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

[vsnet-grb-info 38821] GRB 250615A/EP250615a: FTW optical and NIR observations
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40780 SUBJECT: GRB 250615A/EP250615a: FTW optical and NIR observations DATE: 25/06/18 19:24:32 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the improved localization (Evans et al., GCN 40737; Goad et al., GCN 40739) of GRB 250615A/EP250615a (Dichiara et al., GCN 40736; Yang et al., GCN 40743; Burrows et al., GCN 40745; Tembhurnikar et al., GCN 40752; Frederiks et al., GCN 40753; Barthelmy et al. GCN 40765) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 20 x 180 s starting at 2025-06-17T21:29:37 UT (1.96 days after the trigger). We detect no new source in the 90% Swift/XRT localization (Evans et al., GCN 40737; Goad et al., GCN 40739) down to a 3-sigma depth of r > 23.9 mag i > 23.3 mag J > 21.8 mag. These upper limits are consistent with the previous observations by Kuin et al. (GCN 40747), Becerra et al. (GCN 40748), Magnani et al. (GCN 40749), and Calapai & Giorgio (GCN 40759). The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for the significant Galactic extinction at this location. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38820] sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40779 SUBJECT: sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations DATE: 25/06/18 14:55:00 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), M. Dennefeld (IAP/Sorbonne U.), J. L. Atteia (IRAP), J. Rodriguez (CEA), F. Cangemi (APC), A. Coleiro (APC), Y. Degot-Longui (Pytheas/OHP), J. Balcaen (Pytheas/OHP), report on behalf of a larger collaboration: We observed the field of the SVOM sb25061218 X-ray transient (Rodriguez et al., GCN 40712) using the T120cm and the T193cm equipped with the MISTRAL spectro-imager at Observatoire de Haute-Provence (France). Our T120 observations consisted of multiple epochs from 2025-06-12T22:07 to 2025-06-13T00:46 UT (from 1.52 to 4.17 hr after the trigger) in r-band and covered both uncatalogued X-ray sources seen with Swift/XRT (Evans et al. GCN 40721). We examined the sources visible at the XRT #1 and #2 positions and noted a rebrightening of ~0.3 mag of the SIMBAD object [VV2006] J131446.6+544804 compared to SDSS (r = 18.66 +/- 0.02) and PanStarrs (r = 18.65 +/- 0.01) surveys, possibly associated with the XRT source #1. The magnitudes derived for that source are: date-obs (UT) | exposure time (min) | band, mag (AB) | mag err 2025-06-12T22:07 | 12min | r | 18.33 | 0.02 2025-06-12T22:36 | 12min | r | 18.29 | 0.04 2025-06-12T23:54 | 4min | r | 18.35 | 0.03 2025-06-13T00:46 | 8min | r | 18.36 | 0.03 On 2025-06-13 starting at 20:27 UT (23.85 hr after the trigger), we re-observed the object [VV2006] J131446.6+544804 with the spectro-imager MISTRAL. We obtained 1 minute of observation in r-band and measured a magnitude of r = 18.37 +/- 0.07, consistent with the T120 measurements on 2025-06-12. We also obtained 1 hour of spectroscopic observations using the MISTRAL blue mode with a spectral resolution of ~700 under moderately good conditions. When compared to the SDSS public spectrum, a preliminary analysis of the spectrum shows a flux increase of the Fe II complex between ~6600 AA and ~7000 AA. This increase is roughly consistent with the r-band magnitude variation observed by the T120 and MISTRAL. Our observations suggest that the Swift/XRT source #1 is the X-ray counterpart to [VV2006] J131446.6+544804 source, a known QSO at z~ 0.49. The X-ray detection of this source is the first reported to our knowledge and may indicate that the SVOM trigger is also associated with this event. This object being radio-quiet (2.9 mJy at 1.4GHz, NVSS) without typical lines of TDEs, and the observed r-band magnitudes being nearly constant after the initial increase suggest a likely association with an accretion event onto the central black hole of this QSO and would disfavor a GRB nature of this event. We encourage further observations of [VV2006] J131446.6+544804. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 (Institut Origines) and the SOPHIE observer, Xavier Delfosse. View this GCN Circular online at https://gcn.nasa.gov/circulars/40779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38819] GRB 250617B: Swift/UVOT Detection
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40778 SUBJECT: GRB 250617B: Swift/UVOT Detection DATE: 25/06/18 13:09:34 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250617B 797 s after the BAT trigger (Page et al., GCN Circ. 40760). A source consistent with the XRT position (Osborne et al., GCN Circ 40767) is detected in the initial UVOT exposures. The lack of detection in the uvw2 and uvm2 filters would be consistent with the redshift reported by Corcoran et al. (GCN Circ. 40776). The preliminary UVOT position is: RA (J2000) = 22:11:35.25 = 332.89686 (deg.) Dec (J2000) = +32:43:57.1 = 32.73253 (deg.) with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 797 946 147 18.18 +/- 0.05 v 1130 2528 172 18.72 +/- 0.19 b 1229 1596 58 18.91 +/- 0.18 u 1204 1397 39 18.10 +/- 0.19 w1 1179 2408 156 19.32 +/- 0.28 m2 1155 2384 117 >18.3 w2 1106 2507 175 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.087 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38818] GRB 250617B: Kilonova-Catcher optical afterglow detection
