- GCN Circular #39550
Z.P. Zhu, S.Q. Jiang, X. Liu, J. An, S.Y. Fu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP250302a detected by Einstein Probe (Trigger ID: 01709132186), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 15:47:09 on 2025-03-02, i.e., 11.08 min after the EP trigger, and a series of unfiltered frames with different exposures were obtained.
An uncatalogued and varying optical source is detected within the EP/WXT error circle at coordinates
R.A.(J2000) = 11:18:03.58
Dec.(J2000) = +33:35:09.06
with an uncertainty of ~0.5 arcsec. The source has R ~ 18.3 mag at a median time of 11.58 min after the EP trigger, calibrated with Legacy Survey DR10 and not corrected for Galactic extinction. We conclude that the source is the optical counterpart of EP250302a.
Observations are still ongoing, and spectroscopy is encouraged.
- GCN Circular #39551
Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report:
We observed location of EP250302a (Trigger ID: 01709132186; Zhu et al., GCN 39550) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously. Observations started at 19:28:31 UT on 2025-03-02, corresponding to ~3.87 hr after the EP-WXT trigger. At the location of the optical counterpart reported by Zhu et al. (GCN 39550) we detect a clear source with brightness r~20.3 AB mag. This confirms the fading of the source and its relation to EP250302a.
We note the presence of a GLADE+ galaxy (~570 Mpc; photometric) at an offset of ~20" (Dalya et al. 2022). There is no underlying source at the position of this optical transient in Legacy Survey imaging. Further observations are encouraged.
We thank Michael Schmidt from the staff of the Wendelstein Observatory for obtaining these observations.
- GCN Circular #39553
S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:
we observed the field of the X-ray transient EP250302a (Einstein Probe mission, Trigger ID 01709132186) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2025-03-02 20:40:11 UT (approximately 5 hours after the EP-WXT trigger) stacking 50x40s calibrated Rc-band CCD images.
We detect an optical transient candidate at the position reported by Zhu et al. (GCN 39550). Preliminary photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err.
2025-03-02 20:57:42 UT 5.35 50x40s Rc 20.36 +/-0.08
consistent with other observation reported by Busmann et al., GCN 39551.
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
Further observations are ongoing.
- GCN Circular #39555
Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team:
We observed the field of EP250302a detected by Einstein Probe (Trigger ID: 01709132186) with C-GFT. Our observations were started on 2025-03-02T15:43:07 UTC, ~7.05 mins after the trigger. The optical counterpart (reported by Zhu et al. GCN 39550, Busmann et al., GCN 9551,Leonini et al., GCN 39553) was clearly detected in stacked images of band g,r and i. The results are,
(T-T0)_mid(sec) mag mag_err band
------------------------------------------
462 18.13 +/- 0.10 i
553 18.31 +/- 0.09 g
664 18.14 +/- 0.07 r
The photometry was calibrated with nearby Pan-STARRS1 stars. Further analysis is on-going.
We thank the observation assistants Bowen Li at Jilin observatory for their excellent support.
Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope.
- GCN Circular #39556
C. Y. Dai (NJU), Y.Q. Zhao (USTC, PRIC), X. Mao, S. X. Wen, W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250302a. The transient triggered EP-WXT (ID: 01709132186) at 2025-03-02T15:36:04 (UTC). The light curve shows a burst lasting at least 30s, with a peak of about 9 x 10^(-9) erg/s/cm^2. The spectrum can be fitted by an absorbed power-law with a photon index of 0.6(-0.4/+0.4) (with the column density fixed at the Galactic one of 2.36 x 10^20 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 7.0(-1.6, +2.0) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 169.5151 deg, DEC = 33.5851 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). A secondary burst is detected starting at 2025-03-02T15:56:06 (UTC) and last for ~500 s, the spectrum during the flare can be fitted by an absorbed power-law with a photon index of 1.8(-0.05/+0.0.5) (with the column density fixed at the Galactic one of 2.36 x 10^20 cm^-2), and the derived average unabsorbed 0.5-10 keV flux is 9.6(-0.4, +0.4) x 10^(-11) erg/s/cm^2.
