P. C. Joss

Orbital elements of 4U 0115+63 and the nature of the hard X-ray transients

Extended SAS 3 timing observations of the hard transient X-ray source 4U 0115+63 are reported, and a definitive measurement of the binary orbit of this transient source is presented. It is shown that this source is in a long orbit (period of approximately 24.3 days) that is moderately eccentric (e about 0.34) and that the mean value of the rate of decrease of the pulse period is consistent with the expected spinup of a rotating neutron star that is accreting from a disk. A distance of about 2.5 kpc is inferred, and the B-star optical counterpart is estimated to have an absolute magnitude of approximately -1.5 and a mass of at least 5 solar masses. It is suggested that the companion is a Be star which does not fill its Roche lobe and that the eccentricity and transient nature of the source result from the large orbital separation. It is proposed that hard X-ray transients as a class are collapsed stars (perhaps all neutron stars) in binary systems that are substantially wider than the more persistent X-ray binaries and that the large orbital separation, the small radius of the companion, or both, result in episodic rather than continuous mass transfer onto the X-ray star.

Discovery of a 283-second periodic variation in the X-ray source 3U 0900-40

A 283 s periodic pulsation in the X-ray system 3U 0900--40 has been discovered during observations by the SAS-3 X-ray observatory. Pulse profiles of the 283 s periodicity are presented in five energy intervals covering the range 1--30 keV for the period 1975 July 19.4--23.9. The averaged profile is relatively simple at higher energies and is markedly more complex at lower energies. The peak 1--40 keV intensity observed for the source is 1.2 x 10/sup -8/ ergs cm/sup -2/ s/sup -1/, which corresponds to a luminosity of 2.1 x 10/sup 36/ ergs s/sup -1/ at a distance of 1.2 kpc. A search for soft X-ray emission (E<1 keV) yielded upper limits of 2 x 10/sup -11/ and 5 x 10/sup -11/ ergs cm/sup -2/ s/sup -1/ in the energy intervals 0.16--0.28 keV and 0.5--0.7 keV, respectively. (AIP)

On the optical identifications of five X-ray sources

The data from a recently completed survey of the galactic plane with the SAS-3 modulation collimators provide precise (20″–60″) celestial positions of galactic X-ray sources. Preliminary positions of 60″ precision are reported for five sources. One of these led to the identification of the star, γ Cas, as an X-ray source, and the others lend substantial confidence to previously proposed optical identifications: 3U0352 + 30 = X Per, 3U1145 − 61 =HEN 715, GX301 − 2 = WRA977, and GX304 − 1 = MMV star. These identifications seem to establish the existence of a previously suggested class of De-star X-ray emitters.

The transient periodic X-ray source in Taurus, A0535+26

Light curves of the 104 s periodicity in the transient X-ray source in Taurus (A0535+26) are presented for six energy intervals in the range 1-35 keV for the period 1975 May 30-June 2. The pulse structure ranges from an apparently simple modulation at higher energies to a very complex pattern at lower energies. No Doppler shift is observed in the 104 s pulse period during the three days of observations. This places severe constraints upon possible binary orbital motion. Upper limits on the power at other periodicities are approximately-less-than10 percent for 2 ms-2s and approximately-less-than2 percent for 2 s-2000 s. (AIP)

X-ray nova A0620-00 - Celestial position and low-energy flux

The X-ray nova A0620-00 (Nova Monocerotis 1975) has been observed with the SAS-3 satellite. The 1--10 keV intensity was observed to increase by a factor of 2.3 from August 8 to August 11. It reached and maintained a constant intensity of 1.7x10

The 3U 0900--40 binary system: Orbital elements and masses

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Evidence for the binary nature of A0535+26

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Orbital elements and masses for the SMC X-1/Sanduleak 160 binary system

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Pulse profile and refined orbital elements for SMC X-1

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Observations of Hercules X-1 with SAS-3 during 1975 July

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