Previous IAU Circulars - none
Results of Observations
- GCN Circular #38586
H. Zhou (PMO, CAS), R. D. Liang (NAO, CAS), S.-F. Zhu (USTC), Z. X. Ling (NAO, CAS) report on behalf of the Einstein Probe team:
We report on the detection of an X-ray transient by the Einstein Probe (EP), designated as EP241217a (Trigger ID: 01709129076). The source triggered the on-board processing unit of the Wide-field X-ray Telescope (WXT) at 2024-12-17T05:36:03 (UTC). The WXT position of the transient is R.A. = 46.957 deg, Dec. = 30.901 deg, with an uncertainty of 2.8 arcmin (90%). No previously known bright X-ray sources are found within the error circle around the transient position.
The Follow-up X-ray Telescope (FXT) onborad EP performed an autonomous follow-up observation and found an uncatalogued X-ray source, located at R.A., Dec. = 46.9398, 30.9299 deg with an uncertainty of about 20 arcsec (90%). More information will be updated when the telemetry data is received. The ZTF and PANSTARR images show there are one point source and an extended source within the 90% unceratinty of the localization, and the distances to the FXT position are about 18.9" and 9.7", respectively. Further observations are encouraged to explore the origin of EP241217a.
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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. - GCN Circular #38587
A. J. Levan (Radboud/Warwick), J. C. Rastinejad (Northwestern), D. B. Malesani (DARK/NBI & Radboud), P. G. Jonker (Radboud), J. A. Quirola-Vasquez (Radboud) report for a larger collaboration:
We obtained observations of EP241217a (Zhou et al., GCN 38586) with the GMOS instrument on the Gemini North telescope. Observations in the z band began at 08:04 UT, approximately 2.5 hr after the EP-WXT detection.
Within the EP-FXT error circle (Zhou et al., GCN 38586) we clearly identify a new source, not present in the Pan-STARRS imaging of the field, with an approximate magnitude of z ~ 19.9 and a position ofRA(J2000) = 03:07:46.20 DEC(J2000) = +30:55:45.9
with an uncertainty of <0.5". We suggest this is the optical counterpart of EP241217a.
We thank the staff of Gemini for rapidly obtaining these observations. - GCN Circular #38588
L. Izzo (INAF-OACn and DARK/NBI), and D. B. Malesani (DAWN/NBI and Radboud Univ.) report:
We observed the field of EP241217A (Zhou et al., GCN #38586) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at the MacDonald Observatory, TX, USA. Observations started on 2024 December 17 at 06:37 UT (1.02 hr after the EP trigger). We obtained a series of 3x180 s images in the SDSS-r filter.
The optical object reported by Levan et al. (GCN #38587) is weakly detected in our image. We measure a preliminary magnitude of r = 20.99 +/- 0.21 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog.
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719. We also acknowledge the use of the ECSnoopy package by E. Cappellaro. - GCN Circular #38592
L. L. Fan (HNAS), A. Aryan, T.-W. Chen, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), K. W. Smith, S. J. Smartt (Oxford/QUB), A. Sankar.K, Y.-H. Lee, H.-Y. Miao, Y. J. Yang, M.-H. Lee, W.-J. Hou, C.-C. Ngeow, Y.-C. Pan, C.-H. Lai, H.-C. Lin, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, S. Yang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, 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 EP241217a (Zhou et al., GCN 38586) using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024; arXiv:2406.09270). The first LOT epoch of observations started at 12:56 UT on the 17th of December 2024 (MJD 60661.539), 7.34 hr 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 frame, we clearly detected the optical counterpart candidate proposed by Levan et al. (GCN 38587), and also observed by Izzo et al. (GCN 38588).
Further, we utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on our stacked frames. The details of the observations and measured PSF magnitudes (in the AB system) of the possible counterpart of EP241217a are as follows:Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 60661.539 | 7.34 | 300 * 15 | 21.24 +/- 0.33 | 1".55 | 1.01
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 = 0.52 mag in the direction of the burst (Schlafly & Finkbeiner 2011). - GCN Circular #38593
A. J. Levan (Radboud/Warwick), J. A. Quirola-Vasquez (Radboud), J. C. Rastinejad (Northwestern), D. B. Malesani (DAWN/NBI & Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD) report for a larger collaboration:
Following the detection of EP241217a (Zhou et al. GCN 38586) and its optical counterpart (Levan et al., GCN 38587; Izzo & Malesani, GCN 38588, Fan et al. GCN 38592) we obtained 1600 s of optical spectroscopy with GMOS-N on Gemini-N and the R400 grating. Spectra cover the range ~5500-9500 AA.
