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

[vsnet-grb-info 38306] EP250428b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40277 SUBJECT: EP250428b: Einstein Probe detection of a fast X-ray transient DATE: 25/04/29 17:30:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250428b (GCN Notice ID 01799135422). The WXT position of the source is R.A. = 220.479 deg, DEC = 2.09 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at around 2025-04-28T06:05:31(UTC) and lasted for a few hundreds of seconds, with a peak flux of around 3 x 10^-10 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.77 x 10^20 cm^-2 and a photon index of 1.9 (+0.2, -0.2). The averaged unabsorbed 0.5-4 keV flux is 3.3 (+2.2, -1.3) x 10^-11 erg/cm^2/s. The uncertainties are at the 90% confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed from 2025-04-29T13:41:27 (UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 220.4586 deg, DEC = 2.1002 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. The contact TA of EP250428b is Q. Y. Wu. Please contact him via email qywu(a)bao.ac.cn if needed. 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/40277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38305] Fermi-LAT Gamma-ray Observations of IceCube-250426A
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40276 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250426A DATE: 25/04/29 11:02:04 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250426A neutrino event (GCN 40254) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-04-26 17:44:58.16 UTC (T0) with J2000 position RA = 296.37 (+0.53, -0.50) deg, Decl. = 20.7 (+0.52, -0.52) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250426A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5 sigma) new excess emission (> 100 MeV) within the IC250426A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250426A best-fit position, the >100 MeV flux upper limit (95% confidence) is <6.95e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <4.67e-08(<3.56e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/40276. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38304] EP250427a / GRB 250427A: OHP/T193 photometric observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40275 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations DATE: 25/04/29 08:49:00 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), C. Adami (LAM/Pytheas/AMU), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of the MISTRAL-GRB collaboration: We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager in blue setting. We obtained 2x60sec + 120sec + 3x600sec in the r’ band starting at 02:55:47UT on 2025-04-28 (T0+23.3 h after the trigger). The optical afterglow reported by Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Chornock et al. GCN 40265; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272; Busmann et al. GCN 40273 is detected at a preliminar value of r = 20.3 +/- 0.15 mag (AB). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/40275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38303] EP250427a: EP-FXT follow-up observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40274 SUBJECT: EP250427a: EP-FXT follow-up observations DATE: 25/04/29 07:11:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y. Liu (NAO, CAS) behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250427a (Wang et al., GCN 40257), two follow-up observations have been conducted by EP-FXT. The first follow-up observation was performed at 2025-04-27T08:38:17 (UTC), about 5.6 hours after the trigger, with an exposure time of 4.1 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 277.2728, 7.5625 deg, with an uncertainty of about 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the column density nH fixed at the Galactic value of 3.01e21 cm^-2, and a photon index of 1.89(+0.18, -0.18). The unabsorbed 0.5-10 keV flux is 4.2 (+0.6, -0.5) e-12 erg/s/cm^2. This is consistent with the Swift-XRT refined analysis (D'Elia et al. GCN 40268). The FXT localization is consistant with the positions of the optical conterparts. The detection of the optical and IR counterpart has been reported in several GCNs (Lipunov et al. GCN 40258; Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272), and the event was also detected as the sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al. GCN 40262). And the redshift of EP240527a was measured to be 1.519 (Chornock et al. GCN 40265) or 1.520 (Saccardi et al. GCN40266). The second follow-up observation was performed at 2025-04-28T14:13:49 (UTC), about 35.1 hours after the trigger, with an exposure time of 5.9 ks. The 0.5-10 keV spectrum can also be fitted with an absorbed power-law model, with nH fixed at the Galactic value of 3.01e21cm^-2, and a photon index fixed of 1.66 (+0.44, -0.41). The unabsorbed 0.5-10 keV flux is 5.0 (+2.1, -1.3) e-13 erg/s/cm^2. All uncertainties quoted above are at the 90% confidence level. 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/40274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38302] EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40273 SUBJECT: EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart DATE: 25/04/28 17:06:44 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 counterpart of EP250427a (Wang et al., GCN 40257; Lipunov et al., GCN 40258; Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264; Saccardi et al., GCN 40266; Pérez-Fournon et al., GCN 40267; Xi et al., GCN 40269; Swain et al., GCN 40270; Magnani et al., GCN 40271; de Wet et al., GCB 40272) which was also seen as sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al., GCN 40262) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-04-28T01:48:29 UT (0.92 days after the trigger). We detect the counterpart at r = (20.17 +/- 0.03) mag i = (19.75 +/- 0.03) mag J = (18.91 +/- 0.03) mag. 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 Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40273. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38301] EP250427a: Lesedi optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40272 SUBJECT: EP250427a: Lesedi optical counterpart detection DATE: 25/04/28 13:43:45 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU space), N. Erasmus (SAAO), W.X. Li (NAOC), N.C. Sun (UCAS,NAOC) report: The SAAO 1-m Lesedi telescope located at Sutherland, South Africa, obtained 2x60 s exposures with the Mookodi low-resolution spectrograph and imager in each of the g,r and i bands of EP250427a (Wang et al., GCN 40257) beginning at 00:22:13 UTC on 2025 April 28 (0.87 days post-trigger). We detect the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Liu et al. (GCN 40260), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264), Chornock et al. (GCN 40265), Saccardi et al. (GCN 40266), Perez-Fournon et al. (GCN 40267), and Xi et al. (GCN 40269) with the following AB magnitudes: g = 20.66 +/- 0.09 r = 20.07 +/- 0.07 i = 19.69 +/- 0.08 Data was taken with the SAAO's 1-m Lesedi robotic telescope with the Mookodi low-resolution spectrograph and imager [1] as part of the SAAO “IO” rapid follow-up program [2]. We thank the SAAO IO team members including N. Erasmus, S. Potter, C. van Gend, H. Worters, S. Chandra, D. Cunnama, M. Hlakola, P. Rabe, R. Julie for making these observations possible. [1] https://doi.org/10.1117/1.JATIS.10.2.025005 [2] https://doi.org/10.1117/12.3015250 View this GCN Circular online at https://gcn.nasa.gov/circulars/40272. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38300] EP250427A: COLIBRÍ Continuing Optical Observations
