# Presentation: 799555

## Accretion Disk Spectra of Ultra-luminous X-ray Sources and Galactic superluminal jet sources

- Ken Ebisawa (INTEGRAL Science Data Center, NASA/GSFC)
-  Piotr Zycki, Aya Kubota, T. Mizuno, K. Watarai
*ApJ submitted*

## Introduction and Summary

- “Too-hot” disk problem in ULXs and Galactic super-luminal jet sources
- Observed disk temperature is too high for Schwarzschild disk with L ~ LEdd
- Kerr disk spectra can be much harder when disk is highly inclined
- Reasonable for near edge-on Galactic super-luminal jet sources
- May not explain hard spectra of ULX  (inclination random)
- Slim disk can explain L>LEdd, high disk temperature, and spectral variation of ULXs
- ULXs are black holes with a few tens  M with super-Eddington luminosities
- Slim disk is also observed in Galactic BHC when disk luminosity is extremely high

## 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
- Most probably black holes

## Characteristics of ULX

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

## “Too-hot disk” problem in ULX and superluminal jet sources

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

## “Too-hot disk” problem in ULX and superluminal jet sources

*“**Too-hot disk” problem in ULX and superluminal jet sources*

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

- To explain the observation, either too large mass accretion rate or too small mass is required, 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

- ULXs

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

- Standard accretion disk around Kerr black hole might explain the hard disk spectra (Zhang, Cui and Chen 1997; Makishima et al. 2000)
- Rin = 3 Rs (Schwarzschild)  0.5 Rs (extreme Kerr)
- Higher disk temperature possible than the Schwarzschild case

## Laor, Netzer and Piran (1990)

- extremeKerr disk

- Scwarzschild disk

- Inclined Kerr disk is brighter in high energies!

- cos i

- cos i

## When the disk is face-on, the Kerr disk spectrum is not very different from the Schwarzschild case
Edge on Kerr disk has very harder spectra 
Hard emission from innermost parts is enhanced for inclined Kerr disks  (Doppler boosts)

- Edge on Kerr disk has very harder spectra
- Hard emission from innermost parts is enhanced for inclined Kerr disks  (Doppler boosts)

## Application of Kerr disk spectra to GRO J1655

- GRO J1655-40
- i=70, d=3.2 kpc, Tcol/Teff=1.7 fixed
- M=16 M with a=0.998 (extremely Kerr)
- M=7 M suggests a=0.68 to 0.88  (Gielinski et al. 2001)
*Inclined Kerr disk model works to solve the **“too-small mass problem”!*
- 450 Hz QPO (Strohmayer 2001) supports presence of the  disk around a spinning black hole (Abramowicz and Kluzniak 2001)

## Fitting IC342 spectrum with different inclination angle

*Application of Kerr disk spectra to ULX*

## Application of Kerr disk spectra to ULX

- IC342 Source 1
- face-on Kerr disk (d=4Mpc, Tcol/Teff=1.7,a=0.998)M=29 M and L=14 LEdd
*Super-Eddington problem not solved*
- edge-on (i= 80) Kerr disk (a=0.998)M= 355 M and L=0.9 LEdd
- Super-Eddington problem may be solved,  but unreasonably large mass required
- Standard Kerr disk model not plausible for ULX
- disk inclination should be random
- ~350 M black hole unlikely

## Slim disk   

- Abramowicz et al. (1995)

- Optically thick ADAF disk (slim disk) is stable

## Luminosity of slim disk 

- Optically thick and geometrically thick disk

- ln (rout/rin) ~10
- For standard disk h/r~0.1, Ldisk < LEdd
- For slim disk h/r ~ 1
- 	 Slim disk luminosity can be ~ 10 LEdd

## Characteristics of the Slim disk  

_**Temperature profile**_**(****Watarai et al.2000****)**

**Standard disk**

**Characteristics of the Slim disk  **

- Radial dependence of the disk temperature becomes weaker
*p* = 0.75  0.50

- Advection   Emissivity in the inner disk is suppressed

**Slim disk ****(optically thick ADAF) **

- Standard disk
- (radiation dominate)

***T *****increase**

## Observation of the slim disk

**Multicolor disk blackbody with T(r)~ r****‐p**

_***p***__**-free disk model**_

**Slim disk is observed in Galactic BHC**
**when luminosity is extremely high!**

**Smaller *****p***** gives systematically better fits!**

- Kubota 2001
- PhD thesis

## Slim disk in  GRS1915+105

**Yamaoka 2001 PhD thesis**

**Standard disk model fit **
**(T(r)********r ****-0.75****)**

**High T****in**

**T(r)********r ****-0.5**** favored**

****** ****slim disk**

**Disk oscillation between the **
**standard disk and slim disk**

## Slim disk for ULXs    

- Watarai et al. (2001)
- Ldisk saturates at high Tin
- (due to advection)
- IC342 spectral change
- explained well
- We will demonstrate more quantitatively

## Slim disk model for ULX

- Fitting ASCA IC342 Source 1 spectrum with Watrai’s slim disk model (face-on, Tcol/Teff = 1.7, pseudo-Newtonian potential)
- M=23 M , Ldisk ~ 6 LEdd
- Slim disk model fit successful with reasonable mass and disk luminosity!

## Spectral variation of IC342 Source1

- Standard disk fit

- Slim disk fit

- Mass varies
- Unreasonable, bad model!

- Consistent mass, only mass accretion rate change
- Reasonable, better model!

## Origin of ULXs

- Universal luminosity function of  X-ray binaries(Grimm et al. 2003)
- Luminosity cut-off ~1040 erg/s
- Presumably, ULXs are X-ray binaries with possible maximum stellar-size black holes
- ~40 M black holes theoretically possible (Fryer 1999)