A preliminary reduction of the data shows a bright continuum with a strong break at ~6820 AA, along with several narrow absorption lines, which we interpret as due to Si II, C II, weak C IV, Fe II, Al II, all at a common redshift of z = 4.59 (based on a provisional wavelength calibration). We suggest this is the redshift of EP241217a.
We thank the staff of Gemini-North for the rapid execution of these observations. This work made use of the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). - GCN Circular #38595
M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team:
The location of the EP-WXT event EP241217A (Zhou et al., GCN 38586) was occulted by the Earth at the EP trigger time T0=2024-12-17T05:36:03 UTC. There was no Fermi-GBM onboard trigger around the EP-WXT trigger time. The location becomes visible at around ~T0+104 s.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP trigger time, seeking signals between 64 ms and 32.768 s in duration. A long soft transient was found around T0-42 s, but its localization is not consistent with the EP transient’s one (which is still covered by the Earth at that time). No signal consistent both temporally and spatially is identified, as confirmed by visual inspection of the data.
[1] Goldstein et al. 2019 arXiv:1903.12597 - GCN Circular #38596
M. A. Williams (PSU), M. H. Siegel (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), S. Dichiara (PSU), and P.A. Evans (U. Leicester) report on behalf of the Swift team:
Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected X-ray transient EP241217a. We searched for X-ray sources in 1.6 ks of Photon Counting (PC) mode data. The total exposure at the position of the transient (see below) is 1.537 ks, obtained between T0+24.2 ks and T0+25.7 ks.
An uncatalogued X-ray source is detected within the estimated 90% EP/FXT error region (20 arcsec) and is believed to be associated with the EP source (GCN Circ. 38586). Using 1537 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 46.94156, +30.92977 which is equivalent to:RA (J2000): 03h 07m 45.98s Dec(J2000): +30d 55' 47.2"
with an uncertainty of 4.1 arcsec (radius, 90% confidence). This position is 0.091 arcmin from the EP/FXT position and 3.2 arcsec from the optical counterpart reported by Levan et al. (GCN Circ. 38587). The peak count rate is 0.039 (+0.007, -0.006) ct s-1 (0.3 — 10 keV), which suggests fading from the EP/WXT detection. The observed 0.3-10 keV flux is 1.5 (+0.7, -0.3) × 10-12 erg cm-2 s-1.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.7 (+0.5, -0.4). The best-fitting absorption column is 1.9 x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.89 × 10^-11 (4.99 × 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:Galactic column: 1.9 x 10^21 cm^-2 Photon index: 1.7 (+0.5, -0.4)
The Swift/UVOT began settled observations of the field of EP 241217a 24.3 ks after the EP trigger. A 1639s image taken in the u filter shows no optical transient at the XRT position down to a limit of u=20.83. We show no source consistent with that reported by Levan et al. (GCN Circ. 38587), Izzo et al. (GCN Circ. 38588), and Fan et al. (GCN Circ 38592). The lack of UVOT detection would be consistent with the redshift of z=4.6 reported by Levan et al. (GCN Circ. 38593). - GCN Circular #38603
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 EP241217a ( EP Team et al., GCN 38586) errorbox 26048 sec after notice time and 70566 sec after trigger time at 2024-12-18 01:12:09 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 63 deg. The sun altitude is -17.7 deg.
