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Register a new userPulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
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We review observations of several classes of neutron-star-powered outflows: pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe interacting directly with interstellar medium (ISM), and magnetar-powered outflows. We describe radio, X-ray, and gamma-ray observations of PWNe, focusing first on integrated spectral-energy distributions (SEDs) and global spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering array of morphologies, with jets, trails, and other structures. Several of the 23 so far identified magnetars show evidence for continuous or sporadic emission of material, sometimes associated with giant flares, and a few possible magnetar-wind nebulae have been recently identified.
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In the past few years, gamma-ray astronomy has entered a golden age thanks to two major breakthroughs: Cherenkov telescopes on the ground and the Large Area Telescope (LAT) onboard the Fermi satellite. The sample of supernova remnants (SNRs) detected at gamma-ray energies is now much larger: it goes from evolved supernova remnants interacting with molecular clouds up to young shell-type supernova remnants and historical supernova remnants. Studies of SNRs are of great interest, as these analyses are directly linked to the long standing issue of the origin of the Galactic cosmic rays. In this context, pulsar wind nebulae (PWNe) need also to be considered since they evolve in conjunction with SNRs. As a result, they frequently complicate interpretation of the gamma-ray emission seen from SNRs and they could also contribute directly to the local cosmic ray spectrum, particularly the leptonic component. This paper reviews the current results and thinking on SNRs and PWNe and their connection to cosmic ray production.
During the search for counterparts of very-high-energy gamma-ray sources, we serendipitously discovered large, extended, low surface brightness emission from PWNe around pulsars with the ages up to ~100 kyrs, a discovery made possible by the low and stable background of the Suzaku X-ray satellite. A systematic study of a sample of 8 of these PWNe, together with Chandra datasets, has revealed us that the nebulae keep expanding up to for ~100 kyrs, although time scale of the synchrotron X-ray emission is only ~60 yr for typical magnetic fields of 100 microG. Our result suggests that the accelerated electrons up to ~80 TeV can escape from the PWNe without losing most energies. Moreover, in order to explain the observed correlation between the X-ray size and the pulsar spindwon age, the magnetic field strength in the PWNe must decrease with time.
The previously unidentified very high-energy (VHE; E > 100 GeV) gamma-ray source HESS J1303-631, discovered in 2004, is re-examined including new data from the H.E.S.S. Cherenkov telescope array. Archival data from the XMM-Newton X-ray satellite and from the PMN radio survey are also examined. Detailed morphological and spectral studies of VHE gamma-ray emission as well as of the XMM-Newton X-ray data are performed. Significant energy-dependent morphology of the gamma-ray source is detected with high-energy emission (E > 10 TeV) positionally coincident with the pulsar PSR J1301-6305 and lower energy emission (E <2 TeV) extending sim 0.4^{circ} to the South-East of the pulsar. The spectrum of the VHE source can be described with a power-law with an exponential cut-off N_{0} = (5.6 pm 0.5) X 10^{-12} TeV^-1 cm^-2 s^-1, Gamma = 1.5 pm 0.2) and E_{rm cut} = (7.7 pm 2.2) TeV. The PWN is also detected in X-rays, extending sim 2-3 from the pulsar position towards the center of the gamma-ray emission region. The spectral energy distribution (SED) is well described by a one zone leptonic scenario which, with its associated caveats, predicts a very low average magnetic field for this source. Significant energy-dependent morphology of this source, as well as the identification of an associated X-ray PWN from XMM-Newton observations enable identification of the VHE source as an evolved PWN associated to the pulsar PSR J1303-6305. However, the large discrepancy in emission region sizes and the low level of synchrotron radiation suggest a multi-population leptonic nature. The low implied magnetic field suggests that the PWN has undergone significant expansion. This would explain the low level of synchrotron radiation and the difficulty in detecting counterparts at lower energies, the reason this source was originally classified as a dark VHE gamma-ray source.
In this paper we explore the evolution of a PWN while the pulsar is spinning down. An MHD approach is used to simulate the evolution of a composite remnant. Particular attention is given to the adiabatic loss rate and evolution of the nebular field strength with time. By normalising a two component particle injection spectrum (which can reproduce the radio and X-ray components) at the pulsar wind termination shock to the time dependent spindown power, and keeping track with losses since pulsar/PWN/SNR birth, we show that the average field strength decreases with time as $t^{-1.3}$, so that the synchrotron flux decreases, whereas the IC gamma-ray flux increases, until most of the spindown power has been dumped into the PWN. Eventually adiabatic and IC losses will also terminate the TeV visibility and then eventually the GeV visibility.
Rotation-powered pulsars and magnetars are two different observational manifestations of neutron stars: rotation powered pulsars are rapidly spinning objects that are mostly observed as pulsating radio sources, while magnetars, neutron stars with the highest known magnetic fields, often emit short-duration X-ray bursts. Here we report simultaneous observations of the high-magnetic-field radio pulsar PSR J1119-6127 at X-ray, with XMM-Newton & NuSTAR, and at radio energies with Parkes radio telescope, during a period of magnetar-like bursts. The rotationally powered radio emission shuts off coincident with the occurrence of multiple X-ray bursts, and recovers on a time scale of ~70 seconds. These observations of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars, and suggest that the pair plasma produced in bursts can disrupt the acceleration mechanism of radio emitting particles.
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