In the news this month: supernova spotted in the Pinwheel galaxy
Supernova PTF11kly in M101: the first three nights of observing the supernova show how it brightens very rapidly. CREDIT: Peter Nugent and the PTF collaboration
August 24th saw the discovery of one of the closest supernovae of its kind in recent years. Located in the nearby spiral galaxy M101, the explosion was reported by the Palomar Transient Factory (PTF), a survey of the sky which aims to detect and catalogue transients using two telescopes at the Palomar Observatory in California. Catalogued by the PTF collaboration as PTF11kly, the position of the supernova was distributed rapidly through the Astronomers Telegrams, allowing follow-up by other astronomers using a variety of telescopes across the electromagnetic spectrum.
With transient events like supernovae, such rapid follow-up with other telescopes is extremely useful in trying to understand the physics of what happens in the explosion. Comparatively little is known about the first few hours to days of supernova evolution since they are often discovered days (and sometimes weeks) after the initial explosion.
In the case of PTF11kly, also catalogued as SN2011fe, the event was spotted very early in its evolution, as the brightness was still increasing, and spectroscopic observations by the Liverpool Telescope in the Canary Islands quickly showed that this particular event was of the class known as type Ia supernovae. This kind of event is thought to be caused by a thermonuclear explosion on the surface of a white dwarf star in a binary system, although there are variations in the theoretical models which detailed observations could help to resolve. This particular supernova is the closest example of a type Ia event in almost forty years. This is significant because it is this type of supernova which is used to measure the expansion of the universe, so having a good understanding of the underlying physics of these explosions is essential for cosmological studies.
Since it was discovered so early in its evolution, PTF11kly should continue to brighten over the next few days before it begins to fade. At discovery, the object had a magnitude of 17 but was brightening rapidly. Located in M101, the Pinwheel galaxy in Ursa Major, it is estimated that the supernova could become bright enough to spot with binoculars or a small telescope. In contrast, observations carried out with the Very Large Array, a collection of 27 radio telescopes located in New Mexico, show no radio emission from this supernova. This is not surprising, as so far no type Ia supernova has ever been spotted by radio telescopes, despite numerous searches.
Telescopes of various types will continue to monitor this supernova as it evolves over the following months, and astronomers will use the data collected to test various aspects of the physics and chemistry of supernova models.
This blog post is a news story from the Jodcast, aired in the September 2011 edition.