Elsa Giacani

A VLA Study of the Expansion of Tycho's Supernova Remnant

We have measured the expansion of Tychos supernova remnant (SNR) over a 10 yr interval by comparing new VLA observations at 1375 MHz made in 1994 and 1995 with previous observations made in 1983 and 1984 using the same array configurations, bandwidths, calibrators, and integration times. To compute the expansion of the outer rim, we estimate the expansion rate for radial sectors of 4°. The overall mean expansion obtained is 305 but varies between 1 and 5 around the shell. The weighted average fractional expansion rate is 0.1126% yr-1, corresponding to a power-law index (expansion parameter) ν ≡ d ln R/d ln t = 0.471, with an error of ~6%. We also compute the expansion of interior features, and find a comparable global expansion parameter. The value of ν obtained is in excess of the pure Sedov value of 0.4, indicating that Tychos SNR is still in transition from an earlier phase to the Sedov adiabatic phase of evolution, and supporting expansion into a medium without a strong radial density gradient, as expected for a Type Ia supernova. In addition, the significant local variations that we observe suggest that a unique average expansion rate is an oversimplified description for Tycho. Both radio flux and polarization were found to remain almost constant during the intervening 10 years.

Geometry of the non-thermal emission in SN 1006 - Azimuthal variations of cosmic-ray acceleration

SN 1006 is the prototype of shell supernova remnants, in which non-thermal synchrotron emission dominates the X-ray spectrum. The non-thermal emission is due to the cosmic-ray electrons accelerated behind the blast wave. The X-ray synchrotron emission is due to the highest energy electrons, and is thus a tracer of the maximum energy electrons may reach behind a shock. We have put together all XMM-Newton observations to build a full map of SN 1006. The very low brightness above 2 keV in the interior indicates that the bright non-thermal limbs are polar caps rather than an equator. This implies that the ambient magnetic field runs southwest to northeast, along the Galactic plane. We used a combined VLA/Parkes radio map to anchor the spectrum at low energy, and model the spectra with synchrotron emission from a cut-off power-law electron distribution, plus a thermal component. We present radial and azimuthal profiles of the cut-off frequency. The cut-off frequency decreases steeply with radius towards the center and with position angle away from the maximum emission. The maximum energy reached by accelerated particles, as well as their number, must be higher at the bright limbs than elsewhere. This implies interesting constraints for acceleration at perpendicular shocks. Overall the XMM-Newton data is consistent with the model in which the magnetic field is amplified where acceleration is efficient.

The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44

We present radio observations of a region in the vicinity of the young pulsar PSR B1853+01 in the supernova remnant W44. The pulsar is located at the apex of an extended feature with cometary morphology. We argue on the basis of its morphology and its spectral index and polarization properties that this is a synchrotron nebula produced by the spin-down energy of the pulsar. The geometry and physical parameters of this pulsar-powered nebula and W44 are used to derive three different measures of the pulsars transverse velocity. A range of estimates between 315 and 470 km s-1 is derived, which results in a typical value of 375 km s-1. The observed synchrotron spectrum from radio to X-ray wavelengths is used to put constraints on the energetics of the nebula and to derive the parameters of the pulsar wind.

A joint spectro-imaging analysis of the XMM-Newton and HESS observations of the supernova remnant RX J1713.7-3946

Context. The supernova remnant (SNR) RX J1713.7-3946u2000(also known as G347.3-0.5) is part of the class of remnants dominated by synchrotron emission in X-rays. It is also one of the few shell-type SNRs observed at TeV energies allowing us to investigate particle acceleration at SNRs shock. Aims. Our goal is to compare spatial and spectral properties of the remnant in X- and γ -rays to understand the nature of its TeVxa0emission. This requires the study of the remnant on the same spatial scale at both energies. To complement the non-thermal spectrum of the remnant, we attempt to provide a reliable estimate of the radio flux density. Methods. In radio, we revisited ATCA data and usedxa0HI and mid-infrared observations to differentiate between the thermal and the non-thermal emission. In X-rays, we produced a new mosaic of the remnant and degraded the spatial resolution of the X-ray data to the resolution of the HESS instrument to perform spatially resolved spectroscopy at the same spatial scale inxa0X- and γ -rays. Radial profiles were obtained to investigate the extension of the emission at both energies. Results. We found that part of the radio emission within the SNR contours is thermal in nature. Taking this into account, we provide new lower and upper limits to the integrated synchrotron flux of the remnant at 1.4xa0GHz, of 22xa0Jy and 26xa0Jy, respectively. In X-rays, we obtained the first full coverage of RX J1713.7-3946u2000withxa0 XMM-Newton . The spatial variation in the photon index seen on small scale in X-rays is smeared out at HESS resolution. A non-linear correlation between the X- and γ -ray fluxes of the type

