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

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

Intermediate Mass Black Holes We are looking fr: MBH ~ 102 - 104 Mo Suggested by: Ultra-luminous X-Ray Sources (ULXs) Several globular clusters with excess of dark mass in cores

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

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 < 1040.5 erg s-1 ; MBH ~ 250 Mo (Miller & Colbert 2003)

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:

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~16-104 Mo

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

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 2003 - associated radio emission) Nebulae: isotropic illumination of the interstellar medium by the ULX

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

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,

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

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

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