Small-Scale X-ray Variability in the Cassiopeia A Supernova Remnant

Abstract

A comparison of X-ray observations of the Cassiopeia A supernova remnant taken in 2000, 2002, and 2004 with the Chandra ACIS-S3 reveals the presence of several small scale features (<= 10 arcsec) which exhibit significant intensity changes over a 4 year time frame. Here we report on the variability of six features, four of which show count rate increases from ~ 10% to over 90%, and two which show decreases of ~ 30% -- 40%. While extracted 1-4.5 keV X-ray spectra do not reveal gross changes in emission line strengths, spectral fits using non-equilibrium ionization, metal-rich plasma models indicate increased or decreased electron temperatures for features showing increasing or decreasing count rates, respectively. Based on the observed count rate changes and the assumption that the freely expanding ejecta has a velocity of ~ 5000 km/s at the reverse shock front, we estimate the unshocked ejecta to have spatial scale variations of 0.02 - 0.03 pc, which is consistent with the X-ray emitting ejecta belonging to a more diffuse component of the supernova ejecta than that seen in the optically emitting ejecta, which have spatial scales ~ 0.001 pc.

9 pages, 8 figures, to be published in Astronomical Journal

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Cited by in corpus (35)

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• Direct Observation of the Cooling of the Cassiopeia A Neutron Star
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• The Three-Dimensional Structure of Cassiopeia A
• Magnetic fields in supernova remnants and pulsar-wind nebulae
• Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta
• Proper Motions and Brightness Variations of Nonthermal X-ray Filaments in the Cassiopeia A Supernova Remnant
• Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta
• A cut-off in the TeV gamma-ray spectrum of the SNR Cassiopeia A
• Supernova Remnants Interacting with Molecular Clouds: X-ray and Gamma-ray Signatures
• SNR 1E 0102.2-7219 as an X-ray Calibration Standard in the 0.5-1.0 keV Bandpass and Its Application to the CCD Instruments aboard Chandra, Suzaku, Swift and XMM-Newton
• The Three-Dimensional Structure of Interior Ejecta in Cassiopeia A at High Spectral Resolution
• X-ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A
• Locating the most energetic electrons in Cassiopeia A
• Mixing of Clumpy Supernova Ejecta into Molecular Clouds
• Suzaku X-Ray Imaging and Spectroscopy of Cassiopeia A
• A Decline in the Nonthermal X-ray Emission from Cassiopeia A
• A Comparison of X-ray and Optical Emission in Cassiopeia A
• Fermi-LAT Detection of a Break in the Gamma-Ray Spectrum of the Supernova Remnant Cassiopeia A
• The Circumstellar Medium of Cassiopeia A Inferred from the Outer Ejecta Knot Properties
• Magnetic field amplification in supernova remnants
• Particle acceleration in supernova-remnant shocks
• Energy Dependence of Synchrotron X-Ray Rims in Tycho's Supernova Remnant
• A kinematic study of central compact objects and their host supernova remnants
• Axion dark matter-induced echo of supernova remnants
• Multi-Year X-ray Variations of Iron-K and Continuum Emissions in the Young Supernova Remnant Cassiopeia A
• A Decade-Baseline Study of the Plasma States of Ejecta Knots in Cassiopeia A
• Probing Shock Properties with Non-thermal X-ray Filaments in Cas A
• Kinematics of Supernova Remnants: Status of X-Ray Observations
• Kinematics of Supernova Remnants Using Multiepoch Maximum Likelihood Estimation: Chandra Observation of Cassiopeia A as an Example
• Discovery of Year-Scale Time Variability from Thermal X-ray Emission in Tycho's Supernova Remnant
• Hadronic gamma-ray images of Sedov supernova remnants
• A Study of Radio Knots within Supernova Remnant Cassiopeia A
• The forward and reverse shock dynamics of Cassiopeia A