Download HE and VHE emission from X-ray binaries

Josep M. Paredes
HE AND VHE EMISSION
FROM X-RAY BINARIES
Locating PeV Cosmic-Ray Accelerators: Future Detectors
in Multi-TeV Gamma-Ray Astronomy
Adelaide, 6-8 December 2006
1
OUTLINE
1. X-ray binaries
2. How many microquasars we know
3. µqs as HE and VHE γ-ray sources:
Theoretical point of view
Observational point of view
4. µqs, gamma-ray binaries,……..
5. Summary
2
Microquasars: X-ray binaries with relativistic jets
XB: A binary system containing a compact object (NS or a stellar-mass BH) accreting
matter from the companion star. The accreted matter forms an accretion disc, responsible
for the X-ray emission. A total of 280 XB (Liu et al. 2000, 2001).
HMXBs: (131) Optical companion with spectral type O or B. Mass transfer via decretion
disc (Be stars) or via strong wind or Roche-lobe overflow.
LMXBs: (149) Optical companion with spectral type later than B. Mass transfer via Rochelobe overflow.
280 XB
43 (15%) REXBs
8 HMXBs
35 LMXBs
At least 15 microquasars
Maybe the majority of RXBs are microquasars
(Fender 2001)
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MICROQUASARS IN OUR GALAXY High Energy Detections
Name
Mcomp Radio
(M)
p/t
Jet
INTEGRAL
app Size Note
(AU)
30-50 keV 40-100 keV
(significance) (count/s)
BATSE
COMPTEL EGRET
20-100 keV 160-430 keV 1-30 MeV
(significance) (mCrab)
Others
>100 MeV
High Mass X-ray Binaries
LS I +61 303

p
 0.4 10 700 Prec ? 7.1
V4641 Sgr
9.6
t
 9.5
LS 5039
5.4
p
0.18 10 1000 Prec ?
11±5?
p
0.26
SS 433


2.4 ± 0.5
5.2
5.1 ± 2.1

yes?

3EGJ0241+6103
MAGIC



8.0
1.7 ± 0.2
10.7
3.7 ± 1.8
yes? 3EGJ1824 1514 HESS
~104 106 Prec. 94.7
5.2 ± 0.2
21.7
0.0 ± 2.8


Hadronic, X-ray jet
Cygnus X-1
10.1
Cygnus X-3

p
p

~40
876.7 ± 0.3
1186.8
924.5 ± 2.5
yes
0.69
~104 Radio outb. 1096 78.3 ± 0.3
197.8
15.5 ± 2.1




4651

Low Mass X-ray Binaries

t
> 15
XTE J1550-564
9.4
t
2
Scorpius X-1
1.4
GRO J1655-40
7.02
Circinus X-1
GX 339-4
1E 1740.7-2942
>104
99.1
0.6 ± 0.2
3.8
0.3 ± 2.6

55.3 ± 0.2
17.1
p 0.68
~40
24.7 ± 0.3
460.6
9.9 ± 2.2


t
1.1
8000
40.6
23.4 ± 3.9


5.8 ± 0.5 t

< 4000
58.0 ± 3.5



~106
1.3
> 104


~106
813

p
XTE J1748-288
> 4.5? t
GRS 1758-258

GRS 1915+105 14 ± 4
p
2422
Prec?
59
306
147.3
t 1.2 1.7 ~10 104 Prec?2556
2.7 ± 0.2
46.7 ± 0.2
89.0
-2.3 ± 2.5

