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7–11 Oct 2024
Asia/Yerevan timezone

A problem of classification the eROSITA Tidal disruption events among other variable X-ray sources

9 Oct 2024, 12:25
20m

Speaker

George Khorunzhev ((IKI RAS) SPACE RESEARCH INSTITUTE RUSSIAN ACADEMY OF SCIENCES)

Description

The four completed SRG Observatory half-year all-sky surveys have yielded a significant number of variable X-ray sources.
The SRG/eROSITA telescope has discovered a rich population of tidal disruption events (TDE) that exhibit strong X-ray variability.
Searching for TDE in the X-ray band offers certain advantages over a selection in the optical range.
In X-rays, the background flux of the host galaxy is negligible, allowing us to detect X-ray TDEs with lower luminosity and at greater distances, compared to optical TDE sample.
We present a study of a sample of TDEs selected on the basis of the X-ray flux variability factor (R>10) between surveys. This corresponds to TDEs with peak X-ray luminosities above 5e43 erg/s at a typical redshift of z=0.2 of the eROSITA X-ray TDEs.
Unfortunately, a significant number of AGN show similar X-ray flux variability on a half-year scale, thus contaminating the list of TDE candidates. Furthermore, a considerable number of TDE candidates lack spectroscopic redshift and classification.
A constellation of optical telescopes observes variable SRG sources to obtain a complete spectroscopic sample of TDE.
We present the complex method of spectroscopic classification helps to rule out the most AGN. The key relationship between X-ray luminosity and O[III] (5007A) luminosity can be used to confirm the TDE candidate even for an optical spectrum of moderate quality. This makes it possible to classify X-ray TDE archive sources with lower variability factor (R~5) and to extend the TDE sample to lower luminosities. Only extremely rare - one might even say unique - variable AGN (Sy2 or LINERS) with soft X-ray spectra can be misclassified using to this criterion. Fortunately, with a high quality optical spectrum and considering a full set of the X-ray and optical properties, one can reliably exclude such objects.

Author

George Khorunzhev ((IKI RAS) SPACE RESEARCH INSTITUTE RUSSIAN ACADEMY OF SCIENCES)

Co-authors

Prof. Marat Gilfanov Sergey Sazonov (Space Research Institute (IKI), Russian Academy of Sciences)

Presentation materials