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

[vsnet-grb-info 38156] EP250227a: Further NOT optical observations
by GCN Circulars 10 Apr '25

10 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40132 SUBJECT: EP250227a: Further NOT optical observations DATE: 25/04/10 09:17:11 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> D. B. Malesani (DAWN/NBI and Radboud), J. Sanchez-Sierras (Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick), M. A. Diaz Teodori (NOT and Turku Univ.), report on behalf of a larger collaboration: We obtained ten 300-s observations in the r band of the field of the fast X-ray transient EP250227a (Wen et al., GCN 39532) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. The mid time was 2025 Apr 5.09 UT (36.9 days after the EP trigger). In Malesani et al. (GCN 39533), based on observations taken 22.4 hr after the EP trigger, we noted a possible optical transient (not consistent with the EP/FXT localisation) within the EP/WXT error circle, revealed by image subtraction using the Legacy survey as template. The new observation was obtained with the same instrument, filter, and pixel scale as our early one, in order to provide a better reference. We then carried out again image subtraction using both ISIS (Alard 2000, A&AS, 144, 363) and PyZOGY (Zackay et al. 2016, doi:10.3847/0004-637X/830/1/27). With the new template, no credible residual is detected at the position of the early optical candidate (Malesani et al., GCN 39533), which we thus consider to be spurious. We set an upper limit r > 23.8 AB to any transient within the EP/WXT error circle, at a time of 22.4 hr after the trigger. In our April 5 observation, one faint object is detected inside the EP/FXT error circle (at coordinates RA = 13:36:34.67, Dec = -13:49:23.18, magnitude r = 24.52 +- 0.23 AB). Its probability of a chance association with the X-ray localization is large. As a result, no connection to EP250227a can be established. View this GCN Circular online at https://gcn.nasa.gov/circulars/40132. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38155] GRB 250320B: cubesat Avion detection
by GCN Circulars 10 Apr '25

10 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40131 SUBJECT: GRB 250320B: cubesat Avion detection DATE: 25/04/10 08:46:40 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2025-03-20 ~23:15:22 UT the long-duration GRB 250320B (Fermi GBM detection: GCN #39792; SVOM detection: GCN #39813, AstroSat CZTI detection: GCN #39808) was detected by the DeCoR-1 instrument on the cubesat Avion of the Moscow University project “Constellation-270” [1]. Total amount of photons detected by Avion is 1350 (energy band 40-500 keV), it corresponds to a fluence of ~6*10^(-6) erg/cm^2 in the range 40-500 keV. LC in the energy range of 40-500 keV has two main episodes with a maximum flux of ~5.8 phot/(cm^2*s) in the 1st peak with a duration of ~13 s, and ~5.2 phot/(cm^2*s) in the 2nd peak with a duration of ~11 s. А total duration (T90) of the burst is ~78 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB20250320_Avion_DeCo… Parameters of GRB 250320B as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Constellation-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/40131. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38154] IceCube-250406A: Swift-XRT observations
by GCN Circulars 09 Apr '25

