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

[vsnet-grb-info 41692] EP260131a: SVOM/VT optical observation
by GCN Circulars 01 Feb '26

01 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43589 SUBJECT: EP260131a: SVOM/VT optical observation DATE: 26/02/01 08:04:28 GMT FROM: zhyao(a)bao.ac.cn Z. H. Yao, C. Wu, L. P. Xin, H. L. Li, Y. N. Ma, Y. L. Qiu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) and S. D. Vergani (LUX-Paris Obs.) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260131a detected by EP/WXT (Ding et al., GCN 43574). SVOM/VT began observing the field at 2026-01-31T17:47:46.506 UTC, ~14.3 h after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 43577; Álvarez et al., GCN 43578; Malesani et al., GCN 43581; Schneider et al., GCN 43582; Schneider et al., GCN 43584; Mu el al., GCN 43588) was detected in both VT_B and VT_R band within EP/WXT's (Ding et al., GCN 43574) and EP/FXT's (Wu et al., GCN 43583) error box. The position of this target is R.A., Dec. = 149.902458, -3.307450 degrees, corresponding to: R.A. (J2000) = 09:59:36.59 Dec. (J2000) = -03:18:26.82 with an uncertainty of 0.5 arcsec. The photometric measurements are as follows: mid time (h) | exposure time (s) | band | mag (AB) --------------|-------------------|------|------------- 15.50 | 40*70 | VT_B | 22.38+/-0.05 15.31 | 41*70 | VT_R | 21.70+/-0.03 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 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/43589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41691] EP260131a: Xinglong optical upper limit
by GCN Circulars 01 Feb '26

01 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43588 SUBJECT: EP260131a: Xinglong optical upper limit DATE: 26/02/01 04:16:49 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Haiyang-Mu (NAOC),Junjie-Jin (NAOC), Feng-Xiao (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: Following the detection of EP260131a by EP-WXT (GCN Circular 43574,GCN Circular 43577,GCN Circular 43578), we observed the field of EP260131a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 300s r-band frames with a median time of (2026-01-31 16:25:55(UT)) 13 hr after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (GCN Circular 43574,GCN Circular 43578), down to 5-sigma limiting magnitudes of r ~ 19.1(not good day with thin cloud and bad seeing), calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. Based on the location of the report(GCN Circular 43574,GCN Circular 43578), the target was not observed. View this GCN Circular online at https://gcn.nasa.gov/circulars/43588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41690] GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
by GCN Circulars 01 Feb '26

