EP241021a
GCN Circular 38924
Subject
EP241021a: SMA radio observation
Date
2025-01-13T15:44:13Z (9 months ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
Amar Aryan (Graduate Institute of Astronomy, National Central University, Taiwan),Giorgos Michailidis (Aristotle University of Thessaloniki, Greece), Sourya Ranjan Das (Indian Institute of Space Science and Technology, India), Bhushan Kayastha (University of Chinese Academy of Sciences, China), Garrett K. Keating (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA), and Joshua Bennett Lovell (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA) report:
We observed the field of the fast X-ray Transient EP 241021a (Hu et al. GCN 37834) with the Submillimeter Array (SMA) under program 2024B-S052 (PI: G. Keating) starting on 2024 Dec 25 at 03:13:33 UTC (64.92 days after the EP trigger) for 8.63 hours. Our observations were performed in “dual receiver mode”. We use "Uranus" as flux calibrator, "3c84" as bandpass calibrator and "0224+069" as gain calibrator.
We did not find statistically significant emission at the position of the optical counterpart discovered by Fu et al. (GCN 37840, 37842), and the corresponding radio counterpart reported by Ricci et al. (GCN 37949), Carotenuto et al. (GCN 38014) and Schroeder et al. (GCN 38640). Thus, we estimate a 3-sigma upper limit of ~ 0.8 mJy at 235 GHz.
We thank the the organizers of 2025 Submillimeter Array Interferometry School and the SMA observing staffs for scheduling and executing these observations. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. We recognize that Maunakea is a culturally important site for the indigenous Hawaiian people; we are privileged to study the cosmos from its summit.
GCN Circular 38640
Subject
EP241021a: VLA radio detection
Date
2024-12-19T20:19:55Z (10 months ago)
From
Genevieve Schroeder at Northwestern University <genevieveschroeder@u.northwestern.edu>
Via
Web form
G. Schroeder (Cornell), G. Srinivasaragavan (UMD), A. Ho (Cornell), D. Perley (LJMU), I. Andreoni (UNC), B. Cenko (GSFC), T. Ahumada (Caltech), M. Coughlin (UMN), report:
We observed the field of the fast X-ray Transient EP 241021a (Hu et al. GCN 37834) with the Karl G. Jansky Very Large Array (VLA) under program 24B-497 (PI: Srinivasaragavan) starting on 2024 Dec 14 at 01:36:13 UTC (53.84 days after the EP trigger) for 1.5 hours at mean frequencies of 3, 6, 10, 15, and 33 GHz. The radio counterpart to EP 241021a (Ricci et al. GCN 37949; Carotenuto et al. GCN 38014) is significantly detected in all bands, with a 10 GHz flux density of ~880 microJy at a position of:
RA(J2000) = 01:55:23.432
Dec(J2000) = +05:56:17.82
with an uncertainty of ~0.1" in each coordinate. This position is consistent with the optical (Fu et al. 37840) and X-ray (Wang et al. GCN 37848) positions.
We thank the VLA staff for scheduling and executing these observations.
GCN Circular 38294
Subject
EP241021a and EP241026b: Keck/LRIS spectroscopic observations
Date
2024-11-22T03:40:03Z (a year ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng, Thomas G. Brink, Alexei V. Filippenko (UC Berkeley), and Yi
Yang (Tsinghua Univ., Beijing), report on behalf of the KAIT GRB team:
We observed the field of both EP241021a (Hu et al., GCN 37834) and
EP241026b (Lian et al., GCN 37902) with the Low Resolution Imaging
Spectrometer (LRIS; Oke et al. 1995) on the Keck I 10 m telescope.
Observations were performed on Oct. 30, 2024 UTC, with the 600/4000 grism
and 400/8500 grating.
