Black Hole Binaries: Observations and Explanations(?)

Black Hole Binaries: Observations and Explanations(?) High Energy Astrophysics 10/29/2012

There aren’t too many BHBs, but they’re still pretty diverse. 20 confirmed BHBs (2006) At least 20 candidates (BHC) 17/20 BHBs are also X-ray novae

All confirmed BHBs as of 2006

Ok, cool. So what do we actually see? Unless otherwise stated, all observations are made in X-rays. 1. Light Curves 2. Timing 3. Spectra BHBs most easily discovered due to outbursts. Last from anywhere between 20 days and “many” months. Disk instability explains XRN recurring on 1-60 yr timescales (about half).

Ok, cool. So what do we actually see? Unless otherwise stated, all observations are made in X-rays. 1. Light Curves 2. Timing 3. Spectra Probe fast variability with power-density spectrum (PDS)Focus on shape and amplitude of PDS (given by scaled rms fluctuations from mean rate) Usually computed for particular intervals

Ok, cool. So what do we actually see? Unless otherwise stated, all observations are made in X-rays. 1. Light Curves 2. Timing 3. Spectra

Emission states try to describe an awful lot all at once. First recognized in Cyg X-1 High/soft – bright source, dominated by thermal emission Low/hard – faint source, dominated by power law Γ ~ 1.7, features jets Additional state later detected by Ginga: Very high – L > 0.1 LEdd, power law Γ ~ 2.5. Also QPOs

More observations caused problems for this scheme. Turns out that Cyg X-I’s soft state is dominated by steep power law (SPL), not thermal. Oops. Actually, most transients near maximum luminosity show SPL spectra. QPOs also found over a wide range of luminosities. Low/hard and SPL cut off at different energies

Well, we never get classification schemes right on the first try anyway.

Characteristic spectral energy distributions and power-density spectra of the three spectral states

There is another recent classification scheme as well. Radio jets observed from microquasar/BHB 1E 1740.7-2942 in 1992

Unified model for X-ray states and radio jets Jets correspond with high Γ, low disk luminosity Accounts for X-ray state evolution that we actually observe Progression of disk and jet emission with respect to overall X-ray state.Also note the red and blue plot beneath the HID

Legend ▲ SPL ■ hard ○ intermediate X thermal

Phew. Ok, so what does all this mean in terms of physical models? Thermal: multicomponent thermal emission from inner accretion disk Hard: at least partially inverse Compton and synchotron associated with microquasar jet. SPL: most often modeled as inverse Compton occurring in a non-thermal corona (need to make MeV photons)

What are some other ideas for the SPL component? Global disk oscillations Radial oscillations of accretion structures (accretion creates shocks within the disk) Oscillations occurring in a layer between disk and Comptonizing region Spiral waves in a magnetized disk with energy flow out to co-rotating matter farther out from center

Remember our old friends, the QPOs? We observe them in BHBs also. Low Frequency QPOs: 0.1 – 30 Hz High Frequency QPOs: 40 – 450 Hz LFQPOs seen in 14 systems HFQPOs seen in 5 BHB and 2 BHC systems Obviously we want to relate these back to our X-ray states. So, what patterns do we observe?

LFQPOs correlate with physical features and emission states. SPL contributes > 20% of flux in 2-20 keV Observed in mostly SPL and some hard states Hard and intermediate state LFQPO frequency correlated with disk flux (above)

LFQPOs can also display remarkable levels of stability (or not) GRS 1915+105 has shown to host a stable QPO at 2.0-4.5 Hz for at least 6 months (Morgan et al. 1997)Some can vary on timescales of a minute. Power-Density Spectrum (PDS) for Cygnus X-1 (Paul et al. 1998)

So where do LFQPOs come from? Long term stability suggests accretion process If Keplerian, frequencies too high for inner disk 3 Hz suggests radius of 100 Rg for 10 M⨀ BH, while we expect at most 10 Rg for x-ray emission So… still a bit of an open question.

HFQPOs are of particular interest as a means of studying black holes. Frequencies in expected range for the Innermost Stable Circular Orbit (ISCO) for ~10 M⨀ BH Frequencies stable over large changes in source luminosity Three systems feature HFQPOs in a 3:2 resonance 2νo QPO is stronger with high PL flux 3νo appears with weaker PL flux. “Currently there is no explanation for this result.”

Blue PDS: 13-30 keV Red PDS: 2- or 6-30 keV

HFQPOs also show the most promise as probes of strong gravity Of particular interest due to perceived point of origin Resonant HFQPOs can come from MHD in inner disk, frequencies scale with BH mass Also thoughts of measuring spin, but field is too young NEED MORE HFQPO EMITTING SYSTEMS! Measured relation between resonance frequencies in HFQPOs and black hole masses

Black Hole Binaries: Observations and Explanations(?)