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A Large Catalogue of Ultraluminous X-ray Source Candidates in Nearby Galaxies Madrid: 2010 DOM WALTON IoA, Cambridge, UK In collaboration with Jeanette.

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Presentation on theme: "A Large Catalogue of Ultraluminous X-ray Source Candidates in Nearby Galaxies Madrid: 2010 DOM WALTON IoA, Cambridge, UK In collaboration with Jeanette."— Presentation transcript:

1 A Large Catalogue of Ultraluminous X-ray Source Candidates in Nearby Galaxies Madrid: 2010 DOM WALTON IoA, Cambridge, UK In collaboration with Jeanette Gladstone, Tim Roberts and Andy Fabian

2 OVERVIEW General overview of the catalogue production Present some analysis of the derived source population Focus on and model the spectrum of a specific souce included in the catalogue Demonstrate how it may be possible to distinguish between ULX spectral models in the future Dom WaltonMadrid: 2010

3 ULX - DEFINITION Dom WaltonMadrid: 2010 Two main criteria define a ULX: Point source with L X > ergs s -1 Extra-nuclear location in their host galaxies

4 Dom Walton WHY ARE ULXs INTERESTING? Madrid: 2010 The extreme ULX luminosities appear to exceed the Eddington limit for a standard 10 solar mass black hole. This may be achieved by: - Intermediate mass black holes - Super-eddington emission - Anisotropic emission

5 CATALOGUE PRODUCTION Dom WaltonMadrid: 2010 Began by cross correlating the 2XMM X-ray source and RC3 galaxy catalogues Only kept sources within the elliptical D 25 isophotes of the RC3 galaxies Removed sources with L X < ergs s -1 (although sources with 1  agreement were retained) Also removed sources flagged as extended Removed known contaminants (AGN, stars, etc.)

6 BASIC FILTERING Dom WaltonMadrid: 2010 NGC 5194 & 5195

7 REMOVING LLAGN Dom WaltonMadrid: 2010 L X > ergs s < L X < ergs s -1

8 THE CATALOGUE Dom WaltonMadrid: 2010 Limitations Incompleteness and source confusion The final catalogue contains 655 detections of 475 discrete point sources Most of these sources are located in spiral galaxies, despite the elliptical galaxies in 2XMM observations covering a much larger sky area We find 5 new sources with L X > ergs s -1

9 ESTIMATING CONTAMINATION Dom WaltonMadrid: 2010 The majority of the cosmic X-ray background can be resolved into point sources Moretti et al. (2003) studied the number of background sources resolved with observation sensitivity (per deg 2 ) Using sensitivity maps of the 2XMM observations (provided by Univ. of Leicester), we can estimate fractional contamination contained in the catalogue Contamination ~ 18 %

10 HIGH ENERGY TURNOVER Dom WaltonMadrid: 2010 The highest quality ULX spectra have been shown to display a smooth spectral turnover at high energies (Stobbart et al. 2006; Gladstone et al. 2009) This is often seen around ~6 keV Such curvature is not seen in the spectra of the standard accretion states of X-ray binaries This turnover was suggested to define an 'ultraluminous' accretion state (Roberts 2007; Gladstone et al. 2009)

11 HIGH ENERGY TURNOVER Dom WaltonMadrid: 2010 Basic 2XMM Energy Bands: Hardness Ratios: Adopting an absorbed powerlaw model, we use HR 3 to estimate C 5 under the assumption of no turnover, and compare this with the observed value of C 5. This calculation is performed for = 1 and 3 x cm -2 Band 3: 1.0 – 2.0 keV Band 4: 2.0 – 4.5 keV Band 5: 4.5 – 12.0 keV

12 GALAXY DISTRIBUTIONS Dom WaltonMadrid: 2010

13 DATA QUALITY DISTRIBUTIONS Dom WaltonMadrid: 2010

14 HIGH ENERGY TURNOVER Dom WaltonMadrid: 2010 Curvature Parameter: C (x ) (cm -2 )1 x x Whole Catalogue-17.4 ± ± 1.7 Spiral Galaxies-21.4 ± ± 2.3 Elliptical Galaxies-8.2 ± ± 1.7 High Quality-33.5 ± ± 4.3 Medium Quality-7.5 ± ± 1.3 Low Quality-11.2 ± ± 2.3

15 HIGH ENERGY TURNOVER Dom WaltonMadrid: 2010 Curvature Parameter: C (x ) (cm -2 )1 x x Whole Catalogue-17.4 ± ± 1.7 Spiral Galaxies-21.4 ± ± 2.3 Elliptical Galaxies-8.2 ± ± 1.7 High Quality-33.5 ± ± 4.3 Medium Quality-7.5 ± ± 1.3 Low Quality-11.2 ± ± 2.3

16 HIGH ENERGY TURNOVER Dom WaltonMadrid: 2010 The fraction of sources with observable curvature increases with data quality At first it seems the turnover is more prominent in sources found in spiral galaxies. However, it is important to note: We argue that high energy curvature is likely to be a common intrinsic property of ULXs in all galaxies - data from elliptical sources is poorer than spiral sources - may be lower for elliptical galaxies

17 DISC REFLECTION Dom WaltonMadrid: 2010 Caballero-Garcia & Fabian, 2010

18 OPTICALLY THICK CORONAE Dom WaltonMadrid: 2010 Gladstone, Roberts & Done, 2009 (Done & Kubota, 2006)

19 NGC 4517 ULX1 L X ~ ergs s -1 (assuming association with NGC 4517) Offset from the nucleus by 43” High quality EPIC spectrum Data above 2 keV favours spectral curvature, like other high quality ULX spectra Dom Walton Top: XMM, Bottom: SDSS EPIC-pn EPIC-mos (combined) Madrid: 2010

20 NGC 4517 ULX1 SPECTRUM Dom WaltonMadrid: Powerlaw - Disc Reflection

21 NGC 4517 ULX1 - MODELS Dom WaltonMadrid: 2010 The data are represented equally well by both models: Similar results are obtained to the application of these models to other ULXs: - Reflection: - Comptonisation: χ 2 υ = 518/466 ~ 1.1 χ 2 υ = 525/471 ~ Reflection: most of the emission located within a few R G, super solar iron abundance, steep ionising continuum - Comptonisation: low coronal electron temperature, high coronal optical depth

22 MODEL COMPARISON Dom WaltonMadrid: 2010

23 MODEL COMPARISON Dom WaltonMadrid: 2010

24 SPOT THE SIMILARITY Dom WaltonMadrid: 2010

25 Dom Walton SPOT THE SIMILARITY Madrid: 2010

26 ARABIAN CAMEL Dom WaltonMadrid: 2010

27 ARABIAN CAMEL Hump Dom WaltonMadrid: 2010

28 REFLECTION SPECTRUM Dom WaltonMadrid: 2010

29 REFLECTION SPECTRUM Hump Dom WaltonMadrid: 2010

30 SUMMARY Dom WaltonMadrid: 2010 By cross-correlating the 2XMM and RC3 catalogues, we have compiled a catalogue of 655 detections of 475 ULX candidates With a simple hardness ratio analysis, we argue that spectral curvature above ~3 keV is a common feature in ULXs Reliable data above 10 keV should be able to distinguish between the recent disc reflection and Comptonisation interpretations for this curvature


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