The optical counterpart of EP241021a (Fu et al., GCNs 37840, 37842; Li et
al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849;
Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852;
Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869; Kumar et
al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892;
Freeburn et al., GCNs 37911, 37942, Quirola-Vasquez et al., GCN 37930;
Freeburn et al., GCN 37942; Moskvitin et al., GCN 37951; Pan et al., GCN
37968; Klingler et al., GCN 37990; Carotenuto et al., GCN 38014; Schneider
et al., GCN 38022; Bochenek et al., GCN 38030; Svinkin et al., GCN 38034;
Aryan et al., GCN 38042; Freeburn et al., GCN 38062; Schneider et al., GCN
38071) was reported to be rebrightening (Quirola-Vasquez et al., GCN 37930;
Freeburn et al., GCN 37942; Moskvitin et al., GCN 37951; Pan et al., GCN
37968) before our observation. The spectrum of EP241021a shows a
well-detected continuum throughout the complete range (3400-10,200 Ang)
with 2 x 1200 s exposure time. We clearly detect emission lines of [O II]
3727 Ang, H_beta, and [O III] 4959, 5007 Ang at a redshift of 0.748. We
also detect absorption lines of the Mg II 2796, 2803 Ang doublet at the
same redshifts of 0.748. Two additional sets of Mg II 2796, 2803 Ang
doublets are also detected with slightly lower signal-to-noise ratio (S/N)
at redshifts of 0.48 and 0.62. Our results are consistent with those
reported by Pugliese et al. (GCN 37852) and Pérez-Fournon et al. (GCN
37858).
The reported possible LBT optical counterpart of EP241026b (Rossi et al.,
GCN 37938) was confirmed by Bochenek et al. (GCN 38018). Our spectrum shows
weak traces with 3 x 1200 s exposure time, but still has low S/N owing to
the faintness of the counterpart. We detect the continuum throughout the
complete range (3400-10,200 Ang), but no obvious emission nor absorption
lines are detected. The continuum is detected at ~3400 Ang, suggesting an
upper limit of 1.8 for the redshift.
The data presented herein were obtained at the W. M. Keck Observatory,
which is operated as a scientific partnership among the California
Institute of Technology, the University of California, and the National
Aeronautics and Space Administration. The Observatory was made possible by
the generous financial support of the W. M. Keck Foundation. The authors
wish to recognize and acknowledge the very significant cultural role and
reverence that the summit of Maunakea has always had within the indigenous
Hawaiian community. We are most fortunate to have the opportunity to
conduct observations from this mountain.
GCN Circular 38071
Subject
EP241021a: OHP/T193 further optical observations
Date
2024-11-04T12:48:00Z (a year ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
Benjamin Schneider (MIT), Christophe Adami (LAM/Pytheas/AMU) report on behalf of a larger collaboration:
We re-observed the field of EP241021a (Hu et al., GCN 37834) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. A total of 120 min of exposure (12x600s) were obtained in the r-band starting at 20:29 UT on 2024-11-03 (13.7 days post-trigger). The optical transient is still clearly detected in our stacked image (Fu et al., GCNs 37840, 37842; Li et al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849; Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869; Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892; Freeburn et al., GCNs 37911, 37942, Quirola-Vasquez et al., GCN 37930; Freeburn et al., GCN 37942; Moskvitin et al., GCN 37951; Pan et al., GCN 37968; Klingler et al., GCN 37990; Carotenuto et al., GCN 38014; Schneider et al., GCN 38022; Bochenek et al., GCN 38030; Svinkin et al., GCN 38034; Aryan et al., GCN 38042; Freeburn et al., GCN 38062).
The preliminary magnitude derived for the source is
r = 22.53 +/- 0.12 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 Observatoire de Haute-Provence and in particular Stephane Favard for the MISTRAL observations.
GCN Circular 38062
Subject
EP241021a: continued SOAR observations
Date
2024-11-03T15:45:48Z (a year ago)
From
James Freeburn at Swinburne University of Technology <jamesfreeburn54@gmail.com>
Via
Web form
J. Freeburn (Swinburne/OzGrav), I. Andreoni (UNC)
We continued our observations (Freeburn et al., GCNs 37911, 37942) of the field of EP241021a (Hu et al., GCN 37834) with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode (Prop. ID: SOAR2024B-023). We took two 300s exposures each in g, r and i-band between 2024-11-03T02:16:11 and 2024-11-03T02:50:11 UTC.
