On the location and properties of the GeV and TeV emitters of LS 5039 Víctor Zabalza Max-Planck Institut für Kernphysik, Heidelberg April 17, 2013 Workshop on Variable Galactic Gamma-Ray Sources Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 1 / 18
LS 5039 2 12 1 Superior conjunction 0 1 Inferior conjunction 2 to observer 3 3 2 1 0 1 2 12 Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 2 / 18
Multi-wavelength view: TeV s -1 ] -2 ph cm 5 4 Superior Conjunction Apastron Inferior Conjunction Periastron Superior Conjunction -12 Apastron Inferior Conjunction F > 1 TeV [ 3 2 1 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Orbital Phase (Aharonian et al. 2005) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 3 / 18
Multi-wavelength view: TeV s -1 ) -2 E 2 F(E) (erg cm -11 INFC 0.45 < φ 0.9-12 SUPC φ 0.45 and φ > 0.9-13 11 12 13 E (ev) 14 (Aharonian et al. 2005) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 3 / 18
] 2 Multi-wavelength view: GeV 2.5 year Fermi-LAT results: s 1 2 F(E) [ erg cm E 11 Fermi, 30 months H.E.S.S., SUPC, 2004/05 H.E.S.S., INFC, 2004/05 12 13 3 4 5 6 7 Energy [MeV] (Hadasch et al. 2011) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 4 / 18
Multi-wavelength view: GeV ] 2 2.5 year Fermi-LAT results: s 1 2 F(E) [ erg cm E 11 Fermi, INFC Fermi, SUPC H.E.S.S., SUPC, 2004/05 H.E.S.S., INFC, 2004/05 12 13 3 4 5 6 7 Energy [MeV] (Hadasch et al. 2011) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 4 / 18
Is a single GeV/TeV emitter possible? The GeV and TeV components are difficult to reconcile with a single IC emitter, Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 5 / 18
Is a single GeV/TeV emitter possible? The GeV and TeV components are difficult to reconcile with a single IC emitter, Statistically significant exponential cutoff at few GeV would require complex injection spectrum. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 5 / 18
Is a single GeV/TeV emitter possible? The GeV and TeV components are difficult to reconcile with a single IC emitter, Statistically significant exponential cutoff at few GeV would require complex injection spectrum. In a binary pulsar scenario, most of the energy is injected inside the orbit, but γγ absorption precludes a deep TeV emitter. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 5 / 18
Is a single GeV/TeV emitter possible? The GeV and TeV components are difficult to reconcile with a single IC emitter, Statistically significant exponential cutoff at few GeV would require complex injection spectrum. In a binary pulsar scenario, most of the energy is injected inside the orbit, but γγ absorption precludes a deep TeV emitter. and a synchroton/ic scenario would require an extremely high magnetic field ( 0 G). Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 5 / 18
Is a single GeV/TeV emitter possible? The GeV and TeV components are difficult to reconcile with a single IC emitter, Statistically significant exponential cutoff at few GeV would require complex injection spectrum. In a binary pulsar scenario, most of the energy is injected inside the orbit, but γγ absorption precludes a deep TeV emitter. and a synchroton/ic scenario would require an extremely high magnetic field ( 0 G). Under synchrotron dominant losses, particle spectrum would evolve towards a particle index of 3, resulting in too soft GeV and TeV spectra. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 5 / 18
Requirements for TeV emitter An injected particle spectrum with: High energy cutoff at Ee TeV extremely high acceleration efficiency. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 6 / 18
Requirements for TeV emitter An injected particle spectrum with: High energy cutoff at Ee TeV extremely high acceleration efficiency. Dominant IC losses up to Ee TeV to avoid KN TeV spectrum softening low B Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 6 / 18
Requirements for TeV emitter An injected particle spectrum with: High energy cutoff at Ee TeV extremely high acceleration efficiency. Dominant IC losses up to Ee TeV to avoid KN TeV spectrum softening low B A location distant from the star is needed to avoid τ γγ 1. Flux at E γ > 0 GeV likely modulated by γγ absorption: SUPC, INFC Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 6 / 18
Requirements for TeV emitter (II) 0 0 Magnetic field [G] 1 2 η acc = 20 1 0.1 min(ebreak,emax) [TeV] 3 ηacc = 5 ηacc = ηacc = 20 12 13 Distance to star [ 13 cm] ηacc = 50 ηacc = 0 0.01 Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 7 / 18
Requirements for GeV emitter High efficiency in converting pulsar wind power into non-thermal luminosity. Efficient pulsar wind confinement and particle acceleration, Efficient non-thermal emission mechanism (IC in dense radiation field). Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 8 / 18
Requirements for GeV emitter High efficiency in converting pulsar wind power into non-thermal luminosity. Efficient pulsar wind confinement and particle acceleration, Efficient non-thermal emission mechanism (IC in dense radiation field). An injected particle spectrum with: High energy cutoff at Ee GeV low acceleration efficiency Low energy cutoff at Ee ( 0) MeV Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 8 / 18
Requirements for GeV emitter High efficiency in converting pulsar wind power into non-thermal luminosity. Efficient pulsar wind confinement and particle acceleration, Efficient non-thermal emission mechanism (IC in dense radiation field). An injected particle spectrum with: High energy cutoff at Ee GeV low acceleration efficiency Low energy cutoff at Ee ( 0) MeV A location close to the compact object provides good temporal behaviour: High emission during superior conjunction Low emission during inferior conjunction Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 8 / 18
Candidate locations in a binary pulsar Typical view of pulsar binary: stellar wind shocked stellar wind shocked pulsar wind pulsar wind star pulsar 0.5 1.0 1.5 2.0 2. Sketch from Szostek & Dubus (2011) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 9 / 18
