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Detection of X-ray brightening from the CV GD 1662 by Einstein Probe

ATel #16741; D. Y. Li (NAOC, CAS), Y. F. Liang (PMO, CAS), H. Sun, W. Yuan, W. D. Zhang, C. C. Jin, 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, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, W. X. Wang, Y. L. Wang, S. X. Wen, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, J. Guan, C. K. Li, W. W. Cui, H. Feng, D. W. Han, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, J. Zhang, S. N. Zhang, H. S. Zhao, X. F. Zhao (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team.
on 29 Jul 2024; 14:53 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

Subjects: X-ray, Cataclysmic Variable

Referred to by ATel #: 16742

We report on the detection of X-ray brightening of the cataclysmic variable (CV) GD 1662 by the Einstein Probe (EP). The source was first detected by the Wide-field X-ray Telescope (WXT) on board EP in a single pointing observation (with an exposure time of 1.8 ks) at 2024-07-29T00:32:36 (UTC). The position of the source is R.A. = 352.248 deg, Dec. = -29.749 deg, with an uncertainty of 3.1 arcmin. A backwards search by data stacking finds that the source has brightened since 23th July. An upper limit to the flux of 3.2 x 10^(-12) ergs/cm^2/s is set by the non-detection of stacking data taken by EP-WXT on 20th July.

The WXT spectrum of the last observation can be fitted by an absorbed power law with a photon index of 2.4(-1.7, +2.7), and the NH fixed at the Galactic value of 1.65 x 10^(20) cm^-2. The derived unabsorbed flux in 0.5-4 keV is 1.5(-0.8, +2.1) x 10^(-11) ergs/cm^2/s.

An observation with the Follow-up X-ray Telescope (FXT) on board EP was performed at 2024-07-29T07:00:00. A bright X-ray source was detected at R.A.= 352.2525 deg, Dec.= -29.7792 deg (with an uncertainty of 10 arcsec), consistent with the WXT source position. This position is consistent with that of the CV GD 1662, a previously known X-ray source, with a angular separation of 1.8 arcsec. Previous observations showed that the source is highly variable, with a low 0.5-10 keV flux of 1.3(+/-0.3) x 10^(-13) erg/cm^2/s detected on 2008-10-17, and a high flux of 2.4(+/-0.1) x 10^(-12) erg/cm2/s detected on 2015-08-10, both observed by Swift/XRT. Preliminary analysis shows that the FXT spectrum can be modeled by an absorbed power law with a photon index of 1.63 (-0.09, +0.09), and the derived unabsorbed 0.5-4 keV flux is 4.65 (+0.21, -0.21) x 10^(-12) ergs/cm^2/s.

The WXT detection suggests that this object is undergoing a new phase of brightening. EP will keep monitoring the source in the following days. Multi-band follow-up observations are encouraged.

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.