SEARCH FOR NEW MILLISECOND PULSARS

INTRODUCTION

Following atomic clocks, pulsars are the best clocks known to man. Having pulsars of known periods at various locations in the sky will therefore be very useful and advantageous for exploration in a wide range of areas in astrophysics. The purpose of this project is to find new interesting millisecond pulsars that will serve as probes for astrophysical observations.

Pulsars emit radiation at periods generally ranging from 1 millisecond to 4 seconds. Their remarkable stability in period allows us to use them as excellent probes of the universe--from interstellar medium to gravitational wave background (Fruchter, Tavani, Backer 1995). We can also establish a very precise pulsar-based time standard and make connections among reference frames (Kaspi 1995). This project focuses on search for " millisecond" pulsars, whose periods are the shortest among others, so that we can minimize the uncertainty in measurement of time intervals.

To find as many pulsars as possible, this search will use data taken at radio frequencies around 430 MHz where the intensities would be the highest. In addition, the data is from the largest radio telescope on earth, the 305-meter Arecibo telescope in Puerto Rico. A new and very promising aspect of this particular survey is its unprecedented sampling interval of 80 microsecond. This fast sampling rate will make possible discovery of many short-period pulsars that previous surveys could not detect.

Besides their application as probes, some of the pulsars discovered in this project will likely be inherently interesting. If this search finds sub-millisecond pulsars, it will raise many fascinating puzzles about the nature of the matter that can hold itself under such rapid rotation (Kulkarni 1995). Finding relativistic binaries and pulsars with planets would be particularly exciting too, and we will be able to learn new astrophysics from those.

Currently, no more than a few hundred millisecond pulsars have been found, and the shortest period observed is 1.57 millisecond (PSR B1932+21). The galaxy, however, most likely has as many active millisecond pulsars as there are normal pulsars (Lyne & Graham-Smith 1990). My project will lead to discovery of more millisecond pulsars, quite likely ones with periods shorter than ever found, and hopefully ones in rare regions including away from the galactic plane.

The plan for this project includes cataloging of data, mapping of locations, storage of data, preliminary analysis, search for pulsar signals, and initial timing of any pulsars found.

PLAN

The goal is to analyze all of the available data to find pulsars, and time the discovered pulsars to determine their periods to high accuracy.

The data consist of power measurement at 128 radio frequencies between 426MHz and 434 MHz with band width of 60 kHz at certain times and locations on the sky. They come from the Arecibo telescope between November 1996 and spring 1998, and are stored on about 400 5GB-tapes processed by Penn-State Pulsar Machine (PSPM).

Quantities to be measured and calculated include: locations of the pulsars, dispersion of signals due to interstellar medium, and periods of pulsars using the fast Fourier transform. These calculations must take into account such factors as the motion of the observatory relative to the Sun’s center of mass, proper motion, and parallax if the pulsar is nearby.

This project will make use of high-density tape drives, UNIX workstations, HPSS, and parallel machines. It will also use existing programs designed for pulsar analysis. I will need to create and modify programs and pipelines using shell script, C -programming, and Message Passing Interface (MPI) for parallel machines.

This project will create a valuable catalog of data containing periods and further information about new pulsars so that it can be utilized as a collection of probes in astrophysical studies.

My curiosity and excitement about searching for pulsars as well as my big lifetime goals in the fields of astrophysics and space exploration are more than sufficient to overcome any difficulties conceivable in this project.

CONCLUSION

To make new advances in observations of the universe, reliable probes will be very desirable. Millisecond pulsars prove to be one of the most stable clocks we know, and the goal of this project is to find new ones at various locations on the sky. The data used in this search are ideal because they come from a survey done by the largest radio telescope at the fastest sampling rate ever. In addition, this search has a good possibility of finding peculiar pulsars and other interesting objects along the way.

I would really like to accomplish this goal and learn significantly about analysis of astrophysical data and about research in general.

REFERENCES