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Post Info TOPIC: RX J0852.0-4622


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Posts: 131433
Date:
PSR J0855-4644
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Title: Constraining the geometry of PSR J0855-4644: A nearby Pulsar Wind Nebula with Double Torus/Jet Morphology
Author: Chandreyee Maitra, Fabio Acero, Christo Venter

Aims: PSR J0855-4644 is a fast-spinning, energetic pulsar discovered at radio wavelengths near the south-eastern rim of the supernova remnant RX J0852.0-4622. A follow-up observation revealed the pulsar's X-ray counterpart and a slightly asymmetric PWN suggesting possible jet structures. PSR J0855-4644 is a pulsar with one of the highest \dot{E}/d^{2} from which no GeV \gamma-ray pulsations have been detected.
Methods: With a dedicated Chandra observation, we perform detailed spatial modelling to constrain the geometry of the PWN, in particular the pulsar's line of sight \zeta_{PSR}. We also perform geometric radio and \gamma-ray light curve modelling to further constrain \zeta_{PSR} and the magnetic obliquity \alpha.
Results: The observation reveals that the compact XMM source, thought to be the X-ray pulsar, can be further resolved into a point source surrounded by an elongated axisymmetric nebula with a longitudinal extent of 10". The pulsar flux represents only ~ 1% of the XMM compact source and its spectrum is well described by a blackbody of temperature kT=0.2 keV while the surrounding nebula has a much harder spectrum (\Gamma=1.1 for a power-law model). Assuming the origin of the extended emission is from a double torus yields \zeta_{PSR}=32.5 4.3. Independent constraints from geometric light curve modelling yield \alpha \lesssim 55 and \zeta \lesssim 55, and 10 \lesssim| \zeta-\alpha| \lesssim 30. A \chi^2 fit to the radio light curve yields a best fit at (\alpha,\zeta_{PSR}) = (22, 8), with an alternative fit at (\alpha,\zeta_{PSR}) = (9, 25) within 3\sigma. Such a geometry would explain, in the standard caustic pulsar model picture, the radio-loud and \gamma-ray-quiet behaviour of this high \dot{E}/d^{2} pulsar.

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Posts: 131433
Date:
Supernova Remnant G266.2-1.2
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Title: On the Expansion Rate, Age, and Distance of the Supernova Remnant G266.2-1.2 (Vela Jr.)
Author: G. E. Allen, K. Chow, T. DeLaney, M. D. Filipovic, J. C. Houck, T. G. Pannuti, M. D. Stage

An analysis of Chandra ACIS data for two relatively bright and narrow portions of the northwestern rim of G266.2-1.2 (a.k.a. RX J0852.0-4622 or Vela Jr.) reveal evidence of a radial displacement of 2.40 0.56 arcsec between 2003 and 2008. The corresponding expansion rate (0.42 0.10 arcsec/yr or 13.6 4.2%/kyr) is about half the rate reported for an analysis of XMM-Newton data from a similar, but not identical, portion of the rim over a similar, but not identical, time interval (0.84 0.23 arcsec/yr, Katsuda et al. 2008a). If the Chandra rate is representative of the remnant as a whole, then the results of a hydrodynamic analysis suggest that G266.2-1.2 is between 2.4 and 5.1 kyr old if it is expanding into a uniform ambient medium (whether or not it was produced by a Type Ia or Type II event). If the remnant is expanding into the material shed by a steady stellar wind, then the age could be as much as 50% higher. The Chandra expansion rate and a requirement that the shock speed be greater than or equal to 1000 km/s yields a lower limit on the distance of 0.5 kpc. An analysis of previously-published distance estimates and constraints suggests G266.2-1.2 is no further than 1.0 kpc. This range of distances is consistent with the distance to the nearer of two groups of material in the Vela Molecular Ridge (0.7 0.2 kpc, Liseau et al. 1992) and to the Vel OB1 association (0.8 kpc, Eggen 1982).

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Posts: 131433
Date:
Vela Jr. Supernova Remnant
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Title: A CR-hydro-NEI Model of Multi-wavelength Emission from the Vela Jr. Supernova Remnant (SNR RX J0852.0-4622)
Authors: Shiu-Hang Lee, Patrick Slane, Donald C. Ellison, Shigehiro Nagataki, Daniel J. Patnaude

Based largely on energy budget considerations and the observed cosmic-ray (CR) ionic composition, supernova remnant (SNR) blast waves are the most likely sources of CR ions with energies at least up to the "knee" near 3 PeV. Shocks in young shell-type TeV-bright SNRs are surely producing TeV particles, but the emission could be dominated by ions producing neutral pion-decay emission or electrons producing inverse-Compton gamma-rays. Unambiguously identifying the GeV-TeV emission process in a particular SNR will not only help pin down the origin of CRs, it will add significantly to our understanding of the diffusive shock acceleration (DSA) mechanism and improve our understanding of supernovae and the impact SNRs have on the circumstellar medium. In this study, we investigate the Vela Jr. SNR, an example of TeV-bright non-thermal SNRs. We perform hydrodynamic simulations coupled with non-linear DSA and non-equilibrium ionisation near the forward shock (FS) to confront currently available multi-wavelength data. We find, with an analysis similar to that used earlier for SNR RX J1713.7-3946, that self-consistently modelling the thermal X-ray line emission with the non-thermal continuum in our one-dimensional model strongly constrains the fitting parameters, and this leads convincingly to a leptonic origin for the GeV-TeV emission for Vela Jr. This conclusion is further supported by applying additional constraints from observation, including the radial brightness profiles of the SNR shell in TeV gamma-rays, and the spatial variation of the X-ray synchrotron spectral index. We will discuss implications of our models on future observations by the next-generation telescopes.