Additionally, we note that the optical counterparts (GCN 39550, GCN 39551, GCN 39553, and GCN 39555) lie within the positional uncertainty of EP-FXT.
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 #39557
K.L. Page, P.A. Evans (U.Leicester) and J. DeLaunay (PSU) report on
behalf of the Swift XRT Team:
On 2025 March 02 at 16:36 UT, Swift started observing EP250302a, 3.6 ks
after the trigger (GCN Circ. 39556). A fading X-ray source was identified,
at a position of RA, Dec = 169.51508, +33.5858, which is equivalent to
RA (J2000): 11h 18m 03.62s
Dec (J2000): +33d 35′ 09.0″
with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position
is consistent with the optical counterpart reported in GCNs 39550, 39551,
39553 and 39555.
The X-ray flux at the start of the observation was (5.0 +-/ 1.1) x 10^-11
erg cm^-2 s^-1 (0.3 - 10 keV), fading to a value of (7.1 +/- 0.9) x 10^-12
erg cm^-2 s^-1 at 8 ks post trigger. The decay can be fitted with a
power-law slope of alpha = 2.36 (+0.37/-0.32).
- GCN Circular #39558
L. P. Xin, X. H. Han, P. P. Zhang, J. Wang, C. Wu, Y. L. Qiu, H. B. Cai, H. L. Li, X. M. Lu, R. S. Zhang, Y. J. Xiao, J. S. Deng, Z. H. Yao, Y. N. Ma, J. Y. Wei (NAOC), X. G. Wang, E. W. Liang (GXU) report:
We observed location of EP250302a (Trigger ID: 01709132186, Dai et al., GCN 39556) with F60B telescope in R band at Xinglong observatory, China. Observations started at 15:42:43 UT on 2025-03-02, 6.5 min after the EP-WXT trigger.
The optical counterpart reported (Zhu et al., GCN 39550, Busmann et al., GCN 39553, Leonini et al., GCN 39553, Wu et al., GCN 39555) within the FXT and XRT locations (Dai et al., GCN 39556, Page et al., GCN 39557) was clearly detected in the stacked image with an exposure time of 10*50 sec. The brightness was estimated to be R=18.36+/-0.13 mag calibrated to USNO B1.0 R2 magnitude.
- GCN Circular #39559
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250302a (EP Team et al., GCN 39556) errorbox 328 sec after notice time and 57360 sec after trigger time at 2025-03-03 07:32:04 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 73 deg. The sun altitude is -35.3 deg.
The galactic latitude b = 70 deg., longitude l = 190 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2797947
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
57390 | 2025-03-03 07:32:04 | MASTER-OAFA | (11h 18m 00.44s , +33d 56m 34.8s) | C | 60 | 19.8 |
58371 | 2025-03-03 07:48:24 | MASTER-OAFA | (11h 18m 02.25s , +33d 57m 27.8s) | C | 60 | 19.5 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #39560
C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), M. Dennefeld (IAP/CNRS/Sorbonne U.), E. Le Floc'h (CEA/Irfu), J. P. Palmerio (CEA/Irfu), A. Saccardi (CEA/Irfu), J. Schmitt (OHP/Pytheas/AMU), F. Schüssler (CEA/DPhP), D. Turpin (CEA/Irfu), S. D. Vergani (CNRS, Paris Obs./LUX) report on behalf of the larger collaboration:
We observed the field of the EP250302a (Dai et al. GCN 39556) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 2 exposures (2x600 s) in the r-band. The first epoch started at 23:38:10 UT on 2025-03-02 (8.03h after the trigger) and the second one at 01:02:41 UT on 2025-03-03 (9.43h after the trigger). In both images, we clearly detected the optical counterpart reported by Zhu et al., GCN 39550, Busmann et al., GCN 39551, Leonini et al., GCN 39553 and Xin et al., GCN 39558.