We detect the optical counterpart associated with EP241021a (Fu et al., GCN 37842; Li et al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849; Moskvitin and Spiridonova, GCN 37850; Pugliese et al. GCN 37852; Pérez-Fournon et al. GCN 37858, Bochenek & Perley, GCN 37869; Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892; Freeburn et al., GCNs 37911, 37942; Quirola-Vasquez et al., GCN 37930; Freeburn et al., GCN 37942; Moskvitin et al. GCN 37951; Pan et al., GCN 37968; Bochenek and Perley, GCN 38030; Klingler et al., GCN 37990; Carotenuto et al., GCN 38014; Schneider et al., GCN 38022; Aryan et al., GCN 38042) in g, r and i-bands. With photometric calibration using the Pan-STARRS1 catalogue, with an r=2.5” aperture, we measure r~22.4 AB mag, with a red color g-r~0.2 mag.
GCN Circular 38034
Subject
EP241021a: Upper limit from Konus-Wind observations
Date
2024-11-01T13:52:02Z (a year ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
Konus-Wind (KW) was observing the whole sky at the time of the
detection of a fast X-ray transient EP241021a (2024-10-21 05:07:56 UTC,
hereafter T0; Hu et al., GCN 37834).
Using waiting-mode data within the interval T0 +/- 1000 s,
we found no significant (> 5 sigma) excess over the background
in S1 KW detector, with smallest incident angle,
on temporal scales from 2.944 s to 1000 s.
We estimate an upper limit (90% conf.) on the 20 - 1500 keV peak flux
to 2.5x10^-7 erg/cm^2/s for a typical long GRB spectrum
(the Band function with alpha=-1, beta=-2.5, and Ep=300 keV) and 2.944 s timescale.
All the quoted values are preliminary.
GCN Circular 38030
Subject
EP241021a: Liverpool Telescope optical follow-up observations
Date
2024-11-01T10:33:17Z (a year ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP241021a (Hu et al., GCN 37834) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x200s exposures in the SDSS r’ filter starting at 2024-10-31 23:32:50 UT, approximately 10.77 days after the trigger.
We report a detection in the stacked images of r = 21.95 ± 0.08 mag, consistent with the observations from Schneider et al. (GCN 38022) from the same night, at a position for the optical counterpart reported by Fu et al. (GCN 37840) and other optical observations (Fu et al., GCN 37842; Li et al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849; Moskvitin and Spiridonova, GCN 37850; Pugliese et al. GCN 37852; Pérez-Fournon et al. GCN 37858, Bochenek & Perley, GCN 37869; Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892; Freeburn et al., GCNs 37911, 37942, Quirola-Vasquez et al., GCN 37930; Freeburn et al., GCN 37942; Moskvitin et al. GCN 37951; Pan et al., GCN 37968; Klingler et al., GCN 37990; Carotenuto et al. GCN 38014, Schneider et al. GCN 38022).
The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction.
GCN Circular 38022
Subject
EP241021a: OHP/T193 optical observations
Date
2024-11-01T00:10:43Z (a year ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
Benjamin Schneider (MIT), Christophe Adami (LAM/Pytheas/AMU) report on behalf of a larger collaboration:
We observed the field of EP241021a (Hu et al., GCN 37834) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. A total of 55 min of exposure (1x300s + 5x600s) were obtained in the r-band starting at 21:11:05 UT on 2024-10-31 (~10.7 days after the trigger). The optical transient and its rebrightening (Fu et al., GCNs 37840, 37842; Li et al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849; Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869; Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892; Freeburn et al., GCNs 37911, 37942, Quirola-Vasquez et al., GCN 37930; Freeburn et al., GCN 37942; Moskvitin et al. GCN 37951; Pan et al., GCN 37968; Klingler et al., GCN 37990; Carotenuto et al. GCN 38014) is clearly detected in our stacked image.
The preliminary magnitude derived for the source is
r = 22.01 +/- 0.05 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 Observatoire de Haute-Provence and in particular Jean Balcaen for the MISTRAL observations.
GCN Circular 38014
Subject
EP241021a: AMI-LA radio detection
Date
2024-10-31T15:13:01Z (a year ago)
From
Francesco Carotenuto at University of Oxford <francesco.carotenuto@physics.ox.ac.uk>
Via
Web form
F. Carotenuto (INAF/OAR), J. Bright (Oxford), R. Fender (Oxford)
After the first radio detection with ATCA (Ricci et al. GCN 37949), we observed the Fast X-ray Transient EP241021a (Hu et al. GCN 37834; Fu et al. GCN 37840, Wang et al. GCN 37848) with the Arcminute MicroKelvin Imager - Large Array for a total of 4.7 hours starting on 30 October 2024 at 20:59:50.7 UTC. 3C286 and J0149+0555 were used as flux and time dependent complex gain calibrators, respectively.