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Posts: 131433
Date:
RE: RX J0852.0-4622
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Title: A new nearby pulsar wind nebula overlapping the RX J0852.0-4622 supernova remnant
Authors: F. Acero, Y. Gallant, J. Ballet, M. Renaud, R. Terrier

Energetic pulsars can be embedded in a nebula of relativistic leptons which is powered by the dissipation of the rotational energy of the pulsar. The object PSR J0855-4644 is an energetic and fast-spinning pulsar (Edot = 1.1x10^36 erg/s, P=65 ms) discovered near the South-East rim of the supernova remnant (SNR) RX J0852.0-4622 (aka Vela Jr) by the Parkes multibeam survey. The position of the pulsar is in spatial coincidence with an enhancement in X-rays and TeV gamma-rays, which could be due to its putative pulsar wind nebula (PWN).
The purpose of this study is to search for diffuse non-thermal X-ray emission around PSR J0855-4644 to test for the presence of a PWN and to estimate the distance to the pulsar. An X-ray observation was carried out with the XMM-Newton satellite to constrain the properties of the pulsar and its nebula. The absorption column density derived in X-rays from the pulsar and from different regions of the rim of the SNR was compared with the absorption derived from the atomic (HI) and molecular (12CO) gas distribution along the corresponding lines of sight to estimate the distance of the pulsar and of the SNR.
The observation has revealed the X-ray counterpart of the pulsar together with surrounding extended emission thus confirming the existence of a PWN. The comparison of column densities provided an upper limit to the distance of the pulsar PSR J0855-4644 and the SNR RX J0852.0-4622 (d<900 pc). Although both objects are at compatible distances, we rule out that the pulsar and the SNR are associated. With this revised distance, PSR J0855-4644 is the second most energetic pulsar, after the Vela pulsar, within a radius of 1 kpc and could therefore contribute to the local cosmic-ray e-/e+ spectrum.

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Posts: 131433
Date:
SNR RX J0852.0-4622
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Title: H.E.S.S. deeper observations on SNR RX J0852.0-4622
Authors: Manuel Paz Arribas, Ullrich Schwanke, Iurii Sushch, Nukri Komin, Fabio Acero, Stefan Ohm, for the H.E.S.S. Collaboration

Supernova Remnants (SNRs) are believed to be acceleration sites of Galactic cosmic rays. Therefore, deep studies of these objects are instrumental for an understanding of the high energy processes in our Galaxy. \velajr, also known as Vela Junior, is one of the few (4) shell-type SNRs resolved at Very High Energies (VHE; E > 100 \GeV). It is one of the largest known VHE sources (~ 1.0 radius) and its flux level is comparable to the flux level of the Crab Nebula in the same energy band. These characteristics allow for a detailed analysis, shedding further light on the high-energy processes taking place in the remnant. In this document we present further details on the spatial and spectral morphology derived with an extended data set. The analysis of the spectral morphology of the remnant is compatible with a constant power-law photon index of 2.11 0.05_{stat} 0.20_{syst} from the whole SNR in the energy range from 0.5 TeV to 7 TeV. The analysis of the spatial morphology shows an enhanced emission towards the direction of the pulsar \psr, however as the pulsar is lying on the rim of the SNR, it is difficult to disentangle both contributions. Therefore, assuming a point source, the upper limit on the flux of the pulsar wind nebula (PWN) between 1 TeV and 10 TeV, is estimated to be ~ 2% of the Crab Nebula flux in the same energy range.

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Posts: 131433
Date:
RX J0852.0-4622
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Title: Gamma-Ray Observations of the Supernova Remnant RX J0852.0-4622 with the Fermi LAT
Authors: T. Tanaka, A. Allafort, J. Ballet, S. Funk, F. Giordano, J. Hewitt, M. Lemoine-Goumard, H. Tajima, O. Tibolla, Y. Uchiyama

We report on gamma-ray observations of the supernova remnant (SNR) RX J0852.0-4622 with the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope. In the Fermi LAT data, we find a spatially extended source at the location of the SNR. The extension is consistent with the SNR size seen in other wavelengths such as X-rays and TeV gamma rays, leading to the identification of the gamma-ray source with the SNR. The spectrum is well described as a power law with a photon index of Gamma = 1.85 0.06 (stat) (+0.18,-0.19) (sys), which smoothly connects to the H.E.S.S. spectrum in the TeV energy band. We discuss the gamma-ray emission mechanism based on multiwavelength data. The broadband data can be fit well by a model in which the gamma rays are of hadronic origin. We also consider a scenario with inverse Compton scattering of electrons as the emission mechanism of the gamma rays. Although the leptonic model predicts a harder spectrum in the Fermi LAT energy range, the model can fit the data considering the statistical and systematic errors.

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