Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987apj...319l..77s&link_type=abstract
Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X), vol. 319, Aug. 15, 1987, p. L77-L81.
Astronomy and Astrophysics
Astrophysics
17
Neutron Stars, Pulse Duration, X Ray Binaries, X Ray Sources, Disk Galaxies, Field Of View, Heao, Light Curve, Scintillation Counters, Sodium Iodides
Scientific paper
Her X-1 has been observed in the 13-180 keV energy range by the HEAO 1 A-4 Low-Energy Detectors during selected phases of the 35 d on-off cycle. During a pointing observation in September 1978, the pulse profile was observed to change continuously from its normal shape to an anomalous double-pulsed form. Moreover, at this time the main-on state, normally of the duration 10 d, was seen to terminate after only 7 d. Since such an anomalous pulse profile has also been reported by Truemper et al. in 1986 during a short-on state, three short-on states in the HEAO 1 data were also investigated. One short-on observation had the sensitivity to detect pulsing, and the observed profile also had an anomalous double-pulsed form. Current models for the 35 d cycle of Her X-1 have been examined, and a model with a neutron star undergoing free precession could not explain the sudden change of pulse profile within 20 hr at the end of a main-on state.
Gruber Duane E.
Rothschild Richard E.
Soong Yang
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