# Presentation: 116047

## Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic superluminal jet sources

- Ken Ebisawa
- 	ISDC, NASA/GSFC, USRA
- Piotr Zycki
- 	Copernicus Center
- Aya Kubota
- 	ISAS

## Ultra-luminous X-ray Sources (ULX)

- Discovered with Einstein in nearby spiral Galaxies (e.g., Fabbiano 1988)
- LX(0.5-10 keV)~1039-1040 erg s-1
- Too bright for X-ray binaries, too dim for AGN
- Most sources are located off-center of the Galaxy (Colbert and Mushotzky 1999)
- >100 M not to exceed the Eddington limits?

## Characteristics of ULX

- Significant time variation (Source1 in IC342; Okada et al. 1998)
- Compact object in nature

## Characteristics of ULX

- High-low transition? (Source1 and 2 in IC342; Kubota et al. 2001)
- Orbital modulation (?) from Source 2 (Sugiho et al. 2001) , from a ULX in  Circinus galaxy (Bauer et al. 2001)
- Similar to Galactic black hole candidates

## Characteristics of ULX

- Thermal spectrum, like standard optically thick accretion disk, in the bright state
- Disk temperature too high for given luminosity and mass, assuming Schwarzschild black hole (Okada et al. 1998; Makishima et al. 2000)
- Similar to Galactic superluminal jet sources GRS1915+105 and GRO J1655-40 (Zhang, Cui and Chen 1997)

## Optically thick accretion disk around a Schwarzschild black hole
Innermost radius = 6 Rg = 6 GM/c2
mass, mass accretion rate (luminosity)  spectral shape determined

- Optically thick accretion disk around a Schwarzschild black hole
- Innermost radius = 6 Rg = 6 GM/c2
- mass, mass accretion rate (luminosity)  spectral shape determined

- Maximum disk color temperature for Schwarzschild black hole
- 	T(max)col ~ 1.2 keV ((Tcol/Teff)/1.7) (M/MEdd)1/4 (M/7M)-1/4
- This is directly measured from observed spectral shape
- Kerr disk can be much hotter, as innermost radius 1.24 Rg

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## Too hot accretion disks in ULX and superluminal jet sources
To explain the observation, you need either too large mass accretion rate or too small mass, as long as standard disk around Schwarzschild black hole is assumed

- To explain the observation, you need either too large mass accretion rate or too small mass, as long as standard disk around Schwarzschild black hole is assumed

- M=1.8 M
- L= 0.4 LEdd

- M=9.4 M
- L= 11 LEdd

## Makishima et al. (2000)

- M=const, Ldisk ~Tin4

- Super-Eddington

## How to explain the “too-hot” accretion disk?

- Standard accretion disk around Kerr black hole can explain the hard disk spectra? (Zhang, Cui and Chen 1997; Makishima et al. 2000)
-  Apply Kerr disk spectra to ULX and superluminal jet sources

## Laor, Netzer and Piran (1990)

- “Transfer function” for a=0.998 available with xspec

- Kerr disk

- Scwarzschild disk

- Inclined Kerr disk is brighter in high energies

## Hard emission from very inner parts (1.26 rg < r < 7 rg) is enhanced for inclined Kerr disks  (due to Doppler boost)
When the disk is face-on, emission from inner part is weak, and the spectrum is not very different from the Schwarzschild case

- When the disk is face-on, emission from inner part is weak, and the spectrum is not very different from the Schwarzschild case

## Application of Kerr disk spectra

- GRO J1655-40
- i=70, d=3.2 kpc, Tcol/Teff=1.7 fixedM=16 M and M=3.51017 g s-1with a=0.998*Kerr disk model works to solve too-small mass problem*
- a=0.68 to 0.88 plausible (Gielinski et al. 2001)
- 450 Hz QPO (Strohmayer 2001) supports a standard (geometrically thin) disk around a spinning black hole (Abramowicz and Kluzniak 2001)

## Application of Kerr disk spectra

- IC342 Source 1
- face-on Kerr disk (d=4Mpc, Tcol/Teff=1.7,a=0.998)M=29 M and L=14 LEdd
- edge-on (i= 80) Kerr disk (a=0.998)M= 355 M and L=0.9 LEdd
- Super-Eddington problem may be solved *only if* the disk is highly inclined
- Kerr disk model is not plausible for ULX because  disk inclination should be random

## Origin of hard disk spectra of ULX    

- Optically thick ADAF
- Strong disk comptonization

## From recent study of Galactic black hole candidates

- <date/time>

*From recent study of Galactic black hole candidates*

- Abramowicz et al. (1995)

**Comptonized**
**disk**

**T ******** r ****-0.75**

## From recent study of Galactic black hole candidates

- <date/time>

*From recent study of Galactic black hole candidates*

- Standard optically thick disk
- Gravitational energy release  Radiation
- T( r) r -0.75, Rin = const., Ldisk  Tin4

- Disk instability
- Energy release  Comptonizing plasma
- Disk compotonization

- Optically thick ADAF disk
- Energy release  Advection
- T( r) r -0.5, Ldisk saturates

**Disk**
**Oscillation**

## Optically thick ADAF disk (slim disk)    

- Watarai et al. (2001)
- Standard disk Slim disk
- when L ~ LEdd
- Ldisk saturates at high Tin
- IC342 spectral change
- explained well

## Strong disk comptonization

- IC342 source 1, Schwarzschild disk with M=100 M, L=LEdd (Tin = 0.6 keV)
- Put comptonizing corona with y=(4kTe/mc2)e~0.5  soft photons comptonized and appear in higher energy band
- observed hard spectrum can be explained

## Summary

- Standard accretion disk model around Kerr black hole can explain the hard spectra of Galactic superluminal jet sources (highly inclined system)
- This model is not suitable for ULX, as accretion disks are not preferentially inclined
- Optically thick ADAF model or strong disk comptonization may work for ULX