Supernova Remnants: An Odyssey in Space after Stellar death

Supernova Remnants: An Odyssey in Space after Stellar death

Supernova Remnants: An Odyssey in Space after Stellar death


1st Abstract

Title (1st Abstract)

Magnetic fields in Supernova Remnants and Pulsar-Wind Nebulae: Deductions from X-ray Observations

First Author

Stephen P. Reynolds


North Carolina State University

Presentation options

Invited Talks


4. Magnetic fields in SNRs and PWNe

1st Abstract

Magnetic field strengths $B$ in synchrotron sources are notoriously difficult to measure. Simple arguments such as equipartition of energy can give values for which the total energy is a minimum, but there is no guarantee that Nature obeys it, or even if so, what particle population (just electrons? electrons plus ions?) should have an energy density comparable to that in magnetic field. However, the operation of synchrotron losses can provide additional information, if those losses are manifested in the synchrotron spectra as steepenings of the spectral-energy distribution above some characteristic frequency often called a “break” (though it is more typically a gradual curvature). A source of known age, if it has been accelerating particles continuously, will have such a break above the energy at which particle radiative lifetimes equal the source age, and this can give $B$. However, in spatially resolved sources such as supernova remnants (SNRs) and pulsar-wind nebulae (PWNe), systematic advection of particles, if at a known rate, gives a second measure of particle age to compare with radiative lifetimes. In most young SNRs, synchrotron X-rays make a contribution to the X-ray spectrum, and are usually found in “thin rims” at the remnant edges. If the rims are thin in the radial direction due to electron energy losses, a magnetic-field strength can be estimated. I present recent modeling of this process, along with models in which rims are thin due to decay of magnetic turbulence, and apply them to the remnants of SN 1006 and Tycho. In PWNe, outflows of relativistic plasma behind the pulsar wind termination shock are likely quite inhomogeneous, so magnetic-field estimates based on source lifetimes and assuming spatial uniformity can give misleading values for $B$. I shall discuss inhomogeneous PWN models and the effects they can have on $B$ estimates.

2nd Abstract

Title (2nd abstract)

Asymmetric Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3

First Author (2nd abstract)

Stephen Reynolds

Affiliation (2nd abstract)

North Carolina State University

Additional Authors (2nd abstract)

Kazimierz Borkowski, Peter Gwynne, David Green, Una Hwang, Robert Petre, Rebecca Willett

Presentation options (2nd abstract)


Session (2nd abstract)

10. SNe and SNRs with circumstellar interactions

2nd Abstract

The youngest Galactic supernova remnant (SNR) G1.9+0.3, produced by a (probable) Type Ia SN that exploded around CE 1900, is strongly asymmetric at radio wavelengths, with a single bright maximum in its shell, but exhibits a bilaterally symmetric morphology in X-rays. It has been difficult to understand the origin of these contrasting morphologies. We present the results of expansion measurements of G1.9+0.3 that illuminate the origin of the radio asymmetry. These measurements are based on a comparison of our 2015 400-ks Chandra
observation with earlier Chandra observations, including a 1-Ms observation in 2011. The mean expansion rate from 2011 to 2015 is 0.58% per yr, in agreement with previous measurements. We also confirm that the expansion decreases radially away from the remnant’s center along the major E-W axis, from 0.77% per yr to 0.53% per yr. Large
variations in expansion are also present along the minor N-S axis, but expansion there is strongly asymmetric and varies on small spatial scales. We use the “Demons” method to study the complex motions within G1.9+0.3. This method provides a nonparametric way for measuring these motions globally. We find motions varying by a factor of 5, from 0.09” to 0.44” per year. The slowest shocks are in the north, at the outer boundary of the bright radio emission, with speeds there as low as 3,600 km/s (for an assumed distance of 8.5 kpc), much less than the average shock speed of 12,000 km/s. Such strong deceleration of the northern blast wave most likely arises from the collision of SN ejecta with a much denser than average ambient medium there. The presence of this asymmetric ambient medium naturally explains the radio asymmetry. The SN ejecta have also been strongly decelerated in the N, but they expand faster than the blast wave. In several locations, significant morphological changes and strongly nonradial motions are apparent. The spatially-integrated X-ray flux continues to increase with time. As with Kepler’s SN, the most recent historical SN in the Galaxy, the SN ejecta are likely colliding with the asymmetric circumstellar medium (CSM) ejected by the SN progenitor prior to its explosion. G1.9+0.3 fills the gap between distant Type Ia-CSM SNe and
older Type Ia-CSM SNRs such as Kepler’s SNR, providing us with a unique opportunity to learn about SN Ia progenitors.