EGRET Pulsars in the Fermi Era

Details EGRET Pulsars in the Fermi Era EGRET Pulsars in the Fermi Era

Feb 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.1603c&link_type=abstract

American Astronomical Society, HEAD meeting #11, #16.03; Bulletin of the American Astronomical Society, Vol. 41, p.679

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Until the launch of the Fermi Gamma-ray Space Telescope on 11 June 2008, only six high-confidence gamma-ray pulsars were known above 100 MeV. Although some of these are among the brightest Galactic sources, due to the limited sensitivity of EGRET, it was not possible to study their pulse profiles in detail and measure their spectral cutoffs, with only a handful of photons above 5 GeV. With the excellent sensitivity of the Large Area Telescope (LAT) on Fermi, after only one year of observations of these pulsars we have collected more than an order of magnitude more photons than collected by EGRET in its nine year lifetime. This unprecedented high statistics allowed us to construct high-quality pulse profiles and study their evolution with energy. In particular, a pulse profile as fine as 67 microseconds has been obtained for Vela, uncovering an additional peak moving with energy, and a decrease in the ratio of the first peak to the second peak as had been suggested by the EGRET data. Additionally, it was possible to measure the overall shape of their spectra, demonstrating that all have a power law with simple exponential cutoff shape, with cutoff energies varying from 1.3 GeV for PSR J1057-5226 to 5.8 GeV for the Crab pulsar. Moreover, we have constructed detailed phase-resolved spectra of these pulsars revealing a complex evolution of the spectral parameters with phase. As a result, the study of the six EGRET pulsars has improved our understanding of pulsed emission and is allowing us to test the predictions of the current high-energy pulsed emission models.

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