THE EXPANSION ASYMMETRY AND

AGE OF THE CASSIOPEIA A SUPERNOVA REMNANT

XinZhouXinZhou

2006.06.122006.06.12

Cas A IntroductionCas A Introduction Data obtainData obtain MorphologyMorphology Abnormal chemical distributionAbnormal chemical distribution AsymmetryAsymmetry Motion of central X-ray point sourceMotion of central X-ray point source Age estimatesAge estimates Addition- Light-echo of the SNRAddition- Light-echo of the SNR

Cas A Introduction:Cas A Introduction:

~325 yrs old,the youngest known ~325 yrs old,the youngest known Galactic core-collapse remnantGalactic core-collapse remnant

~3.4 kpc(~11000 ly) differs from the ~3.4 kpc(~11000 ly) differs from the former ~2.8 kpcformer ~2.8 kpc

Well defined radio and x-ray region Well defined radio and x-ray region ~2’’~2’’

Erupted again about 50 yrs agoErupted again about 50 yrs ago

Infra-red warm Infra-red warm dust dust ~10^2K(Spitzer,2~10^2K(Spitzer,24-micron)4-micron)

Optical hot gases Optical hot gases ~10^4K(HST,900n~10^4K(HST,900nm)m)

X-ray very hot X-ray very hot gaes~10^7K and gaes~10^7K and neutron star in neutron star in center of the center of the shell(Chandra,broashell(Chandra,broadband)dband)

Hubble Space Telescope(HST),Wide Hubble Space Telescope(HST),Wide Field Channel of the Advanced Field Channel of the Advanced Camera for Surveys(ACS/WFC),4 Camera for Surveys(ACS/WFC),4 Sloan Digital Sky Sloan Digital Sky Survey(SDSS)filters –just 3 is usedSurvey(SDSS)filters –just 3 is used

Standard pipeline IRAF/STSDAD Standard pipeline IRAF/STSDAD data reductiondata reduction

Background estimationBackground estimation

Data obtain:Data obtain:

High-velocity,outer ejecta High-velocity,outer ejecta knots’ defination:knots’ defination:

Radial distance exceeded 100’’ Radial distance exceeded 100’’ from the remnant’s center of from the remnant’s center of expansionexpansion

Showed a proper motion Showed a proper motion >=0’’.35yr^-1>=0’’.35yr^-1

The Morphology:The Morphology:

AsymmetryAsymmetry

Jet and counter Jet and counter jetjet

gapsgaps

Abnormal chemical Abnormal chemical distribution:distribution:

192 strong [O II] emission fast moving 192 strong [O II] emission fast moving knots(FMK)knots(FMK)

444 strong [N II] emission FMK444 strong [N II] emission FMK

Jets contain the highest velocity [S Jets contain the highest velocity [S II]emitting ejectaII]emitting ejecta

In the other region,N-rich ejecta represent In the other region,N-rich ejecta represent the highest velocity debris followed by the the highest velocity debris followed by the O-rich ejecta,and then the S-rich knotsO-rich ejecta,and then the S-rich knots

Possible reason for Possible reason for asymmetry:asymmetry:

Uneven ejecta decelerations due to Uneven ejecta decelerations due to local ISM density variations and local ISM density variations and cavitiescavities

Bipolar MHD jetsBipolar MHD jets Mildly asymmetrical neutrino-driven Mildly asymmetrical neutrino-driven

explosionsexplosions Nature of the SN explosion engine?Nature of the SN explosion engine?

Aspherical core-collapse Aspherical core-collapse explosionsexplosions

Popular ‘collapsar’ GRB modelPopular ‘collapsar’ GRB model asymmetrical neutrino-driven asymmetrical neutrino-driven

modelmodel Models of magnetorotationally Models of magnetorotationally

induced jetsinduced jets Rotation axis bounceRotation axis bounce

Motion of central X-ray Motion of central X-ray sourcesource

~330 km s^-1~330 km s^-1

Anormolous X-ray Anormolous X-ray pulsars(AXPs),soft gamma-ray pulsars(AXPs),soft gamma-ray repeaters(SGRs)-magnetar modelrepeaters(SGRs)-magnetar model

Wide range of observed ‘kick’ Wide range of observed ‘kick’ velocitiesvelocities

Misalignment between the Misalignment between the progenitor’s spin axis and a NS’s progenitor’s spin axis and a NS’s velocity vectorvelocity vector

Age estimates:Age estimates:

1671.8±17.91671.8±17.9 1671.3±0.9 by Thorstensen et al.(2001) 1671.3±0.9 by Thorstensen et al.(2001)

used 17 knotsused 17 knots

Knot deceleration:Knot deceleration:

The least decelerated northwest limb oThe least decelerated northwest limb offer sronger upper limits to the age 168ffer sronger upper limits to the age 1680.5±18.70.5±18.7

The direct interaction with local gas The direct interaction with local gas ττ dragdrag~ ~ χχ RRkk/v/vk k ~2000yr~2000yr

ττ bb~4~4χχ ^̂1/2 R1/2 Rkk/v/vkk ~50yr~50yr The internal shock driven into the knotThe internal shock driven into the knot 30 to 500 km s^-130 to 500 km s^-1

Questions even not Questions even not solvedsolved

More than one ejecta streams in More than one ejecta streams in both jetsboth jets

GapsGaps The reliability of object choosenThe reliability of object choosen

Light-Echo around:Light-Echo around:

a blend of at least two light echoes a blend of at least two light echoes aroundaround

A brief of Light-Echo:A brief of Light-Echo:

the dust appeared to be moving the dust appeared to be moving outward at the speed of light outward at the speed of light

May help pin down the source and May help pin down the source and the ambientthe ambient