Spectroscopy and Three‐Dimensional Imaging of the Crab Nebula (original) (raw)
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Spectroscopy and 3D imaging of the Crab nebula
2004
Spectroscopy of the Crab nebula along different slit directions reveals the 3 dimensional structure of the optical nebula. On the basis of the linear radial expansion result first discovered by Trimble (1968), we make a 3D model of the optical emission. Results from a limited number of slit directions suggest that optical lines originate from a complicated array of wisps that are located in a rather thin shell, pierced by a jet. The jet is certainly not prominent in optical emission lines, but the direction of the piercing is consistent with the direction of the X-ray and radio jet. The shell's effective radius is ~ 79 seconds of arc, its thickness about a third of the radius and it is moving out with an average velocity 1160 km/s.
The X-ray structure of the crab nebula
Advances in Space Research, 1985
The Crab nebula is so far the only object where the direct interaction between a young pulsar and its surroundings can be studied in all frequency ranges. It is well known that the lifetime of the synchrotron-radiating relativistic electrons in the nebula is so short that these cannot be ejected in the supernova explosion in 10~f4, they have to be replenished continuously. Generally, the shrinking size of the nebula with increasing energies is explained by the decreasing lifetime of the radiating electrons. And, as the dlmer~ions of the 'injector' , the pulsar, are negl~gibly small, the theories predicted a point source at high X-ray energies centered on the pulsar.
Some considerations upon the emission line spectrum of the Crab Nebula
Revista Brasileira de Fisica, 1978
We present a d e t a i l e d program o f t r a n s f e r o f i o n i z i n g r a d i a t i o n i n a d i l u t e d medium, i n which t h e equations o f thermal balance and i o n i z at i o n e q u i l i b r i u r n a r e solved. T h i s program a l l o w s t o b u i l d models o f var i o u s types o f o b j e c t s , l i k e n u c l e i o f g a l a x i e s , supernova remnants,
Modelling the kinked jet of the Crab nebula
Monthly Notices of the Royal Astronomical Society, 2013
We investigate the dynamical propagation of the South-East jet from the Crab pulsar interacting with supernova ejecta by means of three-dimensional relativistic MHD numerical simulations with the PLUTO code. The initial jet structure is set up from the inner regions of the Crab Nebula. We study the evolution of hot, relativistic hollow outflows initially carrying a purely azimuthal magnetic field. Our jet models are characterized by different choices of the outflow magnetization (σ parameter) and the bulk Lorentz factor (γ j ).
A search for a consistent model for the electromagnetic spectrum of the Crab nebula
Astrophysics and Space Science, 1970
An attempt is made to search for a consistent model to explain the electromagnetic spectrum of the Crab nebula (Tau A). It is assumed that there is a continuous injection of electrons at the centre of the nebula with an energy spectrum E -1.54 as evidenced by radio data. This spectrum must steepen to a slope larger than 2 at some energy E~ in order to ensure that the energy input into electrons remains finite. The spectrum must also steepen beyond an energy Ec depending on the magnetic field because of synchrotron energy losses. Two types of models are considered: Class I, in which the whole nebula is characterised by a uniform magnetic field, and Class II, in which besides the general field H0, small filamentary regions of strong field//8 are postulated.
The Astronomical Journal, 2009
We present 3. 6, 4.5, 5.8, 8.0, 24, and 70 µm images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low-and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II]1.644 µm. The 8.0 µm image, made with a bandpass that includes [Ar II]7.0 µm, resembles the general morphology of visible Hα and near-IR [Fe II] line emission, while the 3.6 and 4.5 µm images are dominated by continuum synchrotron emission. The 24 µm and 70 µm images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 µm images reveals a spatial variation in the synchrotron power law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum jet and torus with the steeper diffuse nebula, and suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and T e m i m e t a l . 2 0 0 6 A J ( i n p r e s s ) -2polar jet structures seen in Chandra and HST images can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of ≈ 1264 km s −1 .