~103 X-ray jet 738
4.32 ± 0.03
92.4
61.2 ± 3.7



-12.4







75.3± 0.1
74.3
38.0 ± 3.0
123.4 ± 0.2
208.8
33.5 ± 2.7
The 3rd IBIS/ISGRI soft gamma-ray survey catalog (Bird et al. 2006, ApJ, in press, astro-ph/0611493)
BATSE Earth Occultation Catalog, Deep Sample Results (Harmon et al. 2004, ApJS, 154, 585)
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MULTIFREQUENCY EMISSION IN MICROQUASARS
Adapted from Chaty (Ph.D. Thesis)
• Donor star
IR  UV
(thermal)
• Wind
Visible  radio
(free-free)
•
M
• Dust ?
IR  mm
(thermal)
• Compacts jets
Radio  IR
 X?
 gamma?
(synchrotron)
• Disc
+ corona ?
X  IR
therm + non
therm
• Large scale
ejection
Radio & X
gamma?
Interaction with
environment
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BLACK HOLE STATES
Black holes display different X-ray spectral states:
- Low/hard state (a.k.a. power-law state). Compact radio jet.
- High/soft state (a.k.a. steep power-law state). No radio emission.
- Intermediate and very high states  transitions. Transient radio
emission.
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Fender 2001, ApSSS 276, 69
Corbel et al. 2000, A&A 359, 251
High/Soft
Low/Hard
Grebenev et al. 1993, A&ASS 97, 281
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MQs as high-energy γ -ray sources
Theoretical point of view
Leptonic models:
SSC Atoyan & Aharonian 1999, MNRAS 302, 253
Latham et al. 2005, AIP CP745, 323
EC Kaufman Bernadó et al. 2002, A&A 385, L10
Georganopoulos et al. 2002, A&A 388, L25
SSC+EC Bosch-Ramon et al. 2004 A&A 417, 1075
Synchrotron jet
emission Markoff et al. 2003, A&A 397, 645
Hadronic models:
Pion decay Romero et al. 2003, A&A 410, L1
Bosch-Ramon et al. 2005, A&A 432, 609
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Leptonic high energy models
Synchrotron self Compton model
• Non-thermal flares GRS1915+105
Rodríguez et al.
1995, ApJS 101, 173
(Atoyan & Aharonian 1999, MNRAS 302, 253)
 Flares are caused by synchrotron radiation
of relativistic e suffering radiative,
adiabatic and energy-dependent escape
losses in fast-expanding plasmoids (radio
clouds)

