[en] This paper gives an overview of X-ray pulsars powered by the accretion of matter from a companion star in a close binary system. Recent advances in studies of X-ray pulsars are reviewed, with a special focus on the results of observations by the Hakucho and Tenma satellites. Some topics revealed by the Ginga satellite in the last one and a half years are also included to appeal for a new strategy for studying X-ray pulsars. (author)

[en] The outburst of the X-ray pulser A 0535+26 was observed, and the results of data analysis are reported in this paper. The outburst was detected on October 2, 1980, by the SVC 1/2 counter loaded on 'Hakucho'. The maximum of X-ray intensity was seen on October 10, then the intensity began to reduce, and the intensity on November 3 was not detectable. The energy spectrum of X-ray became soft for the period of 25 days. The outbursts of A 0535+26 have occurred at intervals of about 110 days. The pulse period on the October 9 was 103.67 sec, and became 103.61 sec on October 22. The period was constant for the period from October 22 to November 3. Discussion on this variation is presented. The analysis of pulse delay time was performed. The delay time data were on a smooth delay curve. This shows a Doppler effect of the revolution of A 0535+26. The eccentricity of the orbit of revolution was given by the chi-square analysis. (Kato, T.)

[en] Observation of the X-ray pulser Vela X-1 has been made by 'Hakucho'. Seven series of the data taken in the period from March, 1979, to March, 1981, were analyzed. The pulse period and its time variation rate were obtained by the chi-square fitting of data with an empirical formula. The most probable Doppler curve taken in March, 1980, showed that the time variation rate was necessary for the fitting. The spin-up tendency was seen in the data from December, 1980, to January, 1981. The deduced orbital elements were in good agreement with those obtained by SAS-3 in U.S.A. A long period spin-down tendency was observed. The observed variation rate of pulse period was about 3 x 10^-₄/year. The variation of spin period with the variation rate of 3 x 10^-₃/year was superposed on the basic variation. (Kato, T.)

[en] The X-ray pulsar Vela X-1 has been observed by HAKUCHO in two occasions from March 6 to 27, 1979, and from March 5 to 23, 1980. The time variation of the X-ray intensity and the long term variation of pulsar period were analyzed in detail. The X-ray intensity was significantly variable with time, and the correlation between the mean X-ray intensity and spectral hardness ratio was obtained. The good correlation between them existed when the X-ray intensity was lower than a certain value. In the present status of Vela X-1 observation, the pulsar period was 282.801 +- 0.001 sec, and showed increasing trend with time. This indicates the spin-down of the Vela X-1 pulsar. Some spin-down models are proposed. (Yoshimori, M.)

[en] Eight X-ray pulsars, Her X-1, Cen X-3, 4U 1626-67, OAO 1657-415, A 0535+26, Vela X-1, 4U 1538-52, and GX 301-2, have been observed from Hakucho and Tenma. The pulse periods of all these X-ray pulsars measured with Hakucho and Tenma between March 1979 and October 1983 are summarized together with those of 4U 1700-37 and 4U 1907+09, the pulsations of which were newly discovered by Tenma observations. Several instances of remarkable behavior in pulse-period change are revealed both for the wind-fed and disk-fed pulsars. (author)

[en] The pulse period and x-ray spectrum of 1E2259 + 586 were observed with the Tenma satellite in October, 1983. The heliocentric pulse period was determined to be 6.978675 ± 0.000010 s, which is about 4 x 10^-5 s longer than that obtained with the Einstein Observatory in 1980 and 1981. An averaged spin-down rate is 5 x 10^-13 ss^-1 (or P/P = 7 x 10^-14 s^-1). The x-ray spectrum was found to be much softer than usual binary x-ray pulsars. (author)

[en] A part of the results obtained from the observation using K-9M-60 is presented. The excess in the energy region less than 0.1 KeV found in the energy spectra with the 0.5 μm PPL counter is described. The directional distributions of the L-band (0.15 to 0.3 KeV) and the LL band (0.06 to 0.15 KeV), and the energy spectra were obtained. The excess was seen in the energy spectrum of the LL band. The reason for this excess was considered and discussed. The noise spectrum of the counter is not a cause of the excess. As a result of discussion, it is suggested that the excess is due to other X-ray component with the energy less than L band. If this is true, the origin of the LL band X-ray may be a white dwarf or high temperature plasma. (Kato, T.)

[en] In order to determine the attitude of the rockets and to suppress the influence of ultraviolet ray to the proportional counters for the detection of X-ray, ultraviolet detectors were employed for the rocket experiments. The ultraviolet detectors were photomultipliers and proportional counters. The photomultipliers were Cs Te and sensitive to ultraviolet ray in the wavelength region below 3000 A. The proportional counters were filled with mixed gas of xylene and neon. In these observations, ultraviolet ray in the wavelength range from 1150 to 3200 A was detected. Ultraviolet sources of eta-UMα and Vela-Pup region were observed. The result showed that a sky map observed in this wavelength range was different from that observed in the longer wavelength range. (Yoshimori, M.)

[en] The x-ray pulsar 4U 1626 - 67 was observed with Tenma during the period May 3 through 5, 1983. No appreciable change in the spectrum was observed during x-ray flares. The pulse period of 7.671350 s and the rate of period change are consistent with a stable spin-up at a rate of ∼ 2 x 10^-4 yr^-1. The pulse profile changes drastically at about 15 keV and 2 keV, and the energy spectrum depends on the pulse phase accordingly. No emission line feature of iron around 6 keV was found with an upper limit of the equivalent width of 60 eV (90 % confidence). The observed energy dependence of the x-ray pulse profile was simulated by a calculation based on the anisotropic radiation transfer in a strongly magnetized plasma with a magnetic field strength of ∼ 8 x 10¹² G at the neutron star surface. (author)

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