/40228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38254] GRB 250424A: likely host galaxy
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40227 SUBJECT: GRB 250424A: likely host galaxy DATE: 25/04/24 08:54:58 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We report on the likely host galaxy of the Swift/BAT GRB 250424A (Cenko et al., GCN circ. 40224), with Swift/XRT and Swift/UVOT detections (Cenko et al., GCN circ. 40224) and detections in the optical by Global MASTER-net (Francile et al. GCN circ. 40222) and DDOTI (Becerra et al., GCN circ. 40226) and in the optical and near-IR by REM (Brivio et al., GCN circ. 40225). A catalogued Legacy Surveys DR10 (LS DR10) galaxy (RA, Dec = 217.4999, -35.0252) is visible at the position of the optical and near-IR counterpart of GRB 250424A, with magnitudes in the LS DR10 catalog of g=22.60, r=21.98, i=22.05, and z=21.70. This galaxy is located at about 0.3" from the Swift/UVOT position and 0.2" from the Global MASTER-net position. We propose that this galaxy is the host of GRB 250424A. View this GCN Circular online at https://gcn.nasa.gov/circulars/40227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38253] GRB 250424A: DDOTI Afterglow Detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40226 SUBJECT: GRB 250424A: DDOTI Afterglow Detection DATE: 25/04/24 08:30:40 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observed the field of the GRB 250424A detected by Swift/BAT (Cenko et al., GCN Circ. 40136) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-24 UTC from 07:23 UTC to 7:45 UTC (from T+30.6 h to T+53.5 min after the trigger) and obtained a total exposure of 20 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect a source consistent with the UVOT position (Cenko et al., GCN Circ. 40136) and the previous optical detections (Francile et al., GCN Circ. 40222, Brivio et al., GCN Circ. 40225), with an AB magnitude of: w = 19.4 +/- 0.1 Further observations and analysis are ongoing. This value is not corrected for the Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38252] GRB 250424A: REM optical/NIR afterglow detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40225 SUBJECT: GRB 250424A: REM optical/NIR afterglow detection DATE: 25/04/24 08:19:08 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio (INAF-OAB), A. Melandri (INAF-OAR), M. Ferro, P. D'Avanzo, S. Covino, G. Tagliaferri, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250424A detected by Swift/BAT (Cenko et al., GCN 40224) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 24 at 06:54:31 UT (i.e. 123 s after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Francile et al., 40222) at the Swift/UVOT position (Cenko et al., GCN 40224) with the following magnitudes: r = 17.7 +/- 0.1 (AB; calibrated against the SkyMappercatalogue), at a mid-time of 205 s after the trigger, H = 14.5 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 164 s after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38251] GRB 250424A: Swift detection of a burst with an optical counterpart
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40224 SUBJECT: GRB 250424A: Swift detection of a burst with an optical counterpart DATE: 25/04/24 07:12:30 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> S. B. Cenko (GSFC), V. D'Elia (SSDC & INAF-OAR), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), A. Melandri (INAF-OAR), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:52:28.51 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250424A (trigger=1306404). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 217.513, -35.022 which is RA(J2000) = 14h 30m 03s Dec(J2000) = -35d 01' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 30 sec. The peak count rate was ~25000 counts/sec (15-350 keV), at ~15 sec before the trigger. The XRT began observing the field at 06:56:39.3 UT, 250.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 217.50010, -35.02493 which is equivalent to: RA(J2000) = 14h 30m 00.03s Dec(J2000) = -35d 01' 29.7" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 39 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 254 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 14:29:60.00 = 217.49998 DEC(J2000) = -35:01:30.6 = -35.02518 with a 90%-confidence error radius of about 0.63 arc sec. This position is 1 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.80 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.064. Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/40224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38250] Swift GRB250424.29: Global MASTER-Net observations report
