EP250212a

D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), L. Galbany (ICE-CSIC), K. Phan (ICE-CSIC), B. Hauptmann (NOT and DTU Space) report on behalf of a larger collaboration:

We observed the field of the EP trigger 10202399251, which occurred on 2025 Feb 12 (possibly named EP250212a), using the Nordic Optical Telescope (NOT) equipped with the NOTCam near-infrared imager. Observations were conducted in the J band, for a total of 18x60 s exposures, with a mid time of 2025 Feb 12.837 UT (12.3 hr after the EP trigger).

Within the error circle of the EP/FXT X-ray counterpart, we detect no new sources down to a limiting magnitude of J = 20.9 (Vega), calibrated against nearby stars from the 2MASS catalog.

D. Y. Li (NAOC, CAS), Y. J. Zhang(THU), Y. C. Fu (BNU), W. Yuan (NAOC, CAS) report on behalf of the Einstein Probe team:

We report on the detection of a fast X-ray transient by EP-WXT, designated EP250212a (trigger ID: 10202399251). The WXT position of the source is R.A. = 114.949 deg, DEC = 60.493 deg (J2000) with an uncertainty of 2.9 arcmin in radius (90% C.L. statistical and systematic). The transient started at 2025-02-12T07:44:07 (UTC) and lasted for about 360 seconds seen from WXT light curve. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with a NH of 0.5 (-0.3, +0.3) x 10^22 cm^-2 and a photon index of 2.2 (-0.9, +1.0). The derived average unabsorbed 0.5-4 keV flux is 0.9 (-0.3, +1.0) x10^-9 erg/s/cm2. The peak flux is about 6 x 10^-9 erg/s/cm2. The average spectrum also can be fitted with an absorbed blackbody model, with a NH upper limit of 0.45 x 10^22 cm^-2 and a temperature of 0.6 (-0.1, +0.2) keV.

We performed a follow-up target of opportunity observation with EP-FXT. The observation began at 2025-02-12T13:20:16 (UTC) with an exposure time of 5970 seconds, about 5.6 hours after the burst detected by EP-WXT. Within the WXT error cirlce, an uncatalogued X-ray source was detected at R.A. = 114.9813 deg, DEC = 60.4848 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The X-ray spectrum can be fitted with an absorbed powerlaw with the absorption fixed at the Galactic value of 6.3 x 10^20 cm^-2, and a photon index of 2.1 (-0.3, +0.3).  The derived unabsorbed 0.5-10 keV flux is 3.2 (-0.7, +0.8) x 10^-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. The FXT spectrum can not be well fitted with a black body model. A J-band upper limit of 20.9 mag was given by a NOT observation performed about 12.3 hour after the EP trigger (GCN 39306
Loading...
 
 ).

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).

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 EP250212a (Li et al., GCN 39308
Loading...
 
 ) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 5x90s exposures in the SDSS g’ filter starting at 2025-02-10 20:59:11 UT and 5x90s exposures in the SDSS r’ filter starting at 2025-02-10 21:08:27 UT, approximately 13.3 hours after the X-ray detection.

We performed image subtraction on the stacked images using reference images from Pan-STARRS. Consistent with Malesani et al., (GCN 39306
Loading...
 
 ), we identify no new sources within the error region of the EP/FXT candidate. We derive 3-sigma upper limits of g’ > 20.3 and r’ > 21.0 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction.

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-Kislovodsk robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP250212a ( EP Team et al., GCN 39308
Loading...
 
 ) errorbox  72840 sec after notice time and 1 days 57035 sec after trigger time at 2025-02-13 23:34:42 UT, with upper limit up to  15.6 mag. The observations began at zenith distance = 42 deg. The sun  altitude  is -49.1 deg. 

The galactic latitude b = 30 deg., longitude l = 157 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2776627

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

  143466 | 2025-02-13 23:34:42 |   MASTER-Kislovodsk | (07h 38m 18.21s , +60d 29m 46.9s) |   C |    60 | 15.6 |        
  143651 | 2025-02-13 23:37:47 |   MASTER-Kislovodsk | (07h 38m 19.93s , +60d 29m 53.1s) |   C |    60 | 15.3 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Yinan-Zhu(NAOC), Jiajun-Jia(NAOC), YuGuang-Sun(NAOC),  Zhou-Fan(NAOC),  Hong-Wu(NAOC) report on behalf of a large collaboration:
Following the detection of EP250212a by EP-WXT (Li et al., GCN 39308
Loading...
 
 ), we observed the field of  EP250212a 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 2025-02-12 14:27:29, approximately 6.72 hours after the EP trigger. No optical counterpart was detected, with a 5-sigma limiting magnitude of 20.7, calibrated with Pan-STARRS sources in the field.
Later，We observed the EP250212a by the Xinglong 2.16-m telescope located at Xinglong, Hebei, China. A total of 1200 s N-band exposures were taken , with a median observation time of 2025-02-12 16:15:05, approximately 8.52 hours after the EP trigger. No optical counterpart was detected, with a 5-sigma limiting magnitude of 21.7, calibrated with Pan-STARRS sources in the field.

Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report:

We observed the EP-FXT localization area of EP250212a (Li et al., GCN 39308
Loading...
 
 ) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 18 x 180 s starting at 2025-02-15T23:51:26 UT (3.67 days after the WXT trigger). Earlier observations were not possible due to bad weather. Consistent with Malesani et al. (GCN 39306
Loading...
 
 ), Eyles-Ferris et al. (GCN 39309
Loading...
 
 ) and Junjie-Jin et al. (GCN 39319
Loading...
 
 ) we detect no source at a 3 sigma depth of

r > 23.3 mag
i > 23.0 mag
J > 22.0 mag.

The r- and i-band magnitudes are calibrated against the PS1 catalog and the J-band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction.

We thank Christoph Ries from the staff of the Wendelstein Observatory for obtaining these observations.