unlocking the nature of ulxs using their x-ray spectra

Jeanette Gladstone - University of AlbertaTim Roberts, Chris Done - Durham University

Jeanette Gladstone - University of AlbertaTim Roberts, Chris Done - Durham University

Unlocking the nature of ULXs using their X-ray spectra

Unlocking the nature of ULXs using their X-ray spectra

Jeanette GladstoneMadrid 2010 University of Alberta

Ultraluminous X-ray SourcesUltraluminous X-ray Sources

QuickTime™ and a decompressor

are needed to see this picture.

Early XMM-Newton studies fit with standard disc + power-law (as used in Galactic sources)

Detection of cool disc component suggested IMBH



e.g. NGC 1313 X-1 Miller et al. (2003)

kTin ~ 0.15, ~ 1.8 ~1000M BHs

diskpower-law



QuickTime™ and a decompressor

are needed to see this picture.



Resultant fits are not disc dominated - mass estimates uncertain.



Resultant fits are not disc dominated - mass estimates uncertain.

e.g. NGC 1313 X-1 Miller et al. (2003)

kTin ~ 0.15, ~ 1.8 ~1000M BHs

diskpower-law



Spectral featuresSpectral features



Spectral featuresSoft excess

Spectral featuresSoft excess



Spectral featuresSoft excessHigh energy

break

(e.g. Roberts 2007)

Spectral featuresSoft excessHigh energy

break

(e.g. Roberts 2007)


Explanations for spectral breakExplanations for spectral break

Slim accretion discs (e.g. Watarai et al. 2000)

Fully Comptonised VHS with spectrum modified by ionised fast outflow (Goncalves & Soria 2006).

Disc plus Comptonised corona models - find fits with cool disc and cool, optically thick corona (Stobbart et al. 2006)

Slim accretion discs (e.g. Watarai et al. 2000)

Fully Comptonised VHS with spectrum modified by ionised fast outflow (Goncalves & Soria 2006).

Disc plus Comptonised corona models - find fits with cool disc and cool, optically thick corona (Stobbart et al. 2006)


Understanding ULX spectraUnderstanding ULX spectra

Only the highest quality data (>10,000 counts)Characterise the shape of the spectrumGain greater understanding of spectral shape by

applying current physically motivated models

Only the highest quality data (>10,000 counts)Characterise the shape of the spectrumGain greater understanding of spectral shape by

applying current physically motivated models


Understanding ULX spectraUnderstanding ULX spectra

Sample of 12 sources lying within 10 Mpc, covering the range of ULX luminosities (~ 1039 - a few 1040 erg s-1)


Characterising ULX SpectraCharacterising ULX Spectra

Holmberg IX X-1

model fitdiskpower-law



Holmberg IX X-1

model fitdiskpower-law

11/12 show improvement (2 > 30) with addition of disc component (soft excess)



power-law


Holmberg IX X-1


11/12 >98% statistical improvement for Broken power-law vs. power-law above 2 keV


11/12 >98% statistical improvement for Broken power-law vs. power-law above 2 keV


Sample spectraSample spectra


Sample spectraSample spectraSoft excess + break not seen in any

other accretion state, this is something new …


Sample spectraSample spectraSoft excess + break not seen in any

other accretion state, this is something new …

… but what?


Physically motivated modellingPhysically motivated modelling



Slim discs?Slim discs?



Slim discs?Comptonisation

models?


models?




models?Worked well on

XRBs so why not?



XRBs so why not?





XRBs so why not?



XRBs so why not?

Holmberg IX X-1


Slim disc fitsSlim disc fits

0.4 < p < 0.6 could imply support for slim disc


Holmberg IX X-1

diskpbb


Slim disc fitsSlim disc fits


Problem - 1.1 < Tin < 13 keV, higher disc temperature values are physically unrealistic


Problem - 1.1 < Tin < 13 keV, higher disc temperature values are physically unrealistic

Holmberg IX X-1

diskpbb


Comptonisation modelsComptonisation modelsTwo different

Comptonisation models applied COMPTT EQPAIR

Two different Comptonisation models applied COMPTT EQPAIR

DISKPN + COMPTT

model fitdiskcomptt


Comptonisation modelsComptonisation modelsTwo different

Comptonisation models applied COMPTT EQPAIR

Fit with cool disc + cool optically thick corona ( > 6)

Two different Comptonisation models applied COMPTT EQPAIR

Fit with cool disc + cool optically thick corona ( > 6)

DISKPN + COMPTT

model fitdiskcomptt


Comptonisation modelsComptonisation models

Galactic sources? All thin ( < 1-2) except in VHS ( ~3, kT ~20 keV)


DISKPN + EQPAIR

model fitdiskeqpair


Comptonisation modelsComptonisation models


More extreme - super-Eddington?


