Transcript Cosmic TeVatrons and PeVatrons as Extreme Particle

Lecture 4
Galactic Source Populations
of VHE Gamma Rays
Felix Aharonian
Dublin Institute for Advanced Studies, Dublin
Max-Planck-Institut f. Kernphysik, Heidelberg
VHE gamma-ray observations:
“Universe is full of extreme accelerators on all astronomical scales”
Shell Type SNRs
Giant Molecular Clouds
Star formation regions
Pulsar Wind Nebulae
Compact Galactic Sources
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Binary pulsar PRB 1259-63
LS5039, LSI 61 303 – microquasars?
Cyg X-1 ! (?) - a BH candidate
Galactic Center
Extragalactic objects
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M87 - a radiogalaxy
TeV Blazars – with redshift from 0.03 to 0.18 or even 0.5 ? (3C 279)
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and a large number of yet unidentified TeV sources …
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VHE gamma-ray source populations
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Extended Galactic Objects
Potential Gamma Ray Sources
Extragalactic Sources
Galactic Sources
GeV
GeV
GRBs
AGN
GLX
GeV
CLUST
IGM
EBL
Starburst
Normal
Radiogalaxies
Blazars
Binaries
Binary Pulsars
Pulsars
Pulsar Nebula
GMCs
SNRs
Cold Wind
SFRs
Magnetosphere
ISM
GeV
Microquasars
GeV
GeV
G-CRs
Relativistic
Outflows
Compact Objects
EXG-CRs
Cosmology
Major Scientific Topics
Galactic TeVatrons and PeVatrons - particle accelerators
responsible for cosmic rays up to the “knee” around 1 PeV
SNRs ?
Pulsars/Plerions ?
OB, W-R Stars ?
Microquasars ?
Galactic Center ?
...
Gaisser 2001
* the source population responsible for the bulk of GCRs are PeVatrons ?
Visibility of SNRs in high energy gamma-rays
for CR spectrum with =2
Fg(>E)=10-11 A (E/1TeV)-1 ph/cm2s
p0 –decay (A=1)
A=(Wcr/1050erg)(n/1cm-3 )(d/1kpc) -2
1000 yr old SNRs (in Sedov phase)
Detectability ? compromise between
angle q (r/d) and flux Fg (1/d2)
typically A: 0.1-0.01 q: 0.1o - 1o
TeV g-rays – detectable if A > 0.1
po component
0.1 (Sx/10 mJ)(B/10
mGand
) -2 IC TeV g’s
if electron
spectrum >>dominates
10 TeV if A > synchrotron
X-rays
-2
target of
photon
2.7 K:through
Fg,IC/Fx,sinch
nucleonicmain
component
CRs -field
“visible”
TeV=0.1
(and(B/10mG)
GeV) gamma-rays
!
RXJ1713.7-4639
TeV g-rays and shell type morphology:
acceleration of p or e in the shell to
energies exceeding 100TeV
can be explained by g-rays from pp ->po >2g
and with just ”right” energetics
2003-2005 data
Wp=1050 (n/1cm-3)-1 erg/cm3
but IC canot be immediately excluded…
leptonic versus hadronic
arguments against hadronic models:

nice X-TeV correlaton
well, in fact this is more natural for hadronic
rather than leptonic models

relatively weak radio emission
problems are exaggerated
IC origin ? – very small B-field, B < 10 mG,
and very large E, Emax > 100 TeV
two assumptions hardly can co-exists within
standard DSA models, bad fit of gamma-ray
spectrum below a few TeV, nevertheless …

lack of thermal X-ray emission
=> very low density plasma or low Te ?
we do not (yet) know the mechanism(s)
of electron heating in supernova
remnants so comparison with other
SNRs is not justified at all
Suzaku measurements => electron spectrum 10 to 100 TeV
Variability of X-rays on year timescales witnessing particle acceleration in real time
flux increase - particle acceleration
flux decrease - synchrotron cooling *)
both require B-field of order 1 mG in
hot spots and, most likely, 100mG outside
Uchiyama, FA, Tanaka, Maeda,
Takahashi, Nature 2007
strong support of the idea of amplification of B-field
by in strong nonlinear shocks through non-resonant
streaming instability of charged energetic particles
(T. Bell; see also recent detailed theoretical treatment
of the problem by Zirakashvili, Ptuskin Voelk 2007)
*) explanation by variation of B-field does’t work as demonstrated for Cas A (Uciyama&FA, 2008)
acceleration in Bohm diffusion regime
energy spectrum of synchrotron radiation of electrons in the
framework of DSA (Zirakashvili&FA 2007)
with h=0.67 +/- 0.02keV
(Tanaka et al. 2008)
Strong support for Bohm diffusion - from the synchrotron cutoff
given the upper limit on the shock speed of order of 4000 km/s !
