Gamma-Ray Pulsar Studies with GLAST

Abstract

Abstract. Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies. GAMMA-RAY PULSARS -INTRODUCTIONBalloon and small satellite observations revealed gamma radiation from the Crab (e.g.[1]) and Vela [2] pulsars in the 1970's, becoming early examples of multiwavelength pulsar studies. The number of gamma-ray pulsars grew to at least seven during the Compton Gamma Ray Observatory (CGRO) mission in the 1990's (for a summary, see [3]). These high-energy photons are produced by primary interactions of the energetic particles accelerated in the pulsar magnetosphere. Their potential for studying some basic interaction processes was one stimulus for the development of pulsar models that included gamma rays as a characteristic. With the recent launch of AGILE and the upcoming launch of GLAST, the gamma-ray window on pulsars offers new promise. CHALLENGES AND OPPORTUNITIESAny satellite observations of pulsars present difficulties not found with ground-based observatories. Satellites move rapidly. Clocks on satellites, particularly before the advent of GPS, require careful monitoring and calibration. Data streams are subject to transmission errors, as well as human errors in design and implementation. Making corrections to a system in orbit is often non-trivial. For gamma-ray telescopes, the challenges are compounded by the low detection rate. Even the brightest pulsars produce high-energy gamma rays separated by many pulse periods. A weak pulsar like PSR B1055−52 yielded only 3 detected photons per day when in the field of view of EGRET on the Compton Observatory. During one day the pulsar rotates more then 400,000 times. Gathering statistics required adding data from many observations, often spaced months or even years apart.The sparse nature of gamma-ray pulsar data has made the field highly dependent on timing information from other wavelengths, primarily radio. The radio astronomy community has been highly supportive of the opposite end of the spectrum. The GLAST team greatly appreciates the help of radio astronomers at Arecibo, GBT, Jodrell Bank, Nançay, Parkes, and other telescopes, as ...