EP240801a
GCN Circular 37468
Subject
Fast X-ray Transient EP240801a: GMRT radio observations
Date
2024-09-12T06:28:01Z (a year ago)
From
Arvind Balasubramanian <arvind6895@gmail.com>
Via
Web form
A. Balasubramanian (IIA), D. Eappachen (IIA), J. Quirola-Vasquez (Radboud Univ.), D. K. Sahu (IIA), and G.C. Anupama (IIA) report:
We observed the field of the fast X-ray transient EP240801a (Zhou et al., GCN 36997) with GMRT under the DDT ( PI: D. Eappachen, ddtC385) on 22nd August 2024 in bands 4 (650 MHz) and 5 (1260 MHz) for a total of 4 hours starting from 19:30 UT.
We do not detect any radio source coincident with the position of the optical counterpart reported by Fu et al. (GCN 36998). We used 3C48 for the flux calibration and J2236+284 for complex gain and phase calibration. The CAPTURE-CASA6 pipeline was used for data calibration and imaging. We estimate a 3-sigma radio upper limit of 75 uJy in band 4 and 52 uJy in band 5.
We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.
GCN Circular 37228
Subject
EP240801a: Keck/LRIS spectroscopic redshift confirmation
Date
2024-08-22T08:10:26Z (a year ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
legacy email
WeiKang Zheng, Thomas G. Brink, Alexei V. Filippenko (UCB),
Rebecca Davies and Adam Deller (Swinburne),
report on behalf of the KAIT GRB team:
Following the detection of EP240801a (Zhou et al., GCN 36997),
we observed its GRB optical counterpart (Fu et al., GCN 36998;
Li et al., GCN 36999; Zheng et al., GCN 37000; Aryan et al.,
GCN 37002; An et al., GCN 37004; Pérez-Fournon et al., GCN
37007; Malesani et al., GCN 37008; Zhu et al., GCN 37010;
Moskvitin & Spiridonova, GCN 37012; Quirola-Vásquez et al.,
GCN 37013; Moretti et al., GCN 37014; Turpin et al., GCN 37015;
Pankov et al., GCN 37016; Moskvitin & Spiridonova, GCN 37017;
Ruocco et al., GCN 37024; Pankov et al., GCN 37040; Moskvitin
et al., GCN 37049; Pankov et al., GCN 37146) with the Low
Resolution Imaging Spectrometer (LRIS, Oke et al. 1995) at the
Keck I Observatory (ToO program U232, PI A. V. Filippenko).
Observations started at 2024-08-02 09:36 (~1.02 days after the
burst), and consisted of 3 x 950 s exposures with the 600/4000
grism and 400/8500 grating. The spectrum shows a well-detected
continuum. We detect narrow absorption lines consistent with
Mg II 2796, 2803 Ang doublet as well as Fe II 2600 Ang,
confirming the redshift of z = 1.673 reported by Quirola-Vásquez
et al. (GCN 37013) from GTC.
We thank Josh Walawender and Matthew Wahl from the Keck team for
their support during this Target of Opportunity trigger. 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 37146
Subject
EP240801a: Assy-Turgen optical observations
Date
2024-08-12T06:35:28Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
N. Pankov (HSE, IKI), V. Kim (FAI), M. Krugov (FAI), S. Belkin (IKI, HSE),
A. Pozanenko (IKI) report on
behalf of GRB-IKI-FuN:
We observed the field of EP240801a (Zhou et al, GCN 36997) with AZT-20
telescope of Assy-Turgen observatory. The observation were conducted on
epochs
2024-08-04 17:16, 2024-08-07 19:03, and 2024-08-08 19:36 (UT, starting
time).
The optical source (Fu et al, GCN 36998; Li et al, GCN 36999; Zheng et al,
GCN 37000; Aryan et al, GCN 37002; An et al, GCN 37004; Pérez-Fournon et
al,
GCN 37007; Malesani et al, GCN 37008; Zhu et al, GCN 37010;
Moskvitin & Spiridonova, GCN 37012; Quirola-Vásquez et al, GCN 37013;
Moretti et al, GCN 37014; Turpin et al, GCN 37015; Pankov et al, GCN 37016;
Moskvitin & Spiridonova, GCN 37017; Ruocco et al, GCN 37024; Pankov et al,
GCN
37040; Moskvitin et al, GCN 37049) is detected only on the first epoch.
