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

[vsnet-grb-info 36917] EP250111a: Swift/XRT detection and fading
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38910 SUBJECT: EP250111a: Swift/XRT detection and fading DATE: 25/01/11 14:46:54 GMT FROM: Jamie Kennea at Penn State <jak51(a)psu.edu> J. A. Kennea (PSU), P. A. Evans and K. L. Page (Leicester) on behalf of the Swift/XRT report: At 04:08UT on January 9th, 2025 Swift began a 1.7ks target-of-opportunity observation of the Einstein Probe discovered transient EP250111a (GCN #38905), approximately 2.8 hours after the EP trigger. XRT detects a previously uncatalogued point source at the following coordinates: RA/Dec(J2000) = 97.17996, +56.8970, which is equivalent to: RA(J2000) = 06h 28m 43.19s Dec(J2000) = +56° 53′ 49.1″ with an estimated uncertainty of 5.8 arc-seconds radius (90% confidence). This position lies 5 arc-seconds from the reported localization by the EP FXT reported in GCN #38905. This position lies 5.6 arc-seconds from the reported NOT optical candidate (GCN #38906). The X-ray flux of this source is 3.9(+1.4/-1.1) x 10^-13 erg/s/cm^2 (0.3-10 keV), approximately an order of magnitude fainter than the FXT flux. View this GCN Circular online at https://gcn.nasa.gov/circulars/38910. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36916] EP250108a / AT 2025kg: Swift UVOT detections
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38909 SUBJECT: EP250108a / AT 2025kg: Swift UVOT detections DATE: 25/01/11 13:01:52 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A.J. Levan (Radboud), L. Cotter (UCD), D. B. Malesani (DAWN/NBI & Radboud), A. Martin-Carrillo (UCD), P.G. Jonker (Radboud) report on behalf of a larger collaboration. The location of EP250108a (Lin et al., GCN 38861; Eyles-Ferris, GCN 38878) was observed with the Neil Gehrels Swift Observatory on 10 Jan 2025, starting at 15:17 UT, that is 2.12 days since the onset of the outburst. At the location of the optical counterpart AT 2025kg (the “kangaroo”; Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885; Malesani et al., GCN 38902; Kumar et al., GCN 38907) we clearly identify the source in both the UVW1 and UVW2 filters, with preliminary AB magnitudes of UVW1 = 20.6 +/- 0.2 and UVW2 = 21.4 +/- 0.2. These detections confirm the blue shape of the spectral energy distribution, as also indicated by Zhu et al. (GCNs 38885, 38908) and Malesani et al. (GCN 38902), but also indicate that it does not continue to rise strongly through the UV region. At a redshift of z = 0.176 (Zhu et al., GCN 38908) our measurement corresponds to an absolute AB magnitude of M_UVW1 = -18.9. At 3 days post discovery (likely somewhat later post-onset) AT 2018cow had M_UVW1 = -20.6 AB (Perley et al. 2019, doi:10.1093/mnras/sty3420), suggesting that, in the UV, AT 2025kg is somewhat fainter than AT 2018cow. At the position of AT 2025kg, no significant X-ray emission is detected by XRT, down to a 3-sigma upper limit of 3.8*10^-3 c s^-1, computed using the online tool at the University of Leicester (https://www.swift.ac.uk/user_objects/). We thank the Swift team for the very rapid scheduling of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/38909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36915] EP250108a / AT 2025kg (the "kangaroo”): VLT/X-shooter spectroscopic redshift z = 0.176 and LFBOT classification
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38908 SUBJECT: EP250108a / AT 2025kg (the "kangaroo”): VLT/X-shooter spectroscopic redshift z = 0.176 and LFBOT classification DATE: 25/01/11 12:14:29 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> Z.P. Zhu (NAOC), G. Corcoran (UCD), A. J. Levan (Radboud), L. Izzo (INAF/OACn), R. Eyles-Ferris (Leicester), J. P. U. Fynbo (DAWN/NBI), G. Leloudas (DTU Space), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF/IAPS), D. Xu (NAOC), B. P. Gompertz (U. Birmingham), P. G. Jonker (Radboud), report on behalf of the Stargate collaboration. We observed the optical counterpart AT 2025kg (Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885; Malesani et al., GCN 38902; Kumar et al., GCN 38907) of the transient EP250108a (Li et al., GCN 38861) using the ESO VLT UT3 (Melipal) equipped with the X-shooter instrument. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures by 600 s each. The observation mid time was 2025 Jan 11.08 UT (2.56 days after the EP trigger). Bright, blue continuum is detected over the UVB and VIS arms. Emission lines from Halpha, [O II] 3727/29, and faint [O III] 5007 are visible at a common redshift z = 0.176. At the same redshift, we also detect (narrow) absorption from Ca II H and K. This is thus the likely redshift of EP250108a. In the UV, there is a broad absorption feature, at an observed wavelength of ~3600 AA and with a FWHM of ~15,000 km s^-1. This feature is not identified at the moment. The spectral shape (mostly featureless) and luminosity are overall similar to the early AT 2018cow (e.g., Prentice et al., doi:10.3847/2041-8213/aadd90), both being hot blackbodies. The luminosity (absolute g-band magnitude ~ -20) and blue color robustly put this object in the region of luminous FBOTs (e.g. Ho et al., doi:10.3847/1538-4357/acc533). We tentatively suggest that AT 2025kg belongs to this class of objects, and humorously dub it "the kangaroo". At this redshift, the X-ray peak flux (Li et al., GCN 38861) corresponds to a luminosity of ~1.3*10^46 erg s^-1. We thank excellent support from the observing staff in Paranal, in particular Francesca Lucertini, Rodrigo Palominos, and Linda Schmidtobreick. View this GCN Circular online at https://gcn.nasa.gov/circulars/38908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36914] EP250108a: optical follow-up observations with the Liverpool Telescope
