Studies of the faint Xray source populations

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• Studies of the faint X-ray source populations
• in the SMC
• University of Crete, Greece
• Harvard-Smithsonian Center for Astrophysics
• Vallia Antoniou
• In collaboration with
• Andreas Zezas (CfA), Despina Hatzidimitriou
  (UoC)

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Why do we observe the Small Magellanic Cloud ?

• 2nd nearest star-forming galaxy (60kpc)
• Low interstellar absorption
• Well determined
• metallicity (Z0.2Z?)
• stellar populations (e.g. Harris Zaritsky,
  2004 Gardiner Hatzidimitriou, 1992)
• young ( 8-30Myr) in the center
• intermediate (lt 500Myr) drop rapidly in larger
  distances
• old ( 2-10Gyr) in a fairly regular spheroid
  extending to the
• outer regions of the SMC

NGC 362 Galactic Foreground Cluster
Why do we observe the Small Magellanic Cloud?
47 Tuc
N
E
Anglo-Australian Observatory/Royal Obs.Edinburgh
(UK Schmidt plates by David Malin)
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XRBs in the SMC

• large population of HMXBs
• Be-XRBs most numerous sub-class
• population associated with recent SF
• Classification of different type of sources
  (e.g. Be/SG - XRBs)
• understand the connection between SF and XRB
  formation
• Number statistics of these different classes
• Luminosity functions
• study the faint end of the luminosity
  distribution of XRBs compare it with the LF of
  other galaxies

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X-ray study of the SMC

Chandra observations
XMM-Newton observations
FIELD 2
FIELD 3
FIELD 5
FIELD 1
FIELD 7
FIELD 6
FIELD 6
FIELD 4
FIELD 3
FIELD 5
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Chandra observations

• 122 sources (_at_ 3? level)
• Lx 4 x 1033 erg s-1
• (0.7-10keV)
• (Zezas et al., in prep.)
• 15 pulsars in our fields
• 3 (out of 15) detected in
• our survey
• (Edge et al., 2004)

FIELD 3
FIELD 5
FIELD 7
FIELD 6
FIELD 4
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XMM-Newton observations

• 144 sources (_at_ 3? level)
• Lx 3.4 x 1033 erg s-1
• (0.5-12keV)
• (Antoniou et al., in prep.)
• 3 pulsars in our fields
• 1 detected also in our survey
• 1 detected without pulsations
• (Lx 3.2 x 1034 erg s-1)

NO detections in XMM Field-5 due to high
background (1 SSS Orio et al. 2007)
FIELD 2
FIELD 6
FIELD 1
FIELD 3
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Online compilation of SXPs (Coe last update
June 2007)
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SFH of our Chandra fields

Harris Zaritsky, 2004
42 Myr
42 Myr
422 Myr
422 Myr
FIELD 3
FIELD 5
FIELD 7
42 Myr
27 Myr
FIELD 6
168 Myr
422 Myr
FIELD 4
42 Myr
422 Myr
6.7 Myr
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SFH of our XMM-Newton fields

67 Myr
FIELD 2
17 Myr
FIELD 1
FIELD 6
FIELD 3
Harris Zaritsky, 2004
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Optical study of the SMC

• OGLE-II survey
• (Optical Gravitational Lensing Experiment
  Udalski et al., 1998)
• BVI photometric data for 2.2M stars
• (down to B20, V20.5, I20mag 80 completeness
  at these limits)
• Astrometric accuracy 0.7, photometric errors
  lt0.01mag
• Coverage of our Chandra survey 70, XMM-Newton
  survey lt40
• MCPS survey
• (Magellanic Clouds Photometric Survey Zaritsky
  et al., 2002)
• UBVI photometric data for 5M stars
• (significant incompleteness below V20)
• Less accurate astrometric photometric solutions
  in crowded fields than OGLE-II
• Coverage of our Chandra/XMM-Newton surveys 100

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Optical counterparts of our Chandra sources

• The most likely optical counterpart (113 Chandra
  sources)
• 9 without counterpart
• 42 with single counterpart
• 62 with multiple matches
• with 89 not previously known!!!
• Chance coincidence probability for bright sources
  19
• (Vo lt 18.5, (B-V)o lt -0.11)
• 10 new candidate Be-XRBs
• 2 new candidate HMXBs
• consistent results with previous classifications
  in all cases of overlap
• (18 in total all Be-XRBs)
• Antoniou et al., in prep

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Optical counterparts of our XMM-Newton sources

• The most likely optical counterpart (133
  XMM-Newton sources)
• 11 without counterpart
• 43 with single counterpart
• 79 with multiple matches
• Chance coincidence probability for bright sources
  2
• (Vo lt 18.5, (B-V)o lt -0.11)
• Antoniou et al., in prep

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The largest existing sample of Be-XRB optical
spectra

• Obtained 100 excellent quality spectra with the
  2dF spectrograph (AAT)
• First results confirmed all of the Be-XRB
  tentative classifications based on the CMD
• 52 Be-XRBs (Chandra sources) have high quality
  optical spectra
• Hatzidimitriou et aL., in prep.
• Total number of Be-XRBs in our Chandra fields
  57
• (52 spectroscopic 5 photometric
  classification)

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Number of Be-XRBs in each Chandra field

FIELD 3
FIELD 5
FIELD 7
FIELD 6
FIELD 4
Compilation of Be-XRBs (Liu et al. 2005) our
new Be-XRBs (Antoniou et al., in prep.)
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Number of Be-XRBs in each XMM-Newton field

FIELD 2
FIELD 1
FIELD 6
FIELD 3
Compilation of Be-XRBs (Liu et al. 2005) our
new Be-XRBs (Antoniou et al., in prep.)
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Normalizing the XRB population to the SFR

• Study the Be-XRBs with respect to their related
  stellar populations
• N(Be-XRBs)/N(OB)
• Minimize age effects or variations due to SFR
  differences for populations of different ages
• our candidate SMC Be-XRBs compilation of
  MCs HMXBs
• (Liu et al. 2005)
• OB stars from MCPS
• (Zaritsky et al. 2001)

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X-ray source populations as a function of age

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Comparison with the Milky Way

• sample of Be-XRBs (Lx ?1034erg/s, within 10kpc of
  the Sun)
• - compilations of MCs MW HMXBs (Liu et
  al. 2005, 2006)
• - our candidate SMC Be-XRBs
• OB stars
• - Chandra fields (MCPS Zaritsky et al.
  2001)
• - Galactic (Reed 2001)
• Be-XRBs 2 times more common in the SMC when
  compared to the MW
• There is still a residual excess that can NOT be
  accounted for by the difference in the SF rate
• Difference in solar SMC metallicity (0.2Z?)
  Dray 2006 predict a factor of 3 higher numbers

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Summary

• We present the largest census of Be-XRBs in the
  SMC so far based on a combination of Chandra,
  XMM-Newton, and optical data
• Find a peak of Be-XRBs at ages of 40-60 Myr,
  and possible evidence for variation within this
  age range
• Find an excess of Be-XRBs in the SMC with
  respect to the MW
• In the future
• Extend the analysis to lower luminosities using
  the Chandra deep
• observations
• IMACS - Magellan analysis
• Identify optical counterparts for
  currently unidentified sources
• Derive accurate SFH
• Follow-up spectroscopically the candidate
  counterparts without spectra
• Identify the counterparts for most of the X-ray
  sources
• and probe the connection with the SFH of the SMC
  in more detail

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