Preliminary photometry is the following:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (s) (3sigma)
2024-08-04 17:16:21 3.373472 95*60 r' 23.29 0.14 23.6
2024-08-07 19:03:15 6.437292 65*60 r' n/d n/d 23.9
2024-08-08 19:36:10 7.458070 59*60 r' n/d n/d 24.0
The magnitudes were calibrated using nearby stars from SDSS-DR12 catalog
and are not corrected for the expected Galactic extinction A(r) = 0.252 mag
(S&F 2011) towards the EP240801a source.
The light curve in the r and R filters (AB mags) can be fitted with a
smoothed broken power law (Beuermann et al, 1999) with parameters:
alpha_1 = 1.1, alpha_2 = 0.33, t_break = 1.5 days with fixed smoothing
parameter omega = 1.0. We also note, that there
is a point-like source in the LS DR10 at the position of EP240801a. The
source magnitudes are g = 25.14, r = 24.40, and the photometric redshift of
0.995 +- 0.352, which is marginally consistent with the redshift of 1.673
obtained with GTC spectroscopy (Quirola-Vásquez et al, GCN 37013).
GCN Circular 37049
Subject
EP240801a: BTA BVRI photometry
Date
2024-08-05T17:22:19Z (a year ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Via
legacy email
A. Moskvitin, D. Oparin (SAO RAS), N. Pankov (HSE, IKI), A. Pozanenko (IKI)
report:
We observed the field of the fast X-ray transient EP240801a
(Zhou et al., GCN 36997) with the BTA 6-meter telescope
of SAO RAS equipped with the focal reducer Scoprio-I on August, 3
(t_mid - T0 = 2.629 days) and August, 4 (t_mid - T0 = 3.485 days).
The OT (Fu et al., GCN 36998; Li et al., GCN 36999; Zheng et al.,
GCN 37000; Aryan et al., GCN 37002; An et al., GCN 37004;
Perez-Fournon et al., GCN 37007; Malesani et al., GCN 37008;
Zhu et al., GCN 37010; Moskvitin et al., GCNs 37012, 37017;
Quirola-Vasquez et al., GCN 37013; Moretti et al., GCN 37014;
Turpin et al., GCN 37015; Pankov et al., GCNs 37016, 37040) is clearly
detected in stacked frames. Preliminary photometry of OT in the both epochs
as is follows.
Filter, exp, t_start t_end (UTC) OT, mag
s, (UT) (UT)
B 620 2024-08-03T23:44:36 -- 2024-08-04T00:37:41 23.88 +/- 0.13
V 600 2024-08-03T23:50:17 -- 2024-08-04T00:33:45 23.13 +/- 0.09
Rc 510 2024-08-03T23:47:46 -- 2024-08-04T00:35:28 22.82 +/- 0.07
Ic 510 2024-08-03T23:52:56 -- 2024-08-04T00:30:14 22.05 +/- 0.10
V 900 2024-08-04T20:28:02 -- 2024-08-04T21:01:52 23.55 +/- 0.08
Rc 930 2024-08-04T20:23:36 -- 2024-08-04T21:03:41 22.91 +/- 0.06
The magnitudes were calibrated against nearby Pan-STARRS stars
and not corrected for Galactic extinction.
We note significant reddening (V-Rc) between the two epochs.