We obtained a significant detection of the target with a flux density of ~450 uJy/beam at a central frequency of 15.5 GHz. The rms noise in the field is ~75 uJy/beam. Further AMI-LA observations are planned.
We thank the Mullard Radio Astronomy Observatory staff for operating and maintaining the AMI-LA.
GCN Circular 37990
Subject
EP241021a: Swift-UVOT detection
Date
2024-10-30T23:11:48Z (a year ago)
From
noelklin@umbc.edu
Via
Web form
N. Klingler (UMBC & NASA-GSFC), S. R. Oates (Lancaster Univ.), and R. Eyles-Ferris (Univ. of Leicester) report on behalf of the Swift-UVOT team:
Swift has performed a follow-up observation of EP 241021a, following the optical re-brightening reported by Quirola-Vasquez et al. (GCN 37930).
Swift-UVOT observed the source in the U-band for 4.3 ks, between 2024-10-29 09:32:55 UTC and 2024-10-29 17:19:10 UTC, which corresponds to t0 + 8.18 days and t0 + 8.51 days, respectively. A source is detected at the position of the optical transient (01:55:23.41 +05:56:18.01; Fu et al.; GCN 37840) with (AB) magnitude U = 21.83 +/- 0.23, and a detection significance of 5.2 sigma. No correction has been made for the expected extinction corresponding to E(B-V) of 0.052.
This circular is an official product of the Swift-UVOT team.
GCN Circular 37973
Subject
EP 241021a: further Swift-XRT observations and X-ray counterpart detection
Date
2024-10-30T14:47:43Z (a year ago)
From
Valerio D'Elia at ASDC <valerio.delia@ssdc.asi.it>
Via
Web form
V. D’Elia (ASI-SSDC & INAF-OAR) reports on behalf of the Swift-XRT team:
After the rebrightening reported by Quirola-Vasquez et al. (GCN 37930) 6.7 day post trigger, a further Swift follow-up observation was performed.
The observation was secured between 8.1 and 8.5 days after the EP detection (Hu et al., GCN 37834). The new dataset has an exposure of 4.4 ks. An X-ray source is now detected at the position of the optical transient (see, e.g., Fu et al., GCN 37840) with a S/N of about 3. The count rate of the X-ray counterpart is (3+/-1)E-3 cts s^-1, corresponding to a 0.3-10 keV
observed flux of (1.3+/-0.4)E-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).
This circular is an official product of the Swift-XRT team.
GCN Circular 37968
Subject
EP241021a: Optical rebrightening observations with Mephisto
Date
2024-10-30T13:21:56Z (a year ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Yu Pan, Brajesh Kumar, Weikang Lin, Guowang Du, Yangwei Zhang, Tao Wang, Runnan Jiang, Yaosong Yu, Xingzhu Zou, Xinlei Chen, Jinghua Zhang, Yuanpei Yang, Yuan Fang, Yehao Cheng, Chenxu Liu, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
We observed the field of EP241021a (Hu et al., GCN 37834) on 2024-10-29 with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Two frames of 300s were acquired in uvgriz bands between 15:10:34 to 15:36:22 UT. The OT (Fu et al., GCNs 37840, 37842; Li et al., GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849; Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869; Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al., GCN 37892; Freeburn et al., GCNs 37911, 37942;) for which rebrightening was noticed by Quirola-Vasquez et al., (GCN 37930), Freeburn et al., (GCN 37942), and Moskvitin et al. (GCN 37951) is clearly detected in our stacked r band image with 21.9 +/- 0.2 mag (2024-10-29T15:15:40, Mid-Exp-Time). The limiting magnitudes in other bands are provided below. Further Mephisto observations are planned.
Mid-Time(UT) Band Exp(s) Lim-mag(AB)
2024-10-29T15:31:10 u 300x2 >22.64
2024-10-29T15:15:41 v 300x2 >22.65
2024-10-29T15:31:09 g 300x2 >23.14
2024-10-29T15:31:12 i 300x2 >22.12
2024-10-29T15:15:44 z 300x2 >21.11
--------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
--------------------------------------------------------------------------
GCN Circular 37951
Subject
EP241021a: SAO RAS observations of rebrightening
Date
2024-10-30T00:33:38Z (a year ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
legacy email
A. S. Moskvitin and O. I. Spiridonova (SAO RAS), report
on behalf of the GRB follow-up team.
