TeV Gamma Ray Sky

1
TeV Gamma Ray Sky

• F.A. Aharonian (MPI-K, Heidelberg)

VLVnT2, Catania, Nov 11, 2005
2
TeV Gamma-Ray Astronomy

• a new observational discipline/a branch of High
  Energy Astrophysics
• provides crucial window in the spectrum of
  cosmic E-M radiation
• 0.1 TeV and 100
  TeV
• for exploration of nonthermal phenomena in
  the Universe
• in their most energetic, extreme and
  violent forms
• TeV gamma-rays unique carriers of
  astrohysical information
• are effectively produced in E-M and hadronic
  interactions
• penetrate freely throughout intergalactic and
  galactic B-fields
• are effectively detected by ground-based
  detectors (IACTs)

3
Intensity Shower Energy
Image Shape Background rejection
4
stereoscopic approach
image of source is somewhere on the image axis
need several views to get unambiguous shower
direction
5
H.E.S.S. - High Energy Stereoscopic System
13m diameter dish
920 pixel, 5 deg FoV camera
6
Potential of IACT Arrays

• sensitivity 10-13 (10-14) erg/cm2s
  dynamical range 100 (3) GeV to 30 (300) TeV
• angular resolution 3 (1-2) arcmin
  energy resolution 10 to 20
• detection area 108 to 1010 (1011) cm2
  photon statistics typically gtgt100

• FE erg/cm2 s an indicator how
• deep the energetics in the relevant
• energy band can be probed
• Lg4pd2 FE
• Lg,min 1033 (d/10kpc)2
• Lg,min 1041 (d/100Mpc)2
• two orders of magnitude
• deeper probes than EGRET
• gt 10 arcmin extended sources
• more sensitive than Chandra
• a basis for optimistic expec-
• tations (many sources)?
• YES and NO ...

• IACTs - very effective
• multi-functional tools
• spectrometry
• temporal studies
• morphology
• surveys
• extended sources
• from SNRs to
• Clusters of Galaxies
• transient phenomena
• mQSOs, AGN, GRBs, ...
• Galactic Astronomy,
• Extragalactic Astronomy
• Observational Cosmology

Energy Flux, E2J(E), erg/cm2 s

7
The VHE Sky today
11 Galactic, 11 Extragalactic, GC, plus 15
unidentified not many sources ... but at least 7
source populations !
H1426
1ES 1218
Mrk421
M87
Mrk501
PSR B1259
1ES 1101
1ES1959
SNR G0.9
RXJ 1713
RXJ 0852
Crab
Cas A
LS 5039
TeV 2032
Vela X
GC
1ES 2344
HESS J1303
Cygnus Diffuse
MSH 15-52
PKS 2155
H2356
PKS 2005
gal. compact
Galactic Center
8
H.E.S.S. survey of the central region of
the Galactic Plane 15 more (yet
unidentified) sources
S. Funk
9
TeV g-ray Source Populations

• 
  Extended Galactic Objects
• Shell Type SNRs
• Giant Molecular Clouds (star formation
  regions)
• Pulsar Wind Nebulae plerions
• 
  Compact Galactic Sources
• Binary pulsar PRB 1259-63
• LS5039 a Microquasar
• 
  Galactic Center
• 
  Extragalactic objects
• M87 - a radiogalaxy
• TeV Blazars with redshift from 0.03 to
  0.18
• and a large number of yet unidentified TeV
  sources

10
Major Objectives of TeV g-ray Astronomy

• Origin of Galactic Cosmic Rays
• SNRs, Molecular clouds, Diffuse radiation
  of the Galactic Disk, ...
• Galactic and Extragalactic Sources with
  relativistic flows
• Pulsar Winds, mQSOs, Small and Large Scale
  jets of AGN, GRBs...
• Observational Gamma Ray Cosmology
• Large Scale Structures (Clusters of
  Galaxies), Dark Matter Halos,
• Diffuse Extragalactic Background radiation,
  Pair Halos
• ........
• ....
  