GCN Circular 37040
Subject
EP240801a: Continued optical observations at ZTSh (CraO)
Date
2024-08-05T12:49:48Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
N. Pankov (HSE, IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on
behalf of GRB-IKI-FuN:
We observed the field of EP240801a (Zhou et al, GCN 36997) with ZTSh 2.6 m
telescope of CrAO. The observation were carried out in moderate conditions
with seeing about 2.0 arcsec. We taken series of images in the R-filter. We
clearly detect the optical counterpart (Fu et al, GCN 36998; Li et al, GCN
36999; Zheng et al, GCN 37000; Aryan et al, GCN 37002; An et al, GCN 37004;
Pérez-Fournon et al, GCN 37007; Malesani et al, GCN 37008; Zhu et al, GCN
37010; Moskvitin & Spiridonova, GCN 37012; Quirola-Vásquez et al, GCN
37013; Moretti et al, GCN 37014; Turpin et al, GCN 37015; Pankov et al, GCN
37016; Mo GCN 37017, ) in the stacked images. Preliminary
photometry is as follows:
Date UT start t-T0 Exp. Filter OT Err. UL
(mid, days) (s) (3sigma)
2024-08-02 20:41:58 1.493699 15*120 R 22.27 0.05 23.7
2024-08-03 19:43:38 2.456662 20*120 R 22.60 0.09 23.2
The magnitudes were calibrated using nearby stars from USNO-B1.0 catalog
(R2 magnitudes) and not corrected for the Galactic extinction.
GCN Circular 37024
Subject
EP240801a: Osservatorio Astronomico Nastro Verde upper limit
Date
2024-08-04T09:49:22Z (a year ago)
From
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 <osservatorionastroverde@gmail.com>
Via
Web form
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report:
We imaged the field of the X-ray transient EP240801a detected at 2024-08-01 09:06:03 (UTC) by Einstein Probe (EP, Zhou et al., GCN 36997; Fu et al., GCN 36998; Li et. al. GCN 36999; Zheng et al, GCN 37000; Aryan et al. GCN 37002; An et al., GCN 37004; Pérez-Fournon et al., GCN 37007; Malesani et al., GCN 37008; Zhu et al., GCN 37010; Moskvitin et al., GCN 37012)with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy.
Member of:
AAVSO - American Association of Variable Star Observers.
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili.
AstroCampania Associazione
The observations started at 22:08 UT of 2024/08/01, after about 12 hours after the transient, with clear sky,with principal telescope SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME
I took 27 image of 120 sec each. All images are unfiltered, calibrated with masterdark and masterflat,stacked with Tycho Tracker software.
We have not detected any clearly visible sources, up to 19.5th magnitude with clear skies.
Start End Rlim
20:59:32 UT 21:59:00 UT 19.5
We did not found any optical counterpart.
Magnitudes were estimated with the Gaia DR2 cat. and
are not corrected for galactic dust extinction.
The message may be cited.
GCN Circular 37017
Subject
EP240801a: further SAO RAS optical observations
Date
2024-08-02T23:12:07Z (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 the fast X-ray transient EP240801a
(Zhou et al., GCN 36997) with the SAO RAS 1-meter telescope Zeiss-1000
equipped with the CCD-photometer. We obtained 9 x 300 sec frames
in Rc band on 2024-08-02T20:14:00 -- 2024-08-02T22:09:01 (UTC),
t_mid - T0 = 1.5038 days.
The OT (Fu et al., GCN 36998; Li et al., GCN 36999; Zheng et al.,
GCN 37000; Aryan et al., GCN 37002; An et al., GCN 37004;
Perez-Fournon et al., GCN 37007; Malesani et al., GCN 37008;
Zhu et al., GCN 37010; Quirola-Vasquez et al., GCN 37013;
Moretti et al., GCN 37014; Turpin et al., GCN 37015; Pankov et al.,
GCN 37016) is clearly detected in the stacked frame
with the brightness of R = 22.17 +/- 0.15, calibrated against nearby
Pan-STARRS stars and not corrected for Galactic extinction.