09 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40130 SUBJECT: IceCube-250406A: Swift-XRT observations DATE: 25/04/09 14:22:44 GMT FROM: P.A. Evans at U. Leicester <pae9(a)leicester.ac.uk> P.A. Evans (U. Leicester) and J.A. Kennea (PSU) report on behalf of the Swift-XRT team, Swift-XRT observed the field of IceCube-250406A (IceCube Collaboration, GCN 40103) between 22:21 UT on 2025 April 7 and 03:36 UT on 2025 April 8 (85 to 104 ks after the trigger), gathering 4.1 ks over 7 pointings centred on the position from the refined position notice. Three X-ray sources are detected, all of which have counterparts in the 1RXS Rosat catalogue (Voges et al., 1999) and show no sign of elecated flux compared to those data. The sources are: Source 1: Swift J052456.1+170357 at RA, Dec = 81.23375, +17.0660 which is equivalent to: RA (J2000): 05h 24m 56.10s Dec (J2000): +17d 03' 57.8" with an uncertainty of 4.7 arcsec (radius, 90% confidence), and consistent with the position of 1RXS J052456.3+170400. The mean 0.3-10 keV count-rate is 0.030 (+/-0.007) ct/sec, which corresponds to 1.3 (+/-0.3) x 10^-12 erg/cm^2/s. Source 2: Swift J052427.1+172323 at RA, Dec = 81.11301, +17.3898 which is equivalent to: RA (J2000): 05h 24m 27.12s Dec (J2000): +17d 23' 23.2" with an uncertainty of 5.7 arcsec (radius, 90% confidence), and consistent with the position of 1RXS J052425.7+172301. The mean 0.3-10 keV count-rate is 0.051 (+0.016, -0.013) ct/sec, which corresponds to 2.2 (+0.7, -0.6) x 10^-12 erg/cm^2/s. Source 3: Swift J052425.1+172240 at RA, Dec = 81.10483, +17.3780 which is equivalent to: RA (J2000): 05h 24m 25.16s Dec (J2000): +17d 22' 40.9" with an uncertainty of 8.0 arcsec (radius, 90% confidence), and consistent with the position of 1RXS J052425.7+172301 . The mean 0.3-10 keV count-rate is 0.042 (+0.015, -0.012) ct/sec, which corresponds to 1.8 (+0.6, -0.5) x 10^-12 erg/cm^2/s. Note that sources 2 and 3 correspond to the same Rosat source (due to the comparitively large Rosat position errors). In fact, neither source looks particularly point-like and both are within 30" of * 111 Tau -- a fifth magnitude BY Dra star. At this brightness the star will cause optical loading -- the detection of spurious 'X-rays' which are actually an accumulation of optical photons. We therefore view both of these sources with scepticism. A fourth source is also detected, Swift J052440.8+163236 at RA, Dec = 81.17009, 16.5435 degrees and an uncertainty of 8.4 arcsec (radius, 90% confidence). However, this is classified "poor" which corresponds approximately to a 1-sigma detection and is thus likely spurious. The full XRT analysis can be viewed online at https://www.swift.ac.uk/neutrino/NEUTRINO_FIELD00043/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40130. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38153] IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
by GCN Circulars 09 Apr '25

09 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40129 SUBJECT: IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a) DATE: 25/04/09 14:22:43 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, E. Burns on behalf of the IPN, and E. Bozzo, C. Ferrigno, and S. Mereghetti on behalf of the INTEGRAL SPI-ACS GRB team, report: The long-duration GRB 250321D was detected by Konus-Wind in the waiting mode and INTEGRAL (SPI-ACS) at about 22405 s UT (06:13:25), ~200 s after EP triggered on the fast X-ray transient EP250321a (Hu et al., GCNs 39800, 39833). We have triangulated it to a Konus-SPI-ACS annulus centered at RA(2000)=176.654 deg (11h 46m 37s) Dec(2000)=+10.352 deg (+10d 21' 08"), whose radius is 11.845 +/- 11.845 deg (3 sigma). This localization may be improved. EP250321a is inside the annulus and is consistent with the Konus-Wind ecliptic latitude response, lending support to the association of GRB 250321D and the transient. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB250321_T22405/IPN/ The burst time history and spectrum will be given in forthcoming GCN circulars. View this GCN Circular online at https://gcn.nasa.gov/circulars/40129. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38152] AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
by GCN Circulars 09 Apr '25