More extreme - super-Eddington?

DISKPN + EQPAIR

model fitdiskeqpair


Implications of Corona?Implications of Corona?model fitdiskcomptt

model fitdiskeqpair


Implications of Corona?Implications of Corona?

Masking of innermost regions of the accretion disc

Material and power may be drawn from the disc to feed the corona

Masking of innermost regions of the accretion disc

Material and power may be drawn from the disc to feed the corona

model fitdiskcomptt

model fitdiskeqpair


As accretion rate increases, material & energy fed into corona


Energetic disc-corona couplingEnergetic disc-corona coupling



Observe Outer disc Corona


Observe Outer disc Corona


model fitdiskcorona



Energetically coupled inner disc cannot be seen

Neither feature can give direct information on temperature of inner accretion disc

Energetically coupled inner disc cannot be seen

Neither feature can give direct information on temperature of inner accretion disc

model fitdiskcorona


Spectra of ULXsSpectra of ULXs


Disc- like spectra?Disc- like spectra? Looks disc-like

Recovered disc similar to actual data

Looks disc-likeRecovered disc

similar to actual data




Disc + power-law reveals warm disc fit

Looks disc-like Recovered disc similar

to actual data






Physical meaning? Broadening to create

more realistic disc in this energy band (e.g. Done & Davis 2008)

Looks disc-like Recovered disc similar

to actual data


Physical meaning? Broadening to create

more realistic disc in this energy band (e.g. Done & Davis 2008)


Ultraluminous state spectraUltraluminous state spectraDouble hump feature

First modelled by cool disc

Second modelled by break, or by Comptonising corona when applying more physical models

Double hump feature First modelled by cool

discSecond modelled by

break, or by Comptonising corona when applying more physical models


Ultraluminous state spectraUltraluminous state spectraDouble hump feature

First modelled by cool disc

Second modelled by break, or by Comptonising corona when applying more physical models

Both features, new state?

Double hump feature First modelled by cool

discSecond modelled by

break, or by Comptonising corona when applying more physical models

Both features, new state?


Low temperature discs?Low temperature discs?

IMBH? IMBH?



IMBH?Something else?

So far we have tracked increasing mass accretion rate









Theory predicts that a photosphere + wind are key components of super-Eddington accretion

First observational evidence of photosphere?


First observational evidence of photosphere?








First observational evidence of photosphere? If this is the case we are looking at stellar-mass black hole in an

extreme accretion state


First observational evidence of photosphere? If this is the case we are looking at stellar-mass black hole in an

extreme accretion state


Extreme accretion?Extreme accretion?


Where do we go from here?Where do we go from here?This work provides a prediction for the

evolution of ULXs, so next stage is to follow evolution of ULXs with high quality dataNot the easiest of challenges, given sparsity

of observations of these sourcesRecent studies have found a variety of

spectral behaviours (e.g. Feng & Kaaret 2009, Kajava & Poutanen 2009)

This work provides a prediction for the evolution of ULXs, so next stage is to follow evolution of ULXs with high quality dataNot the easiest of challenges, given sparsity

of observations of these sourcesRecent studies have found a variety of

spectral behaviours (e.g. Feng & Kaaret 2009, Kajava & Poutanen 2009)


Spectral evolution? (Vierdayanti et al. 2010)Spectral evolution? (Vierdayanti et al. 2010)

Using XMM-Newton observations and grouped Swift data (based on count rate)


Swift spectra of Ho IX X-1, stacked on increasing count rate and compared to XMM-Newton data (in light blue). Underlying model is diskbb + comptt




As luminosity increases, kTe

,



,






, This supports theory of

increasing mass accretion rate












Results also show further complexity in spectral variability - difference spectral shape at same flux - hysteresis?





Results also show further complexity in spectral variability - difference spectral shape at same flux - hysteresis?



ConclusionsConclusions Ultraluminous state is characterised by cool disc +

break above 3keV Combination different from other observed accretion

states Application of Comptonisation models explains shape,

and implies more extreme version of VHS Energetic coupling reveals the presence of (large?)

stellar-mass black holes Some sources indicate presence of possibly the most

extreme accretion environments Initial spectral variability studies (with increased data

quality) appear to support this

Ultraluminous state is characterised by cool disc + break above 3keV

Combination different from other observed accretion states

Application of Comptonisation models explains shape, and implies more extreme version of VHS

Energetic coupling reveals the presence of (large?) stellar-mass black holes

Some sources indicate presence of possibly the most extreme accretion environments

Initial spectral variability studies (with increased data quality) appear to support this

unlocking the nature of ulxs using their x-ray spectra

Documents

standard disc powerlaw

slim disc holmberg

comptonisation models

comptonised corona models

broken powerlaw

range of ulx luminosities

accretion state

statistical improvement