GCN Circular 37016
Subject
EP240801a: optical observations at CrAO and AbAO
Date
2024-08-02T15:06:19Z (a year ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
N. Pankov (HSE, IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO),R. Ya.
Inasaridze (AbAO) report on behalf of GRB-IKI-FuN:
We observed the field of EP240801a (Zhou et al, GCN 36997) with ZTSh 2.6 m
telescope of CrAO, and AS-32 0.7 m telescope of AbAO. The observations were
carried out in moderate conditions with seeing of about 2.0 arcsec. We took
a series of images in the R-filter, starting on 2024-08-01 20:28 (UT) at
CrAO (i.e. 11 hours after the EP trigger). We clearly detect the optical
counterpart (Fu et al, GCN 36998; Li et al, GCN 36999; Zheng et al, GCN
37000; Aryan et al, GCN 37002; An et al, GCN 37004; Pérez-Fournon et al,
GCN 37007; Malesani et al, GCN 37008; Zhu et al, GCN 37010; Moskvitin &
Spiridonova, GCN 37012; Quirola-Vásquez et al, GCN 37013; Moretti et al.,
GCN 37014; Turpin et al., GCN 37015) in images from CrAO, while obtaining
upper limit at AbAO. Preliminary photometry is given below:
Date UT start t-T0 Exp. Filter OT Err. UL(3 sigma) Scope
(mid, days) (s)
2024-08-01 20:28:07 0.50492 15x120 R 21.3 0.1 23.7 ZTSh
2024-08-01 20:32:01 0.50970 44x60 R n/d n/d 21.0 AS-32
The magnitudes were calibrated using nearby stars from USNO-B1.0
catalog (R2 mags) and are not corrected for the Galactic extinction
A(R) = 0.237 mag (S&F 2011) towards the EP source. The obtained results are
consistent with observations published earlier.
GCN Circular 37015
Subject
EP240801a: GRANDMA and Kilonova-Catcher optical observations
Date
2024-08-02T14:53:29Z (a year ago)
Edited On
2024-08-02T15:56:16Z (a year ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
D. Turpin (CEA-Saclay/Irfu), S. Aghayeva (Shamakhy Obs.), Z. Vidadi (Shamakhy Obs.), N. Kochiashvili (Abastumani Obs.), S. Antier (OCA), S. Karpov (FZU), M. Coughlin (UMN), C. Andrade (UMN), I. Tosta e Melo (UniCT-DFA), P. Hello, N. Leroy (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), V.Aivazyan (AbAO), R. Inasaridze (AbAO), M. Masek (FZU), M. Prouza (FZU), M. Freeberg (KNC), S. Leonini (KNC, Montarrenti Obs.), Y. Rajabov (UBAI), M. Serrau (KNC) on behalf of the GRANDMA and Kilonova-Catcher collaborations:
We performed observations with GRANDMA and its citizen science project Kilonova-catcher (KNC) on the X-ray transient EP240801a detected by Einstein Probe (EP) WXT on T0 = 2024-08-01T09:06:03 (Zhou et al., GCN 36997). Our observations were made from 2024-08-01T20:32:01 to 2024-08-02T08:49:33 UTC, starting 11.4 hours after the EP trigger.
In most of our images, we did not detect the optical counterpart identified by several other follow-up observations (Fu et al., GCN 36998; Li et al. GCN 36999; Zheng et al. 36999; Aryan et al., GCN 37002; An et al., GCN 37004; Pérez-Fournon et al. GCN 37007; Malesani et al., GCN 37008, Zhu et al. GCN 37010, Moskvitin et al. GCN 37012, Quirola-Vásquez et al. GCN 37013; Moretti et al., GCN 37014). Our 5 sigma upper limits are consistent with the reported detections. In addition, we note a marginal detection in one of our stacked frame taken at a midtime ~15.7h after the EP/WXT trigger time with the following magnitude G = 22.1 +/- 0.5.