The galactic latitude b = -23 deg., longitude l = 155 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2712866
We obtain a following upper limits.Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 70597 | 2024-12-18 01:12:09 | MASTER-OAFA | (03h 07m 45.73s , +30d 58m 27.8s) | C | 60 | 15.7 | 70657 | 2024-12-18 01:12:09 | MASTER-OAFA | (03h 07m 45.73s , +30d 58m 27.6s) | C | 180 | 18.3 | Coadd 70798 | 2024-12-18 01:15:31 | MASTER-OAFA | (03h 07m 46.25s , +30d 56m 36.0s) | C | 60 | 18.1 | 71479 | 2024-12-18 01:26:51 | MASTER-OAFA | (03h 07m 45.08s , +30d 57m 01.2s) | C | 60 | 18.0 | 71678 | 2024-12-18 01:30:10 | MASTER-OAFA | (03h 07m 48.27s , +30d 58m 57.0s) | C | 60 | 17.3 | 71738 | 2024-12-18 01:30:10 | MASTER-OAFA | (03h 07m 48.28s , +30d 58m 57.0s) | C | 180 | 18.3 | Coadd 72347 | 2024-12-18 01:41:19 | MASTER-OAFA | (03h 07m 47.62s , +30d 59m 09.1s) | C | 60 | 16.8 | 72549 | 2024-12-18 01:44:42 | MASTER-OAFA | (03h 07m 50.77s , +30d 59m 13.3s) | C | 60 | 18.4 | 73299 | 2024-12-18 01:57:11 | MASTER-OAFA | (03h 07m 43.89s , +30d 59m 05.1s) | C | 60 | 18.1 | 73359 | 2024-12-18 01:57:11 | MASTER-OAFA | (03h 07m 43.89s , +30d 59m 05.0s) | C | 180 | 19.5 | Coadd 74047 | 2024-12-18 02:09:39 | MASTER-OAFA | (03h 07m 42.54s , +31d 00m 30.4s) | C | 60 | 19.0 | 74252 | 2024-12-18 02:13:05 | MASTER-OAFA | (03h 07m 42.12s , +30d 58m 38.0s) | C | 60 | 18.8 | 74845 | 2024-12-18 02:22:57 | MASTER-OAFA | (03h 07m 48.62s , +30d 59m 56.1s) | C | 60 | 19.6 | 74905 | 2024-12-18 02:22:57 | MASTER-OAFA | (03h 07m 48.62s , +30d 59m 56.1s) | C | 180 | 20.0 | Coadd 75177 | 2024-12-18 02:28:30 | MASTER-OAFA | (03h 07m 48.54s , +30d 59m 10.1s) | C | 60 | 19.1 | 75669 | 2024-12-18 02:36:42 | MASTER-OAFA | (03h 07m 42.11s , +31d 00m 20.4s) | C | 60 | 19.0 | 76004 | 2024-12-18 02:42:16 | MASTER-OAFA | (03h 07m 47.92s , +31d 00m 30.0s) | C | 60 | 19.1 | 76064 | 2024-12-18 02:42:16 | MASTER-OAFA | (03h 07m 47.92s , +31d 00m 30.0s) | C | 180 | 19.8 | Coadd 76821 | 2024-12-18 02:55:53 | MASTER-OAFA | (03h 07m 43.45s , +31d 00m 04.7s) | C | 60 | 19.2 | 77238 | 2024-12-18 03:02:51 | MASTER-OAFA | (03h 07m 40.33s , +31d 02m 00.4s) | C | 60 | 19.2 | 77567 | 2024-12-18 03:08:20 | MASTER-OAFA | (03h 07m 38.60s , +31d 00m 08.7s) | C | 60 | 18.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited. - GCN Circular #38607
Junjie-Jin (NAOC), Yiming-Mao(NAOC), Zheng-Jie (NAOC), Haiyang-Mu(NAOC), Yinan-Zhu (NAOC), Qi-Zhao (NAOC), Feng-Xiao (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: We observed the field of the X-ray transient, EP 241217a by the Xinglong 0.8-m and 216 telescope located at Xinglong, Hebei, China. We obtained 6 x 600 s clear-band by 0.8-m telescop with a median time of 2024-12-17T10:12:27 , i.e., 5.5 hr after the EP trigger. We detected no optical object with the upper limit ～21 mag. Then we performed photometry on the Xinglong 2.16-m telescope located at Xinglong, Hebei, China, and obtained 6x600s clear-band frames with a median time of 2024-12-17T16:50:08 , i.e., 12 hr after the EP trigger. The optical object reported by Levan et al. (GCN #38587) is weakly detected in our image. We measure a preliminary magnitude of r = 21.4 +/- 0.14 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog.
