An analysis of the FIR/RADIO Continuum Correlation in the Small Magellanic Cloud

The local correlation between far-infrared (FIR) emission and radio-continuum (RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ~15 pc. The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is shown to be greatest in the most active star forming regions with a power law slope of ~1.14 indicating that the RC emission increases faster than the FIR emission. The slope of the other regions and the SMC are much flatter and in the range of 0.63-0.85. The slopes tend to follow the thermal fractions of the regions which range from 0.5 to 0.95. The thermal fraction of the RC emission alone can provide the expected FIR/RC correlation. The results are consistent with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray electrons (CRe-s) diffusing away from the star forming regions. Since the CRe-s appear to escape the SMC so readily, the results here may not provide support for coupling between the local gas density and the magnetic field intensity.Comment: 19 pages, 7 Figure

Magnetic fields in cosmic particle acceleration sources

We review here some magnetic phenomena in astrophysical particle accelerators associated with collisionless shocks in supernova remnants, radio galaxies and clusters of galaxies. A specific feature is that the accelerated particles can play an important role in magnetic field evolution in the objects. We discuss a number of CR-driven, magnetic field amplification processes that are likely to operate when diffusive shock acceleration (DSA) becomes efficient and nonlinear. The turbulent magnetic fields produced by these processes determine the maximum energies of accelerated particles and result in specific features in the observed photon radiation of the sources. Equally important, magnetic field amplification by the CR currents and pressure anisotropies may affect the shocked gas temperatures and compression, both in the shock precursor and in the downstream flow, if the shock is an efficient CR accelerator. Strong fluctuations of the magnetic field on scales above the radiation formation length in the shock vicinity result in intermittent structures observable in synchrotron emission images. Resonant and non-resonant CR streaming instabilities in the shock precursor can generate mesoscale magnetic fields with scale-sizes comparable to supernova remnants and even superbubbles. This opens the possibility that magnetic fields in the earliest galaxies were produced by the first generation Population III supernova remnants and by clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review

Reconstruction of the Primordial Power Spectrum using Temperature and Polarisation Data from Multiple Experiments

We develop a method to reconstruct the primordial power spectrum, P(k), using both temperature and polarisation data from the joint analysis of a number of Cosmic Microwave Background (CMB) observations. The method is an extension of the Richardson-Lucy algorithm, first applied in this context by Shafieloo & Souradeep. We show how the inclusion of polarisation measurements can decrease the uncertainty in the reconstructed power spectrum. In particular, the polarisation data can constrain oscillations in the spectrum more effectively than total intensity only measurements. We apply the estimator to a compilation of current CMB results. The reconstructed spectrum is consistent with the best-fit power spectrum although we find evidence for a `dip' in the power on scales k ~ 0.002 Mpc^-1. This feature appears to be associated with the WMAP power in the region 18 < l < 26 which is consistently below best--fit models. We also forecast the reconstruction for a simulated, Planck-like survey including sample variance limited polarisation data.Comment: 8 pages, 5 figures, comments welcom

Pulsar Wind Nebulae with Bow Shocks: Non-thermal Radiation and Cosmic Ray Leptons

Pulsars with high spin-down power produce relativistic winds radiating a non-negligible fraction of this power over the whole electromagnetic range from radio to gamma-rays in the pulsar wind nebulae (PWNe). The rest of the power is dissipated in the interactions of the PWNe with the ambient interstellar medium (ISM). Some of the PWNe are moving relative to the ambient ISM with supersonic speeds producing bow shocks. In this case, the ultrarelativistic particles accelerated at the termination surface of the pulsar wind may undergo reacceleration in the converging flow system formed by the plasma outflowing from the wind termination shock and the plasma inflowing from the bow shock. The presence of magnetic perturbations in the flow, produced by instabilities induced by the accelerated particles themselves, is essential for the process to work. A generic outcome of this type of reacceleration is the creation of particle distributions with very hard spectra, such as are indeed required to explain the observed spectra of synchrotron radiation with photon indices Γ≲ 1.5. The presence of this hard spectral component is specific to PWNe with bow shocks (BSPWNe). The accelerated particles, mainly electrons and positrons, may end up containing a substantial fraction of the shock ram pressure. In addition, for typical ISM and pulsar parameters, the e+ released by these systems in the Galaxy are numerous enough to contribute a substantial fraction of the positrons detected as cosmic ray (CR) particles above few tens of GeV and up to several hundred GeV. The escape of ultrarelativistic particles from a BSPWN—and hence, its appearance in the far-UV and X-ray bands—is determined by the relative directions of the interstellar magnetic field, the velocity of the astrosphere and the pulsar rotation axis. In this respect we review the observed appearance and multiwavelength spectra of three different types of BSPWNe: PSR J0437-4715, the Guitar and Lighthouse nebulae, and Vela-like objects. We argue that high resolution imaging of such objects provides unique information both on pulsar winds and on the ISM. We discuss the interpretation of imaging observations in the context of the model outlined above and estimate the BSPWN contribution to the positron flux observed at the Earth

