Multifrequency VLA observations of the Crab Nebula at different epochs: expansion and radio spectra of filaments

Velusamy, T.; Roshi, D. Anish; Venugopal, V. R.

doi:10.1093/mnras/255.2.210

Cited by 14 publications

(15 citation statements)

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“…over the brightest parts of the SNR,'' with a value of about $ À0:4 to À0.8 (in this work we use to refer to the spectral index of the SED in Jy, F / ). This result allowed him to argue that in Vela X there is no evidence for radial steepening of the spectral index with increasing distance to the pulsar, as seen in the Crab and other pulsar-powered remnants ( Velusamy et al 1992), supporting his hypothesis of a non-pulsar-powered Vela X.…”

Section: Introductionmentioning

confidence: 86%

Vela X at 31 GHz

Hales

Casassus

Álvarez

et al. 2004

ApJ

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Artículo de publicación ISIWe present observations of the Vela X region at 31 GHz using the Cosmic Background Imager ( CBI). We find a strong compact radio source (5.'9 x 4.'1, FWHM) about the Vela pulsar, which we associate with the Vela pulsar wind nebula (PWN) recently discovered at lower radio frequencies. The CBI's 4' resolution for a 45' field of view allows the PWN to be studied in the large-scale context of Vela X. Filamentary structure in Vela X, which stands out in lower frequency maps, is very low level at 31 GHz. By combining the 10 CBI channels, which cover 26 36 GHz, and 8.4 GHz archive data, we study the spectral energy distribution ( SED) of the PWN and the brightest filaments. Our results show that the spectral index alpha (F(nu) proportional to nu(alpha)) of the PWN is flat, or even marginally positive, with a value of alpha(8.4)(31) = 0.10 +/- 0.06, while the Vela X filamentary structure has a negative spectral index of alpha(8.4)(31) = - 0.28 +/- 0.09. The SED inhomogeneity observed in Vela X suggests different excitation processes between the PWN and the filaments. We investigate whether the PWN's flat spectrum is a consequence of variability or truly reflects the SED of the object. We also investigate the nature of the Vela X filamentary structure. A faint filament crosses the PWN with its tangent sharing the same position angle as the PWN major axis, suggesting that it might be an extension of the PWN itself. The SED and bulk morphology of Vela X are similar to those of other well-studied plerions, suggesting that it might be powered by the pulsar. The peak of the PWN at 31 GHz is 80" +/- 20" southwest of the peak at 8.4 GHz. This shift is confirmed by comparing the 31 GHz CBI image with higher resolution 5 GHz Australia Telescope Compact Array observations and is likely to be due to SED variations within the PWN

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Section: Introductionmentioning

confidence: 86%

Vela X at 31 GHz

Hales

Casassus

Álvarez

et al. 2004

ApJ

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“…The filled regions (for the HST and Chandra data) show 1σ uncertainty regions around the best-fit power laws indicated by thick lines. We have also included similar data for the Crab PWN, where the data are from Velusamy et al (1992), Veron-Cetty & Woltjer (1993) and Kaaret et al (2001) for the radio, optical and X-ray bands, respectively. The dotted curved line is a cubic spline fit for the multiwavelength spectrum of the Crab PWN, and the dashed-dotted line is a linear fit for the optical/X-ray region of the Crab PWN.…”

Section: Multiwavelength Spectrum Of the Pwnmentioning

confidence: 99%

The young pulsar PSR B0540-69.3 and its synchrotron nebula in the optical and X-rays

