GRB230918B

This page lists all entries on GRB230918B in GRBweb

Summary Fermi GBM GCN 34734 GCN 34738 GCN 34753

Summary table
Variable Value Source
GRB_name_Fermi GRB230918997
T0 23:55:11.852 UTC Fermi_GBM
ra 307.6600° Fermi_GBM
decl -48.4400° Fermi_GBM
pos_error 4.59e+00° Fermi_GBM
T90 14.08 s Fermi_GBM
T90_error 1.379 s Fermi_GBM
T90_start 23:55:11.852 UTC Fermi_GBM
fluence 2.02e-06 erg/cm² Fermi_GBM
fluence_error 2.33e-08 erg/cm² Fermi_GBM
T100 14.08 s
GBM_located True
mjd 60205.9966649537 Fermi_GBM
Fermi GBM table
GRB_name_Fermi GRB230918997
trigger_name bn230918997
ra 307.6600°
decl -48.4400°
pos_error 4.59e+00°
datum 2023-09-18
t_trigger 23:55:14.924 UTC
T90 14.08 s
T90_error 1.379 s
T90_start 23:55:11.852 UTC
fluence 2.02e-06 erg/cm²
fluence_error 2.33e-08 erg/cm²
flux_1024 3.16e+00 erg/cm²/s
flux_1024_error 2.44e-01 erg/cm²/s
flux_1024_time 1.22e+00 erg/cm²/s
flux_64 4.55e+00 erg/cm²/s
flux_64_error 1.03e+00 erg/cm²/s
GCN 34734 table
GRB_name GRB230918B
GCN_number 34734
Detection_method Fermi GBM final loc
t_trigger 23:55:14 UTC
ra 307.7000°
decl -48.4000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 34734 SUBJECT: GRB 230918B: Fermi GBM Final Real-time Localization DATE: 23/09/19 00:05:51 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 23:55:14 UT on 18 Sep 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230918B (trigger 716774119.92359 / 230918997). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 307.7, Dec = -48.4 (J2000 degrees, equivalent to J2000 20h 30m, -48d 23'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 47.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918997/quicklook/glg_skymap_all_bn230918997.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918997/quicklook/glg_healpix_all_bn230918997.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230918997/quicklook/glg_lc_medres34_bn230918997.gif
GCN 34738 table
GRB_name GRB230918B
GCN_number 34738
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 34738 SUBJECT: GRB 230918B: GOTO detection of a fast-rising transient in the GBM localisation region DATE: 23/09/19 20:58:28 GMT FROM: Ben Gompertz at U of Birmingham B. P. Gompertz; M. R. Kennedy; D. O'Neill; K. Ulaczyk; T. Killestein; K. Ackley; D. B. Malesani; R. Starling; M. J. Dyer; J. Lyman; F. Jimenez-Ibarra; A. Kumar; D. Steeghs; D. K. Galloway; V. Dhillon; P. O'Brien; G. Ramsay; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) in response to GRB 230918B (Fermi GBM team, GCN 34734). Three targeted observations were performed by GOTO-South between 09:15:23 UT and 11:31:06 UT on 2023-09-19, corresponding to 0.39, 0.44 and 0.48 days after trigger. Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks. We identify a fast-rising optical source within the GBM 90% localisation region: Name | RA(J2000) | Dec(J2000) GOTO23aky | 20:54:37.14 | -48:40:29.33 The L-band AB magnitudes at each epoch are measured to be 20.34 +/- 0.16, 20.18 +/- 0.11, and 20.03 +/- 0.10, respectively. This corresponds to a rise of 3.3 +/- 2.0 mag/day. We find no evidence of this source prior to the GRB trigger time in previous GOTO observations (taken ~6 days prior to the GRB) or the ATLAS forced photometry server (Shingles et al. 2021, taken ~ 1 day prior to the GRB). No underlying source is present at the position in the Legacy Server (Dey et al. 2019). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN 34753 table
GRB_name GRB230918B
GCN_number 34753
Detection_method Fermi GBM Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 34753 SUBJECT: GRB 230918B: VLT/X-shooter classification of AT 2023tbf (GOTO23aky) as a dwarf nova DATE: 23/09/20 22:32:36 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University A. Saccardi (GEPI/Paris Obs.), L. Izzo (INAF/OACn & DARK/NBI), J. T. Palmerio (GEPI/Paris Obs. & IAP), D. B. Malesani (Radboud Univ. & DAWN/NBI), P. D'Avanzo (INAF-OABr), V. D’Elia (ASI-SSDC & INAF-OAR), M. Della Valle (INAF/OAC), D. H. Hartmann (Clemson Univ.), K. E. Heintz (DAWN/NBI), P. Jakobsson (U. of Iceland), L. Kaper (U. of Amsterdam), G. Leloudas (DTU Space), A. J. Levan (Radboud Univ.), A. Martin-Carrillo (UCD), B. Schneider (MIT), S. Schulze (OKC), A. de Ugarte Postigo (OCA), and K. Wiersema (U. of Hertfordshire) report on behalf of the Stargate collaboration: We observed the transient AT 2023tbf (GOTO23aky; Gompertz et al., GCN 34738), spatially and temporally consistent with the Fermi GBM GRB 230918B (Fermi GBM team; GCN 34734). We used the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph, starting on 2023 September 20.093 UT. Our data cover the wavelength range 3000-24800 AA and consist of 4 exposures of 600 s each. In the acquisition image, taken on 2023 Sep 20.086 UT, we measure for the transient a magnitude r = 19.64 +- 0.05 AB (calibrated against a single nearby star from the SkyMapper catalog). A strong continuum is detected in the blue end of the spectrum, with a decreasing signal towards the VIS and NIR arms. The UVB shows several broad undulations, not seen in GRB afterglow spectra; in the VIS and NIR arms, the continuum is smoother. The source shows narrow absorption from Ca H and K a z = 0, as well as broad features in correspondence of the Balmer lines, at least H-beta to H-eta, all at z = 0. No features are identified at z > 0. Comparison with template spectra (e.g. Morales-Rueda & Marsh, 2002, MNRAS, 332, 814) allows us to classify AT 2023tbf as a dwarf nova. We thus conclude that AT 2023tbf is not a GRB afterglow and is not associated with GRB 230918B. We acknowledge excellent support from the observing staff at Paranal, in particular Ditte Slumstrup, Xavier Haubois, Francisco Caceres and Paulina Venegas.