EP241021a
GCN Circular 37834
Subject
EP241021a: EP detection of a fast X-ray transient
Date
2024-10-22T07:10:45Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. W. Hu (NAOC, CAS), Y. Wang (PMO, CAS), H. He, S. K. Yang (WHU), Y. H. Cheng (SWIFAR, YNU), W. M. Yuan (NAOC, CAS) on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient, designated EP241021a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2024-10-21T05:07:56(UTC) and lasted for around 100 seconds. The WXT position of EP241021a is R.A. = 28.852 deg, DEC = 5.957 deg (J2000) with an uncertainty of 2.4 arcmin (radius, 90% C.L. statistical and systematic). It has a peak flux of ~1 x 10^-9 erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.48(-1.22, +1.24) (with a column density fixed at the Galactic one of 5 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 3.3(-1.6, +4.8) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
No previously known bright X-ray sources are found within the error circle around the source position. Further follow-up observations are encouraged to identify the nature of this X-ray transient.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 37835
Subject
EP241021a: GOTO optical upper limits
Date
2024-10-22T08:40:57Z (8 months ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, A. Kumar, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) serendipitously covered the field of EP241021a (Hu et al., GCN 37834) in survey mode at 23:44:44 UT on 2024-10-21, approximately 18.5 hours after the trigger. The observation was taken by GOTO-N, and consisted of 4x45s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. No new optical source consistent with the EP/WXT localisation is identified to a 3-sigma limiting magnitude of L > 19.65.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
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 and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 37839
Subject
EP EP241021a: Global MASTER-Net observations report
Date
2024-10-22T12:18:38Z (8 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
legacy email
V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik, D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),
D. Buckley
(South African Astronomical Observatory),
O.A. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),
A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich
(Blagoveschensk Educational State University)
MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP241021a ( EP Team et al., GCN 37834) errorbox 18028 sec after notice time and 1 days 25483 sec after trigger time at 2024-10-22 12:12:39 UT, with upper limit up to 18.3 mag. The observations began at zenith distance = 74 deg. The sun altitude is -21.5 deg.
The galactic latitude b = -53 deg., longitude l = 151 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2645359
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
111913 | 2024-10-22 12:12:39 | MASTER-Tunka | (01h 55m 38.92s , +05d 43m 58.6s) | C | 60 | 18.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 37840
Subject
EP241021a: NOT likely optical counterpart
Date
2024-10-23T04:38:25Z (8 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Y. Fu, Z.P. Zhu, J. An, S.Q. Jiang, X. Liu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), M. Turkki (NOT) report on behalf of a large collaboration:
We observed the field of EP241021a detected by Einstein Probe (EP, Hu et al., GCN 37834), using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT), with 5 x 200 s and 5 x 300 s photometry in the SDSS-z and SDSS-r bands, respectively. Observations started at 23:31:48.4 UT on 2024-10-22, i.e. 1.77 days after the EP trigger.
An uncatalogued source is detected in the individual as well as the stacked frames within the EP/WXT error circle (Hu et al., GCN 37834) and localized at coordinates
R.A. (J2000) = 01:55:23.41
Dec. (J2000) = +05:56:18.01
with an uncertainty of ~ 0.5 arcsec. The source has z = 21.60 +/- 0.11 at 1.77 days post-trigger and r = 21.95 +/- 0.06 at 1.91 days post-trigger, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. The source is not present in the Legacy Survey, which is well deeper than the r-/z-band detection. We thus conclude that the source is very likely the optical counterpart of EP241021a.
GCN Circular 37842
Subject
EP241021a: TRT optical observations
Date
2024-10-23T06:02:51Z (8 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Y. Fu (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Q. Jiang, J. An, X. Liu, Z.P. Zhu, S.Y. Gao, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of EP241021a detected by Einstein Probe (EP, Hu et al., GCN 37834) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, US. Observations started at 09:14:23.699 UTC on 2024-10-22, i.e., 1.17 days after the EP trigger, and a series of 300 s frames were obtained in R- and V- bands.
The uncatalogued source reported by NOT (Fu et al., GCN 37840) is marginally detected in our stacked R- and V- band images, with R ~ 21.6 and V ~ 21.7, calibrated with Legacy-DR10 stars in the field and not corrected for Galactic extinction.
GCN Circular 37843
Subject
EP241021a: Optical upper limits with Kinder observations
Date
2024-10-23T10:07:58Z (8 months ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
S. Yang (HNAS), A. Aryan, T.-W. Chen, Y. J. Yang, W.-J. Hou, M.-H. Lee (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), A. Sankar. K, C.-C. Ngeow, Y.-C. Pan, H.-C. Lin, C.-H. Lai, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCUIA), Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient EP241021a (Hu et al., GCN 37834) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first SLT epoch of observations started at 12:16 UTC on the 22nd of October 2024 (MJD = 60605.512), 1.30d after the EP WXT trigger.
