Supernova Remnants
Thermonuclear Supernovae (SNe Ia) and Their Remnants
One of the unsolved problems in SN research is the nature of Type Ia SNe (SN Ia) progenitor systems. One possible progenitor system is a C-O white dwarf accreting H/He-rich gas from a companion, in which case some circumstellar gas should be present when the SN explodes. Early Constellation-X observations of bright SN Ia (preferably before maximum optical brightness ~20 days after ignition) will constrain the progenitor's circumstellar environment. However, circumstellar material (CSM) in a normal SN Ia has yet to be detected. Currently, Chandra can reach a flux limit of ~10-15 ergs cm2 s-1 (2-10 keV band) in 20 ks. Constellation-X will go an order of magnitude fainter, so will have 3× higher sensitivity to the CSM density. The precise limit depends nearly linearly on how soon after the explosion the SN is observed.
Chandra X-ray image of the Tycho supernova remnant showing iron-rich ejecta (red features), siliconrich ejecta (green features), and featureless spectra from the forward shock (blue rims).
The cosmological importance of SNe Ia have inspired new surveys aimed at detecting early SNe Ia (2 days after the explosion) at distances comparable to the Virgo cluster (~16 Mpc; closer SNe Ia are very rare). Ongoing surveys are projected to discover 1 bright (mag 12-13) early SN Ia per year. Since time is of critical importance, Constellation-X must be able to observe a target of opportunity SN within 2 days.
Another issue for SN follow-up studies is the area of sky available for rapid slew. If Constellation-X's slew capability is limited to some fraction of the sky, then the number of targets it could potentially observe drops by that same fraction. With 20% sky coverage over the course of the 5-year mission, then Constellation-X would have a good chance of targeting one bright SN Ia over its lifetime. This level of sky coverage (20%) is the absolute minimum that would allow this science to be done.
Constellation-X studies on the structure of the shocked ejecta and ambient medium in Type Ia SNe will be instrumental to resolving the current debate over the explosion mechanism and progenitor systems (see Badenes et al. 2003, Badenes and Bravo 2001). Using Chandra observations of the Tycho SNR as a benchmark, several requirements for Constellation- X arise. While an angular resolution of 10"-15" is adequate for studying the clumpy ejecta emission (based on images and spectra from Hwang et al. 2002), better resolution would help distinguish forward shock emission from ejecta at the remnant's rim. The calorimeter's goal of 2-eV spectral resolution gives a resolution R = E/Δ E = 3,000 at the iron Kα lines. In this region, ~10 bright lines are expected from individual charge states spread over a few hundred eV, so even if the velocity of the shocked ejecta in Tycho is ~3,000 km s-1, the kinetic shifts and broadenings should be ~ 60 eV and line blending should not be a major issue.
Simulated X-ray spectra, based on a model of Badenes et al. (2003), of the ejecta emission from Tycho's SNR convolved with the XMM EPIC-MOS (red) and Constellation-X XRS (blue) response functions. The top panel shows the entire band from 0.3-10 keV and the bottom panel shows an expanded view of the low energy region. Prominent line features from several abundant elements in the ejecta are noted.
References
Badenes, C., and Bravo, E. 2001, ApJ, 556, L41Badenes, C., Bravo, E., Borkowski, K. J., and Domnguez, I. 2003, ApJ, 593, 358
Hwang, U., Decourchelle, A., Holt, S. S., and Petre, R. 2002, ApJ, 581, 1101
