EP250207b
GCN Circular 39266
Subject
EP250207b: a new X-ray transient detected by Einstein Probe
Date
2025-02-10T09:16:09Z (4 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
X.-Y. Zhou (PRIC), A. Li (BNU), D.-H. Zhao, X.-P. Xu, Q.-Y. Wu and Y. Liu (NAOC, CAS) report on behalf of the Einstein Probe team:
We report on the detection of an X-ray transient, designated EP250207b, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0=2025-02-07T21:47:56(UTC) and lasted for more than 120 s before the observation ended. The WXT position of the source is R.A. = 167.495 deg, DEC = -7.906 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.24 x 10^20 cm^-2 and a photon index of 0.6 (-0.8/+0.8). The derived average unabsorbed 0.5-4 keV flux is 6.1 (-2.5/+4.2) x 10^(-10) erg/s/cm^2.
Two ToO observations were performed by the Follow-up X-ray Telescope (FXT) . The first observation started at 2025-02-08T14:52:06 (~T0+17h) with an exposure time of 3024 s. An uncatalogued source was detected at R.A. = 167.5130, DEC = -7.8695 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.24 x 10^20 cm^-2 and a photon index of 1.5 (-0.6/+0.6), giving an average unabsorbed 0.5-10 keV flux of 3.6 (-1.4/+3.5) x 10^(-13) erg/s/cm^2. The second observation started at 2025-02-09T18:10:59 (~T0+44h) with an exposure time of 5042 s. The uncatalogued source was detetcted with a declined flux of 6.4 (-2.8/+3.5) x 10^(-14) erg/s/cm^2, indicating its correlation with EP250207b. The uncertainties are at the 90% confidence level for the above parameters.
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 39270
Subject
EP250207b: Gemini GMOS-N z-band observations
Date
2025-02-10T17:04:14Z (4 months ago)
Edited On
2025-02-10T18:02:43Z (4 months ago)
From
P.G. Jonker at Radboud University <p.jonker@astro.ru.nl>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of P.G. Jonker at Radboud University <p.jonker@astro.ru.nl>
Via
Web form
Daniele B. Malesani (DAWN/ NBI and Radboud), Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Javi Sánchez-Sierras (Radboud), Franz Bauer (PUC) report on behalf of a larger collaboration:
We obtained photometric observations of the field of the fast X-ray transient EP250207b discovered by Einstein Probe (Zhou et al., GCN 39266) with the GMOS instrument mounted on the Gemini-North telescope (PI: F. Bauer; program GN-2024B-FT-112). We obtained 6 images with 15 s exposure time each and 6 with an exposure time of 60 s each in the z-band filter beginning at 2025-02-10 10:40 UT, approximately 2.5 days after the EP/WXT trigger.
Within the EP/FXT error circle, comparing our stacked image with Legacy archival images we detect no plausible optical counterpart down to the depth of the Legacy Survey observations. Image subtraction between the GMOS and the Legacy Survey data also reveals no new sources.
We do note the presence of a bright galaxy within the FXT error circle. This galaxy lies at
RA(J2000) = 11:10:02.67
DEC(J2000) = -07:52:12.0
and has an r-band magnitude of r = 17.2. The galaxy is detected but WISE but it is not in ALLWISEAGN, implying it is unlikely to be an AGN. Following the prescription of Bloom et al. 2002 (doi: doi:10.1086/338893 ) we find a probability of 0.5% of such a galaxy lying within the FXT error circle by chance. The galaxy has a photometric redshift of z = 0.074+-0.009 from Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764).
We thank the staff of Gemini for their excellent support in securing these observations.
GCN Circular 39278
Subject
Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
Date
2025-02-11T08:35:07Z (4 months ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
Andrew J. Levan (Radboud), Daniele B. Malesani (DAWN/NBI and Radboud), Peter G. Jonker (Radboud), Jonathan A. Quirola-Vásquez (Radboud), Javi Sánchez-Sierras (Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), report on behalf of a larger collaboration:
We obtained spectroscopic observations of the candidate host galaxy WISEA J111002.65-075211.9 of EP 250207b (Zhou et al., GCN 39266) with the Gemini South telescope and the GMOS spectrograph. A total of 4x180 s observations were obtained, covering the spectral range 3600-7600 AA, with a mean time of about 3.3 days after the high-energy transient.
The spectrum is clearly that of a quiescent galaxy with no detectable emission lines. From a provisional reduction, we identify the presence of Ca H&K, Mg I, and Na I D absorption and determine a redshift of z = 0.082.