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40777 SUBJECT: GRB 250617B: Kilonova-Catcher optical afterglow detection DATE: 25/06/18 11:19:22 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> D. Turpin (CEA-Saclay/Irfu), M. Freeberg (KNC), C. Andrade(UMN), M. Pillas (ULiege), M. Tanasan (NARIT), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250617B (Page et al., GCN 40760) detected by Swift/BAT with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg starting from T_GRB+10hr. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we marginally detect the optical afterglow at the position reported by Swift/UVOT (Page et al., GCN 40760), SAO RAS (Moskvitin et al., GCN 40761), Ondrejov D50 (Jelinek et al., GCN 40762), NUTTelA-TAO (Grossan et al., GCN 40771), SVOM/VT (Mat et al., GCN 40772), NOT (Schneider et al., GCN 40774), COLIBRÍ (Antier et al., GCN 40775) and VLT/X-shooter (Corcoran et al., GCN 40776) We report our follow-up results in the table below: +---------------+-------------+--------------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+=============+==============+================+==============+ | 10.8 | 18 x 300s | r (AB) | 20.85 +/- 0.29 | TEC160FL | +---------------+-------------+--------------+----------------+--------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan images were calibrated using the PanSTARRS DR1 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/40777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38817] GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40776 SUBJECT: GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396 DATE: 25/06/18 10:49:27 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> G. Corcoran (UCD), M. Garnichey (LUX-Paris Obs.), B. Schneider (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.), report on behalf of a larger collaboration: We observed the field of GRB 250617B detected by Swift (Page et al., GCN 40760) and Fermi (Fermi GBM team, GCN 40763; Bala & Meegan, GCN 40766), using the ESO VLT UT3 (Melipal) with the X-shooter. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 900 s each. The observation mid time was 2025 Jun 18.375 UT (11.96 hr after the GRB). In images taken with the acquisition camera, we clearly detect in the g, r, and z bands the optical counterpart reported by Page et al. (GCN 40760), Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), Ma et al. (GCN 40772), Schneider et al. (GCN 40774) and Antier et al. (GCN 40775). We measure a preliminary magnitude: r = 21.30 +/- 0.04 (AB) at mid time 11.21 hr after trigger. The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitude is not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From the detection of multiple absorption lines, which we interpret as Mg II doublet (2796, 2804) and Fe II, we infer a redshift of z = 1.396. At a consistent redshift, we also detect emission lines due to [O II] doublet and H-alpha from the GRB host galaxy. We acknowledge excellent support from the ESO observing staff in Paranal. View this GCN Circular online at https://gcn.nasa.gov/circulars/40776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38816] GRB 250617B: COLIBRÍ optical observations
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40775 SUBJECT: GRB 250617B: COLIBRÍ optical observations DATE: 25/06/18 10:25:49 GMT FROM: Sarah Antier at OCA <sarah.antier(a)oca.eu> Sarah Antier (OCA/IJCLAB), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the GRB 250617B (Page et al., GCN 40760; Fermi GBM Team, GCN 40763) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-06-18 08:09:20 to now UTC (started 11.12 hours after the trigger) and obtained a series of 1 min exposure images in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1/SkyMapper catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart Page et al., GCN Circ. 40760 (also reported by Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), and Ma et al. (GCN 40772)), at a preliminary magnitude using a 6-min stack image at the beginning of the observations: i = 21.17 +/- 0.16 Further observations are ongoing. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/40775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38815] GRB 250617B: NOT NIR observations of the afterglow
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40774 SUBJECT: GRB 250617B: NOT NIR observations of the afterglow DATE: 25/06/18 09:27:29 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> B. Schneider (LAM), X. Liu (NAOC), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), B. P. Gompertz (U. Birmingham), A. A. Djupvik (NOT), S. Bijavara Seshashayana (NOT and Malmo Univ.), report on behalf of a larger collaboration: We observed the field of GRB 250617B detected by Swift (Page et al., GCN 40760) and Fermi (Fermi GBM team, GCN 40763; Bala & Meegan, GCN 40766), using the NOTCam camera mounted on the Nordic Optical Telescope (NOT). We obtained 20x60 s exposures in the J-band starting at 01:02 UT on 2025-05-18 (~4 hr after the Swift trigger). The optical counterpart reported by Page et al. (GCN 40760), Moskvitin et al. (GCN 40761), Jelinek et al. (GCN 40762), Grossan et al. (GCN 40771), and Ma et al. (GCN 40772) is well detected in our stacked image with a preliminary magnitude: J = 19.08 +/- 0.10 (Vega), at mid time 4.24 hr after trigger. The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38814] GRB 250617B: Swift-XRT refined Analysis
