HEAD Division Meeting 1999, April 1999
Session 29. Isolated Pulsars
Poster, Wednesday, April 14, 1999, 8:30am Wed. - 2:00pm Thurs., Gold Room

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[29.05] An ASCA Survey of GeV Sources

M.S.E. Roberts, R.W. Romani (Stanford University), N. Kawai (RIKEN)

We present an ASCA survey of GeV selected EGRET sources with E>1 GeV \gamma-ray photon flux >5.0 \times 10-8 {\rm cm}-2 {\rm s}-1. A combination of archival and new data covers ~75% of the sky contained within the 95% confidence position contours of these sources, and additional data obtained during the current observing cycle will increase this coverage to ~90%. We start with flat-fielded 2-10 keV images from the GIS data, and fit power-law spectra to potential counterparts. SIS, ROSAT, and Einstein data are used to confirm source detections and extend survey coverage. We then use the X-ray sources to identify radio counterparts in continuum survey data. Of the 26 GeV sources above our flux threshhold (Lamb and Macomb, 1997), 3 of the 4 at high galactic latitudes (b\ga 10\circ) are known blazars, while 5 of the low latitude sources are young pulsars. Of the remaining sources, 5 are plausibly associated with known young pulsars and/or plerionic SNR, one is at the Galactic center, and one may be associated with LSI+61 303. We focus here on the remaining 11 sources. By comparison with the known radio and X-ray properties of blazars and pulsars, we can identify potential members of these source classes, and potential new classes of \gamma-ray emitters. We also estimate source luminosities using distances inferred from nearby tracers of star formation (Yadigaroglu and Romani, 1997). Data from several fields are consistent with these sources being synchrotron nebulae surrounding radio-quiet `Geminga-like' pulsars. These data provide incentives for further searches for pulsations at high energies and in the radio. In other fields identification is more problematic. We compare our results to models of the relative beaming fractions inferred from the radio and \gamma-ray ray pulse shapes. The fraction of `pulsar candidate' detections is shown to provide useful constraints on pulsar luminosity evolution and beaming statistics.

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