01 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43587 SUBJECT: GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading DATE: 26/02/01 03:45:33 GMT FROM: William H. Lee at UNAM <wlee(a)astro.unam.mx> We observed the optical afterglow candidate AT2026bwg discovered by Gompertz et al. (GCN 43586), of GRB 260131A (Fermi/GBM Team, GCN 43579), also associated with GRB 260131B (Sugai et al., GCN 43580; Roberts et al., GCN 43585), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-01 02:06 to 03:05 UTC (from 19.45 to 20.46 hours after the trigger) and obtained 23 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. The optical counterpart is clearly detected with preliminary magnitudes of: r = 17.96 +/- 0.01, z = 17.61 +/- 0.01. Since the start of our observations, the source has faded with an apparent average temporal power-law index of -2.01 +/ 0.26 (in r) and -1.50 +/- 0.33 (in z). 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/43587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41689] GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43586 SUBJECT: GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation DATE: 26/01/31 23:32:35 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, D. O’Neill, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 260131A (Fermi/GBM Team, GCN 43579), now associated with GRB 260131B (Sugai et al., GCN 43580; Roberts et al., GCN 43585). Observations covering the initial GBM localisation area of GRB 260131A began at 2026-01-31 20:00:48 UT (+13.35h post trigger) and continued through to 2026-01-31 21:32:06 UT (+14.88h post trigger). 103 images were taken, across 10 unique pointings, covering 215.8 within the 90% localisation contour. ~89.8% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.4 mag in the GOTO-L filter (400 - 700nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source GOTO26akj/AT2026bwg is identified at coordinates: RA,DEC (J2000) = 24.713819, 34.328119, 01:38:51.32, +34:19:41.23 This position is consistent with the MAXI localisation of GRB 260131B (Sugai et al., GCN 43580). The source was initially detected with L = 17.41 ± 0.03 AB mag (t0+13.62h) before fading to L = 17.59 ± 0.04 mag (t0+14.75h). We find no evidence of the source prior to the GRB trigger time in the most recent pre-GRB GOTO observations taken at 19:59:53 on 2026-01-28 (t0-58.66h) down to a 5-sigma depth of L > 19.55 AB mag. We also find no evidence of the source prior to the GRB in the ZTF observations provided by the Lasair broker (Smith et al. 2019) or the ATLAS forced photometry server (Shingles et al. 2021). Due to its temporal coincidence with GRB 260131A/B, apparent fading, and spatial coincidence with the relatively small MAXI localisation region, we consider GOTO26akj/AT2026bwg to be a promising candidate optical counterpart. Further observations to determine the nature of the source are strongly encouraged. 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41688] GRB 260131A/B: Fermi GBM Observation
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43585 SUBJECT: GRB 260131A/B: Fermi GBM Observation DATE: 26/01/31 23:12:56 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:39:30.44 UT on 31 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260131A/B (trigger 791534375/260131277). which was also detected by MAXI (H. Sugai et al. 2026, GCN 43580). The Fermi GBM final real-time Localization (GCN 43579) is consistent with the MAXI position. The MAXI burst triggered on the second pulse of 260131A. We note both bursts have similar locations and are likely the same event. The angle from the Fermi LAT boresight using the MAXI location is 112 degrees. The GBM light curve consists of two separated FRED emission episodes with a duration (T90) of about 257 s (50-300 keV). The time-averaged spectrum from T0-2.0 to T0+280.0 s is best fit by a Band function with an Epeak of 148 +/- 39 keV, alpha is -0.90 +/- 0.16 and beta is -1.76 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (2.82 +/- 0.09)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.6 s in the 10-1000 keV band is 8.3 +/- 0.4 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/43585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41687] EP260131a: COLIBRÍ observations of slow optical fading
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43584 SUBJECT: EP260131a: COLIBRÍ observations of slow optical fading DATE: 26/01/31 15:00:38 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Benjamin Schneider (LAM), Alan M. Watson (UNAM), Fredd Sánchez Álvarez (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260131a (Ding et al., GCN Circ. 43574; Wu et al, GCN CIrc 43583) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-31 04:40 to 11:52 UTC (from 1.14 to 8.35 hours after the trigger) and obtained, respectively, 127, 191, and 320 minutes of exposure in the g, r, and z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. The candidate optical counterpart reported by Li et al. (GCN Circ. 43577), Sánchez Álvarez et al (GCN Circ. 43578), Malesani et al. (GCN Circ 43581), and Schneider et al. (GCN Circ. 43582) is clearly detected in our data. It fades slowly from r ≈ 21.1 to r ≈ 21.4 and z ≈ 20.8 to z ≈ 21.2 during our observations with an apparent average temporal power-law index of -0.16 +/- 0.07. We observe that the g-r color is 0.14 +/- 0.06, consistent with the detection by Schneider et al. (GCN Circ. 43582) down to the atmospheric cutoff. We encourage further observations, especially over the next 24 hours. 