The preliminary magnitudes derived for that source are:
r = 20.75 +/- 0.06 mag (AB)
r = 20.85 +/- 0.07 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction.
In addition, we obtained 2x30 min exposures with the MISTRAL spectroscopic blue setting, covering from 4200 to 8000 AA starting at 00:20:45UT (midtime = T0+8h45).
In a preliminary reduction of the spectrum, we detect a very faint continuum at the GRB position, covering the whole spectral range and suggesting a redshift lower than 2.5.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Neda Heidari and Stephane Favard for the MISTRAL observations.
- GCN Circular #39564
L. Izzo (INAF/OACn and DARK/NBI), R. A. J. Eyles-Ferris (Univ. Leicester), D. Xu (NAOC), A. Saccardi (CEA/Irfu), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. T. Palmerio (CEA/Irfu), N. R. Tanvir (Univ. Leicester), P. G. Jonker (Radboud Univ.), S. D. Vergani (CNRS - Paris Observatory/LUX), A. J. Levan (Radboud Univ. and Warwick Univ.), report on behalf of the Stargate collaboration:
We observed the optical/NIR counterpart (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Becerra et al., GCN 39562) of the fast X-ray transient EP250302a (Dai et al., GCN 39556) using the ESO VLT UT4 (Yepun) equipped with the MUSE integral-field spectrograph.
The observation mid-epoch is 2025 March 3.193 UT (13.03 hr after the initial high-energy trigger), the total exposure time is 76.5 min, and the covered wavelength range is 4750-9300 AA.
The optical counterpart (Zhu et al., GCN 39550) is well detected in the wavelength-stacked “white light” image, as well as in continuum spectroscopy. We also observe several clear absorption features, which we interpret as due to Mg I (2853), Mg II (2804, 2796), and Fe II (2600, 2587, 2383, 2374, 2344), all at a common redshift z = 1.131.
Given the overall good S/N of the spectrum, and the fact that there are no features left un-identified, we consider z = 1.131 to be most likely the redshift of EP250302a.
Our spectra do not cover the blue region where the z = 0.549 features reported by Yang et al. (GCN 39561) would fall, so we cannot confirm the presence of that system, which could be an intervening absorber. No emission lines at z = 0.549 appear in our data.
Thanks to the large MUSE field of view (1' x 1'), further to the optical transient, two neighboring bright galaxies were covered in our observation, including the one noted by Busmann et al. (GCN 39551) and Yang et al. (GCN 39561). For them, we measure the following redshifts:
1) RA = 11:18:05.26, Dec = +33:35:05.6: z = 0.127 from Na I D, Mg b, Hbeta, G band absorption;
2) RA = 11:18:01.03, Dec = +33:35:30.8: z = 0.127 from Halpha, [N II] and [S II] emission.
We conclude that these objects are not physically associated with EP250302a.
We thank Malte Busmann and Brendan O’Connor for sharing a finding chart of the field, and the ESO observing staff in Paranal, in particular Claudia Cid, Monika Petr-Gotzens, and Jonathan Smoker, for efficiently carrying out these observations.
- GCN Circular #39565
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of a fast X-Ray transient EP250302a (Zhu et. al, GCN 39550; Busmann et. al, GCN 39551; Leonini et. al, GCN 39553; Wu et. al, GCN 39555; Dai et. al, GCN 39556; Page et. al, GCN 39557; Xin et. al, GCN 39558; Lipunov et. al, GCN 39559; Adami et. al, GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564) in the R filter with the AZT-33IK 1.5-meter telescope of Mondy observatory. The observations began on 2025-03-02 (UT) 15:50:41.578, i.e. 0.01083 days since trigger. The optical counterpart (firstly reported by Zhu et. al, GCN 39550) is clearly detected in each image of an exposure of 120 sec. The optical light curve displays variable behavior. Initially, the light curve fades until ~1.5e-2 days since trigger, then it is brightening until it reaches peak magnitude of R = 17.26 +/- 0.03 mag at 2025-03-02 (UT) 16:14:42 (0.02751 days since trigger). The further brightness evolution is a decay by the times indicated in Adami et. al, GCN 39560. Our photometry is based on nearby stars from the USNO-B1.0 catalog (see the list below) and has not been corrected for the Galactic extinction.