All our observations and upper limits (5 sigma C.L.) can be found here:
+--------------+------------+-------+-----------+---------------------+
| MJD | T-T0 (hrs) |Filter | Mag (AB) | Instrument |
+==============+============+===================+=====================+
| 60523.855567 | 11.43 | R |20.7 (U.L) | AbAO-T70 |
+--------------+------------+-------+-----------+---------------------+
| 60523.951979 | 13.74 | R |20.2 (U.L.)| UBAI-NT60 |
+--------------+------------+-------+-----------+---------------------+
| 60523.953785 | 13.79 | R |19.3 (U.L.)| KNC-Montarrenti Obs.|
+--------------+------------+-------+-----------+---------------------+
| 60523.997921 | 14.85 | R |18.4 (U.L.)| FRAM-CTA-N |
+--------------+------------+-------+-----------+---------------------+
| 60524.032112 | 15.67 | Gaia G|22.1+/-0.5 | KNC-Dauban Meade 12"|
+--------------+------------+-------+-----------+---------------------+
| 60524.055914 | 16.24 | sdssr |21.0 (U.L.)| KNC-CDK17 |
+--------------+------------+-------+-----------+---------------------+
| 60524.279711 | 21.61 | sdssr |21.2 (U.L.)| KNC-T160FL |
+--------------+------------+-------+-----------+---------------------+
Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog, images taken with Sloan filters were calibrated using the Pan-STARRS DR1 Catalog while images taken with Gaia G filters were calibrated using the Gaia eDR3 catalog.
All the data have been reduced by a single data processing pipeline STDPIPE (Karpov et al., 2022). We use the Skyportal application (skyportal.io) to monitor our observational campaign.
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 37014
Subject
EP240801a: Leavitt Observatory optical observations
Date
2024-08-02T13:20:21Z (a year ago)
From
leavittob@gmail.com
Via
Web form
L. Moretti and E. Pavoni (Leavitt Observatory, Italy), in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report:
We imaged the field of the X-ray transient EP240801a detected by Einstein Probe (EP, Zhou et al., GCN 36997; Fu et al., GCN 36998; Li et. al. GCN 36999; Zheng et al, GCN 37000; Aryan et al. GCN 37002; An et al., GCN 37004; Pérez-Fournon et al., GCN 37007; Malesani et al., GCN 37008; Zhu et al., GCN 37010; Moskvitin et al., GCN 37012), with the telescope of Leavitt Observatory, Italy. Member of:
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili, GRB section.
ATA - Associazione Tuscolana di Astronomia.
The transient event started at 2024-08-01 09:06:03 (UTC).
Our observations started about 11 hours after the EP trigger, with a RC telescope D=250 mm F/D=8.
Weather conditions were good.
We co-added 12 images of 120 sec each. All images are unfiltered, calibrated with masterdark and masterflat.
An uncatalogued optical transient (OT) is marginally detected in the stacked image at coordinates:
R.A. (J2000) = 23:00:39.02
Dec. (J2000) = +32:35:37.2
with the following photometry:
Date UT Middle: 2024-08-01 20:48:27 UTC
CR-mag 21.4 +/- 0.2
Given the low S/N for the OT, we cannot completely rule out it being due to background fluctuation.
Magnitudes were estimated with the Pan-STARRS cat. and converted using Lupton (2005) equations. No corrected for galactic dust extinction.
Reference:
https://leavittobservatory.altervista.org
The message may be cited.
GCN Circular 37013
Subject
EP240801a: GTC spectroscopy and absorption redshift
Date
2024-08-02T10:44:40Z (a year ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
J. Quirola-Vásquez (Radboud Univ.), J. van Dalen (Radboud Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), P. G. Jonker (Radboud Univ), A. J. Levan (Radboud Univ. & Warwick Univ.), F. E. Bauer (PUC), M. E. Ravasio (Radboud Univ.), D. Mata Sanchez (IAC), M. A. P. Torres (IAC), report on behalf of a larger collaboration:
We observed the optical counterpart of EP240801a (Zhou et al., GCN 36997; Fu et al., GCN 36998) using the 10.4 m GTC located in La Palma, Canary Islands. Observations started on 2024 Aug 2.169 UT (0.79 days after the EP trigger), consisted of 4 exposures of 1200 s each, and were carried out using grism R1000R, which covers the wavelength range 5100-10000 AA. The counterpart magnitude was r = 21.98 +- 0.05 (AB) as measured in a 30-s acquisition image, calibrated against nearby Pan-STARRS sources.