We summarize our observation results as follows:Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name 1 | 2024-12-17 10:12:27 | 6x600 s | Clear |> 21.0 | Xinglong 80-cm Telescope 2 | 2024-12-17 16:50:08 | 6x600 s | Clear | 21.4 +/- 0.14 | Xinglong 2.16-m Telescope
- GCN Circular #38612
T. Mohan, V. Swain, R. Kumar, A.P. Saikia, D. Eappachen, A. Balasubramanian, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP241217a reported by EP-WXT (Zhou et al., GCN 38586) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2024-12-17T15:31:11 UT, i.e., 9.9 hours after trigger time. We obtained multiple exposures of 360 seconds in the r', i' and z' filters. We detected the source in i'-band at the coordinates given by Gemini North (Levan et al., GCN 38587). The obtained photometry are as follow:| MJD (mid)| tmid-t0 (in hours) | Filter | Total Exposure (s) | Magnitude (AB) | Lim Mag (5-sigma) | -------------|----- | ------ | ------------------ | -------------- | ---- | | 60661.77892 |13.09| r' | 5x360 | - | 20.8 | | 60661.69600 | 11.10| i' | 3x360 | 19.53 +/- 0.10 | 20.4 | | 60661.75717 |12.57 | i' | 5x360 | 19.92 +/- 0.11 | 20.4 | | 60661.73551 |12.05 | z' | 5x360 | - | 19.2 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The i band flux at the epoch of our observation is higher than the reported r and z band fluxes at earlier epochs in other optical detections (Levan et al., GCN 38587, Izzo et al., GCN 38588, Fan et al., GCN 38592, Jin et al., GCN 38607). We note that there is a WISE source present [WISEA J030746.09+305548.3](https://vizier.cds.unistra.fr/viz-bin/VizieR-S?WISEA%20J030746.09%2b305548.3s://) at the location, with a W1 band magnitude 17.591 +- 0.2.
Further observations are necessary to determine the nature of the source and presence of any variability.
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 #38613
Z.P. Zhu, X. Liu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. Amanda Djupvik (NOT) report on behalf of a large collaboration:
We observed the field of EP241217a detected by Einstein Probe (EP, Zhou et al., GCN 38586), using the StanCam instrument mounted on the Nordic Optical Telescope (NOT), with 9 x 180 s in the R band. Observations started at 19:14:21 UT on 2024-12-17, i.e. 13.6 hr after the trigger.
The previously reported optical counterpart (Levan et al., GCN 38587 & 38593; Izzo et al., GCN 38588; Fan et al., 38592; Jin et al., GCN 38607) is clearly detected in our stacked image, with a preliminary magnitude of R ~ 20.5 mag (AB), calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. - GCN Circular #38615
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP241217a (Zhou et al., GCN 38586) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS i’ filter starting at 2024-12-17 21:03:57 UT, approximately 15.5 hours after the trigger.
We report a detection of the optical counterpart in the stacked images of i = 20.26 ± 0.09 mag, at a position consistent with Levan et al., GCN 38587, Williams et al., GCN 38596. This is in line with i-band decay observations from Mohan et al., GCN 38612. The inferred red r-i colour (by comparison with values reported by Izzo et al., GCN 38588, Fan et al., GCN 38592, Jin et al., GCN 38607, Zhu et al., GCN 38613) is consistent with the high spectroscopic redshift of z~4.6 reported by Levan et al., GCN 38593.
The photometry was obtained using nearby PanSTARRS standards and was not corrected for extinction. - GCN Circular #38618
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 EP241217a (Zhou et al., GCN 38586), also detected by Swift-XRT (Williams et al., GCN 38596) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2024 December 18 at 00:45:27 UT (i.e. 19.1 hours after the EP-WXT trigger), and lasting for about 1 hour.
From preliminary photometry we do not detect any counterpart in the optical and NIR images at the position of the optical afterglow (Levan et al., GCN 38587; Izzo & Malesani, GCN 38588; Fan et al. GCN 38592; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek & Perle, GCN 38615) down to the following 3sigma magnitude upper limits:
r > 20.8 (AB; calibrated against the Pan-STARRS catalogue) at a mid-time of t - t0 = 19.6 hr after the trigger,
H > 16.6 (Vega; calibrated against the 2MASS catalogue) at a mid-time of t - t0 = 19.5 hr after the trigger. - GCN Circular #38624
H. Zhou (PMO, CAS), S.-F. Zhu (USTC), M. H. Zhang (NAO, CAS), H. Sun (NAO, CAS), C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team:
Since 2024-12-17T05:34:10 (UTC, about 113 seconds before the trigger time), EP241217a (Zhou et al., GCN 38586) was detectable for with the Wide-field X-ray Telescope (WXT) at low significance and peaked at about 52 seconds before the trigger. The mean and peak WXT count rate of the EP241217a before the slewing of EP is about 0.3 cnt/s and 1 cnt/s, respectively. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.93 (-0.59, +0.71) (with a fixed Milky Way equivalent hydrogen column density of 1.88 x 10^21 cm^-2). The derived average unabsorbed 0.5-4 keV flux is (7.3+/-2.7) x 10^-10 erg/s/cm^2.