Serafimovich¹,

Shibanov²,

Lundqvist³

et al. 2004

A&A

184

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Abstract. The young PSR B0540-69.3 in the LMC is the only pulsar (except the Crab pulsar) for which a near-UV spectrum has been obtained. However, the absolute flux and spectral index of the HST/FOS spectrum are significantly higher than suggested by previous broad-band time-resolved groundbased UBVRI photometry. To investigate this difference, observations with ESO/VLT/FORS1 and analysis of HST/WFPC2 archival data were done. We show that the HST and VLT spectral data for the pulsar have > ∼ 50% nebular contamination and that this is the reason for the above-mentioned difference. The broadband HST spectrum for the range 3300-8000 Å is clearly nonthermal and has a negative spectral index, F ν ∝ ν −α with α ν = 1.0719 . This is different from the almost flat spectrum of the Crab pulsar, and also steeper than for the previously published broadband photometry of PSR B0540-69.3. We have also studied the spatial variations of the brightness and spectral index of the Pulsar Wind Nebula (PWN) around the pulsar, and find no significant spectral index variation over the PWN. The HST data show a clear asymmetry of the surface brightness distribution along the major axis of the torus-like structure of the PWN with respect to the pulsar position, also seen in Chandra/HRC X-ray images. This is different from the Crab PWN and likely linked to the asymmetry of the surrounding SN ejecta. The HST/WFPC2 archival data have an epoch separation of 4 years, and this allows us to estimate the proper motion of the pulsar. We find a motion of 4.9 ± 2.3 mas yr −1 (corresponding to a transverse velocity of 1190 ± 560 km s −1 ) along the southern jet of the PWN. If this is confirmed at a higher significance level by future observations, this makes PSR B0540-69.3 the third pulsar with a proper motion aligned with the jet axis of its PWN, which poses constraints on pulsar kick models. To establish the multiwavelength spectrum of the pulsar and its PWN, we have included recent Chandra X-ray data, and discuss the soft pulsar X-ray spectrum based on spectral fits including absorption by interstellar gas in the Milky Way, LMC as well as the supernova ejecta. We have compared the multiwavelength spectra of PSR B0540-69.3 and the Crab pulsar, and find that both PSR B0540-69.3 and the Crab pulsar have a weaker flux in the optical than suggested by a low-energy power-law extension of the X-ray spectrum. This optical depression is more severe for PSR B0540-69.3 than for the Crab pulsar. The same trend is seen for the PWNe of the two pulsars, and continues for low energies also out in the radio band. We discuss possible interpretations of this behavior.

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“…Velusamy et al (1992) suggested that the magnetic field increases in the filaments, and therefore that the energy loss of electrons within filaments are more significant than in the nebular region. Nevertheless, they themselves reported, in agreement with Swinbank (1980), that for the filaments in the inner parts of the remnant (r < 100 ), no evidence for a variation in the spectral index is shown.…”

Section: Synchrotron Spectral Indexmentioning

confidence: 99%

Dust in the Tycho, Kepler and Crab supernova remnants

Douvion

Lagage

Césarsky

et al. 2001

A&A

118

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Abstract. SuperNova Remnants (SNR) have been extensively studied in radio, X-rays and optical, but barely in the InfraRed (IR). From IRAS observations, SNR are known to be IR emitters, but the origin of the emission is difficult to assess because of the limited angular and spectral resolution of IRAS observations. ISO follow-up observations of the Cassiopeia-A SNR have shown that the mid-IR radiation from this remnant was dominated by thermal emission from silicate condensates made from SN material. These condensates constitute a probe which can provide unique information about element mixing inside a SN. In this paper, we present ISOCAM observations of the three other young SNR's known in our galaxy: the Kepler SNR, the Tycho SNR and the Crab Nebula. The emission observed from the Kepler SNR is dominated by dust thermal emission. The dust at the origin of the IR emission is circumstellar, not from SN condensates. "Astronomical" silicates, collisionally heated to a temperature of 107 K, can account for both the mid-IR ISO data and the IRAS data. The IR emission from Tycho is probably also emitted by circumstellar or interstellar dust. In order to reproduce both the mid-IR ISO data and the IRAS data, a model with two dust components, one at a temperature of 107 K and the other at 55 K, is needed. The mid-IR emission from the Crab is dominated by synchrotron radiation; no dust is detected.

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Multifrequency VLA observations of the Crab Nebula at different epochs: expansion and radio spectra of filaments

Cited by 14 publications

References 0 publications

Vela X at 31 GHz

Vela X at 31 GHz

The young pulsar PSR B0540-69.3 and its synchrotron nebula in the optical and X-rays

Dust in the Tycho, Kepler and Crab supernova remnants

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