Candidate locations in a binary pulsar However, considering orbital motion yields a different picture: Orbital motion Pulsar Shocked pulsar wind Shocked stellar wind Star Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 / 18
Candidate locations in a binary pulsar However, considering orbital motion yields a different picture: Coriolis turnover Orbital motion Wind standoff Pulsar Shocked pulsar wind Shocked stellar wind Star Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 / 18
Location of the emitters TeV emitter at Coriolis turnover Its distance from the pulsar x 0 can be approximated from the balance of pulsar wind ram pressure, L sd v w x 0 ( ) (2Ω) 2 cṁ w 1/2 R 2 orb Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 11 / 18
Location of the emitters TeV emitter at Coriolis turnover Its distance from the pulsar x 0 can be approximated from the balance of pulsar wind ram pressure, L sd v w x 0 ( ) (2Ω) 2 cṁ w GeV emitter at wind standoff 1/2 R 2 orb Located at the balance location between the pulsar and stellar winds: R s = R orb 1 + η, where η = L sd/c. Ṁ w v w Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 11 / 18
Location of the emitters TeV emitter at Coriolis turnover Its distance from the pulsar x 0 can be approximated from the balance of pulsar wind ram pressure, L sd v w x 0 ( ) (2Ω) 2 cṁ w GeV emitter at wind standoff 1/2 R 2 orb Located at the balance location between the pulsar and stellar winds: R s = R orb 1 + η, where η = L sd/c. Ṁ w v w The postshock flow will have relativistic bulk velocity in the radial direction away from the star. (Bogovalov et al. 2009) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 11 / 18
12 4 Proposed emitter locations 2 Pulsar orbit Wind standoff Coriolis turnover 0 2 4 6 to observer 6 4 2 0 2 4 12 Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 12 / 18
A simple model to test the candidate locations We consider a One Zone model at each of the proposed emitter locations aligned with the star-pulsar axis as the pulsar orbits around the star. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 13 / 18
A simple model to test the candidate locations We consider a One Zone model at each of the proposed emitter locations aligned with the star-pulsar axis as the pulsar orbits around the star. We consider the stationary electron spectrum owing to IC, synchrotron and escape losses, and compute synchrotron and IC spectra. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 13 / 18
A simple model to test the candidate locations We consider a One Zone model at each of the proposed emitter locations aligned with the star-pulsar axis as the pulsar orbits around the star. We consider the stationary electron spectrum owing to IC, synchrotron and escape losses, and compute synchrotron and IC spectra. The injected luminosity required is of 7% and 4% of the pulsar spin-down luminosity for the standoff and coriolis turnover locations, respectively. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 13 / 18
Results: SED E 2 dn/de [erg cm 2 s 1 ] 9 11 12 INFC Sum SUPC Sum INFC, Fermi SUPC, Fermi INFC, HESS SUPC, HESS 13 8 9 11 12 13 14 E [ev] Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 14 / 18
Results: lightcurves FE>0 MeV [ 6 ph cm 2 s 1 ] F0.2 5 TeV [ 12 erg cm 2 s 1 ] 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 Apastron Inferior conjunction Periastron Superior conjunction 0.0 16 Orbital phase (φ) 14 12 8 6 4 2 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Orbital phase (φ) Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 15 / 18
Results Good qualitative agreement with GeV/TeV spectra and lightcurves! Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 16 / 18
Results Good qualitative agreement with GeV/TeV spectra and lightcurves! Doppler boosting at wind standoff emitter is required to avoid symmetrical lightcurve peak and much larger variability fraction. A good fit is obtained with v f 0.2c good test for the presence of boosting! Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 16 / 18
Results Good qualitative agreement with GeV/TeV spectra and lightcurves! Doppler boosting at wind standoff emitter is required to avoid symmetrical lightcurve peak and much larger variability fraction. A good fit is obtained with v f 0.2c good test for the presence of boosting! However, X-ray emission is not well reproduced from neither emitter: A stronger magnetic field than B 0.3 G at the Coriolis turnover would result in too soft TeV spectra. The lower electrons energies at wind standoff position require unlikely high magnetic fields to radiate at kev. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 16 / 18
Conclusions The binary pulsar scenario can provide a natural explanation for the origin of the GeV and TeV components in LS 5039: the wind standoff and Coriolis turnover locations. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 17 / 18
Conclusions The binary pulsar scenario can provide a natural explanation for the origin of the GeV and TeV components in LS 5039: the wind standoff and Coriolis turnover locations. Same model could be used in binaries with known stellar wind properties (i.e., 1FGL J18.6 5956). Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 17 / 18
Conclusions The binary pulsar scenario can provide a natural explanation for the origin of the GeV and TeV components in LS 5039: the wind standoff and Coriolis turnover locations. Same model could be used in binaries with known stellar wind properties (i.e., 1FGL J18.6 5956). Turbulence could be included by using hydrodynamical simulations as input for location and energetics of shocks. Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 17 / 18
Reference V. Zabalza, V. Bosch-Ramon, F. Aharonian, and D. Khangulyan A&A 551, A17 Coriolis turnover Orbital motion Wind standoff Pulsar Shocked pulsar wind Shocked stellar wind Star Víctor Zabalza (MPIK) The GeV and TeV components of LS 5039 18 / 18