Observations of the Crab Nebula and Its Pulsar in the Far-Ultraviolet and in the Optical
Astrophysical Journal, 2000
We present HST/STIS far-UV observations of the Crab nebula and its pulsar. Broad, blueshifted absorption arising in the nebula is seen in C IV 1550, reaching about 2500 km/s. This can be interpreted as evidence for a fast outer shell, and we adopt a spherically symmetric model to constrain the properties of this. We find that the density appears to decrease outward in the shell. A lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy of 1.5EE{49} ergs. A massive 10^{51} erg shell cannot be excluded, but is less likely if the density profile is much steeper than R^{-4} and the velocity is <6000 km/s. The observations cover the region 1140-1720 A. With the time-tag mode of the spectrograph we obtain the pulse profile. It is similar to that in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from NOT, our spectrum of the pulsar covers the entire region from 1140-9250 A. Dereddening the spectrum gives a flat spectrum for E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab pulsar can be fitted by a power law with spectral index alpha_{\nu} = 0.11 +/- 0.04. The main uncertainty is the amount and characteristics of the interstel- lar reddening, and we have investigated the dependence of \alpha_{\nu} on E(B-V) and R. In the extended emission covered by our 25" x 0.5" slit in the far-UV, we detect C IV 1550 and He II 1640 emission lines from the Crab nebula. Several interstellar absorption lines are detected toward the pulsar. The Ly alpha absorption indicates a column density of 3.0+/-0.5\EE{21} cm^{-2} of neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other lines show no evidence of severe depletion of metals in atomic gas.
The inner knot of the Crab nebula
Monthly Notices of the Royal Astronomical Society, 2015
We model the inner knot of the Crab Nebula as a synchrotron emission coming from the non-spherical MHD termination shock of relativistic pulsar wind. The post-shock flow is mildly relativistic; as a result the Doppler-beaming has a strong impact on the shock appearance. The model can reproduce the knot location, size, elongation, brightness distribution, luminosity and polarization provided the effective magnetization of the section of the pulsar wind producing the knot is low, σ ≤ 1. In the striped wind model, this implies that the striped zone is rather wide, with the magnetic inclination angle of the Crab pulsar ≥ 45 • ; this agrees with the previous model-dependent estimate based on the gamma-ray emission of the pulsar. We conclude that the tiny knot is indeed a bright spot on the surface of a quasi-stationary magnetic relativistic shock and that this shock is a site of efficient particle acceleration. On the other hand, the deduced low magnetization of the knot plasma implies that this is an unlikely site for the Crab's gamma-ray flares, if they are related to the fast relativistic magnetic reconnection events.
The Crab nebula energy origin and its high frequency radiation spectra
In the present work there is presented a model describing transfer of the Crab pulsar's spin-down energy into the powerful synchrotron emission of the nebula. The process of the energy transfer consists of several consecutive stages. The physical processes underlying the theoretical model provide us with the synchrotron emission spectrum, which fits well with the observed one.
Search for a Shock Wave around the Crab Nebula
We have searched the region surrounding the Crab Nebula for the existence of a shock wave with the imaging instruments of the Einstein Observatory. The search is complicated by the scattering of nebula and pulsar X-rays from the imperfectly polished surfaces of the telescope mirror, as well as from interstellar grains along the line of sight. Both of these effects lead to the appearance of X-ray emission, in the form of an X-ray halo, beyond the boundaries of the nebula filaments. We show that the size, shape, and intensity of the halo around the Crab Nebula, above the contribution of mirror scattering, is consistent with what is expected from the scattering from interstellar grains. The upper limit on the X-ray emission from a shock wave is about 1% of the total 0.5–4 keV luminosity of the Crab or about 2 × 10^35 erg s^−1 (assuming a distance of 2.2 kpc). This figure applies to a shell whose angular radius is 9 arcminutes. The upper limit is smaller (larger) for a shell of larger (smaller) size. This upper limit is an order of magnitude or more below the flux of Cas A, Tycho, and Kepler SNRs, which are 2 to 3 times younger, but it is still above that of SN 1006.