Centaurus X‐3: A Source of High‐Energy Gamma Rays

Abstract

Centaurus X-3 is a well studied high-mass accreting X-ray binary and a variable source of high-energy gamma rays with energies from 100 MeV to 1 TeV. Previous results have suggested that the origin of the gamma rays is not the immediate vicinity of the neutron star but is sited in the accretion disk, perhaps in an accretion wake. The Durham Mark 6 gamma-ray telescope has been used to measure the gamma-ray Ñux from Centaurus X-3 with much higher sensitivity than previous ground-based measurements. The Ñux above D400 GeV was measured to be (2^0.3) ] 10~11 cm~2 s~1 and appears constant over a period of 2È3 months. In 10 hours of observations there is no evidence for periodicity in the detected gamma rays at the X-ray spin period either from a site in the region of the neutron star or from any other potential site in the orbit.

A Search for Very High Energy Gamma Rays from Active Galactic Nuclei Visible from the Southern Hemisphere

“…These image parameters allow discrimination between the elliptical images, the major axes of which point toward the source direction, produced by a gamma-ray shower, and the broader, more irregular images produced by a hadronic shower. In addition, a measure of the di †erence between the positions of the centroids of the light recorded by the left and right Ñux collectors of the Mark 6 Telescope provides a further discriminant, (Chadwick et al 1998). Gamma D dist rays are identiÐed by selecting events on the basis of image shape and left/right Ñuctuation and then plotting the number of events as a function of the pointing parameter ALPHA ; gamma-ray events from a point source will appear as an excess of events at small values of ALPHA.…”

Search for TeV Emissions from Pulsars in Binary Systems

“…One of these sources, the high-mass X-ray binary Centaurus X-3, is the only binary so far identified as a source of high-energy radiation, being detected at GeV (Vestrand, Sreekumar, & Mori 1997) and TeV (Chadwick et al 1998) energies. Emission from a second binary, the Be X-ray binary PSR 1259À63, was reported by the CANGAROO collaboration, although only at the 4 confidence level (Kifune 1996); however, later observations failed to confirm these results.…”

Recent results from the CANGAROO 3.8 m telescope

“…The 3.8 m telescope has not been in operation since October 1998 to concentrate to the construction of the 7 m telescope. In 1998, before stopping the 3.8 m telescope, we observed two important objects; RX J1713.7-3946 which is a very similar SNR to SN 1006, and Cen X-3 from which a 400 GeV gamma-ray signal was recently detected by the Durham group [9]. Preliminary results on these objects are summarized in the next section.…”