So whats going on ???

Hi Aaron,

Arecibo is a radio telescope so it has to be pointed and can only see a really small patch of the sky at once; to cover the whole sky you have to slew telescope, observe again, and repeat, and so on. With the searches for pulsars there are two main directions that the Arecibo Pulsar Survey is targeting: the inner Galaxy (many stars and many pulsars) and the outer Galaxy (less stars and less pulsars).

The main reason why we had so many discoveries in 2012 is that we were searching data taken by the Arecibo telescope when it was pointing in the inner Galaxy, while now we're mainly looking at the data from the outer Galaxy.

You can see that immediately in this plot, which I took from the PALFA webpage:

The plot shows a schematic of our Galaxy from above, the Sun is at the thick circle with a dot at the center in the top half (below the words "Orion-Cygnus"). Red dots are all known pulsars, blue dots are the pulsars found by the PALFA survey.

Arecibo on the Earth, thus at the position of the Sun in this scale, can basically see two wedges. One going to the bottom right, between 35 and 75 degrees in the angle scale centered on the Sun's position. This is the "inner Galaxy" direction I was referring to. See all the blue dots? Those are all pulsars discovered in PALFA data (not necessarily by Einstein@Home, though).

The other wedge is going to the top, between 170 and 210 degrees on the Sun-centered angle scale. You can easily see that are much fewer pulsar looking to the outer Galaxy just because the Sun is not at the center of the Galaxy and there are less stars looking outwards. Thus, there are less pulsars and also less PALFA discoveries.

Hope that helps, Cheers,
Benjamin