The galaxy is unlike those of collapsar GRBs, consistent with the non-detection of any counterpart in deep imaging (Malesani et al. GCN 39270), which also rules out any FBOT-like emission similar to that seen in other recent FXTs. If this is the host of EP 250207b a possibility is that the transient was created via a compact object merger. However, given the large (10” radius) X-ray error localisation we caution that an origin in a higher redshift system in chance projection to the z=0.082 galaxy remains plausible. We encourage further observations to search for the optical/IR counterpart.
We thank the staff of Gemini, in particular Jeong-Eun Heo, for their excellent support in securing these observations.
GCN Circular 39280
Subject
EP250207b: Global MASTER-Net observations report
Date
2025-02-11T09:27:30Z (4 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
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 EP250207b ( EP Team et al., GCN 39266) errorbox 85997 sec after notice time and 2 days 65886 sec after trigger time at 2025-02-11 09:10:12 UT, with upper limit up to 19.7 mag. Observations started at twilight. The observations began at zenith distance = 46 deg. The sun altitude is -12.9 deg.
The galactic latitude b = 47 deg., longitude l = 265 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2774311
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
238716 | 2025-02-11 09:10:12 | MASTER-OAFA | (11h 10m 01.86s , -07d 30m 20.4s) | C | 60 | 19.6 |
238776 | 2025-02-11 09:10:12 | MASTER-OAFA | (11h 10m 01.86s , -07d 30m 20.4s) | C | 180 | 19.7 | Coadd
238791 | 2025-02-11 09:11:26 | MASTER-OAFA | (11h 09m 58.99s , -07d 28m 45.5s) | C | 60 | 19.4 |
238865 | 2025-02-11 09:12:41 | MASTER-OAFA | (11h 09m 59.00s , -07d 30m 13.6s) | C | 60 | 19.1 |
238957 | 2025-02-11 09:13:57 | MASTER-OAFA | (11h 10m 02.25s , -07d 28m 50.3s) | C | 90 | 19.4 |
239064 | 2025-02-11 09:15:45 | MASTER-OAFA | (11h 09m 56.51s , -07d 29m 42.1s) | C | 90 | 19.3 |
239167 | 2025-02-11 09:17:28 | MASTER-OAFA | (11h 09m 56.54s , -07d 28m 41.5s) | C | 90 | 19.2 |
239273 | 2025-02-11 09:19:14 | MASTER-OAFA | (11h 10m 01.95s , -07d 29m 41.2s) | C | 90 | 19.0 |
239378 | 2025-02-11 09:20:59 | MASTER-OAFA | (11h 09m 56.56s , -07d 30m 41.0s) | C | 90 | 18.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 39281
Subject
EP250207b: Liverpool Telescope possible optical counterpart
Date
2025-02-11T10:20:29Z (4 months ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report:
We observed the field of the X-ray transient EP250207b (Zhou et al., GCN 39266) using the IO:O on the 2m Liverpool Telescope. We obtained 5x90s exposures in the SDSS g’ filter starting at 2025-02-10 00:49:54 UT and 5x90s exposures in the SDSS r’ filter starting at 2025-02-10 00:59:10 UT, approximately 74 hours after the X-ray detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS. We identify a possible counterpart in the g’ band subtraction of g’ = 21.24+/-0.14 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. The source is located at RA, Dec = 167.51128, -7.87019 deg, which is equivalent to:
RA (J2000) : 11:10:02.71
Dec (J2000): -07:52:12.7
This source lies within the error region of the Einstein Probe FXT detection and is the only source within it in our subtracted image. It is consistent with the position of the bright galaxy noted by Malesani et al., GCN 39270 and Levan et al., GCN 39278 with an offset of 0.92 arcsec (1.43 kpc projected) from the position reported by Malesani et al., GCN 39270.
In the r’ band subtraction, the source position is obscured by a subtraction artifact and we cannot currently rule out the possibility that the g’ band detection is also an artifact. Further observations to confirm the nature of the source are planned.
GCN Circular 39287
Subject
EP250207b: Tentative z-band brightening source
Date
2025-02-11T16:01:30Z (4 months ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Via
Web form
Morgan Fraser (UCD), Andrew J. Levan (Radboud), Daniele B. Malesani (DAWN/NBI and Radboud), Peter G. Jonker (Radboud), Jonathan A. Quirola-Vásquez (Radboud), Javi Sánchez-Sierras (Radboud), Franz E. Bauer (PUC), Antonio Martin-Carrillo (UCD), report on behalf of a larger collaboration:
We report on Gemini North + GMOS observations of the localisation region of the fast X-ray transient EP250207b (Zhou et al., GCN 39266). 6x60 s images were taken in z-band on 2025 Feb. 10 (MJD 60716.44; Malesani et al., GCN 39270) and 5x60 s on Feb. 11 (MJD 60717.48).
