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GCN Circular 36016

X-ray transient LXT 240402A: LEIA detection
2024-04-03T16:20:48Z (2 months ago)
EP Team at NAOC/CAS <>
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X. P. Xu , Z. X. Ling , Y. Liu , C. Zhang , W. Chen , H. Q. Cheng , C. Z. Cui , D. W. Fan , H. B. Hu , J. W. Hu , M. H. Huang , C. C. Jin , D. Y. Li , T. Y. Lian , H. Y. Liu , M. J. Liu , Z. Z. Lv,  X. Mao , H. W. Pan , X. Pan , H. Sun , W. X. Wang , Y. L. Wang , Q. Y. Wu , Y. F. Xu , H. N. Yang , M. Zhang , W. D. Zhang , W. J. Zhang , , D. H. Zhao (NAOC, CAS),  D. M. Li, Q. X. Li (BNU),C. Y. Wang, Y. J. Zhang (THU), and W. Yuan (NAOC, CAS) on behalf of the LEIA and Einstein Probe team

We report on a fast X-ray transient LXT 240402A detected by LEIA (Lobster Eye Imager for Astronomy) in 0.5-4 keV. The position of the source is R.A. = 245.438 deg, DEC = 25.800 deg with an uncertainty of 1.5 arcmin (radius, 90%C.L. statistical and systematic). The source was detected by LEIA at 2024-04-02T08:47:41 (UTC). The averaged 0.5-4 keV spectrum can be fitted with an absorbed power law (with the column density fixed to the galactic value of 3.4e20 cm^-2) with a photon index of 0.8 (-0.2/+0.2), giving an unabsorbed flux of ~2.6 (-0.4/+0.5) e-9 erg/s/cm2 in the 0.5-4 keV band. There are two peaks observed in the light curve. The transient event lasted for approximately 200 seconds with a peak flux of ~3e-8 erg/s/cm2 in 0.5-4 keV band. 

Within the error circle of LXT 240402A, there is a radio galaxy (NVSS J162146+254915) at a redshift of ~0.05 with a ROSAT flux of 2.3e-12 erg/s/cm2, which is fainter than the peak flux detected by LEIA by more than three orders of magnitude. Assuming that LXT 240402A is associated with NVSS J162146+254915, the average luminosity of the X-ray transient is esitimated to be 1.5e46 erg/s. More follow-up observations are encouraged to help explore the nature of this transient.

LEIA (Zhang et al. 2022, ApJL, 941, 2; Ling et al. 2023, RAA, 23, 095007) is a soft X-ray Lobster-eye imager (0.5 - 4.0keV) with a FoV of 340 square degrees aboard the experimental satellite SATech-01 of the CAS, launched on July 27, 2022. The above result is preliminary and the final result will be published elsewhere.
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