2. The questions: How can gamma-ray blazar statistics be parameterized? What parameters fit EGRET data best? –Blazar redshift distribution [ N vs z ] –Blazar cumulative flux distribution, [ N(>F) vs F ] –Consider FSRQs and BL Lacs separately Using best-fit models, how many blazars do we expect Fermi to see? Using best-fit models, how much do we expect blazars to contribute to the diffuse gamma-ray background?

3. Some history: Models for blazar statistics assuming radio/gamma connection –Stecker & Salamon 1996, Giommi et al. 2006, Narumoto & Totani 2006 –Assume gamma luminosity  radio luminosity –Maybe correct for different beaming, duty cycle, spectral hardening with flaring –Obtain blazar gamma-ray luminosity functions from radio luminosity functions

4. More history: Radio/gamma connection strongly contested Other models don’t assume such a connection –Chiang & Mukherjee 1998, Narumoto & Totani 2006 –Assume some functional form for the luminosity function –Obtain best-fit parameters using EGRET data alone

5. Yet more history: Other models attempt to build a luminosity function from first principles –Mucke & Pohl 2000, Dermer 2007 –Assume a simple model for the emission properties and cosmic evolution of blazars –Fit to EGRET data, obtain luminosity functions from there

6. How do results of all these studies compare? Fits to EGRET data: all good; SS96 do not fit redshift distribution Predictions for # of blazars detectable by Fermi: –Between 1,000 - 10,000 Predictions for fraction of diffuse background made by blazars: –Between 1% and >=100%

7. What issues are still open/not treated/ have been treated only simplisticly? Which blazars are gamma-ray loud? Is there a relation between radio flux and gamma-ray flux? Blazars are strongly variable. What do we do about that in building a luminosity function? What is the blazar duty cycle? What are the beaming statistics of blazars?

8. The Dermer (2007) approach

9. BL Lacs and FSRQs beamed differently? Radio and gamma-ray emission beamed differently for FSRQs?

10. Beaming factor:  D 3+  (synchrotron, SSC)  D 4+2  (EC)