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Some more science considerations/thoughts …. P. Coppi, Yale

E>30 GeV?. ?. Some more science considerations/thoughts …. P. Coppi, Yale. vs. E>5 GeV?. ?. Real population statistics and fully observed SED peaks would be very useful …. Don’t forget absorption by infrared/optical background!.

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Some more science considerations/thoughts …. P. Coppi, Yale

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

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

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

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

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

  6. Typical  HESS/Veritas observation?

  7. VHE (GeV-TeV) gamma-ray emission is a highly timevariable 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 similarthreshold to GLAST so see same sources. )

  8. GLAST and GRBs Long burst w/optical flash detected by ROTSE, BATSE flux > 99.6% BATSE bursts 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 forthis burst, and reasonable spectrafor bursts ~ 50x fainter.A MAJOR improvement over EGRET! BUT … this is a time integrated spectrum… Look at what BATSE saw during those 32 sec Briggs et al. 1999

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

  10. 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.)

  11. 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 seebrightest bursts at ~ 1 GeV, and there is not much margin for error.

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

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

  14. 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) ]

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

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

  17. Fun stuff: clusters ….

  18. Expected flux levels extremelyuncertain!

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

  20. 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 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… ??? Serendipity: Exciting particle physics?

  21. 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

  22. 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.

  23. As gamma-rays enter realm of mainstream astronomy, similar considerations • for future progress apply as for other sub-fields of astronomy: • Large area survey capability • Improved Sensitivity • Angular resolution!!! (big problem at GeV?) • All-sky monitoring for variable sources (what will replace GLAST? Mostblazars seem to be dead most of the time…) • No gaps in time coverage/high duty cycle… • 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….

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