Engineering topics

Van Paradijs, J.

Publications and source records attributed to Van Paradijs, J..

59 records · Page 4

NASA NTRS1978

Interpretation of tails of X-ray bursts

Four reasons for ruling out the Alcock and Hatchett (1978) proposal concerning the tails of X-ray bursts are advanced. This proposal suggests that the tails of X-ray bursts observed during burst decay are due to the small-angle scattering of the original pulse of X-rays on interstellar dust grains; grains with a typical size of approximately 3 microns are assumed. The arguments against this theory involve differences in burst tail sizes sometimes observed for bursts from the same source; the different kinds of bursts emitted by MXB 1730-335 (rapid burster); an indication that MXB 1730-335 bursts have tails less than 2 s long; and the lack of correlation between relative strength of burst tails and the interstellar absorption.

Van Paradijs, J.↗

NASA NTRS1978

LMC X-1, X-2, and X-3 - Precise positions from the HEAO 1 modulation collimator

Precise (to about 20 arcsec) positions are reported for the Large Magellanic Cloud X-ray sources LMC X-1, X-2, and X-3, determined with the HEAO 1 scanning modulation collimator. The error regions for LMC X-1 and X-3 contain, respectively, the B5 supergiant R148 and a possibly variable B III-IV star. Spectra taken of the latter confirm the spectral type and show that it is a member of the LMC. A search for a previously reported extended component of LMC X-1 yields upper limits which exclude it.

Johnston, M. D.↗

NASA NTRS1978

Average properties of X-ray burst sources

Total integrated fluxes, maximum fluxes, and spectra of X-ray bursts from 10 sources are analyzed, and a uniformity in observed properties is detected. If it is assumed that the peak luminosity in a burst is a standard candle, the data suggest that (1) the effective black body radius observed in bursts is the same for all burst sources; (2) the tails of X-ray bursts are emitted by cooling surfaces whose size is the same for all burst sources (to within + or - 20%); and (3) the total energy emitted from X-ray bursts is the same for all burst sources (to within + or - 30%). This analysis applies to Type I bursts which are emitted by all burst sources and repeat at comparatively long time intervals. The analysis does not apply to Type II bursts, which repeat on time scales of seconds to minutes.

Van Paradijs, J.↗

NASA NTRS1978

Discovery of optical bursts from an X-ray burst source, MXB1735-44

The optical counterpart of 4U 1735-44, X-ray burst source MXB 1735-44, was studied with the 1.5-m telescope at Cerro Tololo, and by SAS 3, during the period between June 1 and 3, 1978. Explanations for the optical activity are discussed in terms of accretion instabilities onto a neutron star, or thermonuclear flashes on the neutron star itself. Attention is given to the timing of the bursts, which indicate that the burst source probably is located in a region within 1-2 light seconds from the X-ray source. In the binary case, it is noted that the optical emission is probably removed from the X-ray heated stellar atmosphere of the possible companion.

Grindlay, J. E.↗

NASA NTRS1978

On two new X-ray sources in the SMC and the high luminosities of the Magellanic X-ray sources

The discovery of two new X-ray sources, SMC X-2 and SMC X-3, in the Small Magellanic Cloud is reported. They have hard spectra, and their luminosities in the energy range 2-11 keV are 1.0 and 0.7 by 10 to the 38th power erg/sq cm per sec, respectively. It is shown that the luminosity distribution of the known Magellanic X-ray sources, which are now nine in number, is shifted toward higher luminosities with respect to that of similar sources in the Galaxy, and that the cause of the shift is probably an underabundance of heavy elements in the material accreted by the X-ray sources.

Clark, G.↗