New high energy γ-ray sources observed by COS B

LOCALISED γ-ray sources contribute to the overall galactic emission; some of these sources have been identified with known astronomical objects1,2, while several unidentified γ-ray sources have also been reported3,4. We describe here a search for γ-ray sources using data from the ESA γ-ray satellite COS B which revealed 10 new unidentified sources. These sources seem to be galactic with typical γ-ray luminosities above 100 MeV in excess of 1035 erg s−1.

Observability of γ-ray pulsars

PULSARS seem to play a major role as γ-ray emitters. Of the 13 objects listed in the first COS B catalogue1 the two brightest, CG185-5 and CG263-2, have been identified with the Crab (PSR0531+21) and Vela (PSR0833–;45) pulsars respectively. This privileged role of pulsars as identified γ-ray sources could be simply related to observational reasons: in fact, because of the poor angular resolution intrinsic to the γ-ray telescopes, the only possibility of identification for individual sources is the time structure of the emission, and the periodical pattern of pulsars is particularly suited. On the other hand, for PSR0531+21 and PSR0833−45, the observed pulsed energy release is essentially in…

COS-B OBSERVATION OF THE MILKY WAY IN HIGH-ENERGY GAMMA RAYS

Angular resolution of an array of tracking-chamber detectors for use in high-energy gamma-ray astronomy

We describe a method of analysis for the reconstruction of the arrival direction of a high-energy photon impacting on the top of the atmosphere by using the directions of the particles on the shower front as measured by a ground-based array of tracking chambers uniformly distributed on a square surface; as an example, an array with enclosed surface of (120×120) m2 has been considered. Estimates on the accuracy of reconstruction are given, after application of the method to computer-simulated shower directions as a function of the number of «smapling» detectors and of their accuracy in the measurement of the «local» shower direction.

Possible pulsed gamma ray emission above 50 MeV from the Crab pulsar.

A SEARCH for pulsed gamma ray emission from NP 0532 has been carried out with a balloon-borne experiment using a spark chamber as the central detector. This pulsar, situated in the Crab Nebula, is already known to pulsate in the radio, optical and X-ray range1–5.

“Study of Pulsar Light Curves by Cluster Analysis”

The distribution of the phase numbers, corresponding to the arrival times of the gamma-ray photons detected by the COS-B satellite from the directions of the Crab and Vela pulsars, is analyzed by a clustering technique with the aim to detect possible microstructures in the pulsed emission. The method is found to be promising especially in view of the future gamma-ray experiments where better photon counting statistics is expected.