Transcript Astrophysics and Cosmology with TeV gamma-rays F.A. Aharonian (MPI-K, Heidelberg)

Astrophysics and Cosmology
with TeV gamma-rays
F.A. Aharonian (MPI-K, Heidelberg)
Fermilab Colloquium, July 13, 2005
1
Gamma-Ray Astronomy
branch of high energy astrophysics for study of the
sky in MeV, GeV, TeV (and more energetic) photons
provides crucial window in the spectrum of cosmic E-M
radiation for exploration of nonthermal phenomena in
the Universe in their most extreme and violent forms
“the last window in the spectrum of cosmic E-M radiation
to be oppened´´ ...
is already (partly) opened
2
the last E-M window ... 15+ decades:
LE or
HE or
VHE or
UHE or
EHE or
MeV : 0.1 -100 MeV (0.1 -10 + 10 -100*)
GeV : 0.1 -100 GeV (0.1 -10 + 10 -100*)
TeV : 0.1 -100 TeV (0.1 -10 + 10 -100*)
PeV : 0.1 -100 PeV
EeV : 0.1 -100 EeV (TDs ?)
the window is opened in MeV, GeV, and TeV bands:
LE,HE
VHE, ....
– domain of space-based astronomy
- domain of ground-based astronomy
* poorly explored
3
Crab Nebula : :
broad-band SED 20 decades
g-rays – 9 decades (detected !)
100 keV – 100 TeV
EGRET
CELESTE
(MAGIC)
4
Status of the field
in 1990s, after several decades of struggles and controversial
developments ground-based gamma-ray astronomy
became an observational discipline and entered the
main stream of modern astrophysics and cosmology with:

viable detection technique –
Imaging Atmospheric
Cherenkov Telescope (IACT) Arrays
emerged as prime tool for detection of VHE g-rays

-
more than 25 reported objects representing several
galactic and extragalactic source populations
the principal results obtained at TeV energies with IACTs
(plus some interesting results with a water Cherenkov detector)
5
Why Cherenkov telescopes ?

large detection area – typically 0.1 km2,

potentially up to 10km2
low energy threshold –typically 0.1-1 TeV,
potentially down to a few GeV
first result: 3s signal from Crab - 3 years observations with
the Whipple non-imaging 10m telescope (1969)
but ... cosmic ray detectors
rather than g-ray telescopes...
CT = an optical reflector with a PMT in focus + fast (ns) electronics
8
Why Imaging ?
because it allow reconstruction of shower parameters:
 (certain) information about arrival direction
 capability to separate g- and proton induced
showers
 larger FoV (larger collection areas)
first result:
10 sigma signal from Crab with the
Whipple imaging 10 m telescope (1989)
a good gamma-ray detector but ...
not yet a telescope...
9
Why Stereoscopy ?

better separation of hadronic and E-M showers
better sensitivity

angular resolution of about 3 arcmin
better sensitivity, source localization, morphology
 energy resolution 10 to 15 per cent
better spectrometry
 rejection of local muons, better rejection of N.S.B.
lower energy threshold, systematics under control
 quite large (up to 5 degree) FoV
extended sources, surveys, huge collection areas
first results:
HEGRA system of small (4m diameter)
IACTs in La Palma (1996-2002)
10
IACT Arrays as perfect g-ray telescopes

in the interval 100 GeV - 10 TeV (TeV Astronomy)
and… (hopefully) also in the intervals

several GeV to 100 GeV

10 TeV to several 100 TeV
(multi-GeV astronomy)
(multi-TeV Astronomy)
11
Stereoscopic Imaging of Air Showers
(almost)
commonly accepted approach:
CANGAROO-III, H.E.S.S., VERITAS, MAGIC-2
for TeV astronomy
5@5, ECO-1000 …
for multi-GeV astronomy
15
H.E.S.S. - High Energy Stereoscopic System
13m diameter dish
920 pixel, 5 deg FoV camera
16
Potential of IACT Arrays
Energy Flux, E2J(E), erg/cm2 s
sensitivity down to 10-13 erg/cm2s
energy resolution 10 to 20 %
angular resolution a few arcminutes
dynamical range : 3 GeV to 100TeV
Crab Nebula
?
HEGRA
EGRET
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
energy range
100 GeV - 10 TeV

energy resolution
15 - 20%


angular resolution
3 - 6 arcmin

30 sec
0.1 Crab
0.01 Crab
10 Crab
20min
25 hours
1 sec
Field of View
5o
0.003 Crab
requires 200 h
10-13 erg/cm2 s level
better than Chandra/XMM for >0.1 deg objects !
sensitivity:
1 Crab