Continuous supply or in-situ acceleration of radio e
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After limiting, from the radio data, the
basic parameter characterizing the
expanding plasmoids, the e may be
accelerated up to TeV energies, and the
fluxes of synchrotron radiation could then
extend beyond the X-ray region and the
fluxes of the IC γ-rays to HE and VHE.
BATSE
0.05 G
0.1G
IR
0.2 G
sub-mm
radio
GRS 1915+105
Exponential cutoff
energies:
20 TeV _____
1 TeV _ _ _ _
30 GeV _ . _ . _
IC scattering or maybe even direct synchrotron emission from the
jets could dominate the high-energy emission above an MeV or so
Atoyan & Aharonian 1999, MNRAS 302, 253, and 2001
B = 0.05 G
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External Compton Scattering - HMXB
•Jet exposed to star, disk and corona photon fields.
Applied to Cygnus X-1 (Romero, Kaufman Bernadó & Mirabel 2002, A&A 393, L61)
Corona (Klein-Nishina regime), disk and companion star (Thomson)
The Compton losses in the different regions will modify the injected
electron spectrum, introducing a break in the power law at the energy
at which the cooling time equals the escape time.
Viewing angle of 30º
Bulk Lorentz factor Γ=5
Radiation absorbed in the local
field trough pair creation
Up-scattering of
star photons (A)
disk (B)
corona (C)
The recurrent and relatively rapid variability could be
explained by the precession of the jet, which results in a
variable Doppler amplification
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Hadronic jet models for
microquasars
• Hadronic models (only) for gamma γ-ray emission:
➢ Conical jet 1014 eV protons interacting with strong stellar wind protons,
assuming efficient wind proton diffusion inside the jet.
➢ Protons are injected in the base of the jet and evolve adiabaticaly.
➢ Applied to explain gamma-ray emission from high mass microquasars
(Romero et al. 2003, A&A 410, L1).
 The γ-ray emission arises from the decay of neutral pions created in the
inelastic collisions between relativistic protons ejected by the compact
object and the ions in the stellar wind.
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The only requisites for the model are a windy high-mass stellar
companion and the presence of multi-TeV protons in the jet.
Spherically symmetric wind and circular orbit
Romero,Torres, Kaufman, Mirabel 2003, A&A 410, L1
Interactions of hadronic beams with moving clouds in the context of
accreting pulsars have been previously discussed in the literature by
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Aharonian & Atoyan (1996, Space Sci. Rev. 75, 357).
• Models from radio to VHE:
➢Released 1014 eV protons from the jet that diffuse through and interact
with the ISM.
➢Computed the broadband spectrum of the emission coming out from
the pp primary interactions (γ-rays produced by neutral pion decay) as
well as the emission (synchrotron, bremsstrahlung and IC scattering)
produced by the secondary particles produced by charged pion-decay.
➢All the respective energy losses have been taken unto account.
➢Applied to impulsive and permanent microquasar ejections.
1) 100 yr
2) 1000 yr,
3) 10000 yr
dMQ/cloud=10pc
Mcloud=105Msun
Ljet=1037 erg/s
Bosch-Ramon et al. 2005,
A&A 432, 609
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MQs as high-energy γ -ray sources
Observational point of view
15
EGRET candidate: LS 5039
Orbital phase 0.2
VLBA, 5 GHz
Jet parameters:
 > 0.15 ,  < 81
TB = 9.4 x 107 K
LS 5039 could be related to the
high energy gamma-ray source
3EG J1824-1514
Equipartition:
Ee = 5 x 1039 erg
B = 0.2 G
The photon spectral index is
steeper than the a < 2 values
