Systematic evaluation of variability detection methods for eROSITA

Buchner, Johannes; Böller, Thomas; Bogensberger, David; Malyali, A.; Nandra, K.; Wilms, J.; Dwelly, T.; Liu, Teng

doi:10.1051/0004-6361/202141099

Cited by 8 publications

(6 citation statements)

References 49 publications

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“…Light curves were also extracted using eSASS and analysed using bexvar to search for variability (Buchner et al 2022 ). Variability in bexvar is quantified by the intrinsic scatter ( σ bexvar ) on the assumed log-normal distribution of count rates in an y giv en time bin (see section 3 of Buchner et al 2022 ).…”

Section: Erosita Obser V Ationsmentioning

confidence: 99%

The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr

Kammoun

Igo

Miller

et al. 2023

Monthly Notices of the Royal Astronomical Society

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SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in the last $\sim 9\, \rm Gyr$. In this paper, we report on the eROSITA/Spectrum-Roentgen-Gamma (SRG) observations of the source from the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 over timescales of a year and of a few days, respectively. When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a Γ = 2.2 ± 0.2 and $E_{\rm cut}=23^{+26}_{-5}\, \rm keV$. Assuming Comptonisation, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and $kT=8-18\, (7.5-14)\, \rm keV$, respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile. The former model results in a black hole mass estimate of the order of 1010 M⊙, slightly higher than prior optical estimates; meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning black hole, and a compact (∼10 rg) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of magnitude over the period of $\sim 900\, \rm days$.

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Section: Erosita Obser V Ationsmentioning

confidence: 99%

The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr

Kammoun

Igo

Miller

et al. 2023

Monthly Notices of the Royal Astronomical Society

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“…Using the source and background spectra extraction regions, we also extract light curves in the 0.2-5 keV band with a bin size of 100s and search for X-ray variability using the maximum amplitude method (Boller et al 2016;Buchner et al 2022). From each light curve, we find the time bin with the lowest count rate upper limit (Rate + ∆Rate) and the bin with the highest count rate lower limit (Rate − ∆Rate, where ∆Rate is the 1-σ count rate uncertainty), and use these two bins to define a vari- The measurement of V and S is dependent on the time bin size.…”

Section: X-ray Variabilitymentioning

confidence: 99%

“…Some low-S cases might be due to random fluctuation. Following Buchner et al (2022), we adopt a threshold of S > 2.6 to guarantee a 3-σ purity. It results in 99 variable sources.…”

Section: X-ray Variabilitymentioning

confidence: 99%

“…It results in 99 variable sources. This method is sensitive in identifying large-amplitude flares but not small-amplitude variabilities (Buchner et al 2022). The counterparts of about half of these variable sources are classified as stars through Gaia's proper motion measurement; the other ones might also include not-yet-identified stars.…”

Section: X-ray Variabilitymentioning

confidence: 99%

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The eROSITA extragalactic CalPV serendipitous catalog

Merloni

Wolf

et al. 2022

A&A

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Context. The eROSITA X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory performed calibration and performance verification (CalPV) observations between September 2019 and December 2019, ahead of the planned four-year all-sky surveys. Most of them were deep, pointing-mode observations. Aims. We present here the X-ray catalog detected from the set of extra-galactic CalPV observations released to the public by the German eROSITA consortium, and the multiband counterparts of these X-ray sources. Methods. We developed a source detection method optimized for point-like X-ray sources by including extended X-ray emission in the background measurement. The multiband counterparts were identified using a Bayesian method from the CatWISE catalog. Results. Combining 11 CalPV fields, we present a catalog containing 9515 X-ray sources, whose X-ray fluxes were measured through spectral fitting. CatWISE counterparts are presented for 77% of the sources. Significant variabilities are found in 99 of the sources, which are also presented with this paper. Most of these fields show similar number counts of point sources as typical extragalactic fields, and a few harbor particular stellar populations.