B=100 mG + Bohm diffusion - acceleration of particles to 1 PeV
RXJ 1713.7-3946
protons:
dN/dE=K E- exp[-(E/Ecut)b]
g-rays:
dN/dE v E-G exp[-(E/E0)bg]
G=+d, d 0.1, bg=b/2, E0 = Ecut/20
Wp(>1 TeV) ~ 0.5x1050 (n/1cm-3)-1 (d/1kpc)2
neutrinos: marginally detectable by KM3NeT
Probing PeV protons with X-rays
SNRs shocks can accelerate CRs to <100 TeV
unless magnetic field significantly exceeds 10 mG
recent theoretical developments: amplification of the B-field up
to >100 mG is possible through plasma waves generated by CRs
>1015 eV protons result in >1014 eV gamma-rays and electrons
“prompt“ synchrotron X-rays
t(e) = 1.5 (e/1keV) -1/2 (B/1mG) -3/2 yr << tSNR
typically in the range between 1 and 100 keV with the ratio Lx/Lg
larger than 20% (for E-2 type spectra)
“hadronic“ hard X-rays and (multi)TeV g-rays – similar morphologies !
three channels of information
about cosmic PeVatrons:
10-1000 TeV gamma-rays
10-1000 TeV neutrinos
10 -100 keV hard X-rays
 g-rays: difficult, but possible with future “10km2“ area multi-TeV IACT arrays
 neutrinos: marginally detectable by IceCube, Km3NeT - don’t expect
spectrometry, morphology; uniqueness - unambiguous signatute!
 “prompt“ synchrotron X-rays: smooth spectrum
a very promising channel - quality! (NexT, NuSTAR, SIMBOL-X)
broad-band emision initiated by pp interactiosn : Wp=1050 erg, n=1cm-3
protons
broad-band
GeV-TeV-PeV
gs
synch. hard X-rays
no competing X-ray radiation mechanisms above 30 keV
probing hadrons with secondary
X-rays with sub-arcmin resolution!
Simbol-X
new technology focusing telescopes
NuSTAR (USA), Simbol-X (France-Italy), NeXT (Japan) will provide X-ray imaging
and spectroscopy in the 0.5-100 keV band with angular resolution 10-20 arcsec
and sensitivity as good as 10-14 erg/cm2s!
complementary to gamma-ray and neutrino telescopes
advantage - (a) better performance, deeper probes
(b) compensates lack of neutrinos and
gamma-rays at “right energies”
disadvantage - ambiguity of origin of X-rays
Searching for Galactic PeVatrons
the existence of a powerful accelerator is not
yet sufficenrt for g-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
older source – steeper g-ray spectrum
tesc=4x105(E/1 TeV) -1 k-1 yr (R=1pc); k=1 – Bohm Difussion
Qp = k E-2.1 exp(-E/1PeV)
Lp=1038(1+t/1kyr) -1 erg/s
Gamma-rays and neutrinos inside and outside of
SNRs
1 - 400yr, 2 - 2000yr, 3 - 8000yr, 4 - 32,000 yr
gamma-rays
SNR: W51=n1=u9=1
neutrinos
d=1 kpc
ISM: D(E)=3x1028(E/10TeV)1/2 cm2/s
GMC: M=104 Mo d=100pc
[S. Gabici, FA 2007]
MGRO J1908+06 - a PeVatron?
HESS
preliminary
Milagro
gamma-ray emitting clouds in GC region
diffuse emission along the plane!
HESS J1745-303
(1) indirect discovery of the site of particle acceleration
(2) measurements of the CR diffusion coefficient
Pulsar Winds and Pulsar Wind Nebulae
(Plerions)
Crab Nebula – a perfect PeVatron of electrons (and protons ?)
1-10MeV
Standard MHD theory
MAGIC (?)
.
100TeV
HEGRA
cold ultrarelativistc pulsar wind terminates
by a reverse shock resulting in acceleration
with an unprecedented rate: tacc=hrL/c, h < 100 *)
synchrotron radiation => nonthermal optical/X-ray nebula
Inverse Compton
=> high energy gamma-ray nebula
Crab Nebula – a very powerful W=Lrot=5x1038 erg/s
and extreme accelerator: Ee > 1000 TeV
Emax=60 (B/1G) -1/2 h-1/2 TeV and hcut=(0.7-2) f-1mc2 h-1 = 50-150 h-1 MeV
h=1 – minimum value allowed by classical electrodynamics
Crab: hcut= 10MeV: acceleration at ~10 % of the maximum rate ( h  10)
maximum energy of electrons: Eg=100 TeV => Ee > 100 (1000) TeV
B=0.1-1 mG
– very close the value independently derived from the MHD treatment of the wind
* for comparison, in shell type SNRs DSA theory gives h=10(c/v)2=104-105
TeV gamm-rays from other Plerions (Pulsar Wind Nebulae)
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 large spin-down flux
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 ! – many famous PWNe are
already detected in TeV gamma-rays - MSH 15-52, PSR 1825, Vela X, ...