1 Crab =3 x 10 -11 erg/cm2 s
0.1 Crab - min detection time
for Whipple – 50-100 hour
 10 Crab (i) strong flares of Mkn 421/501
(ii) energy flux sensitivity of EGRET
(iii) several orders of magnitude
less than typical GRB fluxes


3 arcmin - angular resolution of ASCA
5o FoV plus 0.1 Crab for < 0.5 h –
sufficient for effective surveys !
18
TeV Sky before 2004
TeV sources – not many, but represented by several populations
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Reported TeV Sources

Blazars
before 2004
Markarian 421 Markarian 501
1es2344+514
1es1959+650 1es1426+428 PKS 2155-304

Plerions
Crab Nebula

SNRs
Cas A SN 1006 RX1713.7-394

Radiogalaxies

X-ray binaries

Starburst Galaxies

First Uniden.source
M87
PSR 1706-44
Cen A
Cygnus X-3, Cen X-3, GRS1915+105
NGC 253
TeV J2032+4131
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First (published) H.E.S.S results
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
new TeV Blazars – PKS 2155-304,PKS 2005-489, …
and a large number of yet unidentified TeV sources …
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Expectations - near future !
 GLAST
large source statistics !
“Era of gamma-ray astronomy with thausand sources“ (0.1-10 GeV)
also: a few objects and G- & EXG- backgrounds in 10-100 GeV range

Stereoscopic IACT Arrays
large photon statistics !
tens (hundreds ?, thausands ?) objects based on datasets
consisting of more than 1,000 TeV g-ray photons per source
also: exploration of a few (many ?) objects in > 10TeV domain
22
distinct features of ‘‘Cherenkov Astronomy“ :
huge detection areas (= large photon statistics)
+
nice (a few arcminutes) angular resolution
+
reasonable (10 to 15 %) energy resolution
high quality spectrometric, temporal, and morphological
studies of nonthermal objects representing different
G- and EXG- source population and many “hot“ topics of
HE Astrophysics, Astroparticle Physics and Cosmology
23
Spectrometry beyond 3Ecutoff !
Unprecedented photon statistics
Mkn 421 – 60,000 TeV photons
detected in 2001
Mkn 501 – 40,000 TeV photons
detected in 1997
spectra: canonical power-law
with exponential cutoff
Cutoff = 6.2 TeV and 3.8 TeV
for Mkn 501 and Mkn 421
time average spectra of
Mkn 421 and Mkn 501
TeV
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time variations on sub-hour timescales !
Whipple
RXTE
Mkn 421 – extraordinary
high state in 2001
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Spatially resolved Energy Spectra (HESS)
RX 1713.7-3946
preliminary
morphology
preliminary
and
spectrometry
TeV g-ray Astronomy - a viable discipline in its own right
TeV emission as an extension of GeV domain ?
visibility of sources in GeV g-rays does not
authomatically imply visibility in TeV g-rays,
and vice versa
Reasons ? Efficiency of acceleration process, spectral cutoffs due to
internal and external absorption, diffusion of charged parent particles
... TeV astronomy is not an extension of MeV/GeV astronomy, but
a viable discipline in its own right with several major objectives
27
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
........
....
*energy domain E > 0.1 TeV (VHE astronomy =TeV astronomy)
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Origin of Cosmic Rays:
a mystery since the discovery in 1912 by V.Hess …
but now we are quite close (hopefully) to the solution of
the (galactic) component below the energy 1PeV (1015eV)
thanks to the new generation of ground and space-based
gamma-ray detectors , in particular
HESS and GLAST
29
g-rays as tracers of GCRs
we know a lot about Galactic Cosmic Rays (energy spectra,
composition, propagation…) but we do not know :
acceleration sites, source populations, acceleration mechanisms
reason ?
deflection (diffusion) of CRs in interstellar B-fields
solution ?
probing CRs with high energy gamma-rays:
discrete g-ray sources – productions sites oF CRs
diffuse g-ray emission – propagation of CRs in ISM
the major (historical) motivation of gamma-ray astronomy
(P. Morrison, V. Ginzburg, S. Hayakawa, ...)
30
Galactic PeVatrons – accelerators responsible for
up to (at least) 1 PeV (=1015
CRs
eV) *
SNRs ?
Pulsars/Plerions ?
O & B stars ?
Microquasars ?
Galactic Center ?
Gaisser 2001
...
* the source population responsible for the bulk of GCRs are PeVatrons ?
31
SNRs – the most probable factories of GCRs ?
(almost) common belief based two arguments:


