1. Some more science considerations/thoughts …. P. Coppi, Yale ? ? E>5 GeV? E>30 GeV? vs.

2. Don’t forget absorption by infrared/optical background! Real population statistics and fully observed SED peaks would be very useful …

3. Numerical simulations for 3C 279. Spada et al. 2001

5. In case you still thought things were simple… Mkn 421 2002 X-ray/TeV campaign (Dieter Horns, preliminary) X-ray TeV X-ray hardness ratio (spectrum) Counts

6. If t_var = 6 hours (one night) - one telescope won’t do it!! Lesson from ASCA/X-ray monitoring days…. Need complete time sampling!

7. Typical  HESS/Veritas observation?

9. VHE (GeV-TeV) gamma-ray emission is a highly time variable phenomenon.  We need a “Gamma-Ray Timing Explorer” (GTE) analog to the Rossi “X-Ray Timing Explorer” (RXTE) with the same relative sensitivity at ~ 1 GeV as RXTE at ~1 keV – with no coverage gaps …  …. Ideally, while GLAST is up! (HAWC won’t do this. Would be nice to have similar threshold to GLAST so see same sources. )

11. GLAST and GRBs Long burst w/optical flash detected by ROTSE, BATSE flux > 99.6% BATSE bursts Briggs et al. 1999 Energy Flux at MeV Peak Integration Time for Spectrum ~ 32 s Assume same energy flux at 1 GeV, collection area, photons Great GeV energy spectrum for this burst, and reasonable spectra for bursts ~ 50x fainter. A MAJOR improvement over EGRET! BUT … this is a time integrated spectrum… Look at what BATSE saw during those 32 sec

12. GLAST and GRBs Awesome statistics, even for 64 msec time bins. Allows detection of significant spectral variability on < 1 sec timescales. Just as for blazars, fitting time-integrated spectra when this sort of variability is going on is NOT a good idea. Can GLAST match this X-ray sensitivity?

13. GLAST and GRBs Assume constant GeV flux at peak count rate (optimistic!): N_photon in 1 sec @ 1 GeV = 25 -- o.k. N_photon in 64 msec @ 1 GeV = 1.6 -- not too useful Also, although GLAST has sensitivity at 10 GeV, N_photon in 1 sec @ > 10 GeV ~ 2.5 -- not too useful  GLAST is marginal, and this is for a very bright burst! (N.B. OSSE detected 16 msec variability for this burst at ~ 1 MeV.)

14. GLAST and GRBs Another key component of GRB studies is the AFTERGLOW. Can GLAST study this? [Afterglow is much easier because there is no rapid time variability.] Bottom line: Unless we’re lucky with physics, GLAST will only see brightest bursts at ~ 1 GeV, and there is not much margin for error.

17. M87 – FRI (weak jet) X-RAY Mostly synchrotron emission? Hey, there are some interesting nearby objects – jet emission (synch X-ray? => TeV e-/e+)! Resolved X-ray emission -> in situ acceleration!?

18. D. Harris,2003 M87 jet is not wimpy!!! X-ray variability seen in HST-1 knot too!!

19. An accurate measurement (upper limits) on the GeV-TeV extragalactic diffuse background. Why so interesting? GeV-TeV+ gamma-rays only produced in extreme environments or by “exotic” processes: e.g., black hole jets, supernova blast waves, cosmic strings, relict particle decays, or matter-antimatter annihilation. Background is sum of all nearby GeV-TeV activity in the Universe + all > GeV activity at z > 1. [ Gamma-ray pair production and cascading on intergalactic photon fields GLAST = calorimeter for VHE-EHE Universe! (best limits on BAU/matter-antimatter domains from gamma-rays) ]

20. Blazar Background Models, a la Stecker & Salamon 1996 Including IR/O absorption Don’t forget cascades! Coppi & Aharonian 1997

21. [~MeV] Klein-Nishina effects important? Be careful in interpreting origin of spectral features such as “bumps” and break energies! Can get spectral index harder than 0.5! ERC, blackbody targets ERC, power-law photon targets Moderski et al. 2005 EGRET blazars? Some TeV blazars? [N.B.: Getting strong TeV emission not so easy!]

22. Fun stuff: clusters ….

23. Expected flux levels extremely uncertain!

24. Most sources can think of, even decaying/annihilating CDM particles, trace large scale structure/shocks… look for clustering signal! Bromm et al. 2003

25. Low threshold science objectives: GLAST AGN follow-up UV/optical EBL Diffuse gamma-ray background (extragalactic and galactic) GLAST “hotspot” follow-up GRB, high energy components Microquasars (NIR jet emission detected) SNR/Cosmic Ray accelerators Pulsed emission from plerions (pulsars ) Galaxy clusters UHECR sources/”Haloes” Star formation-related cosmic ray emission from other galaxies ??? Serendipity: Exciting particle physics? What if your “low energy” threshold is 30 GeV? Don’t go halfway or risk losing GLAST-related science! And do a bad of “TeV” science…

26. Aside: really pounding away at >1 TeV relatively easy and interesting too… (cosmic ray, SNR, probe EBL in 10-60 micron region – most poorly constrained by direct counts & impacts star formation history

27. Theorist’s Wish List Rule of thumb: give a theorist a spectrum consistent with a power law (e.g., due to insufficient statistics) and he can fit any model/EBL you like. Need to detect curvature! Ideally measure both sides of low and high energy peaks, simultaneously w/good (< hour-month) time-sampling: UV-MeV, 100 MeV-TeV coverage. [Also very good to get below IR/O absorption threshold.] There will always be some special objects, e.g., Mkn 501, not accessible from a given ground-based site... Want good population statistics …. One “super” telescope not enough – want tightly coordinated space and ground-based telescopes.

28. As gamma-rays enter realm of mainstream astronomy, similar considerations for future progress apply as for other sub-fields of astronomy: a)Large area survey capability b)Improved Sensitivity c)Angular resolution!!! (big problem at GeV?) d)All-sky monitoring for variable sources (what will replace GLAST? Most blazars seem to be dead most of the time…) e)No gaps in time coverage/high duty cycle… f)As broadband/multiwavelength observations as possible! (Think about connections to other instruments/missions, e.g., hard X-ray telescopes like EXIST.) Given current technology, no single instrument configuration or one Instrument can do everything….