09 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40128 SUBJECT: AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A DATE: 25/04/09 12:52:44 GMT FROM: Hugo Ayala at Pennsylvania State University <hgayala(a)psu.edu> The AMON, IceCube, and HAWC collaborations report: The AMON NuEm stream channel found a coincidence alert from the IceCube online neutrino selection + HAWC daily monitoring analysis. The analysis looks for IceCube neutrino events -mostly atmospheric in origin- around the position and transit time of a HAWC cluster of likely gamma rays, as identified in the integrated observations from a single transit, in this case having a duration of 6.06 hours. The HAWC transit interval starts from 2025/04/09 04:21:14 UT to 2025/04/09 10:39:53 UT. A total of 6.3 hrs of integrated HAWC time. The location of the coincidence is reported as RA (J2000): 212.8 deg Dec (J2000): 17.2 deg Location uncertainty (50% containment): 0.25 deg (statistical only). Location uncertainty (90% containment): 0.46 deg (statistical only). The false alarm rate (FAR) of this coincidence is 1.05 per year. We encourage follow-up observations of the alert region contingent on the availability of resources and interest, given the quoted FAR. The source 4FGL J1406.9+1643 is the closest to the best position of the coincidence, with a distance of around 1deg. AMON seeks to perform a real-time correlation analysis of the high-energy signals across all known astronomical messengers. More information about AMON can be found in https://www.amon.psu.edu/ Information on the IceCube collaboration: http://icecube.wisc.edu/ Information on the HAWC collaboration: https://www.hawc-observatory.org View this GCN Circular online at https://gcn.nasa.gov/circulars/40128. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38151] IPN triangulation of GRB 250407A
by GCN Circulars 09 Apr '25

09 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40127 SUBJECT: IPN triangulation of GRB 250407A DATE: 25/04/09 07:14:45 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the MGNS/BepiColombo team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team, report: The very bright, long-duration GRB 250407A (Fermi-GBM detection: The Fermi GBM team, GCN 40104; Mukherjee and Meegan, GCN 40114; BALROG localization: Preis et al., GCN 40105; SVOM-GRM detection: Wang et al., GCN 40120; Konus-Wind detection: Ferderiks et al., GCN 40121) was detected by Fermi (GBM trigger 765733706), Konus-Wind, and BepiColombo (MGNS) at about 56901 s UT (15:48:21). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 110.410 (07h 21m 38s) +35.618 (+35d 37' 06") Corners: 111.023 (07h 24m 05s) +37.563 (+37d 33' 48") 111.028 (07h 24m 07s) +37.670 (+37d 40' 12") 109.794 (07h 19m 10s) +33.403 (+33d 24' 09") 109.787 (07h 19m 09s) +33.265 (+33d 15' 53") --------------------------------------------- The error box area is 364 sq. arcmin, and its maximum dimension is 4.52 deg (the minimum one is 1.4 arcmin). The Sun distance was 89 deg. This localization may be improved. The IPN localization is consistent with, but reduces the area of, the Fermi-GBM final (GCN 40104) and BALROG (GCN 40105) localizations. The X-ray transient detected by SRG-ART-XC (GCN 40110) and Swift-XRT (GCN 40113) is inside the box, which further strengthen the interpretation of the transient as the burst afterglow. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/IPN View this GCN Circular online at https://gcn.nasa.gov/circulars/40127. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38150] EP250407a: Global MASTER-Net observations report
by GCN Circulars 08 Apr '25

08 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40126 SUBJECT: EP250407a: Global MASTER-Net observations report DATE: 25/04/08 23:27:52 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250407a ( EP Team et al., GCN 40118) errorbox 49972 sec after notice time and 85240 sec after trigger time at 2025-04-08 23:08:03 UT, with upper limit up to 18.5 mag. Observations started at twilight. The observations began at zenith distance = 18 deg. The sun altitude is -10.6 deg. The galactic latitude b = 5 deg., longitude l = 262 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2836941 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 85271 | 2025-04-08 23:08:03 | MASTER-OAFA | (08h 59m 01.05s , -38d 53m 39.6s) | C | 60 | 18.2 | 85448 | 2025-04-08 23:11:01 | MASTER-OAFA | (08h 59m 05.07s , -38d 53m 10.9s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40126. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38149] GRB 250407A: LCO detection of a fading optical counterpart
by GCN Circulars 08 Apr '25

