Transcript D. Hatzidimitriou

The XMM-Newton Large Project for M 31: The search for
High-Mass X-ray Binaries
Hatzidimitriou
1,2
D. ,
Williams
3
B.F. ,
Pietsch
4
W.N. ,
Stiele
5
H. , Green
3
G.M. ,
Haberl
4
F. ,
Bonfini,
6,2
P.
University of Athens, Department of Physics – Section of Astrophysics, Astronomy & Mechanics, Greece, 2 Foundation of Research and Technology – Hellas, Heraklion, Greece,
3Department of Astronomy, University of Washington, Seattle, USA, 4Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, 5Osservatorio Astronomico di Brera,
Italy, 6Department of Physics, University of Crete, Heraklion, Crete, Greece
1
Introduction - Aims
Introduction - Aims
 M31 is the nearest spiral galaxy to our own (780 kpc), and thanks to its moderate galactic foreground absorption and favorable inclination (78o), it is an
ideal target for a detailed X-ray inventory of an archetypal low-star formation rate galaxy
 Identification and spectral classification of X-ray sources in nearby galaxies is necessary for correctly interpreting the properties of more distant
ones, particularly since we can classify nearby systems with X-ray and optical data, while more distant ones via X-rays alone
 The HMXRB population in M31 remains elusive, and no HMXRB has been confirmed optically yet. The occurrence of HMXRBs, of the Be type in
particular, are a sensitive star-formation indicator, and probably also sensitive to the metal abundance of the parent galaxy
 Our aim is to identify HMXRBs among the 1948 X-ray sources discovered by XMM-Newton in the direction of M31, by combining X ray and
optical properties
The XMM-Newton M31 Large Project
XMM-Newton EPIC observations of the largest Local Group spiral galaxy M 31, taken between June 2006 and February 2
M 31, down to a limiting luminosity of ~1035 erg/s in the 0.2-4.5 keV band (Stiele et al. 2010). These sources include
 sources within M31, i.e. X-ray binaries, supernova remnants and supersoft sources
 foreground (galactic) stars (Hatzidimitriou et al. 2006, Bonfini et al. 2009)
 background objects, i.e. mostly active galactic nuclei, some normal galaxies and a few clusters of galaxies
Fig.1
XMM-Newton M31 – LP : RGB image using bands 0.2-1.0, 1.0-2.0, 2.0-12.0 keV
Classification criteria of X-ray Sources
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Hardness ratios
X-ray variability
Correlations with catalogues in other wavelengths (optical, radio) – e.g. Local Group Survey (LGS: Massey et al. 2006)
Locus of candidate counterparts on optical Colour Magnitude Diagrams and X-ray Hardness Ratio Diagrams
High Mass X-ray binaries are expected to be classified as hard sources
 A high percentage (65%) of the sources can only be classified as “hard” sources, i. e. they can be X-ray binaries (LMXB
and HMXB) or Crab-like supernova remnants in M 31, or X-ray sources (mainly AGNs) in the background.
 Be-XRBs are expected to have early B spectral types (blue stars) and H-alpha emission
Optical Spectroscopy
 Sample: Hard sources with blue counterparts, brighter than V~21
 We have obtained optical spectra for a sample of 33 objects from the Apache Point Observatory in New Mexico using the
3.5 meter telescope, equipped with the medium dispersion Dual Imaging Spectrograph. For the blue branch, a 400 lines/mm
grating was used, while the red branch was equipped with a 300 lines/mm grating. The spectra cover the wavelength ranges
~3750-5400 Å, and ~5200-8500 Å, with a nominal resolution of 1.83 Å/pixel and 2.31 Å/pixel, respectively.
 In Figure 2, the positions of the objects observed are overlayed on an optical image of M31 (Calar Alto, using HDAP)
 Examples of spectra obtained are shown in Figures 3-4
Fig. 5
Q-parameter distribution for
different classes of object
Colour magnitude Diagram of all
candidate counterparts
Fig. 6
O + B stars in sample
AGNs in sample
All counterparts in LGS
Hardness-Ratio Diagram
Fig. 7
Fig.2
Candidate Be XRB?
(+ Hα diffuse emission)
[PFH 2005] 407
Fig. 3
O & B stars
Be stars (MW)
Candidate HMXRB WN+OB
(Embedded in HII region)
[PFH 2005] 146
HII region
Results
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Four optical counterparts (of sources 407, 688, 696, 757) observed have early B spectral types, visual magnitudes,
reddening free parameter “Q” values, and hardness ratios consistent with Be XRBs
Figures 5-7
Τwo of these [407 (Fig. 3) and 688] show Hα emission (but there is also diffuse Hα emission in both cases)
These are possible Be-XRBs in M31
One Of supergiant which can be candidate Supergiant-HMXB.
Two composite spectra
 HII region + WR star of WN type: candidate HMXB Wolf Rayet WN + O star (Fig. 4)– colliding wind shock emission
 supernova remnant + embedded early type (OB) star
Two old globular cluster spectra, and therefore the X-ray emission may be coming from a LMXB
(one of the sources also shows transient behaviour)
Background sources: Nine Seyfert 1 galaxies with redshifts z~0.7-1.6 + peculiar flaring quasar (Meusinger et al. 2010).
Foreground sources: One cataclysmic variable and one U-Gem (dwarf nova) variable in the Milky Way
New Classification Criteria for identification of X-ray sources, e.g. using Figures 6-7 (Hatzidimitriou et al. 2011)
Fig. 4
References
•Bonfini et al. 2009, A&A, 507, 705
•Hatzidimitriou et al. 2006, A&A, 451, 835
•Hatzidimitriou et al. 2011, in preparation
•Massey et al. 2006, AJ, 131, 2478
•Meusinger et al. 2010, A&A, 512, 1
•Pietsch et al.2005, A&A, 434, 483
•Stiele et al. 2010, A&A, under revision