necessary amount of available energy – 1051 erg
Diffusive Shock Acceleration – 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 - VHE/UHE (up to 100 TeV)
32
Cosmic Ray Accelerators ?
SNRs in our Galaxy: 231(Green et al. 2001
with nonthermal X-ray emission - 10 or so
best candidate - young SNRs
with synchrotron X-rays
SN1006
Diffusive source
Tycho Kepler
CasA
?
30 arcmin
H.E.S.S. PSF
TeV emission
33
RXJ1713.7-3946 is a TeV source !
energy spectrum
G=2.2 -evidence of DSA of protons?
morphology
do we see a shell structure ?
HESS 2004 data: preliminary !
34
RX 1713.7-3946: morphology and energy spectrum obtained with H.E.S.S.
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
hardly can be explained by IC
implications ?
if p0 - hadronic component is detected !
estimate of Wp (with an uncertainty
related to the uncertainty in n/d2 )
TeV-keV correlations …
what this could mean?
if IC - model independent estimate of We
(multi-TeV electrons) and also Le=Lx !
model independent map of B-field
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Origin of radiation ?
 hadronic origin
seems preferable given
the high density environment:
Wp (above 10 TeV) = 3x1049 (n/1 cm-3) -1 erg

IC origin is not excluded, but this model
requires B – field less than 10-20 mG
FA, Nature 2002
More complex scenario, e.g. g-rays from NW+SW are contributed by
protons while gamma-rays from remaining parts are due to IC g-rays,
cannot be excluded
HESS observations with 4 telescope in 2004 and 2005
provide higher quality data and … certain answers ?
36
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
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 ? – very small magnetic field at the level of < 4 mG
37
searching for galactic PeVatrons ...
TeV gamma–rays 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
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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 significantly contribute to gamma-ray production inside the proton accelerator-PeVatron
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older source – steeper gamma-ray spectrum
40
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 (energydependent) 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 ...
41
First Unidentified TeV source TeV J2032+4130 *
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 surve
of the Galactic Disk by H.E.S.S. will reveal (many ?) more new hot spots
*detected earlier by the HEGRA array and Crimean and “recently” by Whipple groups(?)
42
A new unidentified sources is found by HESS !
Feb 2004
March 2004
PSR1259-63
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HESS detected new galactic sources
unidentified HESS sources
44
HESS
Aharonian et al. 2005
TeV and CO data:
narrow distributions
in the Galactic Plane:
NANTEN
CO observations
Fukui et al.2005
because of GMCs ? or
Star Formation Regions ?
or (most likely) both ?
45
Crab Nebula – g-rays up to 100TeV !
1-10MeV
100TeV
Standard MHD theory – cold ultrarelativistc pulsar wind terminates by a reverse
shock resulting in (re)acceleration of electrons up to > 1015 eV
Synchrotron radiation => nonthermal optica and X-ray nebula
Inverse Compton scat. => high energy gamma-ray nebula
Crab Nebula – a
very powerful
and “extreme accelerator“
(tacc=hRg/c)
hcut= 10MeV: acceleration at 1 to 10 % of the maximum rate ( h=10-100)*
maximum energy of electrons:
Eg=100 TeV => Ee > 100 (1000) TeV => B < 1 mG (close to 0.1 mG)
* for comparison, in shell type SNRs DSA theory gives h=10(c/v)2=104-105
46
Challenges