Performing image subtraction between the two average z-band images, we see a marginal transient in the difference image that has brightened between the two epochs, located at coordinates:
RA(J2000) = 11:10:02.8
Dec(J2000) = -07:52:05.8.
A source is present at the transient location in both z-band epochs as well as in the Legacy survey. Aperture photometry of the object in the two epochs is consistent with a modest brightening by 0.25 +/- 0.10 mag between the two epochs.
The position of the source is offset by about 6.5" to the north of the WISEA J111002.65-075211.9 nucleus, the z=0.082 galaxy that lies within the error circle of EP250207b (Malesani et al., GCN 39270; Levan et al., GCN 39278). If the brightening of this source is real, the association with WISEA J111002.65-075211.9 becomes less clear, and the distance of this event would remain undetermined.
We do not see any evidence for transient emission in z-band at the location of the source identified by Eyles-Ferris et al. (GCN 39281) in our subtractions, but we note that the central regions of WISEA J111002.65-075211.9 are subject to substantial uncertainties due to subtraction residuals.
Further observations of this field are planned to establish the reality of this object.
We thank the staff of Gemini for their excellent support in securing these observations.
GCN Circular 39300
Subject
EP250207b: NOT optical counterpart candidate
Date
2025-02-12T15:11:09Z (4 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
X. Liu, J. An, S.Q. Jiang, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), M. A. Diaz Teodori, R. H. Rasmussen, A. M. Kadela (NOT) report on behalf of a large collaboration:
We observed the field of EP250207b detected by EP/WXT (Zhou et al., GCN39266) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A total of 4 x 200 s frames in Sloan r-band were obtained at a mid time of 03:16:13 UT on 2025-02-09, i.e., 1.23 days after the EP trigger time.
We performed image subtraction on our stacked image using both PanSTARRS and Legacy Survey images as templates. Within the EP/FXT error circle, an uncatalogued faint source was detected with a magnitude of r ~ 23.7 mag (AB), calibrated against nearby PanSTARRS stars, at coordinates
R.A.(J2000) = 11:10:03.21
Dec.(J2000) = -07:52:07.20
with an uncertainty of ~ 1 arcsec. It is about 10 arcsec away from the galaxy WISEA J111002.65-075211.9 noted by Malesani et al. (GCN 39270) and Levan et al. (GCN 39278). The brightness of the galaxy in our image shows no brightening compared to PanSTARRS kron magnitude.
In addition, the source reported by Fraser et al. (GCN 39287) is not detected in our stacked image, down to a 5-sigma limiting magnitude of r ~ 23.0 mag (AB).
The magnitudes reported above have not been corrected for Galactic extinction.
Further observations are planned and deep r-band photometry of the field is encouraged.
GCN Circular 39310
Subject
EP250207b: VLA radio upper limits
Date
2025-02-13T15:29:42Z (4 months ago)
From
Roberto Ricci at INAF-IRA <ricci@ira.inaf.it>
Via
Web form
R. Ricci (U Rome), E. Troja (U Rome) and B. O'Connor (Carnegie Mellon) on behalf of a larger collaboration:
We observed the Fast X-ray Transient EP250207b discovered by Einstein Probe (Zhou et al. GCN 39266) at the FXT position (Zhou et al. 39266) with the Very Large Array at the frequency of 6 GHz with a bandwidth of 4 GHz on Feb 12th 07:29 UT mid-time (i.e. 4.40 days after the EP trigger).
The primary calibrator was 3C286 and the phase calibrator J1130-1449. The data were calibrated,
imaged and analysed in CASA using standard procedures.
The target source was not detected in the final cleaned image down to 3-sigma flux upper limit of
21 microJy.
We thank the VLA staff for promptly executing the observations.
GCN Circular 39323
Subject
EP250207b: Xinglong optical upper limit
Date
2025-02-14T10:19:21Z (4 months ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Yue-Sun(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration:
Following the detection of EP250207b by EP-WXT (Zhou et al., GCN 39266
), we observed the field of EP250207b using Tsinghua-NAOC 0.8-m telescope (TNT) located at Xinglong, Hebei, China. A total of 3600 s N-band exposures were taken , with a median observation time of 2025-02-08T16:39:35, approximately 18.86 hours after the EP FXT trigger (2025-02-07T21:47:56). No optical counterpart was detected, with a 5-sigma limiting magnitude of 19.9, calibrated with Pan-STARRS sources in the field.