Ref. stars
RA Dec R2
11:18:11.14 +33:32:45.34 15.74
11:17:47.64 +33:30:50.19 17.69
The light curve image is available at: http://grb.rssi.ru/grb250302B/EP250302a_LC.jpg
- GCN Circular #39567
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of EP250302a (Dai et al., GCN 39556) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the J, H, and K bands, started on 2025 March 03 at 02:15:53 UT (i.e. 10.66 hr after the burst), and lasted for about 1 hour.
From preliminary analysis, we do not find any counterpart at the position of the reported optical afterglow (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., 39565) down to the following 3sigma limit:
H > 16.1 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 11.09 hours after the trigger.
- GCN Circular #39568
A. Reguitti (INAF-OAB) reports on behalf of the CIBO (Coordinamento Italiano Burs
t Ottici) collaboration:
We observed the field of EP250302a (Zhu et al., GCN 39550) from the INAF - Padova Astronomical Observatory located in Asiago (Italy) with the 67/92 Schmidt roboti
c telescope. The observation was carried in the Sloan-i filter, started on 2025 March 02 at 20:01:15 UT (i.e. 4.4 hr after the burst), and lasted for 15 minutes.
In our stacked images, the optical counterpart is detected at the coordinates reported by Zhu et al., GCN 39550:
i = 19.98+-0.17 mag (AB; calibrated against the PS1 catalogue),
at a mid-time of about 4.5 hours after the trigger.
- GCN Circular #39569
T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), D. Berdikhan (NU), B. Grossan (UCB, NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at EP250302a on receipt of an automated GCN / EP position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).
We started observations at 15:42:43 UT on 2025-03-02, 399 seconds after the Einstein Probe trigger (Dai et al., GCN 39556). Observations were made in partially cloudy conditions. A new and changing source consistent with the XRT position (Page et al., GCN 38761) was detected. We report the following photometric values for the optical transient:
tc-t0(s) g'(mag) err r'(mag) err exposure_time (s)
--------------------------------------------------------------
424 - 18.36 0.08 50
628 - 18.35 0.08 300
928 - 18.80 0.13 300
1273 - 18.76 0.07 240
1513 - 18.55 0.06 240
1753 - 18.12 0.04 240
1993 - 17.71 0.03 240
2233 - 17.58 0.02 240
2686 - 17.48 0.03 240
2926 - 17.54 0.02 240
3166 - 17.58 0.02 240
3406 - 17.65 0.02 240
3646 - 17.68 0.03 240
3886 - 17.73 0.03 240
4126 - 17.85 0.03 240
4366 - 17.88 0.04 240
4606 - 17.95 0.03 240
4846 - 18.08 0.04 240
5086 - 18.11 0.03 240
5326 - 18.18 0.04 240
5566 - 18.32 0.04 240
5806 - 18.47 0.04 240
6046 - 18.56 0.04 240
6348 18.93 0.05 18.56 0.04 240
6588 18.99 0.06 18.76 0.04 240
6828 19.01 0.05 18.86 0.05 240
7068 19.05 0.05 18.86 0.05 240
7308 19.06 0.05 18.90 0.05 240
7548 19.12 0.05 18.94 0.05 240
7788 19.28 0.07 19.01 0.06 240
8028 19.43 0.08 19.01 0.06 240
8269 19.53 0.08 19.19 0.07 240
8509 19.34 0.06 19.19 0.06 240
tc-t0 = trigger time minus image center time. Calibration was done with 4 bright Pan-STARRS catalog stars on our images.
Our results are in agreement with those reported in previously published circulars (Zhu et. al, GCN 39550; Wu et. al, GCN 39555; Xin et. al, GCN 39558; Pankov et al., GCN 39565).
We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate.
