The preliminary ALFA pulsar surveys started on August
1st, 2004. In the first day of observations, a new 67.8-ms pulsar, PSR
J1928+1746, was discovered: this was the first new pulsar found with
ALFA. It turned out to be an interesting object. Subsequent timing
analysis has shown that this is a rather young, energetic pulsar, the
characteristic age is only about 80 kyr.
An S-band pointing soon revealed that the pulsar is equally bright at
that frequency, indicating an unusually flat spectrum, unlike that of
almost all other pulsars. This was soon confirmed with observations at
C-band and X-band, that detected the pulsar with signal-to-noise
ratios comparable to those of the 1420-MHz observations. Strangely,
the pulsar could not be detected in a 430-MHz observation. This
pulsar's apparently unusual spectrum might not be so unusual: 1400-MHz
surveys are biased towards finding this kind of object, but the
pulsars found in these surveys were not consistently observed at
higher frequencies.
The lack of follow-up at higher frequencies was, historically, due to
the lack of good receivers operating at those frequencies. The recent
detections of PSR J1928+1746 at 5 and 9 GHz demonstrate that the
Arecibo radiotelescope and its receivers can now achieve excellent
sensitivities across the telescope's whole 10-GHz frequency
range. This might reveal a previously unsuspected population of
pulsars that remain bright at frequencies of several GHz, and change
the established idea that the vast majority of pulsars are steep
spectrum sources.
Pulse profile of PSR J1928+1746 at five different
radio frequencies.
Another interesting characteristic of this pulsar is that it is a
possible counterpart to an unidentified EGRET gamma-ray source,
3EGJ1928+1733. It is a better candidate than a previously suggested
counterpart, PSR J1930+1852. This pulsar is a prime example of a good
candidate for GLAST
follow-up, hopefully the ALFA pulsar surveys will find many such
objects. See Cordes et at. 2006 for details.
Grey-scale map for the probability of the location of
3EGJ1928+1733, an unidentified gamma-ray source catalogued by
EGRET.
The dots indicate the positions of two young, energetic radio pulsars.