Limits on Pulsar Parameters for Pulsed detections with H . E . S . S .

The non-detection of pulsed sub-TeV γ-rays from EGRET pulsars proves that the EGRET pulsed spectra of all γ-ray pulsars should terminate at energies below a few hundred GeV. The spectrum of a typical integrated pulse profile predicted by the polar cap model resemble typically a hard component, followed by a super exponential cutoff between 1 MeV (PSR B1509-58) and tens of GeV (e.g. Crab, PSR B1951+32 etc). Outergap models predict a hard low flux component extending to TeV energies, and the stereo-scopic property of the H.E.S.S. (High Energy Stereoscopic System) ground-based detector (under construction) would have the advantage to discriminate against the background above 50-100 GeV, so that such a second component may be detectable. However, the challenge posed for any ground-based γ-ray detection is to prove that the instrument can detect a pure polar cap origin, whereas an outergap mechanism would provide little challenge given the rapid increase in the effective area A(E) with increasing energy E for Cerenkov telescopes. Using a topological trigger in the non-imaging mode, we show that H.E.S.S. should be able to detect pulsed emission from PSR B1706-44 within a few hours if the cutoff energy is above 30 GeV as suggested by EGRET observations. The recently detected radio pulsar PSR J1837-0604 (pulsar period: 96 ms) associated with the unidentified EGRET source GeV J1837-06010 should also be detectable within a few hours if the source is pulsed and if its cutoff is similar to that of PSR B1706-44. H.E.S.S. should even be able to image middle-aged, low-multiplicity pulsars for which the mean photon energy is expected to be well above 10 GeV. Such observations should provide important constraints on the final evolutionary status of γ-ray pulsars and millisecond pulsars in general.