1. Extragalactic Science Working Group http://cherenkov.physics.iastate.edu/wp/extra.html Armen Atoyan (Université de Montréal), Roger Blandford (Stanford), Markus Boettcher (Ohiou Univ.), James Buckley (Wash. Univ. St. Louis) Alberto Carramiñana (INAOE), Paolo Coppi (Yale), Charles Dermer (NRL), Brenda Dingus (Los Alamos), John Finley (Purdue), Stefan Funk (Slac), Markos Georganopoulos (GSFC), Deirdre Horan (Argonne), Tom Jones (Univ. of Minnesota), Philip Kaaret (University of Iowa), Jonathan Katz (Wash. Univ. St. Louis), Dave Kieda (Utah), Henric Krawczynski (Wash. Univ. St. Louis), Julie Mcenery (GSFC), Reshmi Mukherjee (Columbia), Eric Perlman (FIT), Martin Pohl (ISU), Steven Ritz (GSFC), Meg Urry (Yale), Vladimir Vassiliev (UCLA), Trevor Weekes (SAO), David A. Williams (UCSC) Email: krawcz@wuphys.wustl.edu

2. Extragalactic TeV  - Ray Beams: - Extragalactic Background Light, - Magnetic Fields, - Spacetime. Extragalactic Science Working Group Supermassive Black Holes: Jet Formation, Magnetosphere, Accretion & Growth, UHECRs. Starburst Galaxies, LIG, ULIGs, Galaxy Clusters: Cosmic-Ray Acceleration, Energy Content, and Propagation. M82 CXO/STSI Not Covered In This Science Working Group: GRBs and Dark Matter

3. Quo Vadis? GLAST (2 Years) VERITAS-4 (3  in 50 hrs) Whipple 10 m (3  in 50 hrs) e+e+   e-e-

4. Extragalactic Science Working Group Mini-Contributions: G. Madejski M. Boettcher M. Beilicke A. Carramiñana C. Dermer D. Torres O. Reimer F. Stecker

5. 1. Objects are rapidly variable, current data do not resolve spectral (or flux!) variability Time resolved spectra are crucial to distinguish emission models –lept. vs. hadronic Objects are rapidly variable in the  -ray regime – photons are needed Going to lower energies gains a lot – spectra go as E -2 so one decade increases photon number by x 100 2. GLAST has modest effective area (8000 cm 2 ) – cross-calibration against the TeV observatories difficult! (even using the Crab) 3. Very exciting prospects for studies of EBL – or the intrinsic ambient photon field – for sources at much higher redshift (as a function of redshift) Case for jet-dominated AGN – “blazars” at sub-TeV  -ray energies

6. TeV observations of Mkn 421 with HESS (from S. Wagner)

7. Probe GeV – TeV electron acceleration and cooling time scales (→ identify VHE  -ray radiation as leptonic/hadronic; magnetic field estimates; identify VHE  -ray spectral cutoff as intrinsic vs. IIBR) GeV – TeV Prospects for Intermediate BL Lac Objects Markus Böttcher, Ohio Univ., Athens, OH Intermediate BL Lacs (IBLs): Peak frequencies at IR/Opt. and GeV; Intermediate overall luminosiyt; sometimes  -ray dominated Hadronic models often predict TeV emission; leptonic models don’t. Lept. models predict > 100 GeV spectr. variability on time scales of a few hours:  sy ~ 2 B -1 -2  6 -1 D 1 -1 hr Correlated with spectral var. at opt./X-ray Probe GeV – TeV spectral variability; correlation with opt./X-ray variability W Comae May 1998 ~ 2 hr limit of future array GLAST

9.  -ray horizon should be experimentally measured with Cherenkov telescopes: - EBL SED - lines of sight WPS GLAST Symposium 2007

10. Gamma Ray Emission from Cosmic Rays in Star-Forming Galaxies (see detailed calculations by Diego Torres)

13. A Simple Analytic Treatment of the Intergalactic Absorption Effect in Blazar  -ray Spectra F.W. Stecker (NASA/GSFC) And S.T. Scully (JMU) Stecker, Malkan & Scully 2006, ApJ 648, 774; corrected Table 1, astro-ph/0612048 Stecker & Scully, ApJ Lett. 652, L9  (E ,z) = (A+Bz) +(C+Dz)ln[E  (TeV)] 0.2 TeV < E  < 2 TeV 0.05 < z < 0.4 Absorption Steepens a Powerlaw by:  = C + Dz