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40271 SUBJECT: EP250427A: COLIBRÍ Continuing Optical Observations DATE: 25/04/28 12:30:11 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM)report: We continued our observational campaign of EP250427a (Wang et al., GCN Circ. 40257) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-28 UTC. We observed from 2025-04-28 09:16 to 2025-04-28 09:26 UTC (29.6 to 29.8 hours after the trigger) and obtained 3 stacks in filter r, i, and g, of 3 minutes each. Our observations were performed under regular weather conditions. The data were co-added with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. In the optical position (Perez-Garcia et al., GCN Circ. 40259; Liu et al., GCN Circ. 40260; Becerra et al., GCN Circ. 40261; Brivio et al., GCN Circ. 40264; Chornock et al., GCN Circ. 40265; Saccardi et al., GCN Circ. 40266; Pérez-Fournon et al., GCN Circ. 40267; and Xi et al., GCN Circ. 40269), we measured: r = 20.55 +/- 0.05 Compared to our first epoch (Becerra et al., GCN Circ. 40261), we estimate the fading nature of the OT with a temporal index ~1.2, consistent with the value reported by Swain et al. (GCN Circ. 40270). Further observations and analysis are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40271. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38299] GRB250427A/EP250427a GIT optical afterglow detection:
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40270 SUBJECT: GRB250427A/EP250427a GIT optical afterglow detection: DATE: 25/04/28 12:10:05 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Swain (IITB), A. Salgundi (IITB), Y. Wagh (IITB), A.P. Saikia (IITB), D. Eappachen (IIA), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of of EP 250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with 0.7m GROWTH-India Telescope (GIT) in g and r filters. We started the observation at 2025-04-27 19:19:43 UT, i.e., 15.68 hrs after the EP trigger. The source is detected at EP position and the position reported by TRT network (Liu et al., GRB #40260) and the photometry result follows as: | JD (mid) | t-t0 (hours) | Filter | Exposure (s) | Mag (AB) | | ----------------- | ----------- |------- | ------------------ | -------------- | | 2460793.305359 | 15.68 | r' | 360 | 19.66+/- 0.10 | | 2460793.318148 | 15.98 | g' | 360 | 20.47+/- 0.10 | | 2460793.366678 | 17.15 | r' | 360 | 20.00+/- 0.09 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The object is decaying with powerlaw index of 1.15 +/- 0.04. Further observations are under way. Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267) LT (Qiang Xi et al., GCn #40269). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38298] EP250427a: LT optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40269 SUBJECT: EP250427a: LT optical counterpart detection DATE: 25/04/28 07:34:08 GMT FROM: qiang xi <xiqiang051(a)gmail.com> Qiang Xi (UCAS), I. Pérez-Fournon, F. Poidevin, D.S. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun, Z.X. Niu (UCAS and NAOC), W.X. Li, Y.N. Wang (NAOC): We observed the field of the Einstein Probe WXT event EP250427a (Wang et al., GCN circ. 40257), using the 2.0-meter Liverpool Telescope (LT) located at the Observatorio del Roque de los Muchachos, La Palma, Spain. Observations were carried out with the IO:O instrument, starting on 2025-04-28 at 03:34UT. We obtained a series of 3x60s exposures in each of the u, g, r, i, and z filters. An uncatalogued source is clearly detected in griz bands at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (GCN circ. 40265), Saccardi et al. (GCN circ. 40266), Pérez-Fournon et al. ( GCN circ. 40267). The preliminary r-band photometry for this source is reported below, calibrated with the Pan-STARRS catalog, and not corrected for Galactic extinction. | UTC start | mag | error | filter | exposure time (sec) | | ----------------------- | ----- | ----- | ------ | ------------------- | | 2025-04-28 03:42:36.919 | 20.14 | 0.17 | SDSS-r | 3×60 | View this GCN Circular online at https://gcn.nasa.gov/circulars/40269. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 38297] GRB 250427A: Swift-XRT refined Analysis
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40268 SUBJECT: GRB 250427A: Swift-XRT refined Analysis DATE: 25/04/27 17:49:43 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> V. D'Elia (ASI-SSDC), E. Ambrosi (INAF/IASFPA), K.L. Page (U Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.7 ks of XRT data for the Einstein Probe/WXT-detected burst GRB 250427A, from 22.9 ks to 28.9 ks after the Einstein Probe/WXT trigger. The data are entirely in Photon Counting (PC) mode. We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT error region. We find an XRT position: RA, Dec = 277.27280, +7.5632 which is equivalent to: RA (J2000): 18h 29m 05.47s Dec (J2000): +07° 33′ 47.6″ with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position is 6.9 arcsec from the EP-WXT position, and consistent with the X-ray counterpart found in EP/FXT data (Wang et al. GCN 40257) and with the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264). The light curve is consistent with a constant source with a hint of fading in the last segment. However, given the corresponding optical counterpart and the measured redshift, we believe this to be the X-ray afterglow. Further observations are planned. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.78 (+0.39, -0.28). The best-fitting absorption column is consistent with the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.3 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-1.3) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.78 (+0.39, -0.28) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019750. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0