We observed the field of X-ray transient EP241021a (Hu et al.,
GCN 37834) with the 1-m telescope of SAO RAS, Zeiss-1000
equipped with the CCD-photometer on October 28 and 29.
We detect the OT (Fu et al., GCNs 37840, 37842; Li et al.,
GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849;
Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852;
Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869;
Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al.,
GCN 37892; Freeburn et al., GCNs 37911, 37942; Quirola-Vasquez et al.,
GCN 37930) in rebrightening state with the following results.
date UT_start--UT_end t_mid-T0 exp, s R magnitude R_lim
Oct. 28 19:41:42--23:00:33 7.6758 15 x 300 21.57 +/- 0.08 23.0
Oct. 29 19:55:32--21:03:35 8.6400 12 x 300 21.64 +/- 0.05 23.6
Preliminary photometry was performed in the aperture with r = 2".5,
calibrated against nearby SDSS stars (magnitudes converted with
Lupton 2005 equations) and not corrected for the Galactic extinction.
GCN Circular 37949
Subject
EP241021a: ATCA radio observations
Date
2024-10-29T23:33:50Z (a year ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
R. Ricci (U Rome/INAF-IRA), G. Bruni (INAF-IAPS), F. Carotenuto (U Oxford), , G. Gianfagna (INAF-IAPS), Y. Yao (UC Berkeley) on behalf of a larger group:
We observed the Fast X-ray Transient EP241021a discovered by Einstein Probe (Hu et al. GCN 37834; Wang et al. GCN 37848) at the optical counterpart position (Fu et al. 37840) with the Australia Telescope Compact Array at 5.5 and 9 GHz in continuum mode on Oct 29th 11:00-18:00 UT (i.e. 8.40 days after the EP trigger) under four independent projects.
A bright source was detected at 5.5 GHz with with a flux density of 400 +/- 20 microJy
at the OT position. The rms noise in the final map is 13 microJy/beam.
Further observations are planned.
The observers thank the ATCA staff for promptly scheduling the observations.
GCN Circular 37942
Subject
EP241021a: continued SOAR observations confirm optical rebrightening
Date
2024-10-29T17:04:36Z (a year ago)
From
James Freeburn at Swinburne University of Technology <jamesfreeburn54@gmail.com>
Via
Web form
J. Freeburn (Swinburne/OzGrav), I. Andreoni (UNC), Jonathan Carney (UNC)
We continued our observations (Freeburn et al., GCN 37911) of the field of EP241021a (Hu et al., GCN 37834) with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode (Prop. ID: SOAR2024B-021). We took four 300s exposures each in r and i-band and eight 300s exposures in g-band between 2024-10-28T03:58:11 and 2024-10-28T05:23:16 UTC.
We detect the optical counterpart associated with EP241021a (Fu et al., GCN 37840; Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869; Kumar et al., GCN 37875; Jin et al., GCN 37892; Moskvitin and Spiridonova, GCN 37910; Freeburn et al., GCN 37911; Quirola-Vasquez et al., GCN 37930) at high significance in g, r and i-bands. With photometric calibration using the Pan-STARRS1 catalogue, with an r=2.5” aperture, we measure r~21.96 AB mag, with a red color g-i~0.4 mag. Our results are consistent with Quirola-Vasquez et al., GCN 37930 in that they show an optical rebrightening.
GCN Circular 37930
Subject
EP241021a: Gemini-South detection of optical rebrightening
Date
2024-10-28T15:35:47Z (a year ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
J. A. Quirola-Vasquez (Radboud Univ.), D. B. Malesani (DAWN/NBI & Radboud Univ.), A. J. Levan (Radboud), F. E. Bauer (PUC), P. G. Jonker (Radboud Univ.), report on behalf of a larger collaboration:
We observed the optical counterpart of EP241021a (Fu et al., GCN 37840; Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869; Kumar et al., GCN 37875; Jin et al., GCN 37892), using the Gemini-South (GS) telescope equipped with the GMOS instrument.
