sci15009 — Announcement

How to discover supernovae with the eHST: An end-to-end science case

21 October 2015

A supernova is a stellar explosion that can briefly outshine an entire galaxy, radiating as much energy as the Sun is expected to emit over its entire lifespan, before fading from view over several weeks or months. Supernovae occur approximately once a year per galaxy, meaning that it is not impossible for several to be found when observatories with very high spatial resolution such as Hubble carry out repeat observations of nearby galaxies.

This article presents a step-by-step end-to-end science case for how to search for and find supernovae in Hubble images of NGC 7469 using the new interface of the European Hubble Archive (eHST):

1. Open eHST at http://archives.esac.esa.int/ehst/
2. Click on the search lens button in the left menu or at the bottom of the main page.
3. In the target name field, enter the name of a nearby galaxy — NGC 7469 in our example — and then change the search radius from 5 arcmin to 0 arcmin. This will retrieve only observations with the centre of that galaxy in the field of view. Now click the search button.
4. A new page opens which presents the search results: 36 HST observations, 13 HLA observations, 10 proposals and 196 publications.
5. In the HST observations tab, click on the table icon at the top-right corner of the window and add the observation date column to the table.
6. Click on the title of the observation date column to order the observations by date. You can also send the table to TopCat with the broadcast button at the top right and make a histogram of the observations using the START_TIME variable to see the number of observations as a function of time.
7. Retrieve the 14 WFPC2 observations taken during the years 1999 and 2000. If you have a recent ds9 version or aladin installed on your computer, you can also send the preview files to them by clicking in the broadcast button at the top right of each of the images.
8. On your local computer, open all the files ending in drz.fits.gz with ds9 or with any FITS visualiser tool and arrange them by observing date.
9. Adjust the cuts in all images and match all frames to have the centre of the galaxy nicely centred in each frame.
10. Create a ds9 region file with a J2000 position at 23 03 15.45 +08 52 26.5, save it to disk as a ds9.reg file and load it into all frames.
11. Comparing the images you will notice a point source appearing in the centre of the circular region in some of the images taken in 2000 and disappearing in later images. Congratulations: You have found SN 2000ft!
12. You can now do any measurements for the brightness change, the colours, the extinction and the energy output of the supernova with the Hubble images you have retrieved.

This reproduces work published in Astronomy & Astrophysics by Colina et al. 2007 where they found the optical counterpart with Hubble archival imaging data of SN 2000ft, a supernova previously detected at radio wavelengths.

Contacts

Bruno Merin
Astronomy Archives Science Lead at the ESAC Science Data Centre
Email: bmerin@sciops.esa.int