Low energy γ rays from PSR1822–09

Abstract

Pulsed γ-ray emission in the MeV range (80 keV–6 MeV) has been clearly established^1–4 for the Crab pulsar PSR0531+21 (P = 33 ms). The energy spectrum of the pulsed component follows a power law from the X-ray (100 keV) to the high energy γ-ray range (2. GeV) with an index close to 2.1 (ref. 5). Positive detection of pulsed γ ray emission from the Vela pulsar PSR0833–45 (P = 89 ms) has been claimed in the 10–30 MeV region by Albats et al.⁶, and clearly established⁵ in the high energy range 50 MeV–3 GeV with a power law index of 1.9. This pulsar was also observed in the X-ray range but with apparently conflicting results (ref. 7 and refs therein), some authors reporting positive detection while other have upper limits below the reported values. Other radio pulsars, especially PSR1822–09, and PSR1747–46 have been investigated at energies above ∼50 MeV by the satellites SAS2^8,9 and COS B¹⁰. We report here observations of PSR1822–09 (P = 769 ms) between 80 keV and 6 MeV at balloon altitudes.