ESA Science & Technology - Publication Archive
The results of a second observation in the Virgo region by the ESA COS-B satellite are presented. The presence of a high-energy (50-800 MeV) Gamma-radiation source is confirmed, and its position is consistent with 3C273. The error box at the 90% confidence level containing the quasar is ~2.5 square degrees and the probability of a change coincidence of the gamma-ray source with 3C273 is approximately 10-3. No variation of the gamma-ray fluxes between the two observations in July 1976 and June 1978 is observed within the ~50% uncertainty. Spectral y-ray data for the total 3C273 data set are presented and compared with low and high-energy X-ray contemporary measurements. Recent Einstein Observatory X-ray data on the short term variability of the central part of the QSO are used to show that, within reasonable assumptions, the photon-photon interaction excludes the gamma-ray source from coinciding with the variable X-ray source, thus ruling out comptonisation models for the production of energetic photons.
Published: 15 January 1981
The recently proposed nearby (distance approximately 0.03 pc) cloud of Vidal-Madjar et al. (1978) has an angular extent encompassing the Rho Oph region and the COS-B CG 353+16 source. In an attempt to analyze a possible association between the gamma-ray source and the cloud, usage is made of SAS-3 low energy X-ray data to put an upper limit on the columnar density, and thus such an association can easily be excluded. Furthermore, the possibility is analyzed that the COS-B source is associated with the Rho Oph dark cloud complex, and that the responsible process is the interaction of cosmic rays with the cloud mass. It is seen that a standard Black and Fazio (1973) mechanism can hardly be at work so the quantitative requirements are given for an improved gamma-ray production rate, obtainable, for instance, within the model of Forman et al. (1979).
Published: 16 July 1980
Gamma-ray observations from the COS-B satellite and radio pulse-timing measurements from the Tidbinbilla Deep Space Station are used to determine accurately the relative phases of the radio (2295 MHz) and gamma-ray (above 50 MeV) pulses from the Vela pulsar. Two independent analysis procedures are employed, and both show that the peak of the radio pulse leads the peak of the first gamma-ray pulse by 11.2 plus or minus 0.5 ms. This result, together with the data of Manchester et al. (1978), indicates that the phase delay relative to the radio pulse peak of the pulse components at optical and gamma-ray frequencies are about 11 ms (first gamma-ray), 21 ms (first optical), 42 ms (second optical), and 49 ms (second gamma-ray).
Published: 16 September 1978
The decrease of brightness temperature of relic radiation in the direction of the cluster of galaxies identically testifies to the existence of hot intergalactic gas in clusters.
Published: 01 November 1972
— 20 Items per Page