Cosmic-ray acceleration in supernova remnants

Supernovae are among the most energetic events in the Universe. During the event, they expel their material with enormous speeds into the surroundings. In addition, supernovae are thought to transfer a sizable fraction of their energy into just a few particles: cosmic rays. These cosmic rays acquire so much energy that they escape the supernova material with almost the speed of light. Some of these cosmic rays arrive on Earth, where in an unfortunate case, they can do damage to the electronics onboard satellites. This thesis describes several studies on the observational imprints of cosmic-ray acceleration in supernova remnants. We use optical and X-ray data to study how much energy is lost from the remnants to cosmic rays and how this energy is transferred to the particles

Characterizing the nonthermal emission of Cassiopeia A

We report on our analysis of the 1 Ms Chandra observation of the supernova remnant Cas A in order to localize, characterize, and quantify the nonthermal X-ray emission. More specifically, we investigated whether the X-ray synchrotron emission from the inside of the remnant is from the outward shock, but projected toward the inner ring, or from the inner shell. We tackled this problem by employing a Lucy-Richardson deconvolution technique and measuring spectral indices in the 4.2-6 keV band. We show that most of the continuum emission is coming from an inner ring that coincides with the previously reported location of the reverse shock. This inner ring also includes filaments whose X-ray emission has been found to be dominated by X-ray synchrotron emission. The X-ray emission from these filaments, both at the forward shock and from the inner ring, have relatively hard spectra with spectral index >–3.1. The regions emitting hard X-ray continuum contribute about 54% of the total X-ray emission in the 4.2-6 keV. This is lower than that suggested by extrapolating the hard X-ray spectrum as measured by BeppoSAX PDS and INTEGRAL. This can be reconciled by assuming a gradual steepening of the spectrum toward higher energies. We argue that the X-ray synchrotron emission is mainly coming from the western part of the reverse shock. The reverse shock in the west is almost at rest in our observation frame, corresponding to a relatively high reverse shock velocity of ~6000 km s−1 in the frame of the freely expanding ejecta

Characterizing the nonthermal emission of Cassiopeia A

We report on our analysis of the 1 Ms Chandra observation of the supernova remnant Cas A in order to localize, characterize, and quantify the nonthermal X-ray emission. More specifically, we investigated whether the X-ray synchrotron emission from the inside of the remnant is from the outward shock, but projected toward the inner ring, or from the inner shell. We tackled this problem by employing a Lucy-Richardson deconvolution technique and measuring spectral indices in the 4.2-6 keV band. We show that most of the continuum emission is coming from an inner ring that coincides with the previously reported location of the reverse shock. This inner ring also includes filaments whose X-ray emission has been found to be dominated by X-ray synchrotron emission. The X-ray emission from these filaments, both at the forward shock and from the inner ring, have relatively hard spectra with spectral index >–3.1. The regions emitting hard X-ray continuum contribute about 54% of the total X-ray emission in the 4.2-6 keV. This is lower than that suggested by extrapolating the hard X-ray spectrum as measured by BeppoSAX PDS and INTEGRAL. This can be reconciled by assuming a gradual steepening of the spectrum toward higher energies. We argue that the X-ray synchrotron emission is mainly coming from the western part of the reverse shock. The reverse shock in the west is almost at rest in our observation frame, corresponding to a relatively high reverse shock velocity of ~6000 km s−1 in the frame of the freely expanding ejecta

Erratum: "Cosmic-Ray Acceleration Efficiency versus Temperature Equilibration: The Case of SNR 0509-67.5"

In a recent email, K. Heng informed us that the curves he provided, which were used for Figure 2 of the published article, are incorrect. More specifically, Figure 5 of van Adelsberg et al. (2008) was the correct figure, in contrast to what was written in Helder et al. (2010)