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Barrel or Bilateral-shaped SNRs

Barrel or Bilateral-shaped SNRs. Jiangtao Li May 6th 2009. Outline. 1. Three-dimensional morphology of SNRs. 2. Mechanisms to produce bilateral morphology in radio. 3. Multi-wavelength correlations. 4. What could we do? 5. Sample selection.

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Barrel or Bilateral-shaped SNRs

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  1. Barrel or Bilateral-shaped SNRs Jiangtao Li May 6th 2009

  2. Outline • 1. Three-dimensional morphology of SNRs. • 2. Mechanisms to produce bilateral morphology in radio. • 3. Multi-wavelength correlations. • 4. What could we do? • 5. Sample selection.

  3. 1. Three-dimensional morphology of SNRs.(Kesteven M. J. & Caswell J. L. 1987, A&A, 183, 118) • Radio images of 70 remnants. The majority of SNRs fall into the barrel category? • (a) The appearance is a uniform ring, when viewed end-on (the line of sight is along the barrel axis; i.e. θ~0). • (b) The transition to a two-arc appearance occurs when the grazing line of sight intersects the missing edge of the polar cap (θ~θc). • (c) The two-arc appearance is manifest when the line of sight is oblique to the barrel axis; θ>θc.

  4. G296.5+10.0 Superposition of forward and reversed images 0.3-4.5 keV 843 MHz

  5. SN 1006G327.6+4.6 Chandra: Red 0.50 - 0.91 keV Cyan 0.91 - 1.34 keV Blue 1.34 - 3.00 keV 843 MHz Superposition of forward and reversed images

  6. Outline • 1. Three-dimensional morphology of SNRs. • 2. Mechanisms to produce bilateral morphology in RADIO. • 2.1 The possible mechanisms • 2.2 The effect of Galactic magnetic field • 2.3 The effect of density and magnetic field gradient • 3. Multi-wavelength correlations. • 4. What could we do? • 5. Sample selection.

  7. 2. Mechanisms to produce bilateral morphology inRADIO • 2.1 The possible mechanisms: (Gaensler B. M. 1998, ApJ, 493, 781) (Bisnovatyi-Kogan G. S., Lozinskaya T. A. & Silich S. A. 1990, Ap&SS, 166, 277) • 1. Extrinsic Explanations: • 1.1 Density structure: (a) Large scale density gradient of ISM. (b) Molecular cloud. • 1.2 Ambient magnetic field

  8. 2. Intrinsic Explanations: • 2.1 Anisotropy of the SN explosion • 2.2 Processes not related to SN explosion • (a) Toroidal distribution of ejecta. • (b) The effect of a high velocity progenitor. • (c) The distribution of mass loss and magnetic field in the CSM produced by the progenitor. • (d) The influence of outflows from a central compact object (SS433).

  9. 2.2 The effect of Galactic magnetic field G003.8-00.3 • Highly significant tendency for the bilateral axes of some SNRs to be aligned with the Galactic plane (a sample of 17 SNRs ).

  10. G350.0-02.0 G166.0+04.3 G320.4-01.2 G046.8-00.3 G332.0+00.2 G356.3-01.5

  11. Galactic scale magnetic field (Han J. L. et al. 1997, A&A, 322, 98)

  12. --- The effect of Galactic magnetic field: • (1) magnetic field compression and/or quasi-perpendicular acceleration of electrons in the supernova shock • (2) preprocessing the interstellar medium to produce density stratifications extended along the plane.

  13. 8 Myr 9 Myr 10 Myr 11 Myr --- The effect of Galactic magnetic field: (Raley, Shelton & Plewa 2007, ApJ, 661, 222) Log of Density 12 Myr 13 Myr 14 Myr 15 Myr

  14. 2.3 The effect of density and magnetic field gradient(Orlando S. et al. A&A, 470, 927) • Two main aspects to be explored: • (1) How do asymmetries originate in BSNRs? • (2) What is more effective, the ambient magnetic field or the non-uniform ISM? • 3D MHD simulations of a spherical SNR shock propagating through a magnetized ISM. • Effect of magnetic field: • First, compression of the plasma; • Second, cosmic ray acceleration; • Third, the electron injection.

  15. Initial conditions • Two cases: • 1) through a gradient of ambient density with a uniform ambient magnetic field; • 2) through a homogeneous medium with a gradient of ambient magnetic field strength.

  16. From top to bottom: • Different particle injection cases. • quasi-parallel (top), isotropic (middle), quasi-perpendicular (bottom).

  17. Model GZ1: • Uniform ambient magnetic field, randomized internal magnetic field. • Gradient of ambient density.

  18. Quasi-perpendicular particle injection case. Quasi-parallel particle injection case

  19. 1. The three different particle injection models: The isotropic and quasi-perpendicular cases lead to radio images similar to those observed. The quasi-parallel case may produce radio images unlike any observed SNR. (??) • 2. In models with gradients of the ambient density: the asymmetry increases with increasing value of b. • 3. The close similarity of the radio brightness of the opposed limbs of a BSNR is evidence of uniform ambient B field where the remnant expands. • 4. If b is large, the effect of non-uniform ambient density is comparable to the non-uniform ambient magnetic field. • 5. Strongly asymmetric BSNRs imply either moderate variations of Bor strong (moderate) variations of the ISM density if b < 2 (b ≥ 2) as in the case, for instance, of interaction with a giant molecular cloud.

