Search

The Crab pulsar (PSR0531 + 21) was one of the earliest identified sources of high-energy γ radiation1–6. As such it was selected as the first object of detailed study by ESA's γ-ray astronomy satellite COS B, launched in August 1975. The experiment and mission have been described elsewhere7. In the first 6 yr of operation COS B has made five observations (each of 30–40 days duration) in which PSR0531 + 21 was within 15° of the centre of the field of view. The first of these confirmed the result of the SAS 2 experiment that the γ-ray light curve for energies above a few tens of MeV consisted essentially of two equally strong peaks but the later measurements found a decrease in the strength of the second peak relative to the first. No change was observed in the 2–12 keV X-ray light curve simultaneously measured by COS B. The total data from the five observations contain the first evidence of interpulse emission between the two peaks in the energy range 50–3,000 MeV.

Einstein Observatory and Exosat X-ray data from 1E0630 + 178 reveal a ∼50% periodic emission at ≥59 s. This confirms the earlier SAS 2 and COS B findings on 2CG195 + 4 at E> 50 MeV, and provides the temporal signature for the identification of Geminga. The observations, spanning over a decade (1973–83), also suggest a very high positive period derivative, P, which has become still higher between 1979 and 1983. A simple source scenario is proposed, based on a binary system containing a compact object responsible for the high energy emission, and also taking into account recent ultra high energy γ-ray measurements.

During a search for X-ray counterparts of the COS B≥100 MeV γ-ray sources (see refs 1, 2), observations using the Einstein Observatory revealed a new X-ray source, 1E0630 + 178, inside the ∼1/2 square degree error box of the γ-ray source 2GC195+4, ‘Geminga’3. On the basis of its interesting properties, this source has been proposed as the X-ray counterpart of Geminga. A faint (mv∼21), star-like object lying at the inner boundary of the HRI 98% error box has been suggested4–7as the optical counterpart of the X-ray (and thus the γ-ray) source. No radio counterpart has been detected, despite several searches7,12,13. The region of Geminga was observed with the European Space Agency (ESA) Exosat satellite on 9–10 September 1983, from 22.30 to 07.55 UT. Due to malfunctions in orbit, both Position Sensitive Detectors of the low energy (LE) telescopes were not operable, and only the Channel Multiplier Arrays (CMA1 and 2) gave useful data. The medium energy (ME) and Gas Scintillation Proportional Counter (GSPC) instruments also recorded data although their sensitivity is insufficient to detect this soft ≃0.1 UFU source, also not detected by Einstein's Monitor Proportional Counter (MPC).

CYGNUS XR-1/HDE226868 is a multiple star system in which the secondary is the best astronomical candidate for a black hole. The existence of a third body in the system could affect the mass derived for the secondary from the analysis of spec-troscopic radial velocity curves1. Hence, the presence of a periodicity in the system other than that of the 5.6-d binary orbit has a major bearing on the identification of the secondary with a black hole, especially if such a periodicity can be related to the orbital period of a third body. The existence of a 78.4 (or 39.2)-d periodicity in the optical and low-energy X-ray wavelength region of the emission from this system has been reported by Kemp et al.2,3. The existence of a 39.2-d modulation in the optical and low-energy X-ray luminosities has been questioned by Walker et al.4. We report here a search for a 78.4-d modulation in the high-energy X-ray flux observed with OSO 8 and in the U-band optical polarisation previously observed5, with negative results. We suggest, however, that if such modulation does exist, it is more likely to be related to the rotation of the free modes of oscillation of the primary than to the existence of a third body in the system.

THE discovery of a high-energy γ-ray source at α(1950) = 12h 29 min±6 min, δ(1950)= +3°±1.5° is reported here. Arguments are given for the identification with 3C273. If this identification is correct, the γ-ray luminosity of 3C273 in the energy range 50–500 MeV is 2×1046erg s−1for H0= 60 km s−1Mpc−1.