Microquasars as gamma-ray
sources
Valentí Bosch-Ramon(1)
Josep M. Paredes(1)
In collaboration with:
Gustavo E. Romero(2,3) & Felix Aharonian(4)
(1)Universitat
de Barcelona, Barcelona, Catalunya, España
Argentino de Radioastronomía, Villa Elisa, Buenos Aires, Argentina
(3)Facultad de Ciencias Astronómicas y Geofísicas, UNLP, La Plata, Argentina
(4)Max-Planck-Institut fur Kernphysik, Heidelberg, Germany
(2)Instituto
Outline:
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•
•
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Emissions from a microquasar.
The two EGRET microquasars: LS 5039 and LSI
+61 303 (3EG J1639-4702, Combi et al. (2004,
A&A)).
A model for the unidentified variable EGRET
sources in the galactic plane.
Interaction between microquasars and the ISM.
Conclusions.
EMISSIONS FROM A
MICROQUASAR
•
•
Donor star
IR & UV
(thermal)
Compact jets
Radio & IR
& X?
& ?
(synchrotron
& IC)
Disc
+ corona ?
X & IR
therm + non
therm
•
Wind
Visible & radio
(free-free)
M•
•
Dust ?
IR & mm
(thermal)
•
Large scale
ejection
Radio & X
Interaction with
environment
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LS 5039 and its microquasar nature
High Resolution radio map of the
nearby star LS 5039 obtained with
VLBA and VLA in phased array
mode at 6 cm. The presence of radio
jets is the main evidence supporting
its microquasar nature.
1 milliarcsec is equivalent to 3AU
(~1013 cm) for a distance of 3kpc.
[Paredes et al. (2000, Science)].
Orbital semi-major axis, a ~ 2.6x1012 cm
•Orbital eccentricity, e ~ 0.5(?)
•
Stellar type: ON6.5V((f))
31 erg/s
•Lradio ~ 10
•Spectral index ~ 0.5
•
•
Lx ~ 1034 erg/s
•
X-ray photon index ~ 1.3-1.9
CGRO/EGRET field of
3EG J1824-1514
g-rays
L(>100MeV)∼1035erg·s-1
Observed spectral energy distribution
from the radio to the -rays.
Ribó (2002, PhD thesis)
EGRET candidate: LSI+61303
•
•
Orbital semi-major axis,
a ~ 5x1012 cm
Orbital eccentricity,
e ~ 0.7
•
Stellar type: B0 V (Be)
Lradio ~ 1031-32 erg/s (v.)
•
Spectral index ~ 0-0.4
•
Lx ~ 1034-35 erg/s (v.)
•
X-ray phot. Ind. ~ 1.7
•
Distance ~ 2 kpc
•
This source presents
•
outbursts at radio and X-ray
energies.
Massi et al. (2004, A&A)
Precession could explain:
• the puzzling VLBI structures observed so far
• shortest term variability of the associated EGRET source
EGRET observations of 2CG 135+01 shows
variability on short (~day) and long (~month)
timescales
Tavani et al. (1998, ApJ)
Massi (2004, A&A)
The broadband 1 keV-100 MeV spectrum
remains uncertain (OSSE and COMPTEL
observations were
likely dominated by
the QSO 0241+622
emission)
Harrison
et al.
(2000, ApJ )
Hartman et al. (1999, ApJS)
First proposed as a COS B source by
Gregory & Taylor (1978, Nature)
The EGRET angular resolution is sufficient to
exclude the quasar as the source of gamma-ray
emission
Strickman et al. (1998, ApJ)
(Bosch-Ramon)
A model for EGRET microquasars
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•
•
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We consider an inhomogeneous jet with a highly relativistic
leptonic population (hadrons?: Romero et al. (2003, A&A)).
Leptons are assumed to dominate the radiative processes and
injected following a power-law in energy.
The evolution of the particles in the jet have been taken into
account (adiabatic and radiative ones).
Radiative losses: synchrotron effect, external (star, disk corona)
inverse Compton and synchrotron self-Compton scattering.
High energy emission due to IC processes in the jet:
External Compton (e.g. Georganopoulos et al. (2002, A&A);
Kaufman Bernadó et al. (2002, A&A)).
•
Synchrotron Self Compton (e.g. Atoyan & Aharonian (1999,
MNRAS)).