We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames.
We used the Kinder pipeline (Yang et al. A&A 646, A22) to subtract the stacked images from the SDSS template.
We do not detect the optical counterpart candidate in the position reported by Fu et al. (GCN 37840; 37842). Our observations were affected by bad weather. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60605.512 | 1.30d | 300 * 24 | >19.6 | 2".79 | 1.28
Our optical upper limits are consistent with Gompertz et al. (GCN 37835) and Lipunov et al. (GCN 37839). The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.048 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
GCN Circular 37844
Subject
EP241021a: GSP detects optical candidate counterpart
Date
2024-10-23T10:49:11Z (8 months ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
Web form
W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report the optical follow-up observations of the optical candidate counterpart to the fast X-ray transient EP241021a (Hu et al., GCN 37834, Fu et al., GCN 37840, Fu et al., GCN 37842).
Our observations were conducted on 2024 Oct. 23.3 UT using the 1-meter telescope at the Las Cumbres Observatory node located at McDonald Observatory in USA. The transient is detected in the images with
r = 21.9 + -0.1
i = 21.7 +- 0.1
Further follow-up observations are encouraged.
These observations were taken as part of the Global Supernova Project.
GCN Circular 37845
Subject
EP241021a: 1.3m DFOT Optical observations
Date
2024-10-23T11:12:06Z (8 months ago)
From
Amit Kumar Ror at ARIES <mitturor77894@gmail.com>
Via
email
Amit K. Ror, Ansika Gupta, Tushar Tripathi, Shashi B. Pandey, Kuntal Mishra
(ARIES) report:
We observed the field of EP241021a detected by the Wide-field X-ray
Telescope on board the Einstein Probe mission (Einstein Probe team, Hu et
al. 2024, GCN 37834), with the 1.3m Devasthal Fast Optical Telescope
(DFOT), located at the Devasthal Observatory of the Aryabhatta Research
Institute of Observational Sciences (ARIES), India. The observations were
started on 2024-10-22 at 16:48:07 UT, i.e., ~ 1.49 days after the Einstein
Probe trigger. We have taken multiple frames with an exposure time of 300 s
in the R filter. The observations were taken in the bright moon phase. We
stacked the images after the alignment. We clearly detected optical
emission in our stacked image within the error box of the transient
position by Fu et al. 2024 (GCN 37840). We obtain the following preliminary
magnitude in the stacked image:
Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude
=========================================================
2024-10-22 16:48:07 1.49 R 300s*12 21.62 +/- 0.10
Our detection is consistent with Gompertz et al. 2024, GCN 37835; Lipunov et
al. 2024, GCN 37839; Fu et al. 2024, GCN 37840; Fu et al. 2024, GCN 37842; Yang
et al. 2024, GCN 37843; and Li et al. 2024, GCN 37844
The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue. This circular may be cited.
GCN Circular 37846
Subject
EP241021a: Optical counterpart observations with the Liverpool Telescope
Date
2024-10-23T13:08:45Z (8 months ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
Web form
W. X. Li（NAOC), N. C. Sun (UCAS), J. Maund (ULRH), Y. N. Wang (NAOC) and K. Wiersema (Herts)
report the optical follow-up observations of the optical candidate counterpart to the fast X-ray transient EP241021a (Hu et al., GCN 37834, Fu et al., GCN 37840, Fu et al., GCN 37842, Li et al., GCN 37844, Ror et al., 37845).
Our observations were conducted on 2024 Oct. 23.0 UT (~1.8 days after EP detection) using the 2-meter Liverpool Telescope. The transient is detected in the images with
g = 22.2 +- 0.1
r = 21.9 + -0.1
Further follow-up observations are encouraged.
GCN Circular 37848
Subject
EP241021a: EP-FXT follow-up observation update
Date
2024-10-23T15:51:34Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Wang (PMO, CAS), H. He, S. K. Yang (WHU), Y. H. Cheng (SWIFAR, YNU), J. W. Hu, X. P. Xu, W. Yuan (NAO, CAS) on behalf of the Einstein Probe team
Following the detection of the fast X-ray transient EP241021a (Hu et al., GCN 37834), we performed an observation of EP241021a with the Follow-up X-ray Telescope (FXT) on board Einstein Probe. The observation started at 2024-10-22T17:44:27 (UTC), about 36.5 hours after the EP-WXT detection, with an exposure time of 3023 seconds. An uncatalogued X-ray source is detected at R.A. = 28.8483 deg, DEC = 5.9395 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average FXT spectrum in 0.5-10 keV band can be fitted by an absorbed power law with a photon index of 1.57(+0.53/-0.49) (with a column density fixed at the Galactic one of 5 x 10^20 cm^-2), giving an average unabsorbed flux of 2.3(+1.4/-0.8) x 10^-13 erg/s/cm^2. We consider this FXT source to be the afterglow of the X-ray transient EP241021a, which is 5 arcsec away from the likely optical counterpart (Fu et al., GCN 37840, 37842, Li et al., GCN 37844, Ror et al., GCN 37845, Li et al., GCN 37846).
