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NOTICE:
This Legacy journal article was published in Volume 2, November 1992, and has not been
updated since publication. Please use the search facility above to find regularly-updated information about
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Number 2 November 1992
The Geminga
237ms Pulsar
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Goddard Space Flight Center
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On the cover
This cover figure is from the paper "SAS 2 Observation of Pulsed
High Energy Gamma Radiation from Geminga" by J.R. Mattox, D.L. Bertsch, C.E.
Fichtel, R.C. Hartman, D.A. Kniffen & D.J. Thompson, Ap.J. Letters,
in press.
The recent discovery by Halpern and Holt (1992, Nature, 357, 222)
of 237ms pulsations from Geminga using ROSAT prompted a reexamination of
archival COS B and SAS 2 data. The front cover shows the
gamma-ray phase plot for Geminga for E
70 MeV. Arrival times of the archival SAS 2 and COS B events
were epoch folded with the COS B ephemeris. Phase 0 corresponds to the
epoch time at the solar system barycenter. COS B events were selected
from the energy-dependent cone (Buccheri et al. 1983, A&A,
128, 245)
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The dashed line shows the level of diffuse gamma radiation expected if no
source were present. For comparison the EGRET data (Bertsch et
al. 1992, Nature, 357, 306) are shown in the figure. The
phase of the EGRET data has been adjusted to match COS B, because the
uncertainties in the timing fits for COS B and EGRET data do not
allow an absolute phase comparison. The EGRET histogram contains 5322
events (approximately 36 days of exposure), the COS B histogram 1897
events (approximately 251 days of exposure), and the SAS 2 histogram 82
events (19 days of exposure).
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