•
Computed Spectral Energy Distribution of
LS 5039
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•
•
•
•
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Maximum electron
Lorentz factor:
 max = 105
B=1G
Kinetic luminosity or jet
power:
Lk ~ 1036erg/s
LEGRET ~ 1035 erg/s
B = 10 G
EGRET = 2.2 ± 0.2
Bosch-Ramon & Paredes (2004a, A&A)
Computed Spectral Energy
Distribution of LSI+61303
Hall et al. (2003, ApJ)
B = 1, 10 G
−7
−8
−10
−11
2
log (Iε [photon/cm /s/MeV])
−9
Maximum electron Lorentz factor:
•e max = 105
•
Kinetic luminosity or jet power:
L k ~ 1035 erg/s
•
LEGRET ~ 1035 erg/s
•
EGRET = 2.2 ± 0.2
•
−12
−13
EGRET data
model spectra:
Lac(Rorb=a)
Lac(Rorb=a(1−e))
Lac(Rorb=a(1+e))
5
Bγ=10 G and γmax=10
−14
−15
−16
−17
8
8.5
9
9.5
10
log (Photon energy [eV])
Bosch-Ramon & Paredes
(2004b, A&A, in press)
[astro-ph/0407016]
10.5
The g-ray population in the galactic plane
Log N-Log S diagram for the steady (top) and variable (bottom) sources of the
GRP I:
•
100
−2.92
N~S
10
N (Normalized)
•
1
100
−1.66
N~S
•
10
•
1
10
−8
−2
−1
100
S (x10 ph cm s )
Bosch-Ramon et al. (2004a, A&A, in press)
[astro-ph/0405017]
We have separated all the sources
within 6° of galactic latitude in two
groups: variable and non-variable
sources (Nolan et al. 2003).
Log N-Log S analysis for radio
pulsars gives a very steep powerlaw: βrad. Puls. ~1 (Bhattacharya et al.
2003).
Variable sources seem to be less
concentrated to the inner spiral
arms than the steady sources.
High-mass microquasars have large
proper motions (Ribó et al 2002):
more spread in the galaxy.
A canonic EGRET microquasar
Computed SED of a broadband spectrum:
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Lk~1036 erg/s, Γjet=1.1 & θ=10°
•
B=200 G, γemax=104 & p=2
40
39
IC emission
seed photons
radio emission
star
38
37
•
36
log (εLε [erg/s] )
35
34
sync. IC
33
•
disk
32
31
30
29
corona
cor. IC
radio jet
IC emission is dominated by SSC
scattering, reaching EGRET energies.
star IC
sync.
•
disk IC
28
27
26
25
Ldisk~3x1032, Lcor~3x1032 &
Lstar~5x1038 erg/s
−6 −5 −4 −3 −2 −1 0 1 2 3 4 5
log (Photon energy [eV] )
6
7
8
9
Bosch-Ramon et al. (2004a, A&A, in press)
[astro-ph/0405017]
•
Low luminosities at X-rays, with
harder spectrum at high-energy
gamma-rays (Thomson reg.).
Lradio<< Lx < LEGRET
Interaction between microquasars and molecular clouds
SED for a continuous microquasar at R=10 pc and three different t:
100 yr (1), 1000 yr (2), 10000 yr (3).
•
33
3
synchrotron emission
Bremstrahlung emission
pion−decay emission
32
3
•
2
3
2
log (εLε [erg/s])
31
1
2
•
1
30
•
29
28
1
radio
27
−12
−10
−8
−6
gamma−rays
X−rays
optical
−4
−2
0
2
2
4
6
log (Photon energy [mec ])
Bosch-Ramon et al. (2004b, A&A, submitted)
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A jet of microquasar releases
(accelerate) high energy protons.
These relativistic protons diffuse in
the ISM up to reach a molecular
cloud (D(E)).
Proton-proton interactions produce
g-rays and e-/e+ via pion-decay.
The secondaries generate
significant amounts of synchrotron
radiation and Bremstrahlung.
All these (extended) emission could
be detected from the Earth from
radio to TeV energies.
Microquasars and steady g-ray sources in the galactic plane
SED of a continuous microquasar (solid line) plus a typical EGRET spectrum up to
10 GeV (long-dashed line):
36
•
•
log (εLε [erg/s])
35
•
34
•
100 GeV
1 GeV
33
3
4
2
5
log (Photon energy [mec ])
Bosch-Ramon et al. (2004b, A&A, submitted)
For ancient sources, the g-ray peak
is at EGRET energies.
For molecular clouds of 105 solar
masses, we obtain EGRET fluxes
even at distances of several kpc.
The molecular cloud is at a distance
of 10 pc from the microquasar.
The new generation of Cherenkov
telescopes could even detect this
sources at 100 GeV.
Conclusions
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We can reproduce, in a microquasar scenario, the observed
EGRET broadband spectra and variability with reasonable
parameter values.
Our approach gives restrictions on the electron energy and
the leptonic kinetic luminosity, showing the importance that
B could have in the production of seed photons.
Regarding the subset of variable galactic EGRET sources,
microquasars are likely candidates to be their counterparts.
Moreover, microquasars could be indirect steady sources of
gamma-rays through interaction with the ISM.
Next in the future, multiwavelength campaings and the new
g-ray instruments will allow to unveil the nature of many gray sources, and microquasars could turn out to be a
significant fraction of them.