The likely detection of pulsed high-energy gamma -ray emission from millisecond pulsar PSR J0218+4232
Abstract
We report circumstantial evidence for the first detection of pulsed high-energy gamma -ray emission from a millisecond pulsar, PSR J0218+4232, using data collected with the Energetic Gamma Ray Experiment (EGRET) on board the Compton Gamma Ray Observatory (CGRO). The EGRET source 3EG J0222+4253 is shown to be spatially consistent with PSR J0218+4232 for the energy range 100-300 MeV. Above 1 GeV the nearby BL Lac 3C 66A is the evident counterpart, and between 300 MeV and 1 GeV both sources contribute to the gamma -ray excess. Folding the 100-1000 MeV photons with an accurate radio ephemeris of PSR J0218+4232 yields a double peaked pulse profile with a ~ 3.5sigma modulation significance and with a peak separation of ~ 0.45 similar to the 0.1-10 keV pulse profile. A comparison in absolute phase with the 610 MHz radio profile shows alignment of the gamma -ray pulses with two of three radio pulses. The luminosity of the pulsed emission (0.1-1 GeV) amounts Lgamma =1.64* 1034 * (Delta Omega / 1\ sr)* (d/ 5.7\ kpc)2 \ erg s-1 which is ~ 7% of the pulsar's total spin-down luminosity. The similarity of the X-ray and gamma -ray pulse profile shapes of PSR J0218+4232 , and the apparent alignment of the gamma -ray pulses with two radio pulses at 610 MHz, bears resemblance to the well-known picture for the Crab pulsar. This similarity, and the fact that PSR J0218+4232 is one of three millisecond pulsars (the others are PSR B1821-24 and PSR B1937+21) which exhibit very hard, highly non-thermal, high-luminosity X-ray emission in narrow pulses led us to discuss these millisecond pulsars as a class, noting that each of these has a magnetic field strength near the light cylinder comparable to that for the Crab. None of the current models for gamma -ray emission from radio pulsars can explain the gamma -ray spectrum and luminosity of PSR J0218+4232 .
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2000
- DOI:
- 10.48550/arXiv.astro-ph/0005338
- arXiv:
- arXiv:astro-ph/0005338
- Bibcode:
- 2000A&A...359..615K
- Keywords:
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- STARS: PULSARS: INDIVIDUAL: PSR J0218+4232;
- STARS: NEUTRON;
- GALAXIES: BL LACERTAE OBJECTS: INDIVIDUAL: 3C 66A;
- GAMMA RAYS: OBSERVATIONS;
- X-RAYS: STARS;
- Astrophysics
- E-Print:
- Accepted for publication in A&