Probing pulsar winds using inverse Compton scattering

Ball, Lewis; Kirk, J. G.

doi:10.1016/s0927-6505(99)00112-7

Cited by 65 publications

(95 citation statements)

References 25 publications

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“…However, the situation is ambiguous and such a scenario cannot be proven yet as the combined spectral and lightcurve data allow for different model explanations (Neronov & Chernyakova 2007). The generation of TeV γ-rays within an Inverse Compton (IC) scenario is another explanation for the data (Kirk et al 1999;Ball & Kirk 2000;Dubus 2006a;Khangulyan et al 2007;Sierpowska-Bartosik & Bednarek 2008). In such models PW electrons moving with highly relativistic energies upscatter soft UV photons stemming from the stellar radiation field into the VHE regime.…”

Section: Introductionmentioning

confidence: 99%

Very high energy γ-ray observations of the binary PSR B1259–63/SS2883 around the 2007 Periastron

Aharonian

Akhperjanian

Anton

et al. 2009

A&A

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Aims. This article presents very-high-energy (VHE; E > 100 GeV) data from the γ-ray binary PSR B1259−63 as taken during the years 2005, 2006 and before as well as shortly after the 2007 periastron passage. These data extend the knowledge of the lightcurve of this object to all phases of the 3.4 year binary orbit. The lightcurve constrains physical mechanisms present in this TeV source. Methods. Observations of VHE γ-rays with the HESS telescope array using the Imaging Atmospheric Cherenkov Technique were performed. The HESS instrument features an angular resolution of <0.1• and an energy resolution of <20%. Gamma-ray events in an energy range of 0.5−70 TeV were recorded. From these data, energy spectra and lightcurve with a monthly time sampling were extracted. Results. VHE γ-ray emission from PSR B1259−63 was detected with an overall significance of 9.5 standard deviations using 55 h of exposure, obtained from April to August 2007. The monthly flux of γ-rays during the observation period was measured, yielding VHE lightcurve data for the early pre-periastron phase of the system for the first time. No spectral variability was found on timescales of months. The spectrum is described by a power law with a photon index of Γ = 2.8 ± 0.2 stat ± 0.2 sys and flux normalisation Φ 0 = (1.1 ± 0.1 stat ± 0.2 sys ) × 10 −12 TeV −1 cm −2 s −1 . PSR B1259−63 was also monitored in 2005 and 2006, far from periastron passage, comprising 8.9 h and 7.5 h of exposure, respectively. No significant excess of γ-rays is seen in those observations. Conclusions. PSR B1259−63 has been re-confirmed as a variable TeV γ-ray emitter. The firm detection of VHE photons emitted at a true anomaly θ ≈ −0.35 of the pulsar orbit, i.e. already ∼50 days prior to the periastron passage, disfavors the stellar disc target scenario as a primary emission mechanism, based on current knowledge about the companion star's disc inclination, extension, and density profile.

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Section: Introductionmentioning

confidence: 99%

Very high energy γ-ray observations of the binary PSR B1259–63/SS2883 around the 2007 Periastron

Aharonian

Akhperjanian

Anton

et al. 2009

A&A

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“…Hence, a phase-dependent VHE spectrum will be observed even if the distribution of particles is isotropic and remains constant throughout. This effect has previously been investigated for the Crab pulsar by Bogovalov & Aharonian (2000), and in PSR B1259-63 by Ball & Kirk (2000). Ball & Kirk calculated the radiative drag on the unshocked pulsar wind from scattering of stellar light, using results from Ho & Epstein (1989).…”

Section: Introductionmentioning

confidence: 99%

The modulation of the gamma-ray emission from the binary LS 5039

Dubus

Cerutti

Henri

2007

A&A

102

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Context. Gamma-ray binaries have been established as a new class of sources of very high energy (VHE, >100 GeV) photons. These binaries are composed of a massive star and a compact object. The gamma rays are probably produced by inverse Compton scattering of the stellar light by VHE electrons accelerated in the vicinity of the compact object. The VHE emission from LS 5039 displays an orbital modulation. Aims. The inverse Compton spectrum depends on the angle between the incoming and outgoing photons in the rest frame of the electron. Since the angle at which an observer sees the star and electrons changes with the orbit, a phase dependence of the spectrum is expected. Methods. A procedure for computing anisotropic inverse Compton emission is explained and applied to the case of LS 5039. The spectrum is calculated assuming the continuous injection of electrons close to the compact object: the shape of the steady-state distribution depends on the injected power law and on the magnetic-field's intensity. Results. Compared to the isotropic approximation, anisotropic scattering produces harder and fainter emission at inferior conjunction, crucially at a time when the attenuation due to pair production of the VHE gamma-rays on star light is minimum. The computed light curve and spectra are very good fits to the HESS and EGRET observations, except at phases of maximum attenuation where pair cascade emission may be significant for HESS. Detailed predictions are made for a modulation in the GLAST energy range. The magnetic field intensity at periastron is 0.8 ± 0.2 G. Conclusions. The anisotropy in inverse Compton scattering plays a major role in LS 5039. A simple model reproduces the observations, constraining the magnetic field intensity and injection spectrum. The comparison with observations, the derived magnetic field intensity, injection energy, and slope together suggest emission from a rotation-powered pulsar wind nebula. These results confirm gamma-ray binaries as promising sources for studying the environment of pulsars on small scales.

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“…The intense photon field provided by the companion star not only plays an important role in the cooling of relativistic electrons but also serves as a perfect target for the production of high energy γ-rays through inverse Compton (IC) scattering Kirk et al 1999;Ball & Kirk 2000;Ball & Dodd 2001;Murata et al 2004). Some of these emission models predict wind-powered shock acceleration of electrons to multi-TeV energies, radiating predominantly through the synchrotron and IC channels, with the main energy release in the X-and high energy γ-ray bands, respectively.…”

Section: Introductionmentioning

confidence: 99%

Discovery of the binary pulsar PSR B1259-63 in very-high-energy gamma rays around periastron with HESS

Aharonian

Akhperjanian

Aye

et al. 2005

A&A

322

195

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We report the discovery of very-high-energy (VHE) γ-ray emission of the binary system PSR B1259−63/SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the HESS experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a γ-ray signal from the binary system was detected with a total significance above 13σ. The flux was found to vary significantly on timescales of days which makes PSR B1259−63 the first variable galactic source of VHE γ-rays observed so far. Strong emission signals were observed in pre-and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law F 0 (E/1 TeV) −Γ with a photon index Γ = 2.7 ± 0.2 stat ± 0.2 sys and flux normalisation F 0 = (1.3 ± 0.1 stat ± 0.3 sys ) × 10 −12 TeV −1 cm −2 s −1 . This detection of VHE γ-rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE γ-ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.

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Probing pulsar winds using inverse Compton scattering

Cited by 65 publications

References 25 publications

Very high energy γ-ray observations of the binary PSR B1259–63/SS2883 around the 2007 Periastron

Very high energy γ-ray observations of the binary PSR B1259–63/SS2883 around the 2007 Periastron

The modulation of the gamma-ray emission from the binary LS 5039

Discovery of the binary pulsar PSR B1259-63 in very-high-energy gamma rays around periastron with HESS

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