The talks are in the same order as the Program Schedule.
Rakowski, Cara - Shock Physics in SNRs: an observational perspective
Immler, Stefan - X-Ray Emission from Supernovae as Probes of Stellar Environments
Cara Rakowski (Naval Research Lab (NRC fellow)) , J. Martin Laming (NRL), Parviz Ghavamian (Johns Hopkins)
The outer blast-waves of supernova remnants (SNRs) are an example of ``collisionless shocks'', i.e. the width of the shock transition is tiny compared to the Coulomb mean-free-path. In these shocks the particle heating to postshock temperatures and acceleration to cosmic ray energies must be mediated by plasma waves arising from instabilities, and not just from random Coulomb collisions. The 1/1835 mass ratio of electrons to protons makes the heating and acceleration of electrons particularly difficult. In this talk I will explain the spectroscopic techniques for determining the proton, ion and electron temperatures at a variety of supernova remnant shocks, and present the latest data on the electron to proton temperature ratio from this survey. The observed inverse square dependence of the electron to proton temperature ratio with shock velocity can be explained by a physical model for the electron heating, whereby lower hybrid waves excited in the shock cosmic-ray precursor damp by accelerating electrons along the local magnetic field, echoing recent suggestions in the literature that the cosmic rays are an integral part of the collisionless shock structure. New results including the growth rate for lower-hybrid waves in the cosmic-ray precursor will be discussed.
Daniel Dewey (MIT Kavli Institute) , S. Zhekov (U Colorado), C.R. Canizares (MKI), R. McCray (U Colorado)
We have completed taking deep, high-resolution observations of SN 1987A at 20 years after its explosion with Chandra's grating spectrometers. In March-April of 2007 HETG observations totaling 355 ks were taken as part of the HETG GTO program. Just recently in the Fall of 2007, deep complementary LETG observations (McCray, P.I.) were taken as well; with the full set of deep line-images we can do detailed fitting of spatial-velocity-ionization models of the SN 1987A emission. Presented here are the HETG data which give the highest-resolution X-ray spectra of SN1987A to date. High signal-to-noise is achieved in the 6A to 20A bandpass which includes the H-like and He-like lines of Si, Mg, Ne, as well as bright Fe XVII lines and lines of O VIII. Using simple 3D geometric models, including Doppler velocity effects, we can fit the spectral-images of individual lines to obtain information relevant to the CSM shock interactions taking place in the SN 1987A system.
Stefan Immler (NASA/CRESST GSFC)
The interaction of outgoing SN shocks with material in their environments can give rise to large amounts of X-rays which are uniquely suited to measure the circumstellar matter (CSM) densities and the mass loss rates of their progenitor stars. Since SN shocks travel at speeds a thousand times larger than the stellar wind velocities, the X-ray observations can be used as a “time machine” to look back into the histories of the progenitors over periods of tens of thousands of years in the stellar evolution. I discuss the first comprehensive study of the environments of all SNe detected with orbiting X-ray observatories over the past three decades, with emphasis on recent results of SNe 2006bp, 2006jc and 2005kd obtained with Chandra, XMM-Newton, and Swift.
Stephen Reynolds (North Carolina State University) , K.J. Borkowski (NC State U), J.M. Blondin (NC State U), C. Badenes (Rutgers), J.P. Hughes (Rutgers), U. Hwang (NASA/GSFC), J.M. Laming (NRL)
We present results from our 750 ks Chandra Large Project observation of the remnant of Kepler's supernova of 1604. This spectacular dataset, containing about 30 million counts, allows detailed spectroscopy on arcsecond scales. We have examined the spectra of over 100 small regions, and find that the vast bulk of emission from Kepler can be identified with iron and silicon-rich ejecta. Very few regions show abundances closer to solar, but those are spatially associated with N-rich optical knots, and show some evidence for N enhancement in X-rays as well. Those regions are also the only locations where O is noticeable in the spectra. A few regions are dominated by synchrotron emission, in the form of knots and diffuse patches as well as thin filaments. There are no O-rich regions. We are forced to conclude that Kepler is the remnant of a thermonuclear supernova, although evidence is also strong that the ambient medium into which the blast wave is expanding is circumstellar material lost from the progenitor. Thus Kepler may be an example of a thermonuclear supernova from a more massive progenitor system, perhaps to be identified with "prompt" Type Ia supernovae required to explain the correlation of Type Ia supernova rates with galaxy star formation rates. However, Kepler's kinematics are also unusual and may require a whole new Ia mechanism, such as the thermonuclear explosion of a single star. The implications of different explosion mechanisms for the cosmological use of SNe Ia are considerable. I shall discuss the significance of our observation for shock-acceleration physics and for the nature of the Type Ia phenomenon.