High-energy X-radiation from M-87
Fishman, Gerald Jay
Haymes, Robert C.
Master of Science
M-87 (NGC 4486), a radio galaxy in the Virgo cluster, exhibits several unusual features which prompted a search for high energy X-radiation from it. Soft X-rays have been detected from the galaxy implying an X-ray luminosity of 10 to the 43rd ergs/sec. The X-ray datum, the optical emission from an unusual jet extending from the nucleus of the galaxy and the radio core emission can all be fitted to a single power-law spectrum characterized by a spectral index of -0.80. Polarization of the optical radiation from the jet indicates that the synchrotron mechanism is probably operative there. A balloon-borne experiment was performed in August, 1967 in an attempt to observe a high energy extrapolation of the radiation from M-87. The detector system is similar to that used previously by the Gamma-Ray Astronomy Group at Rice University. The central detector is a sodium iodide scintillator crystal (thallium activated) 5 cm thick with a sensitive area of 75 cm2 . An on-board 128 channel pulse-height analyzer responds to photons in the energy range from 27 keV to 555 keV, so that the differential energy spectrum may be measured. A large crystal surrounding the central crystal acts as an active collimator to produce a half-intensity, half-angle field of view of 12°. The detector mounting is of an equatorial type and uses the geomagnetic field as an azimuth reference. Data were obtained from the Virgo region, centered on M-87, for 63 minutes and from sky background regions for 84 minutes. A flux at the top of the earth's atmosphere of 8.2 ± 3.5 x 10 to the -3 photons - cm -2 - sec -1 was detected from the Virgo region in the energy range from 40 keV to 107 keV. Low upper limits were measured for energies greater than 107 keV and for the 511 keV annihilation line. Due to the large field of view of the detector, the source of the observed radiation could not unambiguously be determined although it is shown that the most probable source is M-87. The present measurement is consistent with a high energy extrapolation of the radio core source in M-87, although there is great need for a confirmation of this high energy X-ray source with a detector of increased angular resolution.