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).
GCN Circular 37849
Subject
EP241021a: KAIT optical observations
Date
2024-10-23T18:16:48Z (8 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
legacy email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of EP240930a (Hu et al.,
GCN 37834; Wang et al., GCN 37848) on Oct 22 and again on Oct
23 UT. A set of 70x60s images were obtained in each night in the
clear (roughly R) filters. We detect the optical afterglow
(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) in the coadd image and
measure the brightness to be 21.2 +/- 0.2 and 21.7 +/- 0.3 mag at
1.14 and 2.12 days after trigger respectively.
GCN Circular 37850
Subject
EP241021a: SAO RAS optical observations
Date
2024-10-23T22:53:51Z (8 months 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 9 x 300 sec. images in Rc band
on October 23, 19:27:12--20:17:25 UT (t_mid - T0 = 2.6141 days).
We clearly 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)
in our stacked frame with the brightness of R = 21.81 +/- 0.06
calibrated against nearby SDSS stars (magnitudes converted with
Lupton 2005 equations) and not corrected for the Galactic extinction.
GCN Circular 37852
Subject
EP241021a: VLT/FORS2 redshift z = 0.75
Date
2024-10-24T10:21:30Z (8 months ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
G. Pugliese (API-UvA), D. Xu (NAOC), L. Izzo (INAF-OACn & DARK/NBI), A. J. Levan (Radboud Univ. and Warwick Univ.), Z.P. Zhu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), V. D'Elia (ASI/SSDC and INAF/OAR), P. G. Jonker (Radboud Univ.), A. Martin-Carrillo (UCD), B. P. Gompertz (Birmingham), A. Rossi (INAF/OAS), A. Saccardi (GEPI/Obs. de Paris) report on behalf of the Stargate collaboration:
We observed the optical counterpart of the fast X-ray transient EP 241021a (Hu et al., GCN 37834) 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). We used the FORS2 spectrograph mounted on the ESO VLT UT1 (Antu), equipped with the 300V grism and no order-sorting filter. Two spectra by 20 min each were secured, with mean epoch 2024 Oct 24.229 UT (about 3.01 days after the trigger). Seeing conditions were excellent at 0.5", as measured in the acquisition image.
In the acquisition image (taken 2.998 days after the trigger), we measure a preliminary magnitude r = 22.06 +- 0.05 (AB, calibrated against nearby objects from Pan-STARRS).
Continuum is detected at least across the range 4600-8600 AA. A strong emission line is visible at 6519 AA, which we identify as due to [O II] 3728 AA at z = 0.75. This interpretation is confirmed by the detection of a doublet in absorption at 4897 AA, which matches well Mg II at z = 0.748.
We note the persistently flat light curve of the optical counterpart (Fu et al., GCN 37840, 37842; Li et al., GCN 37844, 37846; Ror et al., GCN 37845; Moskvitin & Spiridonova, GCN 37850; our own acquisition measurement), which is unusual for a GRB afterglow over such a long time range. We encourage further photometric monitoring at all wavelengths.
We acknowledge the expert support from the ESO observing staff at Paranal, in particular Martina Baratella.
GCN Circular 37855
Subject
EP241021a: No Detection in Fermi-GBM Observation
Date
2024-10-24T16:04:58Z (8 months ago)
From
Eric Burns at LSU <erickayserburns@gmail.com>
Via
Web form
E. Burns (LSU), M. E. Ravasio and P.G. Jonker (Radboud Univ.), and Adam Goldstein (USRA) report on behalf of the Fermi-GBM Team:
Fermi-GBM had full spatial and temporal coverage of the EP WXT signal of EP241021a (Hu et al., GCN 37834).
There was no Fermi-GBM onboard trigger around the event time of EP241021a. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from 30 s before the EP trigger time until 300 s after, seeking signals between 64 ms and 32.768 s in duration. A candidate was found, but it has a localization that is not consistent with the EP trigger and appears to be a soft Galactic source that becomes occulted by the Earth at approximately T0+40 s. No signal consistent both temporally and spatially is identified, as confirmed by visual inspection of the data.