We obtained 4x180 s exposures in the r-band, starting on 2024-10-28 at 00:21:06 UT, i.e., approximately ~6.8 days after the X-ray trigger. We detect the source at an r-band magnitude of ~21.90 AB mag, calibrated against nearby Pan-STARRS objects. Compared to both reports from the literature (e.g., Bochenek & Perley, GCN 37869; Busmann et al., GCN 37878) and our own data, this shows that the source has brightened. Such a brightening is reminiscent of that shown by EP240414a (Shubham et al. 2024, arXiv:2409.19070; van Dalen et al. 2024, arXiv:2409.19056), though occurring at a slightly later epoch.
We thank the staff of the Gemini-South for excellent support.
GCN Circular 37911
Subject
EP241021a: SOAR observations of the optical counterpart
Date
2024-10-27T15:21:13Z (a year ago)
From
James Freeburn at Swinburne University of Technology <jamesfreeburn54@gmail.com>
Via
Web form
J. Freeburn (Swinburne/OzGrav), I. Andreoni (UNC), J. Quirola-Vasquez (Radboud Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), F. E. Bauer (PUC), P. G. Jonker (Radboud Univ)
We observed the field of EP241021a (Hu et al., GCN 37834) with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode (Prop. ID: SOAR2024B-021, SOAR2024B-016). We took four 300s exposures i-band between 2024-10-27T04:56:18 and 2024-10-27T05:16:54 UTC.
We detect the optical counterpart associated with EP241021a (Fu et al., GCN 37840; Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869; Kumar et al., GCN 37875; Jin et al., GCN 37892). With photometric calibration using the Pan-STARRS1 catalogue, we measure an r=2.5” aperture magnitude of:
i = 22.355 +/- 0.066 AB mag
GCN Circular 37910
Subject
EP241021a: further SAO RAS optical observations
Date
2024-10-27T15:01:01Z (a year ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
legacy email
A. S. Moskvitin and O. I. Spiridonova (SAO RAS), report
on behalf of the GRB follow-up team.
We observed the field of X-ray transient EP241021a (Hu et al.,
GCN 37834) with the 1-m telescope of SAO RAS equipped with
CCD-photometer. We obtained 12 x 300 sec. images in Rc band
on October 26, 20:39:47--21:53:44 UT (t_mid - T0 = 5.6728 days).
We detect the OT (Fu et al., GCNs 37840, 37842; Li et al.,
GCNs 37844, 37846; Ror et al., GCN 37845; Zheng et al., GCN 37849;
Moskvitin & Spiridonova, GCN 37850; Pugliese et al., GCN 37852;
Pérez-Fournon et al., GCN 37858; Bochenek & Perley, GCN 37869;
Kumar et al., GCN 37875; Busmann et al., GCN 37877; J-Jin et al.,
GCN 37892) in our stacked frame with the brightness of
R = 23.10 +/- 0.18 calibrated against nearby SDSS stars
(magnitudes converted with Lupton 2005 equations)
and not corrected for the Galactic extinction.
GCN Circular 37906
Subject
EP241021a: e-MERLIN radio observation
Date
2024-10-27T10:44:05Z (a year ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
G. Gianfagna, G. Bruni, L. Piro, A.L. Thakur (INAF-IAPS) report:
We observed the new Fast X-ray Transient EP241021a (Hu et al., GCN 37834) with the e-MERLIN radio telescope under the project CY18212 (PI: Gianfagna) at 5 GHz starting on Oct. 24, 16:44 UT (~3 days after the EP trigger, GCN 37834) for a total of ~11 hours.
1331+3030 was used for flux scale calibration, and 0154+0823 for complex gain. The beam size was 104x36 milli-arcsec. Data were reduced with the e-MERLIN pipeline and imaged with CASA. The image RMS was 45 uJy/beam.
We did not find statistically significant emission at a level above 5-sigma at the position of the optical counterpart reported by Fu et al. (GCN 37840, 37842), Li et al. (GCN 37844, 37846), Ror et al. (GCN 37845), Zheng et al. (GCN 37849), Moskvitin & Spiridonova (GCN 37850), Bochenek et al. (GCN 37869), Kumar (GCN 37875), Busmann (GCN 37877), Jin et al. (GCN 37892). Thus, we estimate a 5-sigma upper limit of ~ 0.2 mJy at 5 GHz. Further e-MERLIN observations are planned.
We thank the e-MERLIN staff, particularly David Williams, for the prompt scheduling and excellent support with these observations. e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC, part of UK Research and Innovation.
