An XMM-Newton View of the Luminous X-ray Source Population of M101 Leigh Jenkins Tim Roberts, Robert Warwick, Roy Kilgard*, Martin Ward University of Leicester, UK *Harvard-Smithsonian CfA, USA XMM-Newton EPIC Consortium Meeting, Palermo. October 14 th -16 th 2003.

Discrete Source Populations in Spirals X-ray Binaries – Black hole/neutron star + stellar companionX-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 RemnantsSupernova Remnants –Thermal emission from collisionally ionized gas Ultraluminous X-ray Sources (ULXs) Ultraluminous X-ray Sources (ULXs) –L X ≥ erg/s i.e. super-Eddington for a 1.4 solar mass neutron star True super-Eddington emission True super-Eddington emission Anisotropic (beamed) emission Anisotropic (beamed) emission Intermediate mass black holes (IMBHs) (L X ≥ 5x10 39 erg/s) Intermediate mass black holes (IMBHs) (L X ≥ 5x10 39 erg/s) –Link with star formation  High Mass X-ray Binaries (HMXBs)?

M101 Grand design supergiant spiralGrand design supergiant spiral Nearby (D~7 Mpc)Nearby (D~7 Mpc) Face onFace on low foreground N Hlow foreground N H  Ideal laboratory for studies of galactic X-ray emission  Ideal laboratory for studies of galactic X-ray emission

EPIC 3-Colour Image X-ray Data 43 ks observation43 ks observation Encompasses entire D 25 ellipseEncompasses entire D 25 ellipse (23.8 arcmin) ~100 sources in field~100 sources in field Red = keV Green= keV Blue = keV

Source Selection Sufficient counts for spectral fitting (> 300 counts in the PN data)Sufficient counts for spectral fitting (> 300 counts in the PN data)  14 suitable sources (excluding 2 bright stars in field)  14 suitable sources (excluding 2 bright stars in field) − Intrinsic X-ray luminosities 3x10 38 – 3x10 39 erg/s i.e. ≥ Eddington limit for accretion onto a 1.4  neutron star Investigate their nature by studying their: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- NewtonAmongst the first detailed spectroscopic studies of a large number of compact sources in a single spiral galaxy with XMM- Newton

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 XMM EPIC DSS Optical

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

Spectra - Quality XMM-1 XMM-14 Brightest – 3800 counts Faintest – 300 counts

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

Spectral Fits – Single-component 9 sources with single- component fits:9 sources with single- component fits:  4 Disc Blackbody (T in = keV)  1 Supersoft ( T in =0.16 keV)  3 Disc Blackbody or Powerlaw  1 Powerlaw (nucleus) Г = 2.2  Consistent with all sources except nucleus being X-ray binaries in the high-soft state Nucleus Г ~ 2.2 XMM-1 T in = 1.3 keV

Spectral Fits – Two-component 5 sources require two- component fits: 5 sources require two- component fits: – Hard powerlaw (Γ = 1.5 – 2 ) + soft excess Cool Disc Blackbody (~ keV) Cool Disc Blackbody (~ keV)  IMBH (T in α M -1/4 ) Cool Blackbody (~ keV) Cool Blackbody (~ keV)  Ouflowing material (black hole wind) MEKAL thermal plasma 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 keV disc blackbody Underlying continuum of 3 sources can also be modelled by a keV disc blackbody XMM-2 PL + DISKBB XMM-5 PL + MEKAL

Source Hardness vs. Luminosity No distinction between sources above and below ULX thresholdNo distinction between sources above and below ULX threshold  Implies same source population Power law ● DISKBB  Supersoft  PL+MEKAL  PL+DISKBB/BBODY

Source Variability - Methods Short-term variabilityShort-term variability –Chi-squared test  Large-amplitude variability –K-S test  Gradual small-amplitude variations Long-term variabilityLong-term variability –Archival data spanning ~11-23 years Einstein, ROSAT, Chandra, XMM Einstein, ROSAT, Chandra, XMM –Observed fluxes normalized to the keV band

Lightcurves – Example (XMM-2) Short-termShort-term –P var > 99.9% over duration of XMM observation Long-termLong-term –Increase by factor of ~30 in XMM observation

Variability - Results Short-termShort-term –11 of 14 sources show some short-term variability ( > 95% level) Long-termLong-term –Majority vary between factor of 2-4 –Transient varies by factor of ~30 –No grouping of sources with certain spectral types Power law ● DISKBB  Supersoft  PL+MEKAL  PL+DISKBB/BBODY

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

What does this mean? Spectral shapes/variability/locations/spectral behaviour consistent with all sources (except nucleus) being accreting BH X-ray binary systemsSpectral 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 limitedIntrinsic 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 ofLikely 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 erg/s