11
SNRs and Origin of Cosmic Rays

• a mystery since the discovery in 1912 by V.
  Hess
• but now we are close (hopefully) to the
  solution of the
• (galactic) component below the energy 1015
  eV thanks to
• HESS capability for deep spectrometric and
  morphological
• studies of g-rays from SNRs in the
  crucial energy band
• 100 GeV to gt 30
  TeV
• GLAST will provide additional (complementary)
• information in the energy domain
  100 MeV-100 GeV
• km3 scale TeV neutrino detectors will provide
  unambiguous
• information about the hadronic
  component of radiation

12
SNRs the most probable factories of GCRs ?

• (almost) common belief based on two arguments
• necessary amount of available energy 1051 erg
• Diffusive Shock Acceleration (DSA) 10
  efficiency and E-2 type
• 
  spectrum up to ?
  at least 1015 eV
• Straightforward proof detection of g-rays (and
  neutrinos) from pp
• interactions (as
  products of decays of secondary pions)
• Objective to probe the content of
  nucleonic component of CRs
• in SNRs within 10
  kpc at the level 1049 -1050 erg
• Realization sensitivity of detectors -
  down to 10-13 erg/cm2 s
• crucial energy
  domain - 100 GeV - 100 TeV

13
Cosmic Ray Accelerators ?
SNRs in our Galaxy 231(Green et al. 2001
with nonthermal X-ray emission - 10 or so
best candidates - young SNRs with nonthermal
synchrotron X-rays
SN1006
Diffusive source
Tycho
Kepler
CasA
30 arcmin
TeV emission
H.E.S.S. PSF
14
energy spectrum and
morphology
RXJ1713.7-3946 is a TeV source !
G2.1-2.1 with a curvature cutoff (?) at high
energies
no significant spectral variation
G2.1-2.2 -evidence of DSA of protons ?
HESS 2004 data preliminary !
15
RX 1713.7-3946
interpretation
the key issue - identification of g-ray
emission mechanisms p0 or IC ? new! -
energy spectra 150GeV-30 TeV
from different parts - NW, S W, E,C if
a coordinate-independent single power law
from 100 GeV to 10 TeV
difficult to explain by IC implications
? if p0 - hadronic component is detected !
estimate of Wp (with an uncertainty
related to the uncertainty in n/d2 )
if IC - model independent estimate of We
(multi-TeV electrons) LeLx and
model independent map of B-field
TeV-keV correlations what this could mean?
16
Origin of radiation ?

• hadronic origin preferable given
• the high density environment
  
• Wp (above 10 TeV) 3x1049 (n/1 cm-3) -1
  erg
• IC origin is not (yet) excluded, but this model
• requires B field less than
  10 mG
• more complex scenarios ? e.g. g-rays from NWSW
  are contributed by
• protons while gamma-rays from remaining parts are
  due to IC g-rays
• HESS observations with 4 telescope in
  2004 and 2005
• provide higher quality data and
  certain answers ?