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38907 SUBJECT: EP250108a: optical follow-up observations with the Liverpool Telescope DATE: 25/01/11 11:54:00 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report: We conducted optical follow-up observations of the possible optical counterpart (Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885; Malesani et al., GCN 38902) of the EP-detected X-ray transient EP250108a (Li et al., GCNs 38861 and 38888) using the IO:O imager at the 2m Liverpool Telescope. Multi-band observations were performed starting on 2025-01-09 UT 22:06:09.685 and 2025-01-10 UT 19:41:48.380 (nearly 1.4 and 2.3 days post-trigger, respectively). Based on our preliminary analysis: In the stacked g-band image observed at ~1.4 days post-trigger, we detected the optical counterpart of EP250108a at a position consistent with the optical counterpart identified by Eyles-Ferris, GCN 38878. Based on our preliminary PSF photometry, the magnitude of the counterpart in the stacked g-band image is 20.2 ± 0.1 (AB); consistent with the magnitudes reported by Zhu et al., GCN 38885. The counterpart exhibits clear signs of brightening (as suggested by Zhu et al., GCN 38885), and we recommend continued follow-up observations. The quoted magnitudes are not corrected for the Galactic extinction in the direction of the EP-transient. Further analysis and observations are planned. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/38907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36913] EP250111a: NOT likely optical counterpart
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38906 SUBJECT: EP250111a: NOT likely optical counterpart DATE: 25/01/11 09:42:34 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> S.Y. Fu, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. H. de la Fuente, S. G. Sorensen (NOT) report on behalf of a large collaboration: We observed the field of EP250111a detected by Einstein Probe (EP, Zhao et al., GCN 38905), using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT). Observations started at 02:58:45.5 UT on 2025-01-11, i.e. 1.63 hr after the trigger, and 9 x100 s frames were obtained in the SDSS-r band. An uncatalogued source is detected in the stacked frame within the EP/FXT error circle (EP, Zhao et al., GCN 38905) and localized at coordinates R.A. (J2000) = 06:28:43.29 Dec. (J2000) = +56:53:54.76 with an uncertainty of ~ 0.5 arcsec. The source has r ~ 20.7 mag, calibrated with Pan-STARRS DR1 and not corrected for Galactic extinction. There was no known NEO object at the above position by checking MPC. We thus conclude the source is very likely the optical counterpart of EP250111a. Further observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/38906. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36912] EP250111a: a new X-ray transient detected by Einstein Probe
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38905 SUBJECT: EP250111a: a new X-ray transient detected by Einstein Probe DATE: 25/01/11 08:44:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Zhao (NAO, CAS), X. L. Chen (YNU), Q. C. Shui (IHEP, CAS), Kaushik Chatterjee (YNU), T. Y. Lian and C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team We report on the detection of an X-ray transient designated EP250111a by the Einstein Probe (EP) mission, which triggered the on-board processing unit at 2025-01-11T01:20:44 (UTC) (trigger ID: 01709130131). The transient event started at 2025-01-11T01:20:24 (UTC) and lasted for 83s 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 fixed Galactic equivalent hydrogen column density of 1.11 x 10^21 cm^-2 and a photon index of 1.01 (-0.52/+0.54). The derived average observed 0.5-4 keV flux is 1.39 (-0.40/+0.53) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. An autonomous observation was performed by the Follow-up X-ray Telescope (FXT) about four minutes later. An uncatalogued source was detected at R.A. = 97.1809, DEC = 56.8983 (J2000) with an uncertainty of about 20 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.11 x 10^21 cm^-2 and a photon index of 2.42 (-0.14/+0.15). The derived average observed 0.5-10 keV flux is 3.43 (-0.33/+0.36) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. More information on this source will be updated when the full telemetry data is received. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 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/38905. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36911] EP250109a/GRB 250109A:SVOM/VT optical counterpart
