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

Barrel or Bilateral-shaped SNRs

Jiangtao LiMay 6th 2009

Outline

• 1. Three-dimensional morphology of SNRs.• 2. Mechanisms to produce bilateral morpho

logy in radio.• 3. Multi-wavelength correlations.• 4. What could we do?• 5. Sample selection.

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.

G296.5+10.0843 MHz 0.3-4.5 keVSuperposition of forward

and reversed images

SN 1006G327.6+4.6

843 MHz

Chandra:Red 0.50 - 0.91 keVCyan 0.91 - 1.34 keVBlue 1.34 - 3.00 keV

Superposition of forwardand reversed images

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.

2. Mechanisms to produce bilateral morphology in RADIO

• 2.1 The possible mechanisms: (Gaensler B. M. 1998, ApJ, 493, 781) (Bisnovatyi-Kogan G. S., Lozinskaya T. A. & Silich S. A. 19

90, 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

• 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).

2.2 The effect of Galactic magnetic field

• Highly significant tendency for the bilateral axes of some SNRs to be aligned with the Galactic plane (a sample of 17 SNRs ).

G003.8-00.3

G350.0-02.0 G166.0+04.3

G046.8-00.3

G320.4-01.2

G332.0+00.2

G356.3-01.5

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

--- 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.

--- The effect of Galactic magnetic field:(Raley, Shelton & Plewa 2007, ApJ, 661, 222)

8 Myr 9 Myr 10 Myr 11 Myr

12 Myr 13 Myr 14 Myr 15 Myr

Log of Density

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 fie

ld or the non-uniform ISM?• 3D MHD simulations of a spherical SNR shock pro

pagating through a magnetized ISM.• Effect of magnetic field: • First, compression of the plasma; • Second, cosmic ray acceleration;• Third, the electron injection.

Initial conditions

• Two cases: • 1) through a gradient of am

bient density with a uniform ambient magnetic field;

• 2) through a homogeneous medium with a gradient of ambient magnetic field strength.

• From top to bottom:

• Different particle injection cases.

• quasi-parallel (top), isotropic (middle), quasi-perpendicular (bottom).

• Model GZ1:• Uniform

ambient magnetic field, randomized internal magnetic field.

• Gradient of ambient density.

Quasi-perpendicular particle injection case.

Quasi-parallel particle injection case

• 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 B or 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.

• 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)

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 SNR

s

• 4. What could we do?• 5. Sample selection.

3. Multi-wavelength correlations

• 3.1 X-ray:• Thermal or non-thermal synchrotron emissi

on??• For large, old remants, mainly thermal??

3.2 Discovery of high energy γ-ray emission

RCW 86

Mainly inverse Compton scattering??

(Aharonian F. et al. 2009, ApJ, 692,1500)

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/6Isotropic: ΘK =∞For quasi-perpendicular case:

The compression ratio of ISMF: σB Maximum energy of electrons: Emax

• 1. Synchrotron radio emission: The azimuthal variation of radio brightness is mostly due to variations of ς and σB.

• 2. Inverse Compton γ-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 variati

on 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 th

e 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.

Radio

IC

• 4. Quasi-parallel injection case:• In the case of the polar-cap model of a SNR (quasi-parallel inje

ction), 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 inj

ection, 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).

Outline

• 1. Three-dimensional morphology of SNRs.• 2. Mechanisms to produce bilateral morpho

logy 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.

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?

• 4. Basic problems:• Energy budget: how much energy into different phase

s?• Multi-wavelength correlation: what is the dominate e

mission 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-p

erpendicular shock.• Particle acceleration: in which cases is most efficient?

• 5. What is different in X-ray?• (1) Different emission mechanisms: X-ray is produce

d 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.

• 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.

Outline

• 1. Three-dimensional morphology of SNRs.• 2. Mechanisms to produce bilateral morpho

logy in radio.• 3. Multi-wavelength correlations.• 4. What could we do?• 5. Sample selection.

5. Sample selection

Thank you very much!