17
New ! Vela Junior (a 2o diameter remnant)
B-fields RXJ 10 mG Vela Jr 4 mG
B-fields RXJ 10 mG Vela Jr 4 mG
CANGAROO , HESS Flux - 1 Crab at 1 TeV
no problem with hadronic gamma-ray models good
news for km3 scale neutrino detectors ! (?)
uncertainty in d as large as factor of 3, n
poorly known if no nearby clouds - Wp could be
as large as 1050 erg
IC origin ? very small B-field, B lt 10 mG,
and very large
Emax gt 100 TeV two assumptions hardly can
co-exists within standard DSA models
18
IC model B-field cannot exceed 10 mG and
does not provide
good spectral fit
19
steeper electron acceleration spectra ? now a
better fit, but conflict with radio and
2 orders of magnitude larger energetics
20
older source ?
21
two zone model ?
tesc50 tB (prop. 1/E) B13 mG, B215mG R3
pc
22
older source ?
23
RXJ 1713.7-3946 Spectrum of protons dN/dEK
E-a exp-(E/Ecut)b
Wp(gt1 TeV) w 0.5x1050 (n/1cm-3)(d/1kpc)2
24
spectra of gamma-rays and neutrinos
25
neutrino fluxes from RXJ1713.7-3946
Alvarez-Muniz and Halzen dN/dE4.14x10-11
(E/1TeV) -2 ph/cm2 s TeV 4.1 x 10-11 ph/cm2
s above 1 TeV 4.1 x 10-12 ph/cm2 s above 10
TeV
Costantini and Vissani dN/dEg1.7 x 10-11
(Eg/1TeV) -2.2 ph/cm2 s TeV
dN/dEn 1.5 x 10-11 (En/1TeV)
-2.2 ph/cm2 s TeV 1.2 x 10-11 ph/cm2 s above 1
TeV 0.8 x 10-12 ph/cm2 s above 10 TeV
our calculations 1. 0.87x10-11 ph/cm2 s
above 1 TeV 0.99 x 10-13 ph/cm2 s above 10
TeV 2. 0.90x10-11 ---
1.70x10-13 --- 3.
0.88x10-11 ---
1.78x10-13 ---
Before flavor oscillations
26
searching for galactic PeVatrons ...
TeV gammarays from Cas A and RX1713.7-3946,
Vela Jr a proof that SNRs are responsible for
the bulk of GCRs ? not yet
the hunt for galactic PeVatrons continues
unbiased approach deep survey of the Galactic
Plane not to miss any
recent (or currently active) acceleration site

SNRs, Pulsars/Plerions,
Microquasars...
not only from accelerators, but also from nearby
dense regions
27
Gamm-rays/X-rays from dense regions surrounding
accelerators

• the existence of a powerful accelerator by itself
  is not sufficenrt for
• gamma radiation an additional component a
  dense gas target - is required

gamma-rays from surrounding regions add much to
our knowledge about highest energy protons
which quickly escape the accelerator and
therefotr do not signifi- cantly contribute to
gamma-ray production inside the proton
accelerator-PeVatron
28
older source steeper g-ray spectrum
tesc4x105(E/1 TeV) -1 k-1 yr (R1pc) k1
Bohm Difussion
Qp / E-2.1 exp(-E/1PeV)
Lp1038(1t/1kyr) -1 erg/s
29
Giant Molecular Clouds (GMCs)
as tracers of Galactic Coismic Rays

• GMCs - 103 to 105 solar masses clouds
  physically connected with
• star formation regions - the likely sites of
  CR accelerators (with
• or without SNRs) - perfect objects to play
  the role of targets !
• While travelling from the accelerator to the
  cloud the spectrum of CRs
• is a strong function of time t, distance to the
  source R, and the (energy-
• dependent) Diffusion Coefficient D(E)
• depending on t, R, D(E) one may expect
  any proton, and
• therefore gamma-ray spectrum
  very hard, very soft,
• 
  without TeV tail, without GeV counterpart ...

30
R10pc to 1 - 100yr 2 1,000yr 3
- 10000yr
to1,000yr R 1 100pc 2 30pc 3
10pc
continuous accelerator of age to Lp1037 erg/s,
ap2, Emax100 TeV, diff.coef.
D(E)1027(E/10GeV)1/2 cm2/s Cloud at a distance
d and density 104 cm-3
31
First Unidentified TeV source TeV
J20324130

• Found by HEGRA seredipiously (6 sigma signal
  accumulated 100h from
• the Cygnus region and confirmed in 2002 by
  pointing observations (130 h)
• Basic features hard power-law spectrum (photon
  index 1.9), constant flux
• and slightly
  extended (about 5 arcmin) source
• Origin ? leptonic (IC) origin is
  almost excluded, possibly dense gas cloud(s)
• illuminated by
  protons arriving from a recent nearby Pevatron
  ?
• if this object is a representative of a large
  source population, the planned survey
• of the Galactic Disk by H.E.S.S. will
  reveal (many ?) more new hot spots
• talk at the 2nd workshop on Unident. Gamma Ray
  Sources, Hong Kong, May 2004
  