----------------------------------
NU = Nazarbayev University, Astana, Kazakhstan
UCB = University of California, Berkeley, USA
FAI = Fesenkov Astrophysical Institute, Kazakhstan
This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
- GCN Circular #39570
S. P. R. Shilling (Lancaster U.) and A. A. Breeveld (UCL-MSSL) reports on behalf of the
Swift UVOT team:
Swift/UVOT observed the field of EP250302a (Dai et al., GCN 39556) for 1029 seconds
in the U-band starting at 16:36:56 UT, 1 hour after the detection by Einstein Probe WXT.
A source consistent with the EP-FXT position (Dai et al., GCN 39556) is detected and
appears to be fading. The preliminary detection magnitudes reported below are calculated
using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).
The magnitude at the start of the observation is 17.64 +/- 0.05 (1 hour post trigger)
and decays to 18.88 +/- 0.12 (~2 hours post trigger).
We note that an X-ray source at the EP-FXT position was independently observed by the
Swift/XRT (Page et al., GCN 39557). We also note that, in addition to the Swift/UVOT,
various other facilities have observed an optical counterpart at this position
(Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553;
Wu et al., GCN 39555; Xin et al., GCN 39558; Lipunov et al., GCN 39559;
Adami et al., GCN 39560; Becerra et al., GCN 39562; Pankov et al., GCN 39565;
Reguitti et al., GCN 39568; Komesh et al., GCN 39569).
- GCN Circular #39572
A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y. J. Yang, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, M.-H. Lee, H.-C. Lin, C.-H. Lai, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, 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 EP250302a (Zhu et al., GCN 39550; Dai et al., GCN 39556) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first SLT epoch of observations in the r band started at 18:30 UT on the 2nd of March 2025 (MJD = 60736.771), ~2.91 hrs after the EP trigger.
We took a total of 12 frames in r-band spanning a period of about 2.91hr to 5.22hr since the EP-WXT trigger. The optical counterpart candidate proposed by Zhu et al., (GCN 39550 ) and confirmed by several other observations (Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; and Izzo et al., GCN 39564), was clearly detected in almost each of the individual frame (besides the last frame).
We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on individual frames. The details of the observation and measured photometry from the first frame (in the AB system) were as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | Seeing | Airmass
SLT | r | 60736.771 | 2.91 | 300 * 1 | 19.60 +/- 0.05 | 1".25 | 1.14
The presented magnitude was calibrated using the field stars from the Pan-STARRS1 catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.06 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011).
- GCN Circular #39574
Yu-Han Yang (U Rome), Eleonora Troja (U Rome), and Rosa Becerra (U Rome) report on behalf of the ERC BHianca team:
A further analysis was performed on the VLT/X-shooter spectrum reported by Yang et al. (GCN 39561). Whereas no significant features are visible in the VIS and NIR arms, we note the presence of absorption features at the edge of the UVB spectrum, consistent with Fe II (2600, 2587, 2383, 2374, 2344) at redshift z=1.131 as reported by Izzo et al. (GCN 39564). We therefore confirm this as the likely redshift of the EP transient.
- GCN Circular #39575
D. Eappachen (IIA), V. Swain (IITB), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP250302a (Dai et al., GCN 39556) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-03-02 20:51:47 UT, i.e., 5.26 hours after the EP trigger. We obtained two exposures of 360 seconds each in both r' and g' filters. We clearly detected the optical counterpart in our stacked images at the position given by HMT-0.5m telescope (Zhu et al., GCN 39550). The photometry results are as follow:
| JD (mid) | t-t0 (hours) | Filter | Exposure (s) | Mag (AB) |
| ----------------- | ------------ |------- | ------------ | --------------|
| 2460737.373565 | 5.36 | r' | 2x360s | 20.40+/- 0.11 |
| 2460737.390706 | 5.78 | g' | 2x360s | 20.66+/- 0.10 |
Our results are consistent with Zhu et al., (GCN 39550); Busmann et al., (GCN 39551); Leonini et al., (GCN 39553); WU et al., (GCN 39555); Xin et al., (GCN 39558); Adami et al., (GCN 39560); Pankov et al., (GCN 39565); Reguitti et al., (GCN 39568); Komesh et al., (GCN 39569); Shilling et al., (GCN 39570).