New Radio and Optical Study of the Supernova Remnant W44

F_{mathrm{X}} propto F_{mathrm{gamma}}^{2.41}

The Interstellar Matter in the Direction of the Supernova Remnant G296.5+10.0 and the Central X-Ray Source 1E 1207.4−5209

is found. If the flux variation is mainly caused by density variation around the remnant then a leptonic model can more easily reproduce the observed X/ γ -ray correlation. In some angular sectors, radial profiles indicate that the bulk of the X-ray emission comes more from the inside of the remnant than in γ -rays.

The neutral gas environment of the young supernova remnant SN 1006 (G327.6+14.6)

Abstract : We present new optical images of the supernova remnant (SNR) W44 in the H-alpha and [S II] lines covering the entire source for the first time. We also report on improved radio image of W44 at 1442.5 MHz, obtained after the reprocessing of existing VLA data. A spectral index a of -0.4 was derived for the whole source, without indication of significant spectral variations between 0.3 and 1.4 GHz across the remnant. Accurate multiwavelength comparisons were made based on existing observations of W44 in the different spectral regimes. We find excellent correlation between optical and radio emission along the northwest border of the remnant, suggesting that the optical radiation is originating through radiative cooling of the shocked gas immediately behind the shock front. Some diffuse optical emission is also observed towards the interior of W44, with no clear radio counterpart. We confirm that over most of the source, the bright X-ray emission corresponds with regions of low radio brightness. At the northern border of the remnant, diffuse X-ray emission exactly overlaps the radio and optical radiation. From the study of the immediate environs of W44 we conclude that the remnant is interacting with molecular clouds along the eastern border. Such a scenario is compatible with the filamentary structure of W44, the excitation of OH masers and the apparent lack of optical emission along the eastern border. To the north, an extended atomic cloud surrounds the remnant, although the interaction is not evident in this case.

Radio emission from supernova remnants

G296.5+10.0 is a high Galactic latitude supernova remnant (SNR), with a bilateral morphology in radio and X-rays. The compact X-ray source 1E 1207.4-5209, classified as a radio-quiet neutron star, is located very close to the remnants center. We report on a survey of the H I distribution in a region of sky, 35 × 35, around the remnant, using the Australia Telescope Compact Array with a spatial resolution of about 35 and a velocity resolution of 0.82 km s-1. The H I distribution is quite smooth, with no obvious large-scale features that can explain the SNR bilateral morphology based on external factors. There are, however, three clouds that we do associate directly with the remnant. Optical filaments outline two smaller features, which appear to have been overtaken by the shock front and are cooling radiatively. Also, a high-velocity cloud gives a lower limit of ~35 km s-1 to the expansion velocity of the shock into the H I gas and a lower limit of ~2 × 1049 ergs for the kinetic energy injected by the supernova explosion into the surrounding interstellar medium. We estimate a distance to the SNR of d = 2.1 kpc and a total mass of at least 1900 M⊙ of associated H I gas. A hole in the H I column density is observed at the same position of the compact X-ray source 1E 1207.4-5209. This H I hole is at the same radial velocity as G296.5+10.0. We argue that this result constitutes concrete evidence that 1E 1207.4-5209 and G296.5+10.0 are physically associated.

Radio and X-ray study of two multi-shell supernova remnants: Kes 79 and G352.7-0.1

Using the Australia Telescope Compact Array, we have carried out a survey of the Hu2009i emission in the direction of the bilateral supernova remnant ( SNR ) SN 1006 (G327.6+14.6). The angular resolution of the data is

Pulsar Wind Nebulae around the Southern Pulsars PSR B1643−43 and PSR B1706−44

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