GCN Circular 37892
Subject
EP241021a: optical follow-up observations with Xinglong Observatory
Date
2024-10-26T14:05:37Z (a year ago)
Edited On
2024-10-28T13:49:36Z (a year ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Edited By
Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov> on behalf of Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
J.J-Jin(NAOC),H.Y. Mu(NAOC), Z.F(NAOC),Y.G. Sun, S.L, R.Wang Y.M Mao report on behalf of a large collaboration:
Following the detection of EP241021a by EP-WXT (Hu et al., GCN 37834), we observed the field of EP241021a using the 80-cm telescope at Xinglong Observatory, NAOC. We obtained 3x600s g-band frames with a median time of 2024-10-22T15:25:50 i.e., 34 hr after the EP trigger.No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle.
Then we performed photometry on the Xinglong 2.16-m telescope with a median time of 2024-10-23T15:57:29 i.e., 58 hr after the EP trigger, and obtained 3x600s V-band frames.
Within the error circle of the EP/WXT, we we detected the optical counterpart of EP241021a, at a position matching the optical counterpart identified by Fu et al., GCN 37840 (see also Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869; Kumar et al., GCN 37875).
We performed aperture photometry on the stacked g and V-band images and calibrated them with Pan-STARRS sources in the field. The observed magnitudes are as follows:
Date_obs | Telescope| UT | Exp. Time | Filter | Mag | Mag_err
----------------------------------------------------------------------------------------
2024-10-22 | 80-cm | 15:25:50 | 3x600s | g | *21.51 | 0.032
2024-10-23 | 216-cm | 15:57:29 | 3x600s | V | 22.468 | 0.477
GCN Circular 37878
Subject
EP241021a: Optical and NIR observations of counterpart with the Fraunhofer Telescope at Wendelstein Observatory
Date
2024-10-25T15:06:09Z (a year ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), Antonella Palmese (Carnegie Mellon U.) and Michael Schmidt (LMU) report:
We observed the counterpart of EP241021a (Hu et al., GCN 37834; Fu et al., GCN 37840) with the 3KK imager at the Fraunhofer Telescope Wendelstein in rzJ simultaneously for 11 x 180 s starting on 2024-10-24T02:12:17 UT (2.88 days after the trigger) and 40 x 180 s starting on 2024-10-24T23:42:00 (3.77 days after the trigger).
The counterpart is marginally detected in the first observations and clearly visible in the second round of observations in all bands. At 3.77 days after the trigger, the counterpart is at r=22.49+/-0.05 mag (not corrected for Galactic extinction) which is consistent with previous reports from Fu et al., GCN 37840; Fu et al., GCN 37842; Li et al., GCN 37844; Ror et al., GCN 37845; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin and Spiridonova, GCN 37850; Pugliese et al., GCN 37852.
We thank the staff of the Wendelstein Observatory for obtaining these observations.
GCN Circular 37877
Subject
EP241021a: Optical and NIR observations of counterpart with the Fraunhofer Telescope at Wendelstein Observatory
Date
2024-10-25T15:06:05Z (a year ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), Antonella Palmese (Carnegie Mellon U.) and Michael Schmidt (LMU) report:
We observed the counterpart of EP241021a (Hu et al., GCN 37834; Fu et al., GCN 37840) with the 3KK imager at the Fraunhofer Telescope Wendelstein in rzJ simultaneously for 11 x 180 s starting on 2024-10-24T02:12:17 UT (2.88 days after the trigger) and 40 x 180 s starting on 2024-10-24T23:42:00 (3.77 days after the trigger).
The counterpart is marginally detected in the first observations and clearly visible in the second round of observations in all bands. At 3.77 days after the trigger, the counterpart is at r=22.49+/-0.05 mag (not corrected for Galactic extinction) which is consistent with previous reports from Fu et al., GCN 37840; Fu et al., GCN 37842; Li et al., GCN 37844; Ror et al., GCN 37845; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin and Spiridonova, GCN 37850; Pugliese et al., GCN 37852.
We thank the staff of the Wendelstein Observatory for obtaining these observations.
GCN Circular 37876
Subject
EP 241021a: Swift-XRT observations
Date
2024-10-25T14:42:21Z (a year ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M. A.
Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore
(U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the Einstein
Probe-detected fast X-ray transient EP 241021a, collecting 2.6 ks of
Photon Counting (PC) mode data between T0+315.9 ks and T0+327.3 ks.
No X-ray sources have been detected consistent with being within 2.0
arcsec of the Einstein Probe position. The 3-sigma upper limit at the
transient position is ~0.003 ct s^-1, corresponding to a 0.3-10 keV
observed flux of 1.3e-13 erg cm^-2 s^-1 (assuming a typical GRB
spectrum).
We note that GCN Circ. 37870 initially incorrectly referred to this
source as GRB 241021A. The results of the XRT-team automatic analysis
of the XRT observations, including a position-specific upper limit
calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021725.
This circular is an official product of the Swift-XRT team.
GCN Circular 37875
Subject
EP241021a: optical follow-up observations with the Liverpool Telescope
Date
2024-10-25T13:51:07Z (a year ago)
From
Amit Kundu at Royal Holloway - U. of London, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report:
We conducted further optical follow-up observations of the EP-detected X-ray transient EP241021a (Hu et al., GCN 37834; Wang et al., GCN 37848) using the IO:O Imager at the 2m Liverpool telescope in SDSS-g (300s x 3 frames) and SDSS-i (300s x 3 frames) bands. Our second observation epoch (for the first epoch, see Li et al., GCN 37846) was taken on 2024-10-24 from 22:28:08.2 to 22:54:55.6 UT (around 3.722 to 3.740 days post-trigger).
In the stack images of both bands, we detected the optical counterpart of EP241021a, at a position matching the optical counterpart identified by Fu et al., GCN 37840 (see also Gompertz et al., GCN 37835; Lipunov et al., GCN 37839; Fu et al., GCN 37842; Yang et al., GCN 37843; Li et al., GCN 37844; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin et al., GCN 37850; Pugliese et al., GCN 37852; Pérez-Fournon et al., GCN 37858; Bochenek et al., GCN 37869).
We performed aperture photometry on the stacked g and i-band images and calibrated them against the nearby SDSS stars. The observed magnitudes are as follows:
Date_obs | Start UT | Exp. Time | T-T0 (d) | Filter | Mag | Mag_err
----------------------------------------------------------------------------------------
2024-10-24 | 22:28:08.2 | 3x300s | 3.722 | SDSS-g | 22.85 | 0.18
2024-10-24 | 22:44:16.8 | 3x300s | 3.734 | SDSS-i | 21.93 | 0.15
The quoted magnitudes are not corrected for Galactic extinction in the direction of the EP-transient.
Further observations are planned. This circular may be cited.
GCN Circular 37869
Subject
EP241021a: Liverpool Telescope optical follow-up observations
Date
2024-10-25T09:33:09Z (a year ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP241021a (Hu et al., GCN 37834) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x150s exposures in the SDSS r’ filter starting at 2024-10-24 23:07:43 UT, approximately 3.25 days after the trigger.
We report a faint detection in the stacked images of r = 22.43 ± 0.14 mag, at a position consistent with the optical counterpart reported by Fu et al. (GCN 37840) and other optical observations (Fu et al., GCN 37842; Li et al., GCN 37844; Ror et al., GCN 37845; Li et al., GCN 37846; Zheng et al., GCN 37849; Moskvitin and Spiridonova, GCN 37850; Pugliese et al. GCN 37852; Pérez-Fournon et al. GCN 37858). The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction. The source faded approximately 0.5 mag in the last 24 hours.
GCN Circular 37858
Subject
EP241021a: GTC OSIRIS+ spectroscopy of the optical counterpart
Date
2024-10-25T00:23:54Z (a year ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon (IAC and ULL), N.C. Sun (UCAS), W. Li (NAOC), F. Poidevin (IAC and ULL),
D.S. Aguado (IAC and ULL), Y. Wang (NAOC), A. Cabrera-Lavers (GRANTECAN and IAC), J.A. Acosta-Pulido, A. López-Oramas, D. Nespral (all IAC and ULL), Z. Niu (NAOC), and F. Acero (CEA Saclay and IAC)
We report on GTC OSIRIS+ spectroscopy of the fast X-ray transient EP241021a, that was discovered
by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 37834) and detected also by the EP Follow-up X-ray Telescope (FXT) (Wang et al., GCN 37848