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40223 SUBJECT: Swift GRB250424.29: Global MASTER-Net observations report DATE: 25/04/24 07:08:43 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-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 Swift GRB250424.29 (trigger No 1306404,14h 30m 03.12s , -35d 01m 19.2s, R=0.05) errorbox 94 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 25 deg. The sun altitude is -52.5 deg. The galactic latitude b = 23 deg., longitude l = 325 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2852168 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 198 | MASTER-OAFA | C | 40 | 19.4 | 244 | MASTER-OAFA | C | 40 | 19.4 | 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/40223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38249] Swift GRB250424.29: Global MASTER-Net OT detection
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40222 SUBJECT: Swift GRB250424.29: Global MASTER-Net OT detection DATE: 25/04/24 07:06:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), 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 (Lomonosov MSU), O.Gress, N.Budnev(ISU), 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 GRB250424.29 99 sec after notice time and 178 sec after trigger time at 2025-04-24 06:55:26 UT. On our first (40s exposure) set we found 1 optical transient within Swift error-box (ra=217.512 dec=-35.0214 r=0.05) brighter than 18.9. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 198 2025-04-24 06:55:26 40 (14h 29m 59.96s , -35d 01m 30.7s) 18.0 The 5-sigma upper limit has been about 18.9mag The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38248] LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
by GCN Circulars 24 Apr '25

24 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40221 SUBJECT: LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates DATE: 25/04/24 05:12:11 GMT FROM: Haibin Zhang at National Astronomical Observatory of Japan (NAOJ) <haibin.zhang(a)nao.ac.jp> Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ), Sean MacBride, Isaac McMahon, Marcelle Soares-Santos (UZH), Ken Herner (Fermilab), Simran Kaur (University of Michigan/UZH), Lillian Joseph (Benedictine U.), and Tom Diehl (FNAL) report on behalf of the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), Subaru Telescope, and Dark Energy Survey Gravitational Wave (DESGW) Team: Between 05:11 and 10:20 UTC on April 3, 2025, we carried out spectroscopic observations with the Subaru/Prime Focus Spectrograph (PFS) following the LVK alert issued for the gravitational-wave event S250328ae (GCN 39898). The Subaru/PFS is a fiber spectrograph capable of observing ~2400 targets simultaneously within a ~1.25 square degree field of view, and covers a wavelength range of 380 nm to 1260 nm with a resolving power of ~2500-5500 (Sugai et al. 2015; Tamura et al. 2024). We observed seven pointings centered on the ICRS coordinates listed below: |RA [deg]|Dec [deg]| | - | - | |144.130530|10.436230| |144.126501|11.595492| |145.151367|9.856599| |145.151367|11.015861| |145.151367|12.175123| |146.176234|11.595492| |146.180717|12.754753| These seven pointings cover the ~50% localization region of the S250328ae event. We observed targets selected from transient candidates of GCN 39934 and 39992 (including candidates before and after vetting), X-ray sources from GCN 39972, and potential host galaxies from GLADE+ (Dálya et al. 2022) and PS1-STRM (Beck et al. 2021) catalogs in our pointings. A total of ~3900 targets were observed with an on-source exposure time of 1800 seconds in six pointings and 900 seconds in one pointing (shortened due to bad weather conditions). We reduced the data on-site using the quick reduction system based on the PFS Data Reduction Pipeline, and then carried out classification (fitting galaxy, QSO, star, and supernova templates) and visual inspection. After classification and visual inspection, we obtained confident spectroscopic redshifts of ~70% of our targets. Among these sources, five candidates listed below were identified to be the possible electromagnetic counterpart to the gravitational-wave event S250328ae (within the ~90% three-dimensional localization volume partly covered by our pointings). Because these five candidates were originally selected from the GLADE+ and PS1-STRM catalogs that do not contain information of variability, we encourage follow-up observations to confirm their