32
Electrons Inverse Compton
larger field
B-field smaller than 3 10-6 G (!) source
age less than 1000 yr (!) otherwise even
for very slow (Bohm) diffusion , the g-ray source
should be largder than 5 arcmin (for d1.6kpc)
faster escape
older source
33
electrons bremsstrahlung
protons pp -gt po -gt gg
g-ray spectrum strongly depends on diffusion
coefficient D(E) D(E)1024(E/1GeV)0.5 h cm2/s
more comfortable parameters
34
A new unidentified sources is found
by HESS !
Feb 2004
March 2004
PSR1259-63
35
HESS detected new galactic sources
unidentified HESS sources
36
HESS
Aharonian et al. 2005
TeV and CO data narrow distributions in
the Galactic Plane because of GMCs ? Star
Formation Regions ? or (most likely) both ?
NANTEN CO observations
Fukui et al.2005
37

• Origin of Extended HESS TeV sources
• mechanisms of gamma-ray production in extended
  sources
• characteristic timescales
• pp p0 gg
  tpp1x1015 (n/1cm-3) -1 sec
• e2.7 K eg
  tIC4x1012 (E/10 TeV) -1 sec
• e-bremsstrahlung
  tbr3x1014 (n/1cm-3) -1 sec
• IC is very effective as long as magnetic field
  B lt 10 mG
• Bremsstrhlung important in dense, n gt 102 cm-3 ,
  environments
• pp interactions dominate over Bremsstrahlung if
  the ratio of energy
• densities of protons to electrons wp/we gt
  10, and Inverse Compton
• component if wp/we gt 500 (n/1cm-3) -1
  (at energies above 10 TeV)

38

• Morphology vs. Energy Spectrum
• morphology pp depends on spatial
  distributions of CR and gas nH(r)xNp(r)
• IC depends only on
  spatial distribution of electrons Ne(r)
• energy spectra depends on acceleration spectrum
  Q(E), energy losses dE/dt,
• age of accelerator to, and character of
  propagation/diffusion coefficient D(E)
• pp generally energy spectrum independent of
  morphology, but for young
• objects energy spectrum could be harder at
  larger distances than near
• the accelerator angular size
  increases with energy
• IC very important are synchrotrin energy
  losses
• weak B-field ( lt10 mG) and/or fast
  diffusion
• 
  angular size increases with energy
• strong B-field (100 mG) and/or slow
  diffusion
• 
  angular size decreases with energy
• irregular shapes of g-ray images because of
  inhomogeneous distrubition

39
Crab Nebula an acceleration of PeV
electrons !
Standard MHD theory cold ultrarelativistc pulsar
wind (G 105-106) terminates by a reverse
shock resulting in acceleration of electrons with
an unprecedented rate tacchrL/c, h lt 100 )
synchrotron radiation gt nonthermal
optical/X-ray nebula Inverse Compton gt
high energy gamma-ray nebula
1-10MeV
.
MAGIC new !
100TeV
HEGRA

• Crab Nebula a very powerful WLrot5x1038
  erg/s
• and extreme accelerator
  Ee gt 1000 TeV
• Emax60 (B/1G) -1/2 h-1/2 TeV and
  hncut(0.7-2) af-1mc2 h-1 50-150 h-1 MeV
• 
  
  
• h1 minimum value allowed by classical
  electrodynamics
• Crab hncut 10MeV acceleration at 1 to 10
  of the maximum rate ( h10-100)
• maximum energy of electrons Eg100 TeV gt Ee
  gt 100 (1000) TeV B0.1-1 mG
• very close the value independently derived from
  the MHD treatment of the wind

for comparison, in shell type SNRs DSA theory
gives h10(c/v)2104-105
40
Challenges

• measurements of the energy-dependent size of IC
  component
• detection of possible hadronic component
• gt 1 TeV neutrinos (marginally)
  detectable by Ice Cube
• to probe location of creation and the Lorentz
  factor of kinetic energy dominated wind through
  IC scatering of wind electrons
• cold wind can be visible/detectable in
  gamma-rays with energy
• E me c2 x wind Lorentz factor G
  (because of K-N effect)
• unique feature of VHE gamma-ray
  astronomy - discovery of
• ultrarelativistic MHD flows through
  bulk motion Comptonzation

41

• TeV gamm-rays from other Plerions ?
  