Continuum is well detected over the entire wavelength range. Several absorption lines are visible, which we interpret as due to Mg II and Fe II at a common redshift z = 1.673, which we suggest to be the likely redshift of EP240801a.
We acknowledge excellent support from the GTC staff, in particular Stefan Geier and Antonio Luis Cabrera Lavers.
GCN Circular 37012
Subject
EP240801a: SAO RAS optical observations
Date
2024-08-02T10:06:40Z (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 the fast X-ray transient EP240801a
(Zhou et al., GCN 36997) with the SAO RAS 1-meter telescope Zeiss-1000
equipped with the CCD-photometer. We obtained 5 x 300 sec frames
in Rc band on 2024-08-01T23:55:51 -- 2024-08-02T00:54:48 (UTC),
t_mid - T0 = 15.32 hours.
The OT (Fu et al., GCN 36998; Li et al., GCN 36999; Zheng et al.,
GCN 37000; Aryan et al., GCN 37002; An et al., GCN 37004;
Perez-Fournon et al., GCN 37007; Malesani et al., GCN 37008;
Zhu et al., GCN 37010) is clearly detected in the stacked frame
with the brightness of R = 21.7 +/- 0.1, calibrated against nearby
Pan-STARRS stars and not corrected for Galactic extinction.
GCN Circular 37010
Subject
EP240801a: JinShan optical observations
Date
2024-08-02T02:38:31Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
Z.P. Zhu, X. Liu, J. An, S.Y. Fu, S.Q. Jiang, L.B. He, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP240801a detected by EP/WXT (Zhou et al., GCN 36997), using the JinShan 100cm-C telescope (100C) located at Altay, Xinjiang, China.
The observation started at 17:17:48 UT on 2024-08-01, ~ 8.20 hr after the EP/WXT trigger and ended at 22:06:04 UT the same night. A series of exposures were obtained in the Sloan g-, r-, i-, and z- filters.
The previously reported optical counterpart by TRT (Fu et al. GCN 36998) has decayed to r = 21.44 +/- 0.06 at 9.63 hr after EP/WXT trigger, calibrated with nearby Pan-STARRS stars and not corrected for Galactic extinction.
The optical counterpart has also been reported by GMG (Li et al., GCN 36999), KAIT (Zheng et al., GCN 37000), Kinder (Aryan et al., GCN 37002), LCO (An et al., GCN 37004; Pérez-Fournon et al., GCN 37007), and NOT (Malesani et al., GCN 37008).
We acknowledge the excellent support from S.W. Luo, M.M. Yang, Z.K. Feng, Q.C. Zhao and L.F. Huo for enabling these observations.
GCN Circular 37008
Subject
EP240801a: NOT optical observations
Date
2024-08-02T00:33:18Z (a year ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud Univ.), J. Quirola-Vásquez (Radboud Univ.), J. van Dalen (Radboud Univ.), P. G. Jonker (Radboud Univ), A. J. Levan (Radboud Univ. & Warwick Univ.), F. E. Bauer (PUC), M. E. Ravasio (Radboud Univ.), D. Mata Sanchez (IAC), M. A. P. Torres (IAC), on behalf of a larger collaboration, D. Xu (NAOC), Z. P. Zhu (NAOC):
We report on optical follow-up observations of the Einstein Probe fast X-ray transient EP240801a (Zhou et al., GCN 36997).
We observed the optical counterpart of EP240801a (Fu et al., GCN 36998) using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT), with an exposure of 3x300 s in the SDSS-r band. Observations started on 2024-08-01T22:37:41 UT, that is ~13.56 hours after the EP trigger, at an airmass of ~2.
An object is detected at a position consistent with the one reported by Fu et al. (GCN 36998), for which we measure a preliminary magnitude r = 21.67 +- 0.04 mag, calibrated against nearby Pan-STARRS sources.
We thank the Nordic Optical Telescope team, in particular Alba Casasbuenas Corral, for making these observations possible.
