1. Paola Rodriguez Hidalgo High Energy Astrophysics
Evidence for Intermediate Mass Black Holes from Ultra-luminous X-Ray Sources
Paola Rodriguez Hidalgo
High Energy Astrophysics

2. Black Hole Masses Stellar Black Holes (< 20 Mo)
Super Massive Black Holes (>106 Mo)
Something in between?

3. Intermediate Mass Black Holes
We are looking fr: MBH ~ Mo
Suggested by:
Ultra-luminous X-Ray Sources (ULXs)
Several globular clusters with excess of dark mass in cores

4. Ultra-Luminous X-ray Sources
Assuming isotropic X-ray luminosity
Assuming accretion around a black hole
LX < LE
If isotropy holds, a given L lower limit M
erg s-1

5. ULXs - IMBHs Applying Eddington: Stellar mass black holes:
LX < 1039 erg s-1 ; MBH ~ 20 Mo
Intermediate-mass black holes:
LX > 1039 erg s-1 ; MBH ~ 20 Mo
LX < erg s-1 ; MBH ~ 250 Mo
(Miller & Colbert 2003)

6. X-ray Energy Spectra of ULXs
Detailed inferences depend on the spectral model used
A popular ULX model is the multi-color disk (MCD) blackbody model: each annulus of the accretion disk radiates as a BB with a radius-dependent temperature.
The inferred temperature of the innermost portion (Tin) is related to MBH:

7. X-ray Energy Spectra of ULXs
Spectral fit of ULXs requires cool accretion disk temperatures (~100 eV)
Thin disk ULXs correspond to a population of high-state IMBHs with M~ Mo

8. ULXs - IMBHs Miller, Fabian & Miller 2004
BH X-ray L vs implied disk temperature

9. Is the X-ray Flux isotropic?
LE is only applicable if isotropic
Looking at their counterparts:
Evidence: diffuse H nebulae found around the X-ray source (i.e. Pakull & Mirioni 200 for NGC 1313)
However, some cases show beaming (Kaaret et al associated radio emission)
Nebulae: isotropic illumination of the interstellar medium by the ULX

10. Some Problems Luminosities need distance determinations
Need a counterpart to determine the distance
Some sources are not what they seemed (i.e., D.M. Clark et al 2005)
The antennae ULXs X-37 is a background quasar

11. More problems… If Eddington is not obeyed
- ULXs could be outbursts - transient ULXs
- super-Eddington emission from accretion disks surrounding stellar mass BHs
In this L range other objects may be confused with ULXs: SNRs, Super-Eddington emission from NS X-ray binaries,

12. Some facts about ULXs
ULXs do not generally reside in the centers of galaxies
Generally unresolved with Chandra (high spatial resolution ~0”.5)
Many show variability (Fabbiano et al. 2003)
Large majority do not have radio counterparts
Hence, ULXs are believed to be powered by accretion onto a compact object
Unrelated to low-level AGN activity
Rule out the hypothesis that they are closely spaced aggregates of lower-luminosity sources
Combined with the observed variability, this rules out that they are youn SN

13. Where do we find ULXs?
Clear correlation between young stellar population and ULXs in a galaxy
ULXs are more numerous in actively star forming galaxies (i.e., the Antennae galaxies)
Also reported in Elliptical galaxies, possibly associated with Globular Clusters (dense environments-ray Energy Spectral ULXs

14. Conclusion/utter questions
Not simple explanation of nature of ULXs (beamed outbursts stellar mass BHs, IMBHs)
Are there IMBH in our Galaxy?