[ITAL]Hubble Space Telescope[/ITAL] and [ITAL]Chandra[/ITAL] Monitoring of the Crab Synchrotron Nebula

Hester, J. J.; Mori, Koji; Burrows, D. N.; Gallagher, J.; Graham, James R.; Halverson, M.; Kader, A.; Michel, F. C.; Scowen, Paul A.

doi:10.1086/344132

Cited by 247 publications

(356 citation statements)

References 4 publications

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“…However, it was not until the Hubble Space Telescope (HST; Hester et al 1995) and Chandra (Weisskopf et al 2000) era when the intricate and complex structure of the nebula was revealed (see Figure 1 for the feature nomenclature introduced by Hester et al 1995). These observations have also shown that the bright inner part of the nebula is very dynamic, with apparent velocities corresponding to up to 0.5c (in projection onto the sky) as measured, e.g., from the shifts in wisp positions (Hester et al 2002). The changes in the nebula are more complex than simple translational motion (e.g.…”

Section: Multiwavelength Properties Of the Crabmentioning

confidence: 85%

“…steady expansion). They include variations in brightness (e.g., Inner Knot; Melatos et al 2005) and shape (e.g., Sprite; Bietenholz et al 2004;Hester et al 2002). The wisp shapes can also be very different and while most of the wisps can be described as a ripple pattern with ripples moving away from the pulsar some of the wisps appear at the same location (e.g., Thin Wisp in Figure 1).…”

Section: Multiwavelength Properties Of the Crabmentioning

confidence: 99%

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Pulsar-Wind Nebulae

et al. 2015

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Section: Multiwavelength Properties Of the Crabmentioning

confidence: 85%

Section: Multiwavelength Properties Of the Crabmentioning

confidence: 99%

Pulsar-Wind Nebulae

et al. 2015

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“…Another possibility to explain the flare brightness is that the emission is highly anisotropic, as would be expected if the emission region moves relativistically toward us. While only mildly relativistic motion with velocities of ≈0.5c is observed inside the nebula (Scargle 1969;Hester et al 2002;Melatos et al 2005), relativistic motion is expected in the pulsar wind and in the downstream medium behind the wind termination (Camus et al 2009). Relativistic bulk motion is particularly expected at the "arch shock" of the wind termination, which has been proposed as the main site of gamma-ray emission (Komissarov & Lyutikov 2011).…”

Section: Discussionmentioning

confidence: 97%

Gamma-Ray Activity in the Crab Nebula: The Exceptional Flare of 2011 April

Buehler

Scargle

Blandford

et al. 2012

ApJ

198

256

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The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in the Crab Nebula lasting for approximately nine days in April of 2011. The source, which at optical wavelengths has a size of ≈11 lt-yr across, doubled its gamma-ray flux within eight hours. The peak photon flux was (186 ± 6) × 10 −7 cm −2 s −1 above 100 MeV, which corresponds to a 30-fold increase compared to the average value. During the flare, a new component emerged in the spectral energy distribution, which peaked at an energy of (375 ± 26) MeV at flare maximum. The observations imply that the emission region was likely relativistically beamed toward us and that variations in its motion are responsible for the observed spectral variability.

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“…For the Crab, we use some of the parameters from the model of Kennel & Coroniti (1984b), assuming that the velocity at the termination shock is c/3, the velocity V adv ∝ r −2 between the termination shock radius R s and a critical radius R c , and V adv remains constant between the critical radius R c and the outer radius of the nebula R out . We assume R s = 15 arcsec in angular size (Hester et al 2002), and in order to set V adv (R out ) = 2000 km s −1 (Kennel & Coroniti 1984a) we further assume R c = 50 1/2 R s . We consider adiabatic expansion energy losses in addition to synchrotron radiation losses for R c < R < R out ; it is dE/dt = −2V adv (R out )E/3r for relativistic particles in a medium with constant flow velocity.…”

Section: Diffusion and Advection Modelmentioning

confidence: 99%

Particle Transport in Young Pulsar Wind Nebulae

Tang

Chevalier

2012

ApJ

103

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The model for pulsar wind nebulae (PWNe) as a result of the magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar wind has been successful in reproducing many features of the nebulae observed close to central pulsars. However, observations of well-studied young nebulae like the Crab Nebula, 3C 58, and G21.5-0.9 do not show the toroidal magnetic field on a larger scale that might be expected in the MHD flow model; in addition, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that pure diffusion models can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Most of our models use an energy-independent diffusion coefficient; power-law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state, transmitting boundary case. Energy-dependent diffusion is a possible reason for the smaller diffusion coefficient inferred for the Crab. Monte Carlo simulations of the particle transport allowing for advection and diffusion of particles suggest that diffusion dominates over much of the total nebular volume of the Crab. Advection dominates close to the pulsar and is likely to play a role in the X-ray half-light radius. The source of diffusion and mixing of particles is uncertain, but may be related to the Rayleigh-Taylor instability at the outer boundary of a young PWN or to instabilities in the toroidal magnetic field structure.

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[ITAL]Hubble Space Telescope[/ITAL] and [ITAL]Chandra[/ITAL] Monitoring of the Crab Synchrotron Nebula

Cited by 247 publications

References 4 publications

Pulsar-Wind Nebulae

Pulsar-Wind Nebulae

Gamma-Ray Activity in the Crab Nebula: The Exceptional Flare of 2011 April

Particle Transport in Young Pulsar Wind Nebulae

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