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
- GCN Circular #39576
A. S. Moskvitin, O. A. Maslennikova (SAO RAS), A. Pozanenko (IKI)
and N. Pankov (HSE, IKI) report on behalf of larger collaboration.
We observed the field of the X-ray transient EP250302a (Dai et al.,
GCN 39556; Page et al., GCN 39557) with SAO RAS 1-m telescope
Zeiss-1000 equipped with CCD-photometer under mediocre weather
conditions. We obtained two sets of 300-sec images in Rc band.
1st set: 2025.03.02, 20:33:49 -- 2025.03.02, 22:09:49 UT
(t_mid - T0 = 0.24010 days = 5.7625 hours);
2nd set: 2025.03.02, 23:55:53 -- 2025.03.03, 01:00:10 UT,
(t_mid - T0 = 0.36942 days = 8.8660 hours).
The OT (Zhu et al., GCN 39550; Busmann et al., GCN 39551;
Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al.,
GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561;
Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al.,
GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling
and Breeveld, GCN 39570; Aryan et al., GCN 39572) is clearly detected
in our stacked frames with the following brightness.
Date UT start t-T0 (mid),d Exp.,s Filter OT Err. UL(3sigm)
2025.03.02 20:33:49 0.24010 8x300 R 20.18 0.09 22.5
2025.03.02 23:55:53 0.36942 7x300 R 20.51 0.10 22.5
Above photometry is preliminary and calibrated against R2 magnitudes
of nearby USNO-B1 stars and not corrected for the Galaxy extinction.
- GCN Circular #39578
C. Wu, D. H. Zhao, Y. N. Ma, L. P. Xin, Y. L. Qiu, H. L. Li, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei(NAOC), J. T. Palmerio(CEA/Irfu) report on behalf of the SVOM team:
The SVOM/VT conducted a ToO follow-up observations of the EP250302a (Zhu et al., GCN 39550) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
The optical counterpart of EP250302a(Trigger ID: 01709132186, Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling and Breeveld, GCN 39570; Aryan et al., GCN 39572, Moskvitin et al., GCN 39576) was clearly detected in VT_R and VT_B images.
The brightness in AB manigutude was estimated to be 21.41 +/-0.09 mag in VT_R (stacked image: 50x60s), and 22.68 +/-0.14 mag in VT_B (stacked iamge: 50x60s), measured at the mid time of 1.03 days post the burst.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
- GCN Circular #39586
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), A. Moskvitin (SAO RAS) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of a fast X-Ray transient EP250302a (Dai et al., GCN 39556; Page et al., GCN 39557) in the R filter with the 1.5-meter telescope of Sayan Solar Observatory (Mondy). The observations began on 2025-03-03 (UT) 19:29:15, i.e. ~1.18 days since trigger. The optical source (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling and Breeveld, GCN 39570; Aryan et al., GCN 39572; Moskvitin et. al, GCN 39576; Wu et. al, GCN 39578) is detected in the stacked image of 28*120 seconds. The preliminary photometry is as follows:
Date UT start t-T0 Exptime Filter OT Err. UL
(mid, days) (s) (3sigma)
2025-03-03 19:29:15 1.18136 28*120 R 22.12 0.14 23.4
The photometry is based on nearby stars from the USNO-B1.0 catalog (R2 magnitudes) and has not been corrected for the Galactic extinction.
