Searching for fast extragalactic X-ray transients in Chandra surveys
Abstract
Recent works have discovered two fast (≈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} {evt yr^{-1} deg^{-2}}} for CDF-S XT-like transients with 0.5-7 keV peak fluxes log Fpeak ≳ -12.6 (erg cm-2 s-1). This event rate translates to {≈ 15^{+20}_{-10}} transients existing among Chandra archival observations at Galactic latitudes |b| > 20°, which can be probed in future work. Future missions such as Athena and the Einstein Probe with large grasps (effective area × field of view) are needed to discover a large sample (∼thousands) of fast extragalactic X-ray transients.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2019
- DOI:
- 10.1093/mnras/stz1605
- arXiv:
- arXiv:1906.02793
- Bibcode:
- 2019MNRAS.487.4721Y
- Keywords:
-
- methods: data analysis;
- stars: activity;
- X-rays: bursts;
- X-rays: galaxies;
- X-rays: general;
- X-rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 17 pages, 11 figures, and 3 tables