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“…In a series of accompanying papers, we will present the identification of the multiwavelength counterparts of point-like (Salvato et al 2022;Schneider et al 2022) and extended (Klein et al 2022) X-ray sources; the resulting clean catalogues of clusters of galaxies (Liu et al 2022a;Bulbul et al 2022), active galactic nuclei (AGN) (Liu et al 2022b;Nandra et al, in prep. ) and stars (Schneider et al 2022); the X-ray variability properties of the detected sources (Boller et al 2022;Buchner et al 2022); the X-ray spectral analysis of the point sources (Liu et al 2022b); the X-ray morphological analysis of the clusters (Ghirardini et al 2022); the optical and lensing analysis of the X-ray clusters (Ramos-Ceja et al 2022;Chiu et al 2022;Bahar et al 2022, Ota et al, in prep. ); the properties of non-active galaxies detected by eROSITA (Vulic et al 2022), and the discovery of some extreme AGN (Toba et al 2022;Brusa et al 2022).…”

Section: Introductionmentioning

confidence: 99%

The eROSITA Final Equatorial Depth Survey (eFEDS)

Brunner

Liu

Lamer

et al. 2022

A&A

Self Cite

219

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Context. The eROSITA X-ray telescope on board the Spectrum-Poentgen-Gamma (SPG) observatory combines a large field of view and a large collecting area in the energy range between ~0.2 and ~8.0 keV. This gives the telescope the capability to perform uniform scanning observations of large sky areas. Aims. SRG/eROSITA performed scanning observations of the ~140 square degree eROSITA Final Equatorial Depth Survey field (the eFEDS field) as part of its performance verification phase ahead of the planned four year of all-sky scanning operations. The observing time of eFEDS was chosen to slightly exceed the depth expected in an equatorial field after the completion of the all-sky survey. While verifying the capability of eROSITA to perform large-area uniform surveys and saving as a test and training dataset to establish calibration and data analysis procedures, the eFEDS survey also constitutes the largest contiguous soft X-ray survey at this depth to date, supporting a range of early eROSITA survey science investigations. Here we (i) present a catalogue of detected X-ray sources in the eFEDS field providing information about source positions and extent, as well as fluxes in multiple energy bands, and (ii) document the suite of tools and procedures developed for eROSITA data processing and analysis, which were validated and optimised by the eFEDS work. Methods. The data were fed through a standard data processing pipeline, which appltes X-ray event calibration and provides a set of standard calibrated data products. A mutiti-stage source detection procedure, building in part on experience from XMM-Newton, was optimised and calibrated by performing realistic simulations of the eROSITA eFEDS observations. Source fluxes were computed in multiple standard energy bands by forced point source fitting and aperture photometry. We cross-matched the eROSITA eFEDS source catalogue with previous XMM-ATLAS observations, which confirmed the excellentt agreement of the eROSITA and XMM-ATLAS source fluxes. Astrometric corrections were performed by cross-matching the eROSITA source positions with an optical reference catalogue of quasars. Results. We present a primary catalogue of 27 910 X-ray sources (542 of which are significantly spatially extended) detected in the 0.2–2.3 keV energy range with detection likelihoods ≥6, corresponding to a (point source) flux limit of 6.5 × 10–15 erg cm–2 s–1 in the 0.5–2.0 keV energy band (80% completeness). A supplementary catalogue contains 4774 low-significance source candidates with detection likelihoods between 5 and 6. In addition, a hard-band sample of 246 sources detected in the energy range 22.3–5.0 keV above a detection likelihood of 10 is provided. In an appendix, we finally describe the dedicated data analysis software package, the eROSITA calibration database, and the standard calibrated data products.

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Systematic evaluation of variability detection methods for eROSITA

Cited by 8 publications

References 49 publications

The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr

The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr

The eROSITA extragalactic CalPV serendipitous catalog

The eROSITA Final Equatorial Depth Survey (eFEDS)

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