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40773 SUBJECT: GRB 250617B: Swift-XRT refined Analysis DATE: 25/06/18 08:23:52 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 250617B, from 779 s to 31.0 ks after the trigger. The data comprise 7 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.90 (+/-0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.16 (+0.19, -0.18). The best-fitting absorption column is 1.9 (+0.6, -0.5) x 10^21 cm^-2, in excess of the Galactic value of 9.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.9 (+0.6, -0.5) x 10^21 cm^-2 Galactic foreground: 9.7 x 10^20 cm^-2 Excess significance: 3.0 sigma Photon index: 2.16 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 0.90, the count rate at T+24 hours will be 0.025 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x 10^-13 (1.2 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01325580. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38813] GRB 250617B: SVOM/VT optical observation
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40772 SUBJECT: GRB 250617B: SVOM/VT optical observation DATE: 25/06/18 08:16:40 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. Q. Wang (GXU), W. K. Zheng (UCB), Y. F. Liang (PMO) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 250617B detected by Swift-BAT（Page et al., GCN 40760; Osborne et al., GCN 40767) and Fermi-GBM (Bala et al., GCN 40766). The observation began at 2025-06-18T01:18:40 UTC, 4.281 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The afterglow (Page et al., GCN 40760; Moskvitin et al., GCN 40761; Jelinek et al., GCN 40762) is detected using VT X-band data, at R.A., Dec 332.89675, 32.73242 degrees: RA (J2000) = 22:11:35.22 Dec (J2000) = +32:43:56.72 with an uncertainty of 0.5 arcsec. The magnitudes in both channels are: date-obs (UT) | exposure time (s) | band | mag (AB) | mag err -----------------------|-------------------|------|----------|-------- 2025-06-18T02:24:34.50 | 70 | VT_B | 21.10 | 0.12 2025-06-18T02:24:34.50 | 70 | VT_R | 20.11 | 0.08 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38812] GRB 250617B: NUTTelA-TAO early time optical observations
by GCN Circulars 18 Jun '25

18 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40771 SUBJECT: GRB 250617B: NUTTelA-TAO early time optical observations DATE: 25/06/18 08:09:56 GMT FROM: Bruce Grossan at LBNL/UCB SSL <Bruce_Grossan(a)lbl.gov> B. Grossan (UCB, NU) , T. Komesh (NU), Z. Maksut (NU), D. Berdikhan (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) observed the field of GRB 250617B on receipt of an automated GCN / BAT position alert, observing in Sloan g' and r' bands with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We find a fading OT consistent with the position given in Palmer, 2025 (GCN 40760). We received the alert and started observations at UT 2025-06-17 21:02:48 (58 seconds between GRB trigger time and notice receipt/response time). Stabilized images commenced at 21:03:10, 80 s after trigger. Observations were made under good conditions for more than 1300 s. The early measurements were sufficiently bright that they are visible in our short frames with no co-addition. Below, we give a selection of these measurements(irregular sampling due to changes in exposure time, camera mode,etc.) Note that these data provide essentially full-time coverage, nearly simultaneous in both bands. We report the following results: ---------------------------------------------------------------------------- g' tstart(*) tm-ttrig(s) g' err r' err exposure_time (s) ------------ ---------- ----- ------ ------ ----- ----------------- 21:03:10.4 80.5 15.29 0.06 14.75 0.09 3.0 21:03:40.4 110.5 15.54 0.10 14.90 0.10 3.0 21:04:46 176 16.12 0.09 15.69 0.04 30.0 21:09:46 476 17.40 0.10 17.02 0.07 30.0 21:15:45 835 17.87 0.12 17.67 0.08 60.0 21:18:45 1015 18.36 0.12 17.81 0.09 60.0 21:23:45 1315 UL18.72 18.00 0.11 60.0 (*) Times for r' are about 1.8 s before times for g'; times are UT June 17. "tm-ttrig" gives the mid time of the exposure minus the trigger time. The Sloan filter g', err, r', err are given in magnitudes. UL denotes no detection; 5 sigma upper limit only. Conditions at later times than given in the table showed a significant deterioriation in stability and sensitivity and so are omitted. ----------------------------------------------------- Because of the very good, quite early, time coverage thus far, we encourage observers capable of longer-term observations (12 hours+) to attempt additional g',r' (and other filters) coverage. We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate. We welcome requests for additional data and collaboration. ---------------------------------- NU = Nazarbayev University, Nur-Sultan, Kazakhstan UCB = University of California, Berkeley, USA HKUST = Hong Kong University of Science and Technology FAI = Fesenkov Astrophysical Institute, Kazakhstan The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan. View this GCN Circular online at https://gcn.nasa.gov/circulars/40771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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