In addition to the autonomous follow-up observation, we performed two follow-up observations of EP241217a with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The first observation began at 2024-12-17T13:21:55 (UTC, 7.64 h after the trigger of EP241217a), and the exposure time is about 3ks. The second observation began at 2024-12-18T09:57:58 (UTC, 28.37 h after the trigger), but the telemetry data has not been received yet.
Preliminary results of the autonomous (Zhou et al., GCN 38586) and the first follow-up observations are summarized:+--------------------------------------------------------------------------------+ T_Start [UTC] | T_mid - T0 [h] | Exp [s] | Flux (0.5-10 keV) [erg/s/cm^2] +--------------------------------------------------------------------------------+ 2024-12-17T05:38:53 | 1.02 | 3132 | (6.23+/-0.46) x 10^-12 * 2024-12-17T13:21:55 | 8.18 | 2966 | (1.35+/-0.22) x 10^-12 +--------------------------------------------------------------------------------+All fluxes are observed values derived with FXT-A data.
* The autonomous follow-up observation lasts for about 6ks with effective exposure time of 3.1ks. The X-ray flux decays quickly in the autonommous follow-up observation, for the first 911s exposure segment, the mid time is about 10.4 min after the trigger and the 0.5-10keV flux is about 2 x 10^-11 erg/s/cm^2.
The derived temporal decay index is about 0.73+/-0.35, and the estimated flux at the Swift-XRT epoch is (1.52+/-0.27) x 10^-12 erg/s/cm^2, which is consistent with the value reported by Swift-XRT (Williams et al., GCN 38596). Considering the shallow decay observed in the optical band (Izzo et al., GCN 38588; Levan et al., GCN 38587; Fan et al., GCN 38592; Jin et al., GCN 38607; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek et al., GCN 38615), more follow-up observations are encouraged to monitor the X-ray transient EP241217a with a moderate redshift of 4.59 (Levan et al., GCN 38593).
The time-averaged FXT spectra of the autonomous and the first follow-up observations are fitted by the absorbed powerlaw model with the fixed Milky Way equivalent hydrogen column density nH of 1.88 x 10^21 cm^-2. The best-fitted model shows that the intrinsic absorption is negligible, and the photon index is 1.76+/-0.11 (1.96+/-0.17) for the autonomous (the first) follow-up observation. Our fitting results are consistent with the Swift-XRT results (Williams et al., GCN 38596).
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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. - GCN Circular #38626
Tomás Ahumada (Caltech), Viraj Karambelkar (Caltech), Geoffrey Mo (MIT), Benjamin Schneider (LAM), Danielle Frostig (CfA), Robert Stein (UMD), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We automatically observed the field of EP 241217a (Zhou et al., GCN 38586;) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations were triggered automatically and began at 2024-11-17T11:51:46 UTC (~6.25 hours after the EP event), consisting of 30 x 120 s exposures. The images were processed using the WINTER data reduction pipeline (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) using images from the UKIRT Hemisphere survey (Dye et al. 2018) as references for image subtraction.
We detect a possible source at the Gemini counterpart location (Levan et al., GCN 38587; Fan et al. GCN 38592; Levan et al. GCN 38593). This source is near the threshold of our stacked image, and we measure a brightness of J ~ 18 +/- 0.4 mag (AB). No source is present at this location in the reference UKIRT images to a depth of ~21 mag (AB).
We caution that our detection is close to the image's limiting magnitude, and we strongly encourage further observations to confirm the source as real and to assess its NIR brightness.
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. - GCN Circular #38627
Viraj Karambelkar (Caltech), Tomas Ahumada (Caltech), and Mansi Kasliwal (Caltech) report:
We observed the location of EP 241217a (Zhou et al., GCN 38586;) in the NIR J-band and Ks-band with the Wide-Field Infrared Camera (WIRC, Wilson et al. 2003) on the 200-inch Hale telescope at Palomar Observatory. Observations began on 2024-12-18 01:40:00 UT (approx. 20 hours after the EP detection), and comprise a series of 36 x 45 s exposures in the J-band and 17 x 30 s in the K-band.
