4U 1626--67: A prograde spinning X-ray pulsar in A 2500 s binary system

Journal Article · Sun Mar 15 04:00:00 EST 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158772· OSTI ID:6316347

Middleditch, J; Mason, K O; Nelson, J E; White, N E

The binary period of 4U 1626--67 has been found from a careful analysis of its optical pulsations. A single lower frequency sidelobe of the 2.4% amplitude 7.68 s optical pulsations from this X-ray pulsar has been detected on at least three different nights in Fourier transforms of high speed photometry obtained with the CTIO 4 m telescope. The 0.42% sidelobe pulsations have a frequency which is 0.4011(21) mHz lower than the frequency of the direct pulsations near 130.26 mHz. The weaker sidelobe pulsations are interpreted as arising from X-ray to optical reprocessing on the companion star and are shifted to the lower frequency by the rotation frequency of the binary because the X-ray pulsar spins in the same sense as as the orbital motion (direct, or prograde). The orbital period is refined by connecting phases to be either 2491.06 s or 2492.32 s +- 0.13 s (the epoch for equal phases for the direct and lower sidelobe pulsations is JD 2,444,048.68162). Third harmonic (3F) structure in the lower sidelobe pulsations has enabled us to detect and measure the Doppler phase modulation due to the projected orbital motion and obtain an inclination-independent measurement of the total orbital separation. A simple geometrical model for the optical pulsations from the companion's Roche lobe is developed to calibrate the systematic effects of the measurements of orbital dimensions.With the help of a new limit of a/sub x/ sin i<0.04 lt-sec established from HEAO 1 data, the corrected values for the orbital parameters are: a/sub c/ sin i = 0.36(10) lt-sec, a/sub x/+a/sub c/ = 1.14(40) lt-sec, i = 18 /sup 0/(+18 /sup 0/, -7 /sup 0/) M/sub x/+M/sub c/ = 1.9(+2.8, -1.4) M/sub sun/, M/sub x/ = 1.8(+2.9, -1.3) M/sub sun/, and M/sub c/<0.5 Msun.

• Research Organization: Lawrence Berkeley Laboratory, University of California, Berkeley
• OSTI ID: 6316347
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 244:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics &amp; Cosmology-- Quasi-Stellar
Radio
&amp; X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
BINARY STARS
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
FOURIER ANALYSIS
IONIZING RADIATIONS
MOTION
ORBITS
PHOTOMETRY
PULSARS
PULSATIONS
RADIATIONS
ROTATION
STARS
STELLAR ATMOSPHERES
STELLAR FLARES
STELLAR RADIATION
X RADIATION