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38904 SUBJECT: EP250109a/GRB 250109A:SVOM/VT optical counterpart DATE: 25/01/11 02:50:01 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> SVOM/VT commissioning team: Y. L. Qiu, H. L. Li, L. P. Xin, C. Wu, X. H. Han, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, Z. H. Yao (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM) SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV) report on behalf of the SVOM team: The further analysis of the candidate(Qiu et al., GCN 38872) for the first ToO observation EP250109a / GRB 250109A(Li et al., GCN 38864; Fermi GBM team, GCN 38873, DeLaunay et al., GCN 38900) showed that it was fading for about 0.5 mag from 4.13 hours to 9.65 hours. The SVOM/VT conducted the second ToO follow-up observations for the transient in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously, from 31.27 hours to 38.79 hours after the burst. The candidate was still clearly detected in VT_R stacked image with VT_R=23.2+/-0.2 in AB magnitude at the mid time of 35.2 hours post the burst, with a total exposure time of 102*100 seconds. Given the continuous fading of about 0.9 mag during VT_R total observations, as well as the optical detection of Zeiss-2000 (Moskvitin et al., GCN 38901) and the XRT detection (Kennea et al., GCN 38899), it is confirmed that this source is the optical afterglow of the burst. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center 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/38904. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36910] GRB 250101B: Fermi GBM Observation
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38903 SUBJECT: GRB 250101B: Fermi GBM Observation DATE: 25/01/11 01:26:07 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA), S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:14:12.65 UT on 01 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250101B (trigger 757466057/250101968). which was also detected by SVOM/GRM (Zhang et al. 2025, GCN 38793). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 70.87, Dec = -3.25 (J2000 degrees, equivalent to J2000 4h 43m, -3d 15'), with a statistical uncertainty of 3.29 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 49 degrees. The GBM light curve consists of a single emission episode with two distinct peaks with a duration (T90) of about 4.5 s (50-300 keV). The time-averaged spectrum from T0-1.0 to T0+5.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.34 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 146 +/- 7 keV. The event fluence (10-1000 keV) in this time interval is (2.418 +/- 0.8)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.77 s in the 10-1000 keV band is 5 +/- 0.2 ph/s/cm^2. 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/38903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36909] EP250108a: further NOT optical observations
by GCN Circulars 11 Jan '25

11 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38902 SUBJECT: EP250108a: further NOT optical observations DATE: 25/01/11 00:43:54 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud and Warwick), A. van Hoof (Radboud), P. G. Jonker (Radboud), D. Xu (NAOC), report on behalf of a larger collaboration: We observed the possible optical counterpart (Eyles-Ferris, GCN 38878; Zhu et al., GCN 38885) of the Einstein Probe transient EP250108a (Li et al., GCN 38861), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the griz filters and began on Jan 10.88 UT (2.36 days after the trigger). Conditions were not ideal, with a nearby full Moon and mediocre seeing (1.7-2"). The counterpart is detected in all filters, and shows a remarkably blue SED. Comparison of the new data with those taken on the night of Jan 9 (Zhu et al., GCN 38885) shows moderate or no change in brightness in the g band, and a fading in the redder filters. The spectral slope can be roughly fitted with a power-law F_nu propto nu^2, consistent with a hot black-body. The bright, blue optical spectral shape and the lack of X-ray emission (Li et al., GCN 38888) of this transient are very unusual among GRB and FXT afterglows, as already noted by Zhu et al. (GCN 38885). If associated with EP250108a, the transient is revealing an uncommon emission component, or could be due to a different progenitor. We acknowledge expert support from the NOT observing staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/38902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 36908] GRB 250109A / EP250109a: Terskol (INASAN) and SAO RAS observations
by GCN Circulars 10 Jan '25

10 Jan '25

TITLE: GCN CIRCULAR NUMBER: 38901 SUBJECT: GRB 250109A / EP250109a: Terskol (INASAN) and SAO RAS observations DATE: 25/01/10 22:51:16 GMT FROM: Moskvitin Alexander at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO), A. Pozanenko (IKI), N. Kapitanov (INASAN), N. Pankov (IKI, HSE) report on behalf of larger GRB follow-up GRB IKI FuN collaboration. We observed the field of the GRB 250109A / EP250109a (Li et al., GCN 38864; Fermi GBM team, GCN 38873) with two telescopes, 2-m Zeiss-2000 of Terskol observatory and 1-m Zeiss-1000 of SAO RAS on January 9. We obtained 100 x 60 sec. images R band on Jan. 09, 19:36:42--21:28:07 UT with 2-m telescope and 11 x 300 sec. images in Rc band on Jan. 09, 21:12:33--22:23:56 UT with 1-m telescope. In the stacked image of Zeiss-2000 observation we marginally detect the afterglow candidate (Qiu et al., GCN 38872) within XRT error circle (Kennea et al., GCN 38899). Photometry of the staked images is the following: Date UT start t-T0, h(mid) Filter Exp.,s OT, err, UL(3sigma) Telescope 25-01-09 19:36:42 14.254 R 100 x 60 22.5 0.4 22.4 Zeiss-2000 25-01-09 21:12:33 15.518 Rc 11 x 300 n/d n/d 22.2 Zeiss-1000 The photometry is based on nearby stars of the PS1 catalog (Lupton 2005 transformations) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/38901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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