on the location and properties of the gev and tev emitters...

On the location and properties ofthe GeV and TeV emitters of LS 5039

Vıctor Zabalza

Max-Planck Institut fur Kernphysik, Heidelberg

April 17, 2013

Workshop on Variable Galactic Gamma-Ray Sources

Vıctor Zabalza (MPIK) The GeV and TeV components of LS 5039 1 / 18

LS 5039

−3 −2 −1 0 1 2×1012

×1012

to observer

Superior conjunction

Inferior conjunction

Multi-wavelength view: TeV

Orbital Phase0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

(Aharonian et al. 2005)

Multi-wavelength view: TeV

E (eV)

1110 121013

10 1410

-1110INFC

0.9≤ φ0.45 <

> 0.9φ 0.45 and ≤ φ

(Aharonian et al. 2005)

Multi-wavelength view: GeV

2.5 year Fermi-LAT results:

Energy [MeV]

310 410

610 710

Fermi, 30 months

H.E.S.S., SUPC, 2004/05

H.E.S.S., INFC, 2004/05

(Hadasch et al. 2011)

Multi-wavelength view: GeV

2.5 year Fermi-LAT results:

Energy [MeV]

310 410

610 710

Fermi, INFC

Fermi, SUPC

H.E.S.S., SUPC, 2004/05

H.E.S.S., INFC, 2004/05

(Hadasch et al. 2011)

Is a single GeV/TeV emitter possible?

The GeV and TeV components are dicult to reconcile with a singleIC emitter,

Statistically signi cant exponential cuto at few GeV would requirecomplex injection spectrum.

In a binary pulsar scenario, most of the energy is injected inside theorbit, but γγ absorption precludes a deep TeV emitter.

and a synchroton/IC scenario would require an extremely highmagnetic eld (∼ 100 G).

Under synchrotron dominant losses, particle spectrum would evolvetowards a particle index of −3, resulting in too soft GeV and TeV spectra.

Requirements for TeV emitter

An injected particle spectrum with: High energy cuto at Ee ∼ 10 TeV→ extremely high accelerationeciency.

Dominant IC losses up to Ee ∼ 10 TeV to avoid KN TeV spectrumsoftening→ low B

A location distant from the star is needed to avoid τγγ ≫ 1. Flux at Eγ > 100 GeV likely modulated by γγ absorption: SUPC ↓, INFC ↑

Requirements for TeV emitter (II)

1012 1013

Distance to star [1013 cm]

10−3

10−2

10−1

eld[G]

ηacc = 20

ηacc =

acc =10

ηacc =

acc =50

ηacc =

100 0.01

Requirements for GeV emitter

High eciency in converting pulsar wind power into non-thermalluminosity.

Ecient pulsar wind con nement and particle acceleration, Ecient non-thermal emission mechanism (IC in dense radiation eld).

An injected particle spectrum with: High energy cuto at Ee ∼ 10 GeV→ low acceleration eciency Low energy cuto at Ee ∼ (10 − 100)MeV

A location close to the compact object provides good temporalbehaviour:

High emission during superior conjunction Low emission during inferior conjunction

Candidate locations in a binary pulsar

Typical view of pulsar binary:

ked pu

lsar wind

pulsar wind

stellar wind

star pulsar

0.5 1.0 1.5 2.0 2.

Sketch from Szostek & Dubus (2011)

However, considering orbital motion yields a dierent picture:

Shocked pu

lsar wind

Shocked stellar wind

Orbitalmotion

Pulsar

However, considering orbital motion yields a dierent picture:

Shocked pu

lsar wind

Windstando

Coriolisturnover

Orbitalmotion

Pulsar

Location of the emitters

TeV emitter at Coriolis turnoverIts distance from the pulsar x0 can be approximated from the balance ofpulsar wind ram pressure,

x0 ≈ (Lsdvw

(2Ω)2cMw)

1/2∝ R2orb

GeV emitter at wind standoLocated at the balance location between the pulsar and stellar winds:

Rs =Rorb

1 +√η, where η =

Lsd/cMwvw

The postshock ow will have relativistic bulk velocity in the radialdirection away from the star. (Bogovalov et al. 2009)

x0 ≈ (Lsdvw

(2Ω)2cMw)

1/2∝ R2orb

Rs =Rorb

Lsd/cMwvw

x0 ≈ (Lsdvw

(2Ω)2cMw)

1/2∝ R2orb

Rs =Rorb

Lsd/cMwvw

Proposed emitter locations

Pulsar orbit

Wind stando

Coriolis turnover

−6 −4 −2 0 2 4×1012

4×1012

to observer

A simple model to test the candidate locations

We consider a One Zone model at each of the proposed emitterlocations aligned with the star-pulsar axis as the pulsar orbits aroundthe star.

We consider the stationary electron spectrum owing to IC,synchrotron and escape losses, and compute synchrotron and ICspectra.

The injected luminosity required is of 7% and 4% of the pulsarspin-down luminosity for the stando and coriolis turnover locations,respectively.

Results: SED

108 109 1010 1011 1012 1013 1014

E [eV]

10−13

10−12

10−11

10−10

10−9

rgcm−

INFC SumSUPC SumINFC, FermiSUPC, FermiINFC, HESSSUPC, HESS

Results: lightcurves

Orbital phase (φ)0.00.20.40.60.81.01.21.41.6

[10−

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0Orbital phase (φ)

10121416

F 0.2−

0−12

1 ] Sup

Results

Good qualitative agreement with GeV/TeV spectra and lightcurves!

Doppler boosting at wind stando emitter is required to avoidsymmetrical lightcurve peak and much larger variability fraction. Agood t is obtained with vf ≈ 0.2c→ good test for the presence ofboosting!

However, X-ray emission is not well reproduced from neither emitter: A stronger magnetic eld than B ≈ 0.3 G at the Coriolis turnover wouldresult in too soft TeV spectra.

The lower electrons energies at wind stando position require unlikelyhigh magnetic elds to radiate at keV.

Results

Good qualitative agreement with GeV/TeV spectra and lightcurves! Doppler boosting at wind stando emitter is required to avoidsymmetrical lightcurve peak and much larger variability fraction. Agood t is obtained with vf ≈ 0.2c→ good test for the presence ofboosting!

Results

Good qualitative agreement with GeV/TeV spectra and lightcurves! Doppler boosting at wind stando emitter is required to avoidsymmetrical lightcurve peak and much larger variability fraction. Agood t is obtained with vf ≈ 0.2c→ good test for the presence ofboosting!

Conclusions

The binary pulsar scenario can provide a natural explanation for theorigin of the GeV and TeV components in LS 5039: the wind standoand Coriolis turnover locations.

Samemodel could be used in binaries with known stellar windproperties (i.e., 1FGL J1018.6−5956).

Turbulence could be included by using hydrodynamical simulationsas input for location and energetics of shocks.

Conclusions

Reference

V. Zabalza, V. Bosch-Ramon, F. Aharonian, and D. Khangulyan A&A 551, A17

Shocked pu

lsar wind

Windstando

Coriolisturnover

Orbitalmotion

Pulsar

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