We detect a possible source at the Gemini counterpart location (Levan et al., GCN 38587; Fan et al. GCN 38592; Levan et al. GCN 38593). We measure a brightness of J ~ 20.7 +/- 0.1 mag (AB) and K ~ 19.3 +/- 0.1 mag (AB). We thank Héctor Arce and the P200 staff for granting the observations.
We subsequently observed this transient with NIRES (Wilson et al. 2004) on the Keck II telescope starting 2024-12-18 05:00:00 UT. We thank Michael Lui, and the Keck staff for facilitating the observations. - GCN Circular #38633
A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report:
We observed the field of Einstein Probe and Swift-XRT detected transient EP241217a (Zhou et al., GCN 38586; Williams et al., GCN 38596) with the IO:O Imager at the 2m Liverpool telescope. We observed 200s x 3 frames in the r-band starting at 2024-12-19 UT 02:14:33.2 (~1.86 days post-trigger).
Preliminary photometry on the stacked image was performed and calibrated against the SDSS catalogue stars.
We do not detect any source at the location of the optical counterpart candidate of EP241217a (Levan et al., GCN 38587; Izzo & Malesani, GCN 38588; Fan et al. GCN 38592; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek & Perle, GCN 38615; Brivio et al., GCN 38618) down to a limiting magnitude of > 22.
This circular may be cited. - GCN Circular #38636
Dezi Liu, Yu Pan, Xiangkun Liu, Brajesh Kumar, Xianao Wang, Chenxi Shang, Xufeng Zhu, Yuanpei Yang, Xingzhu Zou, Xinlei Chen, Yehao Cheng (all SWIFAR, YNU), Ye Li (PMO, CAS), Guowang Du, Tao Wang, Yuan Fang, Jinghua Zhang, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We observed the field of EP241217a reported by EP-WXT (Zhou et al., GCN 38586) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous multi-band uvgriz band observations were initiated on 2024/12/17 between 14:07:34 to 15:48:12 UT. Multiple frames were obtained with exposure times of 180s and 300s in different bands. In our r i z band images, there is clear detection of the optical counterpart candidate (Levan et al., GCN 38587; Izzo et al., GCN 38588; Fan et al., GCN 38592; Jin et al., GCN 38607; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek et al., GCN 38615) but no detection in the stacked images of u v g bands. The field was observed again in uvgriz bands on 2024/12/18 (starting from 12:43:30 UT) and three frames of 300s in each band were taken. We found a marginal detection of the transient in the i band stacked image but not in other bands. Our preliminary results for the initial frames for 2024/12/17 and 2024/12/18 (upper limits indicate 3 sigma) are listed below:UT start band Exp Mag/LimMag(AB) 2024/12/17T14:07:34 z 180s 18.73 +/- 0.13 2024/12/17T14:11:28 r 300s 21.15 +/- 0.27 2024/12/17T15:05:43 i 300s 19.34 +/- 0.06 2024/12/17T15:24:11 g 300s*6 >23.15 2024/12/17T15:24:11 u 300s*6 >22.64 2024/12/17T14:50:44 v 300s*7, 180s*1 >22.88 2024/12/18T13:00:36 u 300s*3 >22.91 2024/12/18T13:00:36 g 300s*3 >22.91 2024/12/18T12:43:30 v 300s*3 >22.80 2024/12/18T12:43:30 r 300s*3 >22.65 2024/12/18T12:43:30 z 300s*3 >20.62 2024/12/18T13:00:36 i 300s*3 21.99 +/- 0.52
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Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m 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.
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E. Pavoni and L. Moretti (Leavitt Observatory, Italy),
Members of: GRB/UAI - Gamma Ray Burst section of Unione Astrofili Italiani ATA - Associazione Tuscolana di Astronomia
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), report:
We observed the field of EP241217a (Zhou et al., GCN 38586) with the RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Italy.
Our observations started about 11.25 hours after the EP-WXT trigger, at the following position:RA (J2000): 03h 07m 46s Dec(J2000): +30d 55' 47"
Weather conditions were good.
We utilized the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A) to align and stack 39 individual frames of 120 sec each, with a median time of 2024-12-17T17:36:16 (UTC). All images are unfiltered.
