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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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slide1

E>30 GeV?

?

Some more science considerations/thoughts ….

P. Coppi, Yale

vs.

E>5 GeV?

?

slide2

Real population statistics and fully observed SED peaks would be very useful …

Don’t forget

absorption by

infrared/optical

background!

slide5

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)

slide6

If t_var = 6 hours (one night) - one telescope won’t do it!!

Lesson from ASCA/X-ray monitoring days…. Need complete time sampling!

slide9

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. )

glast and grbs
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

glast and grbs1
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?

glast and grbs2
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.)

glast and grbs3
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.

slide17

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!?

slide18

X-ray variability seen in HST-1 knot too!!

M87 jet is not wimpy!!!

D. Harris,2003

slide19

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) ]

slide20

Blazar Background Models,

a la Stecker & Salamon 1996

Don’t

forget

cascades!

Including IR/O absorption

Coppi & Aharonian 1997

slide21

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]

slide23

Expected flux

levels extremelyuncertain!

slide24

Most sources can think of, even decaying/annihilating

CDM particles, trace large scale structure/shocks…

look for clustering signal!

Bromm et al. 2003

slide25

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?

slide26

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

slide27

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.

slide28

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….