• Crab Nebula is a very effective accelerator
• 
  but not an effective IC g-ray emitter
• We see TeV gamma-rays from the Crab Nebula
  because of
• very large spin-down luminosity
  
• but gamma-ray flux ltlt spin-down flux
  
• 
  because of large magnetic field
• but the strength of
  B-field also depends on
• less powerful pulsar weaker
  magnetic field
• higher gamma-ray efficiency
  
• detectable gamma-ray
  fluxes from other plerions
• HESS confirms this
  prediction !

Plerions Pulsar Driven Nebulae
42

MSH 15-52
dN/dE ? E-G G 2.27?0.03?0.15 ?2/n
13.3/12 Flux gt 280 GeV 15 Crab Nebula

• the energy spectrum - a perfect hard power-law
  with photon index G2.2-2.3
• over 2
  decades !
• cannot be easily explained by IC
• hadronic (po-decay) origin of g-rays ?

since 2.7 K MBR is the main target field, TeV
images reflect spatial distributions of
electrons Ne(E,x,y) coupled with synchrotron
X-rays, TeV images allow measurements of B(x,y)

43
G0.90.1 (2)

• Spectrum
• F(gt0.2TeV) (5.7?0.7stat?1.2syst) 10-12 cm-2 s-1
• ?2 Crab flux, ?50 Crab luminosity
• Power-law ? 2.40?0.11stat?0.20syst

• Morphology
• Compatible with a point source
• Position compatible with the PWN position
• Emission not consistent with the SNR shell

Radio (90 cm)
B.Khelifi
44
HESS J0835-456 (Vela X)

• Energy Spectrum
• F(gt1TeV) (1.23?0.12stat?0.25syst) 10-11 ph/cm2s
• ?75 Crab flux, ?7 Crab luminosity
• power-lawexponential cut-off
• G 1.48 ? 0.02stat ? 0.20 syst
• Ec 17.41 ? 1.41stat ? 3.5syst TeV

• Morphology
• ?L 23.4'?1.2' , ?l 15.6'?1.2'

HESS J0835-456
pulsar
IC spectrum ?
contours ROSAT
should be IC image of electrons ...
B.Kelifi, preliminary
45
PSR1259-63 - a unique high energy laboratory

• binary pulsars - a special case with strong
  effects associated with the
• optical star on both
  the dynamics of the pulsar wind
• and the radiation
  before and after its termination
• the same 3 components - Pulsar/Pulsar/Wind/Synch.
  Nebula - as in plerions
• both the electrons of the cold wind and
  shocke-accelerated electrons are illuminated
  by
• optical radiation from the companion star
  detectable IC g-ray emission
• the photon field is a strong function of time,
  thus the only unknown parameter is B-field
• TeV electrons are cooled and and radiate in deep
  Klein-Nishina regime with
• very interesting effects on both synchrotron
  X-ray and IC gamma-rays

HESS detection of TeV gamma-rays from
PSR1259-63 at lt 0.1Crab level several days
before the periastron and 3weeks after the
periastron
but with characteristic timescales much shorter
- less than 1 h !
46
energy flux of starlight close to the
periastron around 1 erg/cm3 B-field is
estimated between 0.1 to 1 G
predictable X and gamma-ray fluxes ?
time evolution of fluxes and energy spectra of X-
and g-rays contain unique information about the
shock dynamics, electron acceleration, B(r), ...
47
while the gamma-ray energy spectrum
can be (more or less) explained by IC the
lightcurve is still a puzzle deep
theoretical (in particular MHD) studies
needed to understand the source
48
new ! HESS discovered TeV g-rays from a
microquasar !