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/43584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41686] EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43583 SUBJECT: EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations DATE: 26/01/31 13:33:19 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu (NAO, CAS), T. Wu , H. C. Ding (AHNU) , H. Sun (NAO,CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260131a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Ding et al., GCN 43574). The refined analysis of the WXT data shows that the event started at T0=2026-01-31T03:28:00.15 (UTC), and lasted for approximately 340 seconds, after which the observation was interrupted due to Earth occultation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.36 × 10^20 cm^-2, an intrinsic hydrogen column density of 5 (-3/+3) × 10^21 cm^-2, and a photon index of 1.9 (-0.8/+0.9). The derived average unabsorbed 0.5-4 keV flux is 6.3 (-1.5/+3.6) × 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP autonomously observed this source a few minutes after the on board trigger. The source was initially occulated the Earth and entered the FXT field of view since 2026-01-31T04:14:01 (UTC, T0+2.7 ks). The effective exposure time of the observation is around 3 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 149.9017, DEC = -3.3074 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position and also the optical counterpart (Li et al., GCN 43577; Álvarez et al., GCN 43578; Malesani et al., GCN 43581; Schneider et al., GCN 43582). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.36 × 10^20 cm^-2, an intrinsic hydrogen column density of 1.5 (-1.1/+1.3) × 10^21 cm^-2, and a photon index of 2.2 (-0.4/+0.4). The derived average unabsorbed 0.5-10 keV flux is 4.4 (-0.6/+0.6) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. 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/43583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41685] EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43582 SUBJECT: EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937 DATE: 26/01/31 12:24:23 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Saccardi (CEA/Irfu), J. An (NAOC), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), V. D'Elia (ASI-SSDC), S. D. Vergani (LUX-Paris Obs.), N. Habeeb (U. Leicester), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF-IAPS) report on behalf of the Stargate collaboration: We observed the optical counterpart (Li et al., GCN 43577; Sánchez Álvarez et al., GCN 43578, Malesani et al, GCN 43581) of EP 260131a (Ding et al., GCN 43574) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 1200 s each. Observations started on 2026 January 31 at 07:30:09 UT (3.98 hr after the burst). In a stacked image of 3x60 s secured in the r-band (3.79 after trigger), we measure r = 21.20 +/- 0.04 (AB), calibrated against nearby stars from Pan-STARRS. In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From detection in the blue down to 3090 AA, and the lack of hydrogen absorption, we set a redshift upper limit z < 1.54. Furthermore, we detect multiple absorption lines, which we interpret as Al II, Mn II, Fe II, Mg II doublet, and Ca II at a common redshift of z = 0.937. The non-detection of fine-structure transitions at z = 0.937 does not allow us to firmly associate this redshift with the GRB, however, the absence of unidentified features at higher redshift and the good S/N over the full continuum, support z = 0.937 as the most likely redshift. We acknowledge the excellent support of the ESO observing staff in Paranal, in particular Elisa Garro. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/43582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41684] EP260131a: NOT early detection of the counterpart in "rapid response mode"
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43581 SUBJECT: EP260131a: NOT early detection of the counterpart in "rapid response mode" DATE: 26/01/31 09:00:08 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), J. N. D. van Dalen (Radboud), J. A. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), K. Valeckas (NOT) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260131a (Ding et al., GCN 43574) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were triggered using the recently implemented automatic “Rapid Response Mode” and obtained in the SDSS r and z bands, consisting of 5x180 s and 9x150 s exposures, respectively, starting on 2026-01-31 at 04:56:50 UTC (~2.5 min after the GCN Notice, or 52 min after the WXT trigger). We detect the counterpart reported by Li et al. (GCN 43577) and Sánchez Álvarez et al. (GCN 43578). In our first frame (mid time 53.5 min after trigger), we measure r' = 21.18 +- 0.10 (AB) and from a stacked z-band image we measure z' = 20.75 +- 0.06 at time 75.2 min after the WXT trigger. The above magnitudes are calibrated against nearby stars from the Pan-STARRS catalog and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43581. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41683] GRB 260131B: MAXI/GSC detection
by GCN Circulars 31 Jan '26

31 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43580 SUBJECT: GRB 260131B: MAXI/GSC detection DATE: 26/01/31 08:53:31 GMT FROM: Motoko Serino at Aoyama Gakuin U. <serino(a)phys.aoyama.ac.jp> H. Sugai (Chuo U.), D. Iijima, M. Serino (AGU), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 06:43:02 UT on January 31, 2026. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (24.348 deg, 34.351 deg) = (01 37 23, +34 21 03) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.11 deg and 0.09 deg, respectively. The roll angle of long axis from the north direction is 26.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 801 +- 56 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (23.945, 34.685) deg = (01 35 46, +34 41 06) (J2000) (R.A., Dec) = (23.826, 34.499) deg = (01 35 18, +34 29 56) (J2000) (R.A., Dec) = (25.021, 33.970) deg = (01 40 05, +33 58 11) (J2000) (R.A., Dec) = (25.142, 34.154) deg = (01 40 34, +34 09 14) (J2000) There was no significant excess flux in the previous transit at 05:10 UT and in the next transit at 08:16 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/43580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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