How To Take Part

Your task is to hunt for new supernovae in images taken by the Palomar Transient Factory. They observe the same patch of sky roughly once every five days, and our task is to look for changes.

You'll always be given three images : a new image, a reference and a subtraction.

The new image is the most recent, usually taken just a few hours ago. The reference image is the result of several observations added together; this is what this bit of sky normally looks like.

The subtraction image is the new image minus the reference image. Any differences between the two - like a new supernova - will show up most clearly here.

NEW		REFERENCE		SUBTRACTION
	-		=

Although some supernovae will appear with their host galaxy, this won't always be the case :

NEW		REFERENCE		SUBTRACTION
	-		=

Don't be put off if the SN is hidden in the 'new' image - that's why we have the subtracted image.

NEW		REFERENCE		SUBTRACTION
	-		=

To help you make your selections, you'll be asked a series of questions about each candidate.

Q: Is there a candidate centered in the crosshairs of the right-hand image?

Our computer program is set up to provide a single candidate at the centre of the crosshairs of subtraction image - the right-hand image. If you can see a candidate there, click 'Yes', or if something's gone wrong, then click 'No' here.

Click on the images to see the answer:

NEW	REFERENCE	SUBTRACTION
Yes	Yes	Yes
Yes	Yes	Yes
No	No	No
No	No	No

Q: Has the candidate itself subtracted correctly?

Look at the candidate itself. If all of the candidates' pixels are white, then click 'yes' and move on. If not - for example, if there are black and white pixels scrambled together, or there's a 'bullseye' pattern - then click 'no'.

Click on the images to see the answer:

NEW	REFERENCE	SUBTRACTION
No - Bullseye	No - Bullseye	No - Bullseye
No - black/white	No - Bullseye	No - Bullseye

Q: Is the candidate star-like and approximately circular?

We're getting close now. If it looks just like a star - a round, symmetrical dot in the centre of the image, click 'yes'. Otherwise click 'no' and tell us whether you rejected it because the image is particularly small (just 1 or 2 pixels across), elongated (not circular) or otherwise distorted, or spread over a large area ('diffuse').

Click on the images to see the answer:

NEW	REFERENCE	SUBTRACTION
No - Too small	No - Too small	No - Too small
No - Distorted	No - Distorted	No - Distorted
Yes - Good	Yes - Good	Yes - Good

Q: Is the candidate centred in a circular host galaxy?

The chances are you've now identified a real, astrophysical transient source. But there's one last question, designed to separate variable stars in our galaxy from supernovae in other galaxies.

Look at the host of the candidate - the object with which the candidate is associated (if there is one!). If the candidate appears in the centre of its host, and additionally if that host appears circular, then answer yes to this question. If there is no host at all, or if the candidate is off centre, or if the host is non-circular, then answer no. Here are a few examples:

Click on the images to see the answer:

NEW	REFERENCE	SUBTRACTION
Yes - centred in circular host	Yes - centred in circular host	Yes - centred in circular host
Yes - centred in circular host	Yes - centred in circular host	Yes - centred in circular host
No - candidate off centre	No - candidate off centre	No - candidate off centre
No - host not circular	No - host not circular	No - host not circular