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10 Sept 2011-
PIRATE captures pinwheel moments before explosion

PIRATE obtained what is possibly the last recorded image of the pinwheel galaxy M101 in Ursa Major before the now famous supernova SN2011fe/PTF11kly went off.

The explosion in the spiral galaxy M101 at a distance of 6.4 Mpc is the closest type Ia supernova for 40 years, and kick-started the most detailed study yet of any type Ia supernova. They are thought to occur when a white dwarf star gaining mass by accretion from a companion star is pushed over its stable mass limit. Type Ia supernovae are hugely significant for cosmological distance measurements as they are thought to reach a fixed maximum luminosity. Distances derived under this assumption show that the expansion of the Universe is accelerating.

SN 2011fe/PTF11kly was discovered by the Palomar Transient Factory project on 24 Aug 2011, and reached a peak brightness of about 10 magnitudes in early September.

By coincidence, PIRATE imaged M101 between 18 - 24 Aug. The supernova is clearly detected in the 24 Aug image (Figure 1, lower panel), but there is no sign of it in the 23 Aug image (Figure 1, upper panel). At the time of writing no later image of M101 is known that shows no trace of the supernova. Thus the PIRATE image places limits on the actual outburst time and informs theoretical models of the outburst mechanism and nature of the progenitor system.

The PIRATE images below show the galaxy M101 (inverted greyscale, to emphasize detail), with the position of SN2011fe/PTF11kly indicated by the cross hair. The celestial coordinate system is overlaid. Images taken by Stefan Holmes, in collaboration with Ulrich Kolb, Carole Haswell (OU), Vadim Burwitz and Juan Rodriguez (OAM).
Upper panel: 23 Aug 2011
Lower panel: 24 Aug 2011



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