measurements of the energy-dependent size of IC component
detection of possible hadronic component
> 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 flows through bulk motion Comptonzation
47
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 << “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
48
MSH 15-52
dN/dE  E-G
G = 2.270.030.15
2/n = 13.3/12
Flux > 280 GeV
15% Crab Nebula
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)
the energy spectrum - a perfect hard
power-law with photon index G=2.2-2.3
over 2 decades !
• cannot be easily explained by IC…
• hadronic (po-decay) origin of g-rays ?
49
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
HESS: detection of TeV gamma-rays from PSR1259-63 at < 0.1Crab level
several days before the periastron and 3weeks after the periastron
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
* but with characteristic timescales much shorter - less than 1 h !
50
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), ...
51
if 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
52
new !
HESS detects TeV g-rays from a microquasar* !
VLBA-VLA image
Paredes et al. 2000
NASA,, ESA, and F. Mirabel
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 >> 1)
and
*
outside binary system (jet termination site) cannot be excluded
mQSOs – one of the highest priority targets of the HESS project
53
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 emision 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 g-g absorption …
*only a few remarks about the problem …
54
Impact of the intergalactic absorption
55
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 timedependent modeling of multiwavelength data (broad-band SED)
but this is a very hard (almost impossible) task
accept a principle “the intrinsic spectrum Jo(E)=Jobs(E) exp[t(E)]
should be reasonable”
but what means “reasonable” ?

or:
if gamma-rays are of hadronic (pp->po->gg) origin –
measure the spectrum of TeV neutrions
nice dream … and still not sufficient (intrinsic absorption of gs)
* absorption does not mean spectral cutoff
56
Gamma-rays and X-rays from DM in GC
Eo=10 TeV,
B=1, 3, 10 mG
B=2.5 mG,
Eo=8, 25, > 1000 TeV
59
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
*expect neutrinos from EGRET AGN but not from TeV blazars

proton synchrotron
no neutrinos
very large magnetic field B=100 G + accelaration rate
c/rg
“extreme accelerator“ (of EHE CRs) / Poynting flux dominated flow
60
Cooling and acceleration times in Markarian 501
in TeV blazars synchrotron cooling time always << 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
61
1ES1426+428 - a special case:
many puzzles:



difficult to believe... TeV gamma-rays from this source at z=0.129 despite
the intergalactic absorption >> 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
62
near future
observations of 1ES1426+428 (Whipple/HEGRA/CAT) with
different instruments and different times - no robust conclusions
further bservations of 1ES1426+428 and 2155-304, and especially
discovery of new blazars with similar and larger redshifts (z > 0.11),
very important and promising ...
let assume (hope) that new observations will confirm the conclusion
that only a specific class of EBL model allows reasonable intrinsic
TeV spectra of these blazars ... then what ... ?
63
two options

claim that EBL is “detected“ between O/NIR and MIR !

propose extreme hypotheses, e.g.
violation of Lorentz invariance, non-cosmological origin of z ...
or propose less dramatic ideas, e.g
TeV emission from blazars due to the comptonization of
cold ultrarelativistic winds with Lorentz factor > 106
Solution ?
detect many blazars at different redshifts and ... try to detect
Pair Halos formed (unavoidably) around TeV extragalactic sources
64
Gamma Rays from a cold ultrarelativistic wind ?
in fact not a very exotic scenario
65
Pair Halos
when a gamma-ray is absorbed its energy is not lost !
absorption in EBL leads to E-M cascades suppoorted by