GCN Circular 37858
Subject
EP241021a: GTC OSIRIS+ spectroscopy of the optical counterpart
Date
2024-10-25T00:23:54Z (8 months 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).
We observed the optical counterpart of EP241021a reported by Fu et al. (GCN 37840) with the OSIRIS+
instrument of the Gran Telescopio Canarias (GTC) and its R500R grism. Three spectra of 1800 sec each
were obtained starting at 2024-10-24T01:28:47 UT (about 2.848 days after the trigger) in excellent
observing conditions. The combined reduced spectrum shows a high S/N continuum and narrow emission
lines from the likely host galaxy of [O II] 3727 AA , Hbeta, and [O III] 4959, 5007 AA at a redshift
of z = 0.75, in agreement with the results of Pugliese et al. (GCN 37852) using VLT/FORS2 at shorter wavelengths.
The optical counterpart has also been detected by other teams in different imaging programmes
(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; and Moskvitin and Spiridonova, GCN 37850).
This EP transient has not been detected in Fermi-GBM observations (Burns et al., GCN 37855).
Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish
Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island
of La Palma. We acknowledge the excellent support from the GTC observing staff.
GCN Circular 37869
Subject
EP241021a: Liverpool Telescope optical follow-up observations
Date
2024-10-25T09:33:09Z (8 months 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 37875
Subject
EP241021a: optical follow-up observations with the Liverpool Telescope
Date
2024-10-25T13:51:07Z (8 months 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 37876
Subject
EP 241021a: Swift-XRT observations
Date
2024-10-25T14:42:21Z (8 months 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 37877
Subject
EP241021a: Optical and NIR observations of counterpart with the Fraunhofer Telescope at Wendelstein Observatory
Date
2024-10-25T15:06:05Z (8 months 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 37878
Subject
EP241021a: Optical and NIR observations of counterpart with the Fraunhofer Telescope at Wendelstein Observatory
Date
2024-10-25T15:06:09Z (8 months 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 37892
Subject
EP241021a: optical follow-up observations with Xinglong Observatory
Date
2024-10-26T14:05:37Z (8 months ago)
Edited On
2024-10-28T13:49:36Z (8 months 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 37906
Subject
EP241021a: e-MERLIN radio observation
Date
2024-10-27T10:44:05Z (8 months 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 37910
Subject
EP241021a: further SAO RAS optical observations
Date
2024-10-27T15:01:01Z (8 months 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 37911
Subject
EP241021a: SOAR observations of the optical counterpart
Date
2024-10-27T15:21:13Z (8 months 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 37930
Subject
EP241021a: Gemini-South detection of optical rebrightening
Date
2024-10-28T15:35:47Z (8 months 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 37942
Subject
EP241021a: continued SOAR observations confirm optical rebrightening
Date
2024-10-29T17:04:36Z (8 months 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 37949
Subject
EP241021a: ATCA radio observations
Date
2024-10-29T23:33:50Z (8 months 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 37951
Subject
EP241021a: SAO RAS observations of rebrightening
Date
2024-10-30T00:33:38Z (8 months 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 37968
Subject
EP241021a: Optical rebrightening observations with Mephisto
Date
2024-10-30T13:21:56Z (8 months 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 37973
Subject
EP 241021a: further Swift-XRT observations and X-ray counterpart detection
Date
2024-10-30T14:47:43Z (8 months 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 37990
Subject
EP241021a: Swift-UVOT detection
Date
2024-10-30T23:11:48Z (8 months 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 38014
Subject
EP241021a: AMI-LA radio detection
Date
2024-10-31T15:13:01Z (8 months 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 38022
Subject
EP241021a: OHP/T193 optical observations
Date
2024-11-01T00:10:43Z (8 months 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 38030
Subject
EP241021a: Liverpool Telescope optical follow-up observations
Date
2024-11-01T10:33:17Z (8 months 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 38034
Subject
EP241021a: Upper limit from Konus-Wind observations
Date
2024-11-01T13:52:02Z (8 months 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 38062
Subject
EP241021a: continued SOAR observations
Date
2024-11-03T15:45:48Z (8 months 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 38071
Subject
EP241021a: OHP/T193 further optical observations
Date
2024-11-04T12:48:00Z (8 months 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 38294
Subject
EP241021a and EP241026b: Keck/LRIS spectroscopic observations
Date
2024-11-22T03:40:03Z (7 months 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 38640
Subject
EP241021a: VLA radio detection
Date
2024-12-19T20:19:55Z (6 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 38924
Subject
EP241021a: SMA radio observation
Date
2025-01-13T15:44:13Z (5 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.