GCN Circular 37007
Subject
EP240801a: follow-up observation with LCOGT
Date
2024-08-01T23:07:03Z (a year ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
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I. Pérez-Fournon, F. Poidevin, D. S. Aguado, J. A. Acosta-Pulido, A. López-Oramas, D. Nespral (IAC and ULL), and F. Acero (CEA Saclay and IAC)
We report on optical follow-up observations of the Einstein Probe fast X-ray transient EP240801a (Zhou et al. GCN 36997).
We observed the field of EP240801a using one of the 1-meter telescopes at the Las Cumbres Observatory node located at Siding Spring Observatory (Australia), with a single 300-sec exposure in SDSS-g band starting on 2024-08-01T16:45:15 (UTC), ~ 7.65 hours after the EP trigger, at an airmass of ~ 2.3. We detect the optical counterpart at the position reported by Fu et al. (GCN 36998) with g = 21.43 +/- 0.2 mag, calibrated with PanSTARRS and not corrected for Galactic extinction.
Detections of the optical counterpart have also been reported by Li et al. (GCN 36999), Zheng et al.(GCN 37000), Aryan et al. (GCN 37002), and An et al.(GCN 37004).
This work makes use of observations from the Las Cumbres Observatory global telescope network (program IAC2024B-004).
GCN Circular 37004
Subject
EP240801a: GSP follow-up observations of the candidate counterpart
Date
2024-08-01T18:47:30Z (a year ago)
From
Wenxiong Li <liwenxiong1992@gmail.com>
Via
Web form
J. An, D. Xu, W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farrah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report:
Following the detection of the fast X-ray transient EP240801a by the Einstein Probe (Zhou et al., GCN 36997), we initiated observations of the fast X-ray transient location starting on Aug 1 at 10:26 UT (~1.3 hours after the trigger) in the r band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at McDonald Observatory in the USA.
The optical counterpart reported by Fu et al. (GCN 36998), Li et al. (GCN 36999) and Zheng et al. (GCN 37000) was detected with r = 20.54+/-0.08 mag.
These observations were taken as part of the Global Supernova Project.
GCN Circular 37002
Subject
EP240801a: Kinder follow-up observations of the candidate counterpart
Date
2024-08-01T18:22:32Z (a year ago)
Edited On
2024-08-01T18:44:18Z (a year ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan (NCU), A. K. H. Kong (NTHU), H.-Y. Hsiao, W.-J. Hou, T.-W. Chen, Y. J. Yang (all NCU), S. Yang (HNAS), J. Gillanders (Oxford), C.-C. Ngeow, C.-S. Lin, C.-H. Lai, A. Sankar. K, M.-H. Lee, Y.-C. Pan, H.-C. Lin, J.-K. Guo (all NCU), S. J. Smartt (Oxford/QUB), H.-W. Lin (UMich), G. H. Sun, Z. N. Wang (both HNAS), 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 EP240801a (Zhou et al., GCN 36997) 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 13:45 UTC on the 1st of August 2024 (MJD = 60523.573), 4.66 hrs after the EP 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. In the stacked frames, we clearly detect the optical counterpart reported by Fu et al., (GCN 36998), and confirmed by Li et al. (GCN 36999) and Zheng et al. (GCN 37000).
Moreover, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the PSF photometry on our stacked frame. The details of the observations and measured photometry (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60523.573 | 4.66 hrs | 300 sec * 12 | 20.9 +/- 0.3 | 1".83 | 1.63
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) = 0.10 mag in the direction of the transient (Schlafly & Finkbeiner 2011).
