EP260526a

J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: 

EP-FXT performed a follow-up observation of EP260526a (detected by EP-WXT, GCN 44712
Loading...
 
 ; and followed by LCO, GCN 44713
Loading...
 
 ) about 27 hours after the WXT detection, with an exposure time of 6 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 236.0897, DEC = -23.7507 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 2.13 x 10^21 cm^-2 and a photon index of 1.8 (+1.5/-1.0). The derived unabsorbed 0.5-10 keV flux is approximately 5.2 (+5.2/-2.7) x 10^-14 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 

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).

A. P. C. van Hoof (Radboud), R. A. J. Eyles-Ferris (Leicester), J. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration:

We observed the field of the X-ray transient EP260526a (Yang et al, GCN 44712
Loading...
 
 ) using LCO 1m telescopes located at the Cerro Tololo observatory equipped with SINISTRO instruments. A series of 5x300 s exposures were taken using the SDSS-r filter and 3x300 s using the SDSS-z filter, starting on 2026-05-27 at 08:07:52 UT (i.e., ~1.4 days after the first X-ray detection).

No new source is detected within the EP/WXT uncertainty region compared with the Legacy and Pan-STARRS surveys. From the stacked images, we obtain the following 3-sigma upper limits, consistent with those reported by Becerra et al. (GCN 44710
Loading...
 
 ):


r > 22.5
z > 20.6

These upper limits are in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalogue, and are not corrected for Galactic extinction.

J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: 

We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260526a. The transient did not trigger the onboard unit, a GCN notice (ID: 06800001478) was sent manually. The WXT position of the source is R.A. = 236.063 deg, DEC = -23.771 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at 2026-05-26T09:43:34 (UTC) and lasted for about 140 seconds. The average WXT 0.5-4.0 keV spectrum can be fitted with an absorbed powerlaw model, with a fixed Galactic hydrogen column density of 2.13 x 10^21 cm^-2 and a photon index of 1.98 (+0.78/-0.70). The unabsorbed 0.5-4.0 keV flux is 8.2 (+2.8/-2.2) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 

Further FXT observations are scheduled. Additional information will be updated when the telemetry data are received. 

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).