Inverse Compton scattering on 2.7 K CMBR photons
photon-photon pair production on EBL photons
if the intergalactic field is sufficiently strong, B > 10-11 G,
the cascade e+e- pairs are promptly isotropised
formation of extended structures – Pair Halos
66
how it works ?
mean free path of parent
photons
information about EBL flux at
Gamma-radiation of pair halos can be
recognized by its distinct variation in
spectrum and intensity with angle ,
and depends rather weakly (!) on the
features of the central VHE source
two observables – angular and energy
distributions allow to disentangle two
variables
67
Pair Halos as Cosmological Candles



informationabout EBL density at fixed cosmological epochs
given by the redshift of the central source
unique !
estimate of the total energy release of powerful AGN during the
active phase
relic sources
objects with jets at large angles - many more g-ray emitting AGN
but the “large Lorents factor advantage“ of blazars now
disapeares: beam
isotropic source
therefore more powerful central objects needed
powerful QSOs and Radiogalaxies (sources of EHE CRS ?)
as better candidates for Pair Halos
this requires low-energy threshold detectors
68
EBL at different z and corresponding mean freepaths
1.
2.
3.
4.
z=0.034
z=0.129
z=1
z=2
1.
2.
3.
4.
z=0.034
z=0.129
z=1
z=2
69
SEDs for different z within 0.1o and 1o
EBL model – Primack et al. 2000
Lo=1045 erg/s
70
Brightness distributions of Pair Halos
z=0.129
z=0.129
E=10 GeV
A. Eungwanichayapant, PhD thesis, Heidelberg, 2003
71
TeV g-rays from GC
GC – a unique site that
harbors many interesting
sources packed with unusually high density around
the most remarkable object
3x106 Mo SBH – Sgr A*
HESS:
FoV=5o
many of them are potential g-ray
emitters - Shell Type SNRs
Plerions, Giant Molecular Clouds
Sgr A * itself, Dark Matter …
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 << 1 arcmin
72
Position?
systematic and statistical errors on source location
by HESS are comparable: 20-30 arcseconds
Chandra GC survey
NASA/UMass/D.Wang et al.
CANGAROO (80%)
H.E.S.S. (95%)
Whipple
(95%)
Contours from Hooper et al. 2004
73
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
74
TeV g-rays from central <10 pc region of GC *

Annihilation of DM ? mass of DM particles > 12 TeV ?

Sgr A* : 3 106 Mo BH ? yes
even the inner R < 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 dense molecular
gas (clouds) ?
easily
75
or
Dark Matter ?
annihilation of SUSY or other DM candidate particles
76
DM Annihilation?


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HESS Spectrum requires a
> 10 TeV DM particles
most WIMPs models favour a
< 2 TeV mass neutralinos
other DM particle candidates ?
GMSB: Gauge mediated
Supersymmetry Breaking
Kalusa-Klein Dark Matter
also a rather cuspy profile and a
high density of DM in the very
central part (around SBH/Sgr A*)
Wimp annihilation
spectra have a cutoff
at ~(0.2…0.3) M
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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 explaind by DM annihilation for
n(r) profile like r-a with a > 1.1 i.e. Qg(r)=C1n2 = Qor-2a
[note that the same can be the case of CR interactions with gas
Qg(r)=C2ncr(r) nH(r)=Qor-(a1+a2) ,
e.g. CR density decreases like r-2 and the gas density like r-0.2 ]
but the absolute intensity of the TeV signal requires much sharper
density profile n(r) within < 0.1 pc
DM TeV signal from GC - point-like with an angular size << 1 arcmin
C1 and C2 – interaction constants (cross-sections)
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CONCLUSION:
unfortunately TeV g-ray data cannot provide information about
Qg(r) (and therefore about DM cusp), inside 1 pc (less than 30”)
what about synchrotron X-radiation of secondary electrons ?
(from decays of p+/- mesons accompanying neutral p mesons) :
Lx: comparable with Lg , h: few (B/1 mG) (Eg/10 TeV)2
keV
provided that the B-field inside 0.1 pc exceeds 1 milliGauss
important: synchr. cooling time of secondary electrons is shorter
than other characteristic times (unlike radio emitting electrons)
=> X-rays are produced “simultaneously” with po – decay grays
important: Chandra detected 1.4 arcsec size diffuse X-ray
emission around Sgr A* – this can be used to
constrain the flux of the DM TeV signal …
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X-ray and g-ray fluxes associated with DM in GC
B=2.5 mG
different g-ray spectra
fixed g-ray spectrum
B=1, 3, 10 mG
production and cooling of electrons in a constant B-field over 1010 yr
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