J/ApJ/786/20 Classification of 2XMM variable sources (Lo+, 2014)
Automatic classification of time-variable X-ray sources.
Lo K.K., Farrell S., Murphy T., Gaensler B.M.
<Astrophys. J., 786, 20 (2014)>
=2014ApJ...786...20L 2014ApJ...786...20L (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Morphology
Keywords: catalogs - methods: statistical - X-rays: general
Abstract:
To maximize the discovery potential of future synoptic surveys,
especially in the field of transient science, it will be necessary to
use automatic classification to identify some of the astronomical
sources. The data mining technique of supervised classification is
suitable for this problem. Here, we present a supervised learning
method to automatically classify variable X-ray sources in the Second
XMM-Newton Serendipitous Source Catalog (2XMMi-DR2). Random Forest is
our classifier of choice since it is one of the most accurate learning
algorithms available. Our training set consists of 873 variable
sources and their features are derived from time series, spectra, and
other multi-wavelength contextual information. The 10 fold cross
validation accuracy of the training data is ∼97% on a 7 class data
set. We applied the trained classification model to 411 unknown
variable 2XMM sources to produce a probabilistically classified
catalog. Using the classification margin and the Random Forest derived
outlier measure, we identified 12 anomalous sources, of which 2XMM
J180658.7-500250 appears to be the most unusual source in the sample.
Its X-ray spectra is suggestive of a ultraluminous X-ray source but
its variability makes it highly unusual. Machine-learned
classification and anomaly detection will facilitate scientific
discoveries in the era of all-sky surveys.
Description:
The 2XMMi-DR2 catalog (Cat. IX/40) consists of observations made with the
XMM-Newton satellite between 2000 and 2008 and covers a sky area of
about 420 deg2. The observations were made using the European Photon
Imaging Camera (EPIC) that consists of three CCD cameras - pn, MOS1,
and MOS2 - and covers the energy range from 0.2 keV to 12 keV. There
are 221012 unique sources in 2XMM-DR2, of which 2267 were flagged as
variable by the XMM processing pipeline (Watson et al. 2009,
J/A+A/493/339). The variability test used by the pipeline is a Χ2
test against the null hypothesis that the source flux is constant,
with the probability threshold set at 10-5.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 95 1284 2XMM variable sources classification
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See also:
IX/40 : The XMM-Newton 2nd Incremental Source Catalogue (2XMMi)
(XMM-SSC, 2008)
J/A+A/493/339 : XMM-Newton serendipitous Survey. V. (Watson+, 2009)
J/MNRAS/416/1844 : 2XMM ultraluminous X-ray source candidates (Walton+, 2011)
Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Name 2XMM identifier (2XMM JHHMMSS.s+DDMMSS and
2XMMi JHHMMSS.s+DDMMSS in Simbad)
24- 28 F5.3 --- PAGN Probability source is an AGN
30- 34 F5.3 --- PCV Probability source is a CV
36- 40 F5.3 --- PGRB Probability source is a GRB
42- 46 F5.3 --- PSSS Probability source is a SSS
48- 52 F5.3 --- PStar Probability source is a star
54- 58 F5.3 --- PULX Probability source is a ULX
60- 64 F5.3 --- PXRB Probability source is a XRB
66- 70 F5.3 --- Pmax Maximum classification probability
72- 75 A4 --- RFC Output from Random Forest classifier
77- 82 F6.3 --- CM Classification margin
84- 90 A7 --- Sample Source in known or unknown sample
92- 95 A4 --- Class Actual class; known sources only
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Jun-2017