Maximum likelihood estimation of single X-ray point-source parameters in ROSAT data

Boese, F. G.; Doebereiner, S.

doi:10.1051/0004-6361:20010092

Cited by 14 publications

(17 citation statements)

References 17 publications

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“…After the image-based detection steps described above were completed, a photon-based algorithm (Boese & Doebereiner 2001) was applied to use the full spatial resolution. The ten merged lists were used as input for a maximum likelihood evaluation of the candidate X-ray sources.…”

Section: A8 Maximum Likelihood Detectionmentioning

confidence: 99%

Second ROSAT all-sky survey (2RXS) source catalogue

Boller

Freyberg

Truemper

et al. 2016

A&A

468

460

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Aims. We present the second ROSAT all-sky survey source catalogue, hereafter referred to as the 2RXS catalogue. This is the second publicly released ROSAT catalogue of point-like sources obtained from the ROSAT all-sky survey (RASS) observations performed with the position-sensitive proportional counter (PSPC) between June 1990 and August 1991, and is an extended and revised version of the bright and faint source catalogues. Methods. We used the latest version of the RASS processing to produce overlapping X-ray images of 6.4• × 6.4• sky regions. To create a source catalogue, a likelihood-based detection algorithm was applied to these, which accounts for the variable point-spread function (PSF) across the PSPC field of view. Improvements in the background determination compared to 1RXS were also implemented. X-ray control images showing the source and background extraction regions were generated, which were visually inspected. Simulations were performed to assess the spurious source content of the 2RXS catalogue. X-ray spectra and light curves were extracted for the 2RXS sources, with spectral and variability parameters derived from these products. Results. We obtained about 135 000 X-ray detections in the 0.1−2.4 keV energy band down to a likelihood threshold of 6.5, as adopted in the 1RXS faint source catalogue. Our simulations show that the expected spurious content of the catalogue is a strong function of detection likelihood, and the full catalogue is expected to contain about 30% spurious detections. A more conservative likelihood threshold of 9, on the other hand, yields about 71 000 detections with a 5% spurious fraction. We recommend thresholds appropriate to the scientific application. X-ray images and overlaid X-ray contour lines provide an additional user product to evaluate the detections visually, and we performed our own visual inspections to flag uncertain detections. Intra-day variability in the X-ray light curves was quantified based on the normalised excess variance and a maximum amplitude variability analysis. X-ray spectral fits were performed using three basic models, a power law, a thermal plasma emission model, and black-body emission. Thirty-two large extended regions with diffuse emission and embedded point sources were identified and excluded from the present analysis. Conclusions. The 2RXS catalogue provides the deepest and cleanest X-ray all-sky survey catalogue in advance of eROSITA.

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Section: A8 Maximum Likelihood Detectionmentioning

confidence: 99%

Second ROSAT all-sky survey (2RXS) source catalogue

Boller

Freyberg

Truemper

et al. 2016

A&A

468

460

View full text Add to dashboard Cite

show abstract

“…The width of the effective survey point spread function (FWHM about 45 arcsec) and the use of a maximum likelihood (ML) detection algorithm (Boese & Döbereiner 2001;Cruddace et al 1987), delivering best estimates for point-like sources, limit the reliability of the derived source properties in cases where 2 or more X-ray sources are within the acceptance window used by the algorithm (typically a circle of 300 arcsec diameter) and in cases where X-ray sources are clearly extended. The authors of the BSC paper demonstrated that 90% of point-like X-ray sources (stars) have a positional accuracy of ≤25 arcsec.…”

Section: The X-ray Data Basementioning

confidence: 99%

“…It established the first all sky survey in the X-ray regime with an imaging telescope (Trümper 1983). Using a maximum likelihood source detection algorithm (Cruddace et al 1987;Boese & Döbereiner 2001) about 80 000 sources with a likelihood ≥10 have been found in the sky images of the ROSAT All-Sky Survey (RASS). Different attempts are underway to identify parts of this large data base with counterparts in other wavelength regimes to enable investigations of the broad band properties of different astronomical object classes.…”

Section: Introductionmentioning

confidence: 99%

Galaxy identifications in the ROSAT All-Sky Survey

Zimmermann

Boller

Döbereiner

et al. 2001

A&A

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Abstract. In a correlation study of the ROSAT All-Sky Survey Bright Source Catalogue (RASS-BSC) with the Catalogue of Principal Galaxies (PGC) 904 X-ray sources were found that possess possible extragalactic counterparts within a search radius of 100 arcsec. A visual screening process was applied to classify the reliability of the correlations. 547 correlations have been quoted as reliable identifications. From these, 349 sources are known as active galaxies. Although for the other sources no hints for activity were found in the literature, 69% of those for which we have distances show X-ray luminosities exceeding those of normal galaxies, a clear sign that these galaxies also own hitherto unreported X-ray active components. Some objects are located inside or in the direction of a known group or cluster of galaxies. Their X-ray flux may therefore be in part affected by hot gas emission. Luminosity and log N− log S distributions are used to characterize different subsamples. Nuclei that are both optically and X-ray active are found predominantly in spirals. Two special source samples are defined, one with candidates for X-ray emission from hitherto unknown groups or clusters of galaxies, and one with high X-ray luminosity sources, that are likely candidates to possess hitherto unreported active galactic nuclei. Besides a compilation of X-ray and optical parameters, also X-ray overlays on optical images for all the objects are supplied as part of this work.

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“…Descriptions of the use of the Cash statistic for source detection can be found in Boese & Doebereiner (2001) and Mattox et al (1996) to give just two examples. The expressions developed in the present paper are not based on either treatment but comparison reveals close similarities.…”

Section: Map Vs Peak Sensitivitymentioning

confidence: 99%

Maximum-likelihood detection of sources among Poissonian noise

Stewart¹

2009

A&A

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A maximum likelihood (ML) technique for detecting compact sources in images of the X-ray sky is examined. Such images, in the relatively low exposure regime accessible to present X-ray observatories, exhibit Poissonian noise at background flux levels. A variety of source detection methods are compared via Monte Carlo, and the ML detection method is shown to compare favourably with the optimized-linear-filter (OLF) method when applied to a single image. Where detection proceeds in parallel on several images made in different energy bands, the ML method is shown to have some practical advantages which make it superior to the OLF method. Some criticisms of ML are discussed. Finally, a practical method of estimating the sensitivity of ML detection is presented, and is shown to be also applicable to sliding-box source detection.

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Maximum likelihood estimation of single X-ray point-source parameters in ROSAT data

Cited by 14 publications

References 17 publications

Second ROSAT all-sky survey (2RXS) source catalogue

Second ROSAT all-sky survey (2RXS) source catalogue

Galaxy identifications in the ROSAT All-Sky Survey

Maximum-likelihood detection of sources among Poissonian noise

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