- GCN Circular #39596
N. Pankov (HSE, IKI), A. Moskvitin (SAO RAS), O. I. Spiridonova (SAO RAS), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We performed optical observations of the field of a fast X-Ray transient EP250302a (Dai et al., GCN 39556; Page et al., GCN 39557) in the R filter with the 2.6-meter telescope of the Crimean Astrophysical Observatory (CrAO) and the 1-meter Zeiss-1000 telescope of the Special Astrophysical Observatory of the RAS (SAO RAS). The observations began on 2025-03-03 (UT) 01:51:40, i.e. 1.42750 days since trigger. The optical source (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling and Breeveld, GCN 39570; Aryan et al., GCN 39572; Moskvitin et. al, GCN 39576; Wu et. al, GCN 39578; Pankov et. al, GCN 39586; Gupta et. al, GCN 39593) is not detected in the stacked images from both telescopes. The preliminary upper limits are as follows:
Date UT start t-T0 Exptime Filter UL Telescope
(mid, days) (s) (3sigma)
2025-03-03 01:51:40 1.44460 9*300 Rc 22.7 Zeiss-1000/SAO RAS
2025-03-04 23:21:23 2.33286 14*120 R 23.3 ZTSh/CrAO
The photometry is based on nearby stars from the USNO-B1.0 catalog (R2 magnitudes) and has not been corrected for the Galactic extinction.
- GCN Circular #39698
B. O'Connor (CMU), D. Pasham (MIT), J. Hare (Catholic/GSFC), report on behalf of a larger collaboration:
We observed EP250302a (Dai et al., GCN 39556) with the Chandra X-ray Observatory through Director's Discretionary Time (PI: O'Connor) for ~20 ks starting on 2025-03-11 at 14:04:47 UT, corresponding to 8.9 d (observer frame) after the EP trigger. We detect a clear X-ray source at the position of the optical (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling and Breeveld, GCN 39570; Aryan et al., GCN 39572; Moskvitin et. al, GCN 39576; Wu et. al, GCN 39578; Pankov et. al, GCN 39586; Gupta et. al, GCN 39593) and X-ray (Dai et al., GCN 39556; Page et al. GCN 39557) counterpart at:
RA, DEC (J2000) = 11:18:03.6, +33:35:09.6
with an uncertainty of ~0.8". The source flux is consistent with the afterglow decay inferred from Swift/XRT. Further analysis is planned.
We thank Pat Slane for rapidly approving our DDT request, and the entire staff of the Chandra X-ray Observatory, in particular Vinay Kashyap, for rapidly scheduling these fast observations.
- GCN Circular #39778
Ailing Wang (IHEP), Tao An (SHAO), Cuiyuan Dai and Xiangyu Wang (NJU), report on behalf of a larger collaboration:
We report radio observations of EP250302a (GCN 39556) conducted with the Karl G. Jansky Very Large Array (VLA) on 2025 March 15, UT02:17-03:38 (approximately T0+13 days after the initial trigger). Observations were carried out across three frequency bands (Ku/X/C bands). The preliminary results show 4-4.5 sigma detection at the position reported by X-ray and optical observations (e.g., GCN 39550, 39557). The image noise ranges from 6.4 to 10 microJy/beam. The source exhibits a relatively flat spectrum between 4 and 18 GHz. Follow-up VLA observations are planned to verify the detection and trace the flux density evolution.
- GCN Circular #39907
P. Minaev (IKI), A. Pozanenko (IKI), S. Grebenev (IKI), I. Chelovekov (IKI)
and IKI GRB-FuN
We searched the INTEGRAL dataset for gamma-ray emission from the X-ray
transient EP250302a, detected with WXT EP (Dai et al., GCN 39556). No
significant excess above the background was detected during the EP250302a
in any of the detectors. The source EP250302a is located 71 degrees
off-axis of the INTEGRAL telescopes' field of view. In particular, for the
SPI-ACS detector, the upper limit (3-sigma) for the fluence from an event
with a duration of 100 sec (during the first and second EP250302a episodes)
is 3.2e-6 erg*cm^-2 using the softest simulated CPL spectrum with Ep = 20
keV. The SPI-ACS estimating is based on the calibration given in the paper
https://ui.adsabs.harvard.edu/abs/2023MNRAS.525.2411M
We thank the INTEGRAL Observatory and all the staff who have served it for
over 22 years. Blessed be the memory of its deeds.
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