HESS J1825 (PSR J1826-1334)
energy-dependent image - electrons!
red –
below 0.8 TeV
yellow – 0.8TeV -2.5 TeV
blue –
above 2.5 TeV
Pulsar‘s period: 110 ms, age: 21.4 kyr,
distance: 3.9 +/- 0.4 kpc
Luminosities:
spin-down:
X: 1-10 keV
g: 0.2-40TeV
Lrot= 3 x 1036 erg/s
Lx=3 x 1033 erg/s (< 5 arcmin)
Lg=3 x 1035 erg/s (< 1 degree)
the g-ray luminosity is comparable to the TeV luminosity of the Crab Nebula, while the
spindown luminosity is two orders of magnitude less !
Implications ?
(a) magnetic field should be significantly less than 10mG.
but even for Le=Lrot this condition alone is not sufficient to achieve 10 % g-ray production
efficiency (Comton cooling time of electrons on 2.7K CMBR exceeds the age of the source)
(b) the spin-down luminosity in the past was much higher.
Gamma-ray
Binaries
Mirabel 2006
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
but with characteristics radiation and dynamical timescales less than hours
both the cold ultrarelativistic wind and shocke-accelerated electrons
are illuminated by optical radiation from the companion star
=> detectable IC gamma-ray emission
on-line watch of creation/termination of the pulsar wind accompanied
with formation of a shock and effective acceleration of electrons
HESS: detection of TeV gamma-rays
from PSR1259-63 several days before the
periastron and 3 weeks after the peristron
the target photon field is function of time, thus the only
unknown parameter is B-field? Easily/robustly predictable
X and gamma-ray fluxes ?
unfortunately more unknown parameters - adiabatic losses, Doppler boosting, etc.
One needs deep theoretical (especially MHD) studies to understand this source
time evolution of fluxes and energy spectra of X- and gamm-rays contain
unique information about the shock dynamics, electron acceleration, B(r),
plus … a unique probe of the Lorentz factor of the cold pulsar wind
Probing the wind Lorentz factor with comptonizied radiation
Khangulyan et al. 2008
GLAST
the effect is not negligible, but not
sufficient to explain the lightcurve
Loretz factors exceeding 106 are excluded
TeV Gamma Rays From microquasars?
HESS, 2005
MAGIC, 2006
microqusars or binary pulsars?
independent of the answer –
particle acceleration is linked
to (sub) relativistic outflows
LS5039 and LS I +61 303 as TeV gamma-ray emitters
scenarios? g-ray production region within and outside the
binary system cannot be excluded
periodicity expected? yes
–
because of periodic variation of the geometry
(interaction angle) and density of optical photons – as target photons for IC scattering
and gg absorption, as a regulator of the electron cut-off energy; also because of
variation of the B-field, density of the ambient plasma (stellar wind), ...
periodicity detected ! is everything OK ?
may be OK, but a lot of problems and puzzles with interpretation of the data …
LS 5039 as a perfect TeV clock
and an extreme TeVatron
close to inferior conjuction - maximum
close to superior conjuction – minimum
one needs a factor of 3 or better sensitivity compared to
HESS to detect signals within different phase of width
0.1 and measure energy spectra (phase dependent!)
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can electrons be accelerated to > 20 TeV in presence of radiation?
yes, but accelerator should not be located deep inside the binary
system, and even at the edge of the system h < 10
does this excludes the model of “binary pulsar”
yes, unless the interaction of the pulsar and stellar winds create a
relativistic bulk motion of the shocked material (it is quite possible)
can we explain the energy dependent modulation by gg absorption ?
yes, taking into account the anysotropic character of IC scattering ?
can the gamma-ray producton region be located very deep inside the system
no, unless magnetic field is less than 10(R/R*)-1 G (or perhaps not at all)
future key observations
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TeV observations with a sensitivity a factor of 3 (or so) better than HESS, to
measure, in particular, the fluxes and spectra within narrow phases ,   
very import are both 10 TeV (maximum electron energy and no absorption) and
0.1 TeV regions (maximum absorption, maximum anysotropy effect, etc.)
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GeV observation (GLAST) to measure the cascade component
X-ray observations - synchrotron radiation of primary and secondary electrons
neutrinos - if g-ray are of hadronic origin, and less than several percent of the
original flux escapes the source, one may expect neutrino flux marginally detectable
by km3 volume detectors (current limit from X-ray observations), could be higher
If GLAST detects high (cascade) fluxes