This collaborative project will discover and study a large sample of neutron stars and also search for a variety of radio transient sources using the Arecibo L-band Feed Array (ALFA) at the Arecibo telescope. The science return results from both the hundreds of expected new pulsars and from rare, individual objects that will serve as laboratories for probing fundamental areas in physics and astrophysics.
The pulsar survey will complement and transcend previous surveys by reaching more than twice the distance of the very successful multibeam survey using the Parkes telescope. The work is expected to lead to discoveries of rare objects that will be used as laboratories for basic physics and astrophysics to probe the equation of state of nuclear matter, gravity in compact, high-mass binaries, and gravitational-wave backgrounds. Discoveries may include the first black-hole/neutron-star binary, which would allow unprecedented studies of gravity in the strong-field limit. The large sample of new pulsars, when combined with existing ones, will contribute to the understanding of neutron stars as end products of stellar evolution, and will enable state-of-the-art modeling of the Milky Way Galaxy with respect to its ionized components. Also, use of the large number of pulsars as tracers will allow delineation of some ambiguously defined spiral arms of the Galaxy.
The ultimate goals of the project will be enabled by the availability in 2008 of a new spectrometer that utilizes the full capabilities of the 7-beam system at Arecibo, and the availability of computer and data storage systems that can process and archive the large volume of data generated. Specific tasks include developmental activities related to the commissioning at Arecibo of the large bandwidth spectrometer, the setting up of the infrastructure required to analyze the data, and the intensive data analysis required to find new pulsars, all of which will be conducted in collaboration with the Pulsar ALFA Consortium, an international group of about 30 researchers. Over the 3-year project, about 1000 Terabytes of data will be analyzed using several computer clusters. Post-discovery studies will include timing campaigns and multiwavelength observations. A web-based system will provide access to source catalogs, timing models, and intermediate data products that can be used as a resource for synergistic studies. Raw data will be archived for long-term data mining applications and use in multiwavelength campaigns, such as future gamma-ray space telescope observations that require radio counterpart observations.
The large data volume requires development of data management for streamlined analysis, archival and retrieval. The project therefore serves as a prototype for future data-intensive surveys in astronomy, and will enable eventual connection to multi-user facilities such as national and international virtual observatories. The project will also contribute to the training of graduate students, and to the teaching of undergraduate students by their inclusion in certain aspects of data analysis.
This award has supported a collaborative observational astronomical program that is on-going at the Arecibo telescope in Puerto Rico, the world's largest and most sensitive single-dish radio telescope. The project is for a major radio pulsar and transients survey that uses an innovative 7-pixel receiver system operating at a wavelength of 20 centimeters. Pulsars are the rapidly-spinning compact and massive remnants formed in supernova explosions at the end of the lives of stars about 10 times more massive than our Sun. A collimated beam of radio waves is often emitted along the direction of the ultra-strong magnetic field attached to these stars made up mostly of neutrons, and as they rotate, given a fortuitous alignment, observers on Earth may detect pulses once at every turn, in light-house-like fashion. Nearly half a century after their first discovery, there are still only about 2000 pulsars known in our Galaxy - less than ordinary stars visible with the naked eye at night from a dark location. Prior to the beginning of this project, there were about 100 pulsars known in the portion of the Milky Way visible from Arecibo. While less than half of the eventual survey is completed, this work has already doubled the number of pulsars known in this area - and many of them are among the faintest and farthest known in the Galaxy. This will help us to better characterize the population of these stars in the Galaxy, providing a more unbiased picture of the overall population, not just that near the Earth. In addition, pulsars are beacons that lend themselves to the study of the diffuse Galactic interstellar medium, including its tenuous plasma and magnetic fields. The new discoveries, farther as they are than the average pulsars discovered in less sensitive surveys, will be particularly useful for these studies. In any survey of the unknown, we hope to find unusual or particularly interesting objects. So far, this survey has resulted in the discovery of a class of pulsars previously unknown in the Galactic disk: binary systems where one pulsar spinning hundreds of times per second (a so-called millisecond pulsar) moves together with another star in an eccentric orbit. We have also discovered a young pulsar in a short-period binary where relativistic effects are clearly detectable, helping to test certain aspects of Einstein's general theory of gravitation. This survey is exceedingly sensitive to radio pulses or transients, whatever their origin - even from far, far outside our own Galaxy. We believe that we have detected just such a pulse, possibly originating in a cataclysmic event in a far-off galaxy. This so-called Fast Radio Burst is the first such example detected anywhere other than with the Parkes telescope in Australia, and therefore strengthens the case for the ubiquity of this newly identified class of extra-Galactic events, now a research area of great interest. A variety of students and researchers are active in this program - including citizen scientists distributed throughout the world. Data collection at the Arecibo telescope generally proceeds remotely - much of it has been carried out by high school and undergraduate students operating from Arecibo Remote Command Centers at the University of Texas in Brownsville, and the University of Wisconsin in Madison (UWM). Some of these students also participate in data analysis - which is made complicated by the presence of Earth-generated radio frequency interference, now ubiquitous owing to the prevalence of cell phones, satellites, etc. Together with clever algorithms developed in the course of this work by graduate students and other researchers, the students at all levels sift through the data, and through the interference, searching for - and occasionally finding - new pulsars. A different impact of this work has involved the collaboration with hundreds of thousands of citizen scientists that donate their idle computer time, via a screen saver developed by Einstein@Home, a volunteer global distributed computing activity hosted by UWM. In this way, tens of pulsars have been discovered in the Arecibo data set, while engaging huge numbers of people worldwide in the excitement of scientific activity.
