文档库

最新最全的文档下载
当前位置:文档库 > Prospects of observing pulsed radiation from gamma-ray pulsars with H.E.S.S

Prospects of observing pulsed radiation from gamma-ray pulsars with H.E.S.S

a r X i v :a s t r o -p h /0010179v 1 10 O c t 2000Prospects of observing pulsed radiation from gamma-ray pulsars with H.E.S.S.O.C.de Jager 1,A.Konopelko 2,B.C.Raubenheimer 1and

B.Visser 1

1Unit for Space Physics,Potchefstroom University,Potchefstroom,2520,South Africa 2Max Planck Institut f¨u r Kernphysik,Postfach 103980,D-69029Heidelberg,Germany Abstract.Observations and theoretical studies have demonstrated that the pulsed spectra of all gamma-ray pulsars terminate at energies below a few hundred GeV.In most cases we expect this cutoffenergy E o to be around 10GeV.Only with next-generation ground-based γ-ray telescopes,which are expected to have non-zero trigger probabilities near 10GeV,can we expect to detect pulsations.The large γ-ray fluxes below E o ,together with the associated sharp pulse profiles,compensate for the lack of imaging capability near threshold.For H.E.S.S.we find that the pulsed component of PSR B1706-44should be detectable near threshold,whereas the unidentified GeV EGRET sources should be detectable if the superexponential cutoffenergy is larger than ∼30GeV for relatively hard pulsar photon spectra (∼E −1.5).A Introduction Whereas gamma-ray pulsars are known to count amongst the brightest sources in the 1-30GeV range (Lamb &Macomb,1997),only their plerions,supernova shells and extragalactic sources appear to be visible at TeV energies.This is not

unexpected,since pulsed γ-rays are known to be created in strong magnetic fields and magnetic pair production results in a superexponential cutoffabove a charac-teristic energy E o .Simulations of pair cascades have shown that E o is usually in the 10GeV region (Daugherty &Harding,1996),but this cutoffdepends on several parameters,such as the altitude of γ-ray production above the polar cap,the ob-server’s viewing angle relative to the spin axis,and the magnetic inclination angle relative to the spin axis.A γ-ray/e +/−cascade develops and those photons which escape pair creation (with E

dN γ/dE =k (E/E n )−g exp (−(E/E o )b ).(1)