  20. 6. BSNRs with different intensities of the emission of the radio arcs can be produced by models with a gradient of density or of magnetic field strength perpendicular to the arc. • 7. Remnants with two slanting similar arcs can be produced by models with a gradient of density or of magnetic field strength running centered between the two arcs. • 8. For symmetry or slanting symmetry cases, the symmetry axis of the remnant is always aligned with the gradient of density or of magnetic field. • Direction of magnetic field determines the direction of the arcs, the gradient of magnetic field determines the strength of the arc (ratio between arc and off-arc regions), and the angle between magnetic field and the gradient of magnetic field determines asymmetry of the two arcs. (For density distribution and gradient, case is similar)

  21. Outline • 1. Three-dimensional morphology of SNRs. • 2. Mechanisms to produce bilateral morphology in radio. • 3. Multi-wavelength correlations. • 3.1 X-ray • 3.2 Discovery of high energy γ-ray emission • 3.3 Relation between synchrotron radio and IC γ-ray emission in SNRs • 4. What could we do? • 5. Sample selection.

  22. 3. Multi-wavelength correlations • 3.1 X-ray: • Thermal or non-thermal synchrotron emission?? • For large, old remants, mainly thermal??

  23. 3.2 Discovery of high energy γ-ray emission (Aharonian F. et al. 2009, ApJ, 692,1500) Mainly inverse Compton scattering?? RCW 86

  24. 3.3 Relation between synchrotron radio and IC γ-ray emission in SNRs(Petruk O., Beshley V., Bocchino F. & Orlando S. et al. 2009, MNRAS) • The injection efficiency ς(fraction of accelerated electrons) Quasi-parallel: ΘK =π/6 Isotropic: ΘK =∞ For quasi-perpendicular case: The compression ratio of ISMF: σB Maximum energy of electrons: Emax

  25. Radio • 1. Synchrotron radio emission: The azimuthal variation of radio brightness is mostly due to variations of ςand σB. • 2. Inverse Comptonγ-ray emission: The azimuthal variation of IC brightness is mostly determined by variations of ς, σB and Emax. • 3. Isotropic injection case: • Azimuthal variation: If Emax is constant over the SNR surface, the azimuthal variation of surface brightness in radio and IC γ–rays is opposite. • Why?: This happens because the IC image is affected by large radiative losses of the emitting electrons behind a perpendicular shock, while the larger magnetic field increases the radio brightness there. • Compensation: Variation of Emax over the SNR surface may (to some extent) hide this effect. The maximum energy should increase with obliquity in this case. IC

  26. 4. Quasi-parallel injection case: • In the case of the polar-cap model of a SNR (quasi-parallel injection), the maxima in surface brightness are expected to coincide in radio and ICγ-rays, unless the increase of Emax with obliquity is very strong. • 5. Quasi-perpendicular injection case: • Limbs may also coincide in the case of quasi-perpendicular injection, if the lack of electrons (due to radiative losses) in regions of large magnetic field is compensated for by a strong enough increase in ς and/or Emax with Θ0. (???) • 6. Effect of isotropic compression/amplification of the ISMF: • In this case the dependence of Emax(Θ0) must follow variation ς(Θ0), namely it should be largest (smallest) at the parallel shock for quasi-parallel (quasi-perpendicular) injection. • Key parameters: ς(Θ0), σB(Θ0) and Emax(Θ0).

  27. Outline • 1. Three-dimensional morphology of SNRs. • 2. Mechanisms to produce bilateral morphology in radio. • 3. Multi-wavelength correlations. • 4. What could we do? • 4.1 What we are interested? • 4.2 How to do the work? • 5. Sample selection.

  28. 4. What could we do? • 4.1 What we are interested? • 1. We are interested in dynamics of SNR in smooth distributed ISM, not some special cases such as molecular cloud, dusty knots, superwind bubbles. • 2. We are interested in extrinsic processes (density and magnetic distribution), not asymmetric explosion or other intrinsic processes. • 3. The most related bands are: radio (synchrotron, electron injection and magnetic amplification), X-ray (bremsstrahlung, shock heating) and γ-ray (IC, particle acceleration and radiation field). All the energy is from electron, so what determines a electron will emits in which process?

  29. 4. Basic problems: • Energy budget: how much energy into different phases? • Multi-wavelength correlation: what is the dominate emission process in different parts of a SNR? • Electron injection: quasi-parallel, quasi-perpendicular or isotropic. • Electron energy distribution: Emax. • Magnetic amplification: in quasi-parallel and quasi-perpendicular shock. • Particle acceleration: in which cases is most efficient?

  30. 5. What is different in X-ray? • (1) Different emission mechanisms: X-ray is produced mainly thermal, especially for SNR with large age. • (2) Synchrotron emission is determined by both high energy particles and magnetic field, which could be unrelated things; X-ray thermal emission is determined mainly by density and temperature, in SNRs, they are partially related. • (3) X-ray emission could be affected by radiative cooling seriously, especially in radiative phase, while radio not. • (4) X-ray emission is not necessary correlated with radio emission, so we can use X-ray emission to detect BSNRs independently.

  31. 4.2 How to do the work? • Using radio data to get the magnetic energy density. • Using X-ray data to get the electron energy density. • Using γ-ray data to get the electron energy distribution. • Other choices: • Using non-thermal hard X-ray emission to get the electron energy distribution.

  32. Outline • 1. Three-dimensional morphology of SNRs. • 2. Mechanisms to produce bilateral morphology in radio. • 3. Multi-wavelength correlations. • 4. What could we do? • 5. Sample selection.

  33. 5. Sample selection

  34. Thank you very much!

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