usually found for pulsars
Merk et al.1996, A&ASS 120, 465
It is the only simultaneous X-ray/radio source
within the 3EG J1824-1514 statistical contours.
Paredes et al. 2000, Science 288, 2340
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Synchrotron
Radiation
Radio, L0.1-100 GHz ~ 11031 erg/s
e-
e-
e-
g-ray, E > 100 MeV, Lg ~ 41035 erg/s
Inverse Compton
Scattering
X-ray
L3-30 keV ~ 51034 erg/s
UV, E ~ 10 eV
e-
Lopt ~ 11039 erg/s
ge ~ 103
O6.5V((f))
evjet  0.15c
e-
Proposed scenario
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GRO J1823-12 (l/b: 17.5/-0.5)
3EG J1812-1316
GRO J1817-15
3EG J1823-1314
3EG J1826-1302
3EG J1824-1514
µ-quasar LS 5039
Summary
• complicated source region
• possible counterparts:
- 3 known g-sources (unid. EGRET)
(MeV emission: superposition ?)
- micro quasar RX J1826.2-1450/LS 5039
(sug. counterpart of 3EG J1824-1514;
Paredes et al. 2000)
• work in progress
Collmar 2003, Proc. 4th Agile Science Workshop
18
Discovery of the TeV counterpart by HESS (Aharonian et al. 2005). Good
position agreement with LS 5039. Good extrapolation of the EGRET
spectrum.
19
A black hole in LS 5039 ?
Radial velocity curve of LS 5039
New spectroscopic observations of LS 5039
INT 2.5 m telescope (July 2002 and 2003)
New orbital ephemeris!!
P = 3.9060 ± 0.0002 d
e = 0.35 ± 0.04
Periastron at phase 0.0
And assuming pseudo-synchronisation
at periastron:
i = 20.3˚ ± 4.0
Mcompact = 5.4 (+1.9-1.4) M
Casares et al., 2005, MNRAS, 364, 899
20
With the new orbital ephemerides → correlated TeV and X-ray orbital
variability.
HESS
RXTE
(Casares et al. 2005),
21
3.9 day orbital modulation in the TeV gamma-ray flux
Aharonian et al. 2006, A&A, in press (astro-ph/0607192)
VHE γ-rays can be absorbed by optical photons of energy
hνε, when their scattering angle θ exceeds zero.
22
We have enough information to build up a Spectral Energy Distribution
that can be modeled to extract physical information (Paredes et al. 2006, A&A 451,
259).
23
EGRET candidate: LSI+61303
The radio emitting X-ray binary LSI+61 303, since its discovery, has been proposed
to be associated with the γ-ray source 2CG 135+01 (= 3EG J0241+6103)
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 528, 454
The EGRET angular resolution is sufficient to
exclude the quasar QSO 0241+622 as the
source of γ-ray emission.
Hartman et al. 1999, ApJS 123, 79
Strickman et al. 1998, ApJ 497, 419
Periodic emission
Radio (P=26.496 d) ↔ accretion at periastron passage
Taylor&Gregory 1982, ApJ 255, 210
Optical and IR Mendelson&Mazeh 1989, MNRAS 239, 733;
Paredes et al. 1994 A&A 288, 519
X-rays Paredes et al. 1997 A&A 320, L25
γ-rays ???
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3EG J0241+6103 variability
INTEGRAL variability
Tavani et al. 1998, ApJ 497, L89
EGRET observations of
3EG J0241+6103
shows variability on
short (days) and long
(months) timescales
Massi et al. 2005 (astro-ph/0410504)
Hermsen et al. 2006
Rome, “keV to TeV connection”Workshop,
18 October 2006
25
Chandra Image of LSI+61303
5”
Chandra PSF
Obtained using the Chandra simulator
Surface brightness distribution
LSI+61303
PSF
Paredes et al. 2006
26
Flux changes on timescales of few hours.
Factor of two variability
MAGIC has observed
LSI during 6 orbital cycles
 A variable flux
(probability of statistical
fluctuation 310-5)
detected
 Marginal detections at
phases 0.2-0.4
 Maximum flux
detected at phase 0.6-0.7
with a 16% of the Crab
Nebula flux
 Strong orbital
modulation  the
emission is produced by
the interplay of the two
objects in the binary
 No emission at
periastron, two maxima in
consecutive cycles at
similar phases  hint of
periodicity!
Flux time variability