variability. |ID_PFS|ATNAME|RA [deg]|Dec [deg]|Type_PFS|Redshift| | - | - | - | - | - | - | |761|AT2019uib|145.718857|12.412288|QSO|0.130| |9238|N/A|145.412644|12.717089|QSO|0.096| |13647|N/A|144.989553|10.636089|QSO|0.136| |17165|N/A|145.733559|11.593362|QSO|0.120| |19826|N/A|145.351893|12.503455|QSO|0.136| No counterparts to X-ray sources (GCN 39972) are recovered within their reported error bounds by our observations. We do not identify any transient candidates (GCN 39934 and 39992) we observed within the ~90% three-dimensional localization volume of S250328ae. These transient candidates falling outside the ~90% localization volume are listed below. |ID_ DESGW|ATNAME|RA [deg]|Dec [deg]|Type_ DESGW|Type_PFS|Redshift| | - | - | - | - | - | - | - | |2290036|AT2025gek|145.199481|10.828527|SN_LIKE|SN Ic|0.233| |2290467|AT2020woa|144.388798|10.255536|SN_LIKE|SN Ib|0.050| |2292782|AT2025geo|144.928578|10.349243|SN_LIKE|SN Ia|0.182| |2290334|AT2025geq|145.235616|12.469694|SN_LIKE|SN Ia|0.186| |2290623|AT2025gen|144.112464|11.641817|AGN_LIKE|SN II|0.204| |2291223|N/A|146.389563|13.131801|AGN_LIKE|QSO|0.540| |2293190|AT2025cvb|144.191297|10.828462|SN_LIKE|SN Ia|0.140| |2290143|AT2025ggv|146.033906|11.088812|SN_LIKE|QSO|1.437| |2292040|AT2025ges|144.438216|9.885617|AGN_LIKE|SN Ia|0.434| |2290059|N/A|144.679961|10.018211|AGN_LIKE|QSO|0.209| |2292786|N/A|144.037664|10.810454|AGN_LIKE|SN Ia|0.254| |2293517|AT2025geu|145.956024|12.381673|AGN_LIKE|QSO|0.507| |2295862|N/A|145.361115|12.521385|AGN_LIKE|QSO|0.969| |2290563|N/A|145.149074|11.756403|AGN_LIKE|QSO|0.255| |2289995|AT2025ggx|144.57373|10.274445|SN_LIKE|SN II|0.358| We are grateful to the staffs at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind supports in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has the cultural, historical, and natural significance in Hawaii. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38247] EP250421a: Nickel optical upper limit
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40220 SUBJECT: EP250421a: Nickel optical upper limit DATE: 25/04/23 23:13:36 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> Katherine Mora, Eyouel Abate, Ansel Parke, WeiKang Zheng and Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: We observed the field of EP250421a (Zhao et al., GCN 40198) with the 1-m Nickel telescope located at Lick observatory, California. Observations were performed in the R band with 600s x 6 exposures. In our coadd image, we do not detect the optical afterglow (Lee et al., GCN. 40192; Fu et al., GCN 40193; Liu et al., GCN 40197), with an upper limit of R > 20.5 (Vega) at a mid-time of 14.9 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38246] EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
by GCN Circulars 23 Apr '25

23 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40219 SUBJECT: EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963 DATE: 25/04/23 18:19:28 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Maria E. Ravasio (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the optical and X-ray counterpart (Levan et al., GCN 40160; Sbarrato et al., GCN 40166) of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154, 40165), also identified as GRB 250416C (Svinkin et al., GCN 40167; Wang et al., GCN 40184). Observations were carried out using the Gemini South telescope located on Cerro Pachon, Chile, equipped with the GMOS-S instrument in spectroscopy mode. Observations started on 2025-04-17 at 07:44:43 (i.e., ~0.58 days after the EP detection), and consisted of 4 exposures of 900 s each using the B480 grating, covering the wavelength range between ~4000 and 9500 AA. In our spectrum, we clearly detect an emission line at 7317 AA. Considering the most likely options for this feature (Halpha, Hbeta, [O III], [O II]), the interpretation more consistent with the data is the (unresolved) [O II] 3727/3729 doublet at z = 0.963. In all other cases, we would expect to see other features which would fall over well-covered regions of the spectrum, which are not observed. We thus suggest that this is the redshift of the host galaxy of EP250416a. The spectrum shows tentative absorption features at the expected locations of Mg II (2796, 2803 AA) and Mg I (2852 AA) at z = 0.962, although the signal to noise in the blue region of the spectrum is badly affected by the bright Moon, hence we cannot conclusively determine an absorption redshift. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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