An XMM-Newton View of the Luminous X-ray Source Population of M101

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An XMM-Newton View of the Luminous X-ray Source
Population of M101
XMM-Newton EPIC Consortium Meeting, Palermo.
October 14th-16th 2003.

• Leigh Jenkins
• Tim Roberts, Robert Warwick, Roy Kilgard, Martin
  Ward
• University of Leicester, UK
• Harvard-Smithsonian CfA, USA

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Discrete Source Populations in Spirals

• X-ray Binaries Black hole/neutron star
  stellar companion
• High State dominated by thermal accretion disc
  emission
• Low State dominated by powerlaw emission
  (comptonization of accretion disc corona)
• Supernova Remnants
• Thermal emission from collisionally ionized gas
• Ultraluminous X-ray Sources (ULXs)
• LX 1039 erg/s i.e. super-Eddington for a 1.4
  solar mass neutron star
• True super-Eddington emission
• Anisotropic (beamed) emission
• Intermediate mass black holes (IMBHs) (LX
  5x1039 erg/s)
• Link with star formation ? High Mass X-ray
  Binaries (HMXBs)?

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M101

• Grand design supergiant spiral
• Nearby (D7 Mpc)
• Face on
• low foreground NH
• ? Ideal laboratory for studies of galactic
  X-ray emission

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X-ray Data

• 43 ks observation
• Encompasses entire D25 ellipse
• (23.8 arcmin)
• 100 sources in field

Red 0.2-0.5 keV Green0.5-2.0 keV Blue
2.0-4.5 keV
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Source Selection

• Sufficient counts for spectral fitting (gt 300
  counts in the PN data)
• ? 14 suitable sources (excluding 2 bright
  stars in field)
• Intrinsic X-ray luminosities 3x1038 3x1039
  erg/s i.e.
• Eddington limit for accretion onto a 1.4 ?
  neutron star
• Investigate their nature by studying their
• Locations
• Spectral shapes
• Timing properties ? variability ? accretion
• Amongst the first detailed spectroscopic studies
  of a large number of compact sources in a single
  spiral galaxy with XMM-Newton

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Source Locations

• Sources spread over galaxy
• Positions correlate with
• Nucleus
• HII regions (star formation)
• Spiral arm structure
• ? Indicates that all sources are likely to be
  associated with M101

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Source Locations

• Sources spread over galaxy
• Positions correlate with
• Nucleus
• HII regions (star formation)
• Spiral arm structure
• ? Indicates that all sources are likely to be
  associated with M101

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Spectra - Quality
Brightest 3800 counts
Faintest 300 counts
XMM-1
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Spectral Models

• Absorbed single and two-component
• Powerlaw
• Non-thermal emission from accreting objects
• Multicolour Disc Blackbody
• Thermal emission from accretion disc in a
  high/soft state
• Blackbody
• Outflowing material Black hole wind model
• MEKAL
• Thermal emission from collisionally ionized gas
  (e.g. stellar winds, supernovae)

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Spectral Fits Single-component

• 9 sources with single-component fits
• 4 Disc Blackbody
• (Tin0.96-1.33 keV)
• 1 Supersoft (Tin0.16 keV)
• 3 Disc Blackbody or Powerlaw
• 1 Powerlaw (nucleus)
• ? 2.2
• ? Consistent with all sources except nucleus
  being X-ray binaries in the high-soft state

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Spectral Fits Two-component

• 5 sources require two-component fits
• Hard powerlaw (G 1.5 2 ) soft
  excess
• Cool Disc Blackbody (0.1-0.3 keV)
• IMBH (Tina M-1/4)
• Cool Blackbody (0.1-0.2 keV)
• Ouflowing material
• (black hole wind)
• MEKAL thermal plasma
• Hot (1 keV) photoionized plasma surrounding
  high-mass star
• Cool (0.2 keV) thermal emission related to star
  formation activity
• Underlying continuum of 3 sources can also be
  modelled by a 1-1.5 keV disc blackbody

XMM-2 PL DISKBB
XMM-5 PL MEKAL
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Source Hardness vs. Luminosity

• No distinction between sources above and below
  ULX threshold
• Implies same source population

• Power law
• DISKBB
• Supersoft
• PLMEKAL
• PLDISKBB/BBODY

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Source Variability - Methods

• Short-term variability
• Chi-squared test ? Large-amplitude variability
• K-S test ? Gradual small-amplitude variations
• Long-term variability
• Archival data spanning 11-23 years
• Einstein, ROSAT, Chandra, XMM
• Observed fluxes normalized to the 0.5-2 keV band

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Lightcurves Example (XMM-2)

• Short-term
• Pvar gt 99.9 over duration of XMM observation

• Long-term
• Increase by factor of 30 in XMM observation

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Variability - Results

• Short-term
• 11 of 14 sources show some short-term variability
  ( gt 95 level)

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Spectral Changes

• Compare source hardness in XMM observation to
  Chandra data for 9 sources (2 years earlier)
• General trend is softening with increasing
  luminosity same as behaviour of many Galactic
  XRBs e.g. Cyg X-1

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What does this mean?

• Spectral shapes/variability/locations/spectral
  behaviour consistent with all sources (except
  nucleus) being accreting BH X-ray binary systems
• Intrinsic X-ray luminosities imply black hole
  masses of 2-23 M? (i.e. stellar-mass) if
  Eddington limited
• Likely to be looking at the high-luminosity end
  of
• X-ray binary source population no requirement
  for IMBHs
• Supported by fact that cumulative X-ray
  luminosity functions of compact sources in
  star-forming galaxies extend to ULX luminosities
  no break at 1039 erg/s