Results of MAGIC fist observation cycle on Galactic sources
Albert et al. 2006
J. Rico (IFAE)
LS I +61 303: the film
Albert et al. 2006
The average emission has a maximum at phase 0.6.
 Search for intra-night flux variations (observed in radio and x-rays)
yields negative result
 Marginal detections occur at lower phases. We need more
observation time at periastron passage
 Parts of the orbit not covered due to similarities between orbital
period (26.5 days) and Moon period

Results of MAGIC fist observation cycle on Galactic sources
J. Rico (IFAE)
Radio 15 GHz /Ryle, simultaneous with MAGIC obs.
The TeV flux maximum is detected at phases 0.5-0.6,
overlapping with the X-ray outburst and the onset of
the radio outburst.
Concerning energetics, a relativistic power of several
1035 erg s-1 could explain the non thermal luminosity of
the source from radio to VHE gamma-rays. This
power can be extracted from accretion in a slow
inhomogeneous wind along the orbit (Bednarek 2006,
MNRAS 268, 579).
Spectrum for phases 0.4 and 0.7
This spectrum is consistent with that of
EGRET for a spectral break between 10
and 100 GeV.
The flux above 200 GeV corresponds to
an isotropic luminosity of ~7 x 1033 erg s-1,
at a distance of 2 kpc.
The intrinsic luminosity of LS I +61 303 at
its maximum is a factor ~6 higher than that
of LS 5039, and a factor ~2 lower than the
combined upper limit (<8.8 x 10 -12 cm-2 s-1
above 500 GeV) obtained by Whipple
29
(Fegan et al. 2005, ApJ 624, 638).
LSI+61303 VLBA images over full orbit
---------Orbital
Phase
10 AU
New VLBI observations show
a rotating jet-like structure
Dhawan et al. 2006, VI MIcroquasars Workshop, Como, Setember 2006
3.6cm images ~3d apart. Beam 1.5x1.1mas 3x2.2 AU.
Contours +_0.2mJy, increment sqrt(2).
Mirabel 2006, (Perspective) Science 312, 1759
A possible scenario comes from the application of the pulsar wind nebulae
formed with the interaction of a relativistic pulsar wind with the ISM but where the
wind of the companion plays the role of the ISM. The stagnation point, where the
pressure from the two winds is balanced, is within the binary system. Particles
are accelerated at the termination shock and produce the non-thermal
synchrotron emission (Dubus 2006, A&A 456, 801).
32
UV photons from the companion star suffer inverse Compton scattering by the
same population of non-thermal particles, leading to emission in the GeV-TeV
energy range.
Particles move downstream away from the pulsar at a speed v (initially ≈c/3). A
cometary nebula of radio emitting particles is formed. It rotates with the orbital
period of the binary system. We see this nebula projected (Dubus 2006, A&A 456, 801).
33
PSR B1259-63
PSR B1259-63 / SS 2883 is a binary system containing a B2Ve donor
and a 47.7 ms radio pulsar orbiting it every 3.4 years, in a very eccentric
orbit with e=0.87. No radio pulses are observed when the NS is behind
the circumstellar disk (free-free absorption). VHE gamma-rays are
detected when the NS is close to periastron or crosses de disk (Aharonian et
al. 2005).
34
The VHE spectrum can be fit with
a power-law and explained by IC
scattering processes.
The lightcurve shows significant
variability and a puzzling behavior
not
predicted
by
previously
available models (Aharonian et al. 2005).
35
Detection of new VHE sources?
• Three TeV sources (all HMXBs)
discovered up to now:
LS 5039
O+BH?
LS I +61 303
Be+NS?
PSR B1259-63 Be+NS
Since these sources are located in the Galactic plane, a sensitivity better by
a factor X with respect to current instruments means detecting ~3X sources.
• Binaries with short orbital periods, difficult for Be but likely for O donors,
should be ‘on’ all the time, although strong variability due to absorption is an
issue. Detectable in deep enough surveys.
• Binaries with long orbital periods and high eccentricities should display an
‘on/off’ behavior, more with higher values. Detectable in long monitorings.
36
but what about gamma-rays from
Colliding winds of massive stars ?
Binary pulsars ?
IC spectra of WR 147
Gamma-ray emission should be expected
either through:
Leptonic processes (IC)
(Chen & White 1991, ApJ 366, 512)
Relativistic bremsstrahlung
(Pollock 1987, A&A 171, 135)
Hadronic interactions of co-accelerated ions
with the dense wind material
A. Reimer et al. 2006, A&SS (astro-ph/0611647)
(White & Chen 1992, ApJ 387, 81)
37
Unidentified TeV source: TeV J2032
• SIGNIFICANCE + 6.1 by
HEGRA
• STEADY in flux over 4
years of data taking
• EXTENDED with radius ~
(6.2  1.2  0.9) arcmin
• HARD SPECTRUM with
index -1.9  0.1stat  0.3sys
• INTEGRAL FLUX > 1 TeV
at the level of ~ 5% Crab
Aharonian et al. 2002, A&A 293, L37
38
VLA, 20 cm
Paredes et al. 2006, ApJ Letters, in press
39
GMRT, 45cm
At 10 kpc, these objects would present luminosities likely requiring the
presence of a compact object, and thus pointing to an X-ray binary nature.
(for a model of microquasars -X-ray binaries with jets- powering
extended TeV hadronic emission, see Bosch-Ramon et al. (2005)).
40
Summary
 Microquasars are among the most interesting sources in the galaxy from the
viewpoint of high-energy astrophysics.
 Models predict that radio jets could be natural sites for the production of high energy
photons via both Compton scattering and maybe direct synchrotron emission.
 Leptonic and hadronic processes could be behind TeV emission.
 Up to now, above ~ 500 keV, a handful of µqs have been detected:
Cygnus X-1 at  1 MeV, GRO J1655-40 at ~1 MeV,
GRS 1915+105 and Cygnus X-3 at TeV?
LS 5039 and LSI+61303: 100 MeV - few TeV
 More microquasars will be detected soon with the Cherenkov telescopes and
GLAST. This will bring more constraints to the physics of these systems.
 Multiwavelength (multi-particle) campaigns are of primary importance.
41