In the stacked frame, we did not detect any optical counterpart at the position of the optical afterglow, with the following upper limit:Time (UTC) Limit (clear filter) 2024-12-17T17:36:16 >20.8
Magnitudes were estimated with the BP-band of Gaia DR3 catalogue (*) and are not corrected for galactic dust extinction.
The upper limit is consistent with other already reported (Lipunov et al., GCN 38603; Junjie-Jin et al. GCN 38607; Mohan et al. GCN 38612; Brivio et al. GCN 38618).
The message may be cited.
Reference: https://leavittobservatory.altervista.org
(*) https://gea.esac.esa.int/archive/documentation/GEDR3/Data_processing/chap_cu5pho/cu5pho_sec_photSystem/cu5pho_ssec_photRelations.html - GCN Circular #38641
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP241217a (Zhou et al., GCN 38586) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x200s exposures in the SDSS i’ filter starting at 2024-12-19 20:29:08 UT, approximately 2.62 days after the trigger.
We do not detect any object at the position of the optical counterpart (Levan et al., GCN 38587, Williams et al., GCN 38596). The 3-sigma limiting magnitude of the stacked images is i > 22.4 mag. The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. - GCN Circular #38652
R. Ricci (U Rome), E. Troja (U Rome) and M. Yadav (U Rome) report on behalf of a larger collaboration:
On Dec 19th the e-MERLIN UK radio interferometer observed EP241217a (Zhou et al., GCN 38586) as part of the ORP project CY18M011 (PI: Troja et al.) at the position provided by Gemini-North (Levan et al GCN 38587). The observations started at 12:00 UT and terminated at 20:54 UT (mid elapsed time = 2.45 days after the trigger). e-MERLIN observed at 5 GHz with a total Bandwidth of 512 MHz in four sub-bands of 128 channels each. 1331+3030 (3C286) was used as flux calibrator and 0301+3037 as phase calibrator. The data were processed using the e-MERLIN CASA calibration pipeline (v1.1.19) [1] and also imaged in CASA with a restoring beam size of 60 x 40 mas. No clear detection was found in the final image. We estimated a 3-sigma rms noise of 96 microJy/beam.
The Authors thank the e-MERLIN support team and in particular David Williams for promptly scheduling and performing 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.
[1] e-MERLIN CASA pipeline (eMCP): https://ui.adsabs.harvard.edu/abs/2021ascl.soft09006M/abstract - GCN Circular #38736
Jin-Ji Li, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Hao-Nan Yang, Yan Yu, Hao-Ran Zhang, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm telescope team:
We observed the field of the fast X-ray transient EP241217A (Zhou et al., GCN 38586), which was also detected by Swift-XRT (Williams et al., GCN 38596), using the Sun Yat-sen University 80cm telescope, with 130 × 20 s exposures in J band. Our observations began at 2024-12-18 17:51:36 UTC, 36.26 hours after the EP trigger.
We did not detect any counterpart in the stacked images at the position of the optical afterglow (Levan et al., GCN 38587; Izzo et al., GCN 38588; Fan et al., GCN 38592; Jin et al., GCN 38607; Mohan et al., GCN 38612; Zhu et al., GCN 38613; Bochenek et al., GCN 38615; Liu et al., GCN 38636), down to a 5-sigma depth of J ~ 17.8 Vega magnitudes. - GCN Circular #38749
Tao An, Yuanqi Liu (Shanghai Astronomical Observatory, China), Jinjun Geng, Xuefeng Wu (Purple Mountain Observatory, China) report on behalf of the EP radio follow-up team:
We report VLA radio observations of EP241217a. Following the Einstein Probe (EP) detection (GCN 38586) and subsequent X-ray detections by Swift/XRT (GCN 38596, 38624), we conducted radio follow-up observations with the Karl G. Jansky Very Large Array (VLA).
We detected a point radio source at the position reported by the EP/FXT and Swift/XRT on 2024 December 21 UT01:00. Data calibration used the VLA calibration and imaging pipeline in CASA 6.5.4.9. The preliminary analysis suggests a flux density of 20±6.6 microJy (at 3 GHz), 58±4 microJy (at 6 GHz) and 99.3±4.1 microJy at 10 GHz.
We have obtained multi-band, multi-epoch VLA monitoring observation time and are conducting long-term monitoring of this interesting object.
We thank the TAC and operations team of VLA for making these observations in a timely manner. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
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Jochen Greiner, last update: 01-Jan-2025 [Disclaimer]