• LS 5039 X-ray binary - BH O7 star
• presence of two basic components for TeV
  gamma-ray production !
• 0.2c jet as accelerator of electrons (protons ?)
• 1039 erg/s luminosity star as source of seed
  photons for IC or pg
• scenario ? both gamma-ray production region
  within (despite tgg gtgt 1) and
• outside binary system (jet
  termination site) cannot be excluded

mQSOs one of the highest priority targets of
the HESS project
49
LS5039 as a (detectable) neutrino source ? )

• if TeV gamma-rays are produced within the
  binary system (R lt 1012cm)
• severe absorption of gt100 GeV gamma-rays
  (g starlight -gt ee-)
• up to a factor of 10 to 100
  higher initial luminosity
• severe radiative (synchrotron and
  Compton) losses
• difficult to accelerate
  electrons to multi-TeV energies
• Conclusions ? TeV gamma-rays of hadronic origin
  with high luminosity,
• and consequently high
  detectable TeV neutrino fluxes (!?)
• TeV neutrino fluxes strongly depend o the
  production site of g-rays
• the base of the jet/accretion disk and/or
  wind/atmosphere of the star
• X-ray binaries as sources of TeV
  neutrions (V.Berezinsky, 1976, ...)
• 
  
  again a hot topic ...

) astro-ph 0508658
50
TeV Blazars and Diffuse Extragalactic

Background Radiation

• two topics relevant to different
  research areas

TeV Blazars ideal laboratories to study particle
acceleration and MH structures in relativistic
jets, and powerful factories of GeV/TeV g-ray
beams DEBRA (also EBL, CIB,)
thermal emission components - between O/UV and
FIR produced by stars and
absorbed/re-emitted by dust,
and accumulated over the entire history of the
Universe

• but tightly coupled through intergalactic gg
  absorption

51
impact of the intergalactic absorption on the
understanding of physics of TeV blazars
52
Models

• SSC or external Compton currently
  most favoured models
• easy to accelerate electrons to TeV energies
• easy to produce synchrotron and IC gamma-rays
• recent blazar observations require more
  sophisticated leptonic models
• Hadronic Models
• protons interacting with ambient plasma
  neutrinos
• very slow process
  
• protons interacting with photon fields
  neutrinos
• low efficiency severe absorption of TeV
  g-rays
• Proton Synchrotron
  no neutrinos
• very large magnetic field B100 G
  accelaration rate c/rg
• extreme accelerator (of EHE CRs) /
  Poynting flux dominated flow

expect neutrinos from EGRET AGN but not from
TeV blazars
53
X-TeV flares of 1ES 1959650 in 2002

• Basic conclusions
• correlations
• X-TeV do correlate
• No optical TeV (X) correlations
• Radio essentialy stable
• puzzles
• strong TeV flare on June 4 not
• accompanied by an X-ray activity
• MAGIC also does not see strong
• TeV-keV correlations
• hadronic origin of TeV emision ?
• actually pg implies stronger TeV-X
• correlations than IC models

54
1ES 1426428 a different blazar ?
IC ?

Proton synchrotron?

• 1ES 1426428 does not agree with
• the red-blue phenomenology

55
Cooling and acceleration times in Markarian 501
in TeV blazars synchrotron cooling time always ltlt
photomeson colling time
no neutrinos from TeV
blazars
no VHE gamma-rays from most powerful and distant
AGN and QSOs but (possibly)
detectable fluxes of VHE and UHE neutrinos
56

• TeV g-rays - carriers of unique cosmological
  information
• about epochs and
  history of evolution of galaxies
• such information can be extracted through
  studies of intergalactic
• absorption features in the energy spectra of
  blazars of given z, if
• one can unambiguously identify the
  intergalactic absorption features
• two (both not perfect) approaches
• measure the intrinsic spectrum based on
  comprehensive time-
• dependent modeling of multiwavelength
  data (broad band SED)
• a very hard problem
• accept a principle the intrinsic spectrum
  Jo(E)Jobs(E) expt(E) should be reasonable
• but what means
  reasonable ?
• or if gamma-rays are of hadronic (pp -gt
  po-gtgg) origin
• measure the spectrum
  of TeV neutrinos
• a dream and still not sufficient
  (intrinsic absorption of gs)

absorption does not mean spectral cutoff
57
New blazars detected at large z ! HESS
H2356-309 (z0.165), 1ES1101-232 (z0.186)

MAGIC 1ES1218304
(z0.182)

