Tips on Pulsar Searching

A few tips on pulsar hunting, and a clarification on terminology

  1. Each data set, or link on the database’s Skymap, is called a pointing, in reference to where the telescope was pointing in the sky. There’s a caveat here, as this is not the normal use of the term "pointing." Normally, when a telescope looks at an object, it tracks with the object. Meaning, we pointing the telescope at say, the Crab nebula, and we look at it for 10 minutes. Since the Earth moves during this time, the apparent location of the nebula in the sky moves.

    We have all this technology that accounts for the rotation of the earth and allows us to compensate for the Earth’s rotation and keep the telescope pointed at the Crab nebula as long as we want. So, in traditional astronomy, when we talk about a pointing, it is that one location in the sky to which the telescope points.

    For the PSC however, the telescope was immobilized due to the track repair. So the sky constantly drifted overhead, as the telescope was not able to take into account the Earth’s rotation. Therefore, the telescope did not point at any one location for more than a few seconds. What we call a pointing is really the collection of a chunk of sky–say, as much sky as drifted by in 5 minutes, processed all together. We overlap the pointings as well, so that each position in the sky gets processed twice. For example, if observations start at 1:00pm, the data from 1:00:00pm to 1:05:00pm is one pointing, and the data from 1:02:30pm to 1:07:30pm is the next pointing, and so on. We’ll get to why this is important in a minute.

  2. For each pointing, when we process the data, we go over a bunch of trial values for the period and dispersion measure (you know this already). We put the 30 most likely candidates on the database for you. Each of these is called a plot. The regular plots are technically called prepfold plots. And then there are, of course, the single pulse plots.
  3. Ok, so we have pointings and plots. As was mentioned, all data gets processed twice. SO, if you see a potential pulsar in the prepfold plots, you should immediately do four things, in this order:
    • See if any other prepfold plots in that pointing also have a potential pulsar. Since we are processing over a range of dispersion measures, and they are trial values, a pulsar should show up in two plots with similar dispersion measures. For example, you would see it in the prepfold plot with a dispersion measure of, say, 48, and in the prepfold plot of 50.
    • See if it shows up in the single pulse plots. If you notice the name in the title of the single pulse plots, it says something like DMs30-100. Which means it is searching over the range of dispersion measures from 30-100. So, if the pulsar shows up in the prepfold plots with DMs of 48 and 50, you may see it in the single pulse plot of DMs30-100, but not DMs300-600.
    • Since each of the data gets processed twice, like I said above, then the pulsar should show up in adjacent pointings. So, look for the pulsar in the adjacent pointings on either side. For example, if you see a potential pulsar in the pointing 07:42, also look at 07:41 and 07:43.
    • Check and see how far away the pulsar is, and see if this makes sense. Use the Distance Calculator in the right column on the home page.

These are just general guidelines, and there are always exceptions. But the four questions above are the ones astronomers will ask first.