Transcript shtern_gamma.pptx

Gamma-ray Astronomy of XXI Century
100 MeV – 10 TeV
1 keV
1 GeV
1 TeV
Compton
g-conversion + calorimeter Cherenkov
telescopes EGRET, Fermi
telescopes
Coded
mask
Collimators
Focusing
1MeV
Objects visible in gamma-rays:
- GRBs
- Blazars & AGNs
- Gamma-ray pulsars
- Supernova remnants
- Diffuse background
1991 – 2000 «Compton, EGRET»
30 MeV – 100 GeV
2008 Fermi 20 MeV – 300 GeV
2000
- Cherenkov telescopes
20 GeV - 50 TeV
Batse GRBs
Fermi
Pass 7 vs. Pass 6
Pass 6
Pass 7
The break is very close to
the He II absorption
threshold!
Pass 6 front/back
Gamma-ray bursts
Express search for transients
in Fermi data
Coincidence time + location
2o
50 s
3-x coincidence
Near-polar horizon
Fall 2009 (4 of 12 GRBs)
Now ~100
GRB
Geminga
Vela pulsar
3C454
GRB
GRB
GRB
Short ~1.5 s
Time, s
> 30 GeV
Quasars
Cyg A
M 87
3C 273
E > 1 GeV
E > 100 MeV
3C454.3
3C454.3
g – g -> e+ e-
He II Lya edge
53 eV
Stern & Poutanen
Photon-photon absorption breaks in
Fermi spectra of bright blazars
gGeV + gUV  e+ eJet
Broad line
region
Poutanen & Stern 2010
Stern & Poutanen 2011
Stern & Poutanen 2014
Pass6
Stacking analisys
Stern & Poutanen 2012
Fortunately
unpublished
g – g absorption He II Lya and H Lya
medium ionization
x = 1.5
medium ionization
High ionization
x = 2.5
high ionization
4s
6s
Broad line
region~
103 Rg
Infrared dust
radiation~
105 Rg
CMB
108 Rg
Where the GeV radiation comes from?
Looks like from ~ 103 RG
G~ sqrt(R/Rc)
The jet launch is from the BH (Blandford-Znajek)
Disk launch implies >104 RG
Emission mechanism is still unknown
1. Fermi acceleration in the jet due to internal perturbation (internal
shocks, turbulence) + external Compton + some synchrotron
Don’t speak about synchrotron – self Compton!!!
1. Photon breeding Stern & Poutanen 2006 – 2008
High energy photons produce a viscous friction between the jet and the
external environment (works at G > 20 and a “strong” external
environment)
The jet is decelerated down to G ~ 15 independently of initial G
FSRQs (broad emission lines, softer spectra, softer
low energy hump, very powerful)
Versus
BL Lacs (no broad emission lines, harder spectra,
harder low energy hump, less powerful)
BL Lacs z ~ 0.05 – 0.4
Гамма-пульсары
Gamma-pulsars
Absorbed
spectra of
gamma-pulsars
Ea ~ 1 – 5 GeV
Fermi Yield
Blazars
1100
(650 – BL-Lacs + 450 – FSRQs)
AGNs
680
Gamma-ray pulsars
137 +29
Unidentified
1000
The diffuse background
Galactic plane
po production?
Diffuse emission
from dark regions
of the sky (0.25)
Galactic center 4o
Here people
“observed” the
dark matter
annihilation line
Galactic emission
Galactic plane
Galactic center
Cosmic rays + gamma pulsars
CTA ~ 0.4 km2 (North) + 4 km2 (South)
H.E.S.S. II 105 m, energy threshold 20 GeV
MAGIC
~104 m2
Threshold 25 GeV
Mkn 421
VERITAS 105 m2
50 GeV
Arizona
Gamma-400
4100 kg
Calorimeter
25 lr
Conclusions:
1. Gamma-ray astronomy becomes a precise science due to
Fermi.
2. The uncertainties in calibration much exceed statistical
errors
3. The main task for Cherenkov telescopes is the crosscalibration with Fermi and coordinated observations (IMHO)
4. The gap between X-rays and 100 Mev should be covered by
any means
5. Open data are of crucial importance