Observation of the ms-pulsar PSR J0218+4232 by EGRET

W. Hermsen, L. Kuiper

F. Verbunt

D.J. Thompson

A. Lyne, S. Ord, I. Stairs

G. Cusumano


We report the likely detection of pulsed high-energy gamma rays (100-1000 MeV) from the binary millisecond pulsar PSR J0218+4232 in the EGRET data, analysing all data collected over more than seven years of CGRO observations. PSR J0218+4232 appears to be below 1 GeV the dominant counterpart of the EGRET source 2EG J0220+4228/3EG J0222+4253; above 1 GeV BL Lac 3C66A is the obvious counterpart. Pulse-phase folding yielded a 3-sigma signal for a double pulse profile (separation about 0.5), which is statistically identical in shape to the X-ray profiles measured earlier by ROSAT (below 2.4 keV) and recently by BeppoSAX (up to 10 keV). Comparing spatial and timing analyses shows that the high-energy gamma-ray emission from the pulsar is consistent with being 100We compare in detail the absolute phases of the complex radio profile with the absolute phases of the EGRET profile (accuracy better than 100 microseconds) and the BeppoSAX profile (likely accuracy about 600 microseconds), and will present the total emission spectrum from radio up to high-energy gamma rays. This first likely detection of high-energy gamma rays from a millisecond pulsar challenges models explaining the production of such extreme non-thermal emission. Since the magnetic field strength of this pulsar near the light- cylinder radius appears to be similar to that of the Crab, an origin of the high-energy gamma rays in an outer gap, seems plausible.

File translated from TEX by TTH, version 2.32.
On 23 Aug 1999, 11:46.