08 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40125 SUBJECT: GRB 250407A: LCO detection of a fading optical counterpart DATE: 25/04/08 21:48:17 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) Following the detection by Fermi GBM of the bright and likely long Gamma-Ray Burst GRB 250407A (Fermi GBM team, GCN circ. 40104; Preis and Greiner, GCN circ. 40105; and Mukherjee et al., GCN circ. 40114) and the associated X-ray afterglow by SRG/ART-XC (Molkov et al., GCN circ. 40110), we observed the field with the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Teide Observatory (Tenerife, Spain) in the SDSS g, r, and i filters. The observations started at 2025-04-07 21:06:04 UTC, about 5.29 hours after the Fermi trigger. We detect the optical afterglow in the r and i filters, but not in the g filter, at the position reported by Zheng and Filippenko (GCN circ. 40116) and Ducoin et al. (GCN circ. 40117), that is consistent within the errors with the SRG/ART-XC (Molkov et al., GCN circ. 40110), Swift-XRT (Dichiara et al., GCN circ. 40113) and EP-WXT (Zheng et al., GCN circ. 40119) X-ray afterglow positions. GRB 250407A has also been detected by SVOM/GRM (Wang et al., GCN circ. 40120) and Konus-Wind (Frederiks et al., GCN circ. 40121). A fading of the optical brightness between our LCOGT observations and those of KAIT (Zheng and Filippenko, GCN circ. 40116) and COLIBRÍ/DDRAGO (Ducoin et al., GCN circ. 40117) is detected. We measure the following preliminary r and i magnitudes and limiting (5-sigma) g-band magnitude, calibrated against Pan-STARRS DR2 stars, that are not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | limiting magnitude (5 sigma) ------------------------------------------------------------------------------------------------------ 2025-04-07 21:06:04 19.67 0.11 r 300 ----- 2025-04-07 21:10:26 ----- ---- g 180 20.45 2025-04-07 22:01:01 19.92 0.20 r 180 ----- 2025-04-07 22:15:32 19.53 0.19 i 180 ----- This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40125. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38148] Fermi-LAT gamma-ray observations of IceCube-250406A
by GCN Circulars 08 Apr '25

08 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40124 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250406A DATE: 25/04/08 19:44:10 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), C. Bartolini (INFN Bari), 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 IC250406A neutrino event (GCN 40103) 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 2025-04-06 at 22:50:35.34 UTC (T0) with J2000 position RA = 81.47 (+0.54, -0.53) deg, Decl. = 16.96 (+0.42, -0.50) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250406A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, 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 (>5sigma) new excess emission (> 100 MeV) within the IC250406A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250406A best-fit position, the >100 MeV flux upper limit (95% confidence) is <1.72e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <2.13e-08 (<1.58e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. The closest catalogued gamma-ray source to the IC250406A best-fit position is 4FGL J0521.2+1637 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), associated with the compact steep spectrum quasar 3C 138, located approximately 1.15° away from the IceCube event, outside the 90% neutrino localization region. Since October 2024, the source has exhibited strong and prolonged gamma-ray flaring activity (see ATel #16845, ATel #17107). A preliminary analysis confirms that this enhanced activity is ongoing, with a daily averaged gamma-ray flux (E > 100 MeV) of (0.39± 0.29) × 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), as observed on April 6, 2025. This represents an increase in flux by a factor of approximately 93 compared to the average flux reported in the 4FGL-DR4. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, 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/40124. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38147] EP250407a: Swift-XRT observations
by GCN Circulars 08 Apr '25

08 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40123 SUBJECT: EP250407a: Swift-XRT observations DATE: 25/04/08 19:20:26 GMT FROM: Maia Williams at PSU <mjw6837(a)psu.edu> M. A. Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analyzed 2100 s of XRT data for the recently reported transient EP250407a (GCN #40118), from T0+36.5 ks to T0+42.4 ks after detection by Einstein Probe WXT. The data are entirely in Photon Counting (PC) mode. No X-ray sources have been detected within the estimated 90% EP-WXT error region (2.5 arcmin), with an upper limit on count rate of 5.3 × 10^-3 ct/s. For a typical GRB-like spectrum, this equates to an upper limit on flux of 2 x 10^-13 erg/s/cm^2 (0.3-10 keV). The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/EP/EP_FIELD00033/. View this GCN Circular online at https://gcn.nasa.gov/circulars/40123. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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