Transcript for Analyzing the Ages of Supernova Remnants

Slide 1:
I am Donna Young and I work with the NASA/Chandra X-Ray Center outreach office. This is an overview and introduction to the DS9 Estimating the Ages of Supernova Remnants investigation developed by the Chandra mission. For a more comprehensive introduction to the DS9 image analysis software and individual investigations, please watch the short webinar introduction at the beginning of the imaging section.

Slide 2:
The Chandra X-Ray Observatory is in an extreme orbit that ranges from 16,000 km at closest approach to Earth to more than a third of the distance to the moon. The highly inclined orbit takes 64 hours with 55 uninterrupted hours of observing time. The 2 sets of 4 nested hyperbolic/parabolic mirrors match the grazing incidence of the incoming X-Ray photons and direct them to a focal point at the end of the spacecraft. The photons are detected by one of two scientific instruments – the HRC (high resolution camera) or ACIS (advanced CCD imaging spectrometer). A high energy transmission grating is lowered into the focal plane with the ACIS and a low energy transmission grating for the HRC.

Slide 3:
The photons are detected, converted to a voltage and recorded. Every 8 hours there is a data download to the Deep Space Network (DSN) in Spain, Australia or Goldstone in Barstow, CA. The data is then transmitted through the system to Cambridge, MA where the data is analyzed by Chandra scientists. Unique to X-Ray observations and the mirror/grating/scientific instruments aboard the Chandra spacecraft, for each individual X-ray photon detected the amount of energy, the position (x-y coordinates) and time arrival are known – resulting in a high resolution analysis of the objects being observed.

Slide 4:
There is an extensive teachers guide for this investigation and an answer key, as well as both a pencil and paper version and the version that requires the use of the ds9 image analysis software.

Slide 5:
The download instructions for the ds9 software are located at http://chandra-ed.harvard.edu/. The software can be downloaded to Windows, MacOSX or Linux environments. The website also has self-guided tutorials and activities to learn how to use the software and the analysis tools. All the instructions and websites are included within the Analyzing the Ages of Supernova Remnants (SNRs) student handout, so students do not need to learn the software beforehand, or use the tutorials or activities unless the teacher requires it.

Slide 6:
This investigation is for the Cas A SNR. This remnant was used as the calibration extended source object for the Chandra mission. The date for the Cas A event is still undetermined.

Slide 7:
Unlike the Tycho and Kepler supernova events which were recorded on the dates that the appeared in the sky, no one may have witnessed the Cas A event. There are some intriguing possibilities though. The collapse of Cas A might have been observed in 1860 by John Flamsteed, the first Royal Astronomer at Greenwich. It may have been noticed as a celestial event on the day that King Charles II was born. It may be recorded in an ice core strip from the Greenland Ice Sheet. For more information about these possibilities look at the Ice Core Records – From Volcanoes to Supernovas investigation at the beginning of the classroom ready educational materials at http://chandra.harvard.edu/edu/formal/index.html. It is also possible to estimate the age of the event by calculating the expansion rate and extrapolating backwards in time.

Slide 8:
Following the instructions in the handout, students will download the ds9 tool box, and access the Cas A observational data. Starting with the diameter of the remnant in pixels, unit conversions and the small angle formula is used along with some basic physics relationships to calculate the expansion rate and determine a possible date for the Cas A supernova event. A major point of the calculations is the use of approximations and mathematical modeling in determining this type of information.

Slide 9:
A task specific scoring rubric is provided to use in assessing the understanding and communication of that understanding by the students. Since the students now know how to use the ds9 tools to estimate the age of Cas A, they can now use those same tools to analyze the age of other supernova remnants in the Chandra X-Ray Center public archive. Once the ages have been calculated, students can access the selected SNRs in the Photo Album and determine if their answers are in an “acceptable” range with the currently accepted values.

Slide 10:
The Chandra educational materials website has excellent supporting resources for multiwavelength astronomy and stellar evolution. You can request available ancillary classroom materials using the materials request form. If you have any questions, please email me.