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arXiv · 1906.02793

Searching for fast extragalactic X-ray transients in Chandra surveys

Guang Yang·W. N. Brandt·S. F. Zhu·F. E. Bauer·B. Luo·Y. Q. Xue·X. C. Zheng
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Abstract

Recent works have discovered two fast ($\approx 10$ ks) extragalactic X-ray transients in the Chandra Deep Field-South (CDF-S XT1 and XT2). These findings suggest that a large population of similar extragalactic transients might exist in archival X-ray observations. We develop a method that can effectively detect such transients in a single Chandra exposure, and systematically apply it to Chandra surveys of CDF-S, CDF-N, DEEP2, UDS, COSMOS, and E-CDF-S, totaling 19~Ms of exposure. We find 13 transient candidates, including CDF-S XT1 and XT2. With the aid of available excellent multiwavelength observations, we identify the physical nature of all these candidates. Aside from CDF-S XT1 and XT2, the other 11 sources are all stellar objects, and all of them have $z$-band magnitudes brighter than 20. We estimate an event rate of $59^{+77}_{-38}\ \rm{evt\ yr^{-1} deg^{-2}}$ for CDF-S XT-like transients with 0.5-7 keV peak fluxes $\log F_{\rm peak} \gtrsim -12.6$ (erg cm$^{-2}$ s$^{-1}$). This event rate translates to $\approx 15^{+20}_{-10}$ transients existing among Chandra archival observations at Galactic latitudes $|b|>20^{\circ}$, which can be probed in future work. Future missions such as Athena and the Einstein Probe with large grasps (effective area $\times$ field of view) are needed to discover a large sample ($\sim$ thousands) of fast extragalactic X-ray transients.

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Guang Yang, W. N. Brandt, S. F. Zhu, F. E. Bauer, B. Luo, Y. Q. Xue, X. C. Zheng. 2019-06-06. Searching for fast extragalactic X-ray transients in Chandra surveys. https://doi.org/10.1093/mnras%2Fstz1605

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