HESS
1 ES 1101 G 2.90.2
H 2356 (x 0.1) G 3.10.2
Preliminary
58
reconstructing gamma-ray spectra with different
EBL models
HESS collaboration, submitted to Nature
59
HESS robust upper limits on EBL at O/NIR

• EBL (almost) resolved at NIR
• Universe more transparent
• intrinsic gamma-ray spectra

direct measurements
upper limits
lower limits from galaxy counts
60
1ES1426428 - a special case

• many puzzles
• difficult to believe... TeV gamma-rays from
  this source at z0.129 despite
• the intergalactic absorption gtgt 10
• TeV peak significantly higher than the X-ray peak
• violation of the red-blue blazar
  paradigm cannot be easily explained
• by standard SSC or external Compton models
• only a specific class of EBL models allows
  reasonable instrinsic TeV spectrum

61
TeV g-rays from GC
GC a unique site that harbors many
interesting sources packed with un-
usually high density around the most
remarkable object 3x106 Mo SBH Sgr A
many of them are potential g-ray emitters -
Shell Type SNRs Plerions, Giant Molecular
Clouds Sgr A itself, Dark Matter
HESS FoV5o
all of them are in the FoV HESS ! and can be
probed down to a flux level 10-13 erg/cm2 s
and localized within ltlt 1 arcmin
62
Position?
systematic and statistical errors on source
location by HESS are comparable
20-30 arcseconds
63
two comments

• typically (often) theorists face problems of
  interpreting g-ray
• observations in the frameworks of
  "standard" models, but in the
• case of TeV observations of GC we face an
  opposite problem
• TeV data can be explained within several
  (essentially different)
• scenarios and by several
  different radiation mechanisms
• the FoV, PSF, and sensitivity of HESS (and
  GLAST) perfectly match
• the performance of other relevant instruments
  at other wavelengths
• (Chandra, XMM, INTEGRAL, VLT, radio and mm
  telescopes, etc.)
• both for compact objects like Sgr A and
  diffuse structures
• HESS and GLAST can provide perfect temporal,
  spectroscopic and
• morphological studies over six (100 MeV
  to 100 GeV) g-ray decades

64
TeV g-rays from central lt10 pc region of GC

• Annihilation of DM ? mass of DM particles gt 10
  TeV ?
• Sgr A 3 106 Mo BH ? yes, but lack of
  variability
• even the inner R lt 10 Rg region is
  transparent for TeV g-rays !
• SNR Sgr A East ? why not ?
• Plerionic (IC) source(s) why not ?
• Interaction of CRs with GMCs ? easily
  

65
Sagittarius A - point-like but not variable
syst. error
power-law index 2.3
Contours - radio
66
Point-like but not variable TeV source an
argument in favor of DM origin of detected TeV
gamma-rays ?

• angular size of TeV signal can be explained by
  DM annihilation for
• n(r) profile like r-a with a gt 1.1 i.e.
  Qg(r)C1n2 Qor-2a
• but the absolute intensity of the TeV signal
  requires much sharper
• density
  profile n(r) within lt 0.1 pc
• Note that the same can be the case of CR
  interactions with gas
• Qg(r)C2ncr(r)
  nH(r)Qor-(a1a2) ,
• e.g. CR density decreases like r-2 and the gas
  density like r-0.2
• absolute g-ray fluxes can be explained naturally
  by interactions
• of run-away
  protons with surrounding dense gas

C1 and C2 interaction constants
(cross-sections)
67
A concluding remark

• We are just at the gates of the Paradise of
• TeV astrophysics and
  Cosmology
• condition for entrance? FE gt 10-14 erg/cm2 s
  (0.03-100 TeV)
• realization ? 1 to 10 km2
  scale IACT arrays (super-HESS)
• timescales short (years)
  - no technological challenges
• price for the ticket very reasonable
  including
• 
  (almost) 100 guarante for
• 
  the success (great discoveries)
• several tens (100 ?) of 15m diameter class 5
  deg FoV telescopes
• 
  located on 3.5-4 km
  a.s.l.
• another major objective reduction of the
  energy threshold down to
• 
  lt 10 GeV energies (different approaches,
  
• 
  different astrophysical objectives /motivations)