Most of the advances in pulsar astronomy were due to the discovery of
new objects. A major increase in search sensitivity has already started
a new era of discovery at the Arecibo Observatory.
This increase in search sensitivity is due first and foremost
by the ALFA receiver and the pulsar surveys it makes possible, which
are now being carried by the Pulsar Consortium. Preliminary estimates
(see below) indicate that the Arecibo
Galactic plane survey using ALFA could find many hundreds of new
pulsars. It is still speculative to guess what this
survey will find, but from its superior spectral and time resolution
it is safe to say that the percentage of millisecond pulsars and
double neutron stars relative to the total of known pulsars will
increase significantly. This survey will be able, for the first time,
to search for pulsars with rotational frequencies in excess of 1000
Hz, and to search for extreme binary systems. Among the many expected
scientific payoffs will be new laboratories for the study of
gravitational physics and the study of dense matter. A prime example
of this is the discovery of the second most relativistic
binary pulsar known, PSR J1906+0746.
Simulation of the P-ALFA pulsar survey, in Galactic X-Y
coordinates (center of the Galaxy is at (0,0). Red dots indicate
positions of known pulsars, blue indicates positions of expected
detections by the Arecibo P-ALFA survey. The black stars indicate
positions of new pulsar discoveries already made
by this survey. See below for
documentation with the details on these simulations.
Data taking
With ALFA, we need about 47 pointings to cover one square degree,
compared to about 330 pointings needed to cover one square degree with
similar density with a single-pixel feed. Up until now, we have
been using the Wideband Arecibo Pulsar Processors (
WAPPs) to detect the signal from
ALFA's seven beams. These cover 100 MHz of band (with dual
polarization capability), initially centered at 1420 MHz and now at
1440 MHz. For search purposes, we produce 256-channel spectra every 64
microseconds.
From August 1 to October 8 2004, we conducted a preliminary survey that
covered the two regions closest to the Galactic plane (|b| < 1
degrees) visible from Arecibo: the "Inner Galaxy" (40 < l < 75
degrees) and the "Anti-center" (170 < l < 210 degrees). Each pointing
was 134 seconds for the Inner Galaxy and 67 seconds for the
Anti-center. This was done in sparse mode, where we do only 1/3 of the
pointings needed to cover the whole region. This preliminary survey
found a total of 11 new pulsars, and detected 30 previously known
pulsars. For a detailed description of this survey, and the strategy
of the present survey, see
Cordes
et al. (2006).
Since March 16 2005, we have started the main ALFA pulsar survey.
This will cover the Galactic plane (|b| < 5 degrees) visible
with the Arecibo 305-m radio telescope (35 < l < 75 degrees), it is
unclear what the latitude coverage will be in the Anti-center. Each
pointing lasts about 268 seconds in the Inner Galaxy and 134 seconds in
the Anti-center.
In 2007, we will have new back-ends which will be capable of covering
300 MHz (from 1225 MHz to 1525 MHz, the bandwidth covered by ALFA) for
each of the seven beams (see
preliminary specifications
here).
This will lead to greatly increased search sensitivity, provided we
can deal with all the radio frequency interference.
Data processing and storage
All detections to date have been made with a quick reduction package
that allows us to find pulsars almost in real time. This is made
possible by reducing the spectral and time resolution by a factor of
16, and using a computer cluster, the
Arecibo Signal
Processor to search for pulsars in the data.
This is a nice and quick way of detecting slow pulsars, but the
sensitivity to fast pulsars is severely degraded. Re-processing
these data with full resolution is, computationally, a very
challenging task, that is only now starting to be addressed. This will
be essential for detecting many fast (both young and recycled) pulsars
so far hidden by Galactic plasma.
It is expected that, over the next 6 years or so, this survey will
generate over
1000 Terabytes of data. This will be stored at
the
Cornell University Center
for Advanced Computing,
and processed at the participating institutions in dedicated computer
clusters.