GCN Circular 37000
Subject
EP240801a: KAIT optical counterpart observations
Date
2024-08-01T17:41:44Z (a year 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, automatically responded to the fast X-ray
transient EP240801a from the Einstein Probe (Zhou et al. GCNC 36997)
starting at 09:27 UT, ~0.41 hours after the trigger. A set of clear
(roughly R) filter images were obtained. The optical counterpart
reported by Fu et al. (GCN 36998) and Li et al. (GCN 36999) was
clearly detected in our coadded images. The preliminary photometry
results are shown below calibrated to the PS1 catalog:
Tmid-T0(hr) exp(s) Mag err
0.41 6x20s 19.86 0.07
0.54 6x40s 20.02 0.05
0.73 5x60s 20.05 0.04
0.93 5x60s 20.11 0.07
1.54 7x60s 20.17 0.06
1.93 9x60s 20.09 0.06
GCN Circular 36999
Subject
EP240801a: GMG observation
Date
2024-08-01T17:06:44Z (a year ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
email
R.-Z. Li, B.-T. Wang, J. Mao, X.-L. Zhang and J.-M. Bai (YNAO, CAS) report:
We observed the field of EP240801a (Zhou et al., GCN 36997, T0 at 2024-08-01T09:06:03) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2024-08-01T16:19:22, about 7.22 hours after the trigger.
The optical counterpart of EP240801a, not visible in the Pan-STARRS1 r-band image, was marginally detected at the coordinates (J2000):
RA = 23h00m39.02s
DEC = +32d35m37.2s
, with a positional uncertainty of 0.5" or better. The position is consistent with TRT observation (GCN 36998).
The preliminary analysis results are shown as follows:
+---------------+------------+----------+--------------+--------------+
| Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma UL |
+===============+============+==========+==============+==============+
| 7.39 | 1200 | R | 21.21 ± 0.12 | 21.9 |
+---------------+------------+----------+--------------+--------------+
The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.092 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).
We note that this optical counterpart has become fainter compared to the TRT observation (R = 20.32 ± 0.16 mag, GCN 36998).
GCN Circular 36998
Subject
EP240801a: TRT optical counterpart detection
Date
2024-08-01T14:58:20Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Y. Fu, J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, S.Q. Jiang, Z.P. Zhu, D. Xu, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:
We observed the field of EP240801a detected by Einstein Probe (EP, Zhou et al., GCN 36997), using the 0.7-m telescope of the Thai Robotic Telescope (TRT) network, located at Sierra Remote Observatories, USA. Observations started at 11:06:18 UT on 2024-08-01, i.e. 2.24 hr after the trigger, and 6 x 300 s frames were obtained in the R-band.
An uncatalogued source is detected in the individual as well as the stacked frames within the EP/FXT error circle (Zhou et al., GCN 36997) and localized at coordinates
R.A. (J2000) = 23:00:39.019
Dec. (J2000) = +32:35:37.20
with an uncertainty of ~ 0.5 arcsec. The source has R = 20.32 +/- 0.16 mag, calibrated with PanSTARRS and not corrected for Galactic extinction. There is no known source at the above position by checking MPC.
We thus conclude that the source is the optical counterpart of EP240801a.
Further observations are planned.
GCN Circular 36997
Subject
EP240801a: EP-WXT detection and EP-FXT follow-up observation of a fast X-ray transient
Date
2024-08-01T14:46:45Z (a year ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), W. X. Wang, J. W. Hu, Z. X. Ling, C. C. Jin, Y. Liu, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient (trigger ID: 01709015181), designated EP240801a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2024-08-01T09:06:03 (UTC). The position of the source is R.A. = 345.140 deg, DEC = 32.610 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for more than 80 seconds. The lightcurve of the transient observed by the WXT exhibits a rapid brightening profile. The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 1.9(+/-0.9) (with a free column density value of 3.1(+/-3.1) x 10^21 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 4.8(+/-3.1) x 10^-10 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
The autonomous EP-FXT follow-up observation started about 180s after the WXT trigger, and the observation clearly shows an uncatalogued X-ray source located at R.A. = 345.1630 deg, DEC = 32.5927 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The 0.5-10 keV light curve of the transient decays smoothly and lasts about 200s since the start time of the autonomous follow-up observation. The average 0.5-10 keV spectrum can be fitted by an absorbed power law with a photon index of 3.2(+/-0.4) (with a free column density value of 1.5(+/-0.7) x 10^21 cm^-2), giving an average unabsorbed flux of 1.5(+/-0.3) x 10^-11 erg/s/cm^2.
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).