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Studies low-mass x-ray binary pulsar. Accretion discs; Stars; Duration of star spin-down.

The ASCA satellite has observed the 50-ms pulsar PSR B0540–69 and its associated supernova remnant SNR 0540–693 in the Large Magellanic Cloud 15 times in total, at least once a year, between 1993 June and 1999 November, including six observations with the pulsar as the main target. In all the observations, a point-like X-ray source was clearly detected at the position of PSR B0540–69 and the X-ray pulsations were detected at large significance. Folded light curves are identical throughout the observations, showing one broad pulse with a small notch at the top. Pulse frequency history during the 6.4 yr of the ASCA observations is well characterized by a second-order polynomial with a breaking index of 2.10±0.05 , assuming no glitches occurred during the period. The frequency history smoothly follows the Ginga and ROSAT results and connects to the RXTE results without a measurable discontinuity. The X-ray spectrum of the whole source is well represented by a single power-law model of photon index, α=2.00±0.02 , and a small photoelectric absorption, N[sub H]=(4.3±0.2)×10[sup 21] cm[sup -2] . The X-ray spectrum can also be represented by a pulsed power-law spectrum with photon index of 1.80±0.05 with 24 per cent in amplitude at 1 keV, embedded in a constant power-law component with photon index of 2.17±0.02 ascribed to a nebular component. Spectral properties of the X-ray emission from the pulsar and the nebula remain unchanged over the six years and are quite similar to those of the Crab pulsar and nebula. [ABSTRACT FROM AUTHOR]

Abstract: Since the typical magnetic field strengths of neutron stars reach 1012 Gauss, the cyclotron resonance produced by a transition between Landau levels appears in the X-ray band. Systematic measurements of cyclotron absorption features in bright sources have been carried out extensively with Ginga, RXTE, BeppoSAX, and INTEGRAL. The cyclotron resonance phenomena can now be studied with a higher sensitivity over a wider hard X-ray band than before, thanks to the Hard X-ray Detector onboard the fifth Japanese X-ray satellite, Suzaku, launched in July, 2005. Suzaku observed Hercules X-1 mainly for calibration purposes, and successfully confirmed its well-known cyclotron absorption feature. Furthermore, the transient pulsar A0535+262 was observed with Suzaku on 14 September, 2005, in the decay phase of its minor outburst (Finger, M.F. Renewed Activity from A0535+26. The Astronomer’s Telegram, vol. 595, 2005). The cyclotron resonance of A0535+262 was successfully detected in absorption at about 45keV (Inoue, H., Kunieda, H., White, N., Kelley, R., Mihara, T., Terada, Y., Takahashi, H., Kokubun, M., Makishima, K. Suzaku detection of cyclotron line near 50keV for A0535+26. The Astronomer’s Telegram vol. 595, 2005; Terada, Y., Mihara, T., Nakajima, M., et al. Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku. ApJL 648, L139–L142, 2006), even though the object was as dim as 30mCrab at 20keV. Compared with previous measurements of the same feature achieved at much brighter phases (e.g., Kretschmar, P., Kreykenbohm, I., Pottschmidt, et al. Integral observes possible cyclotron line at 47keV for 1A0535+262. The Astronomer’s Telegram, vol. 601, 2005; Wilson, C.A., Finger, M.H. RXTE confirms cyclotron line near 50keV for A0535+26. The Astronomer’s Telegram 605, 2005), the Suzaku results give a new constraint to luminosity-related changes in the resonance energy that are observed in other binary pulsars (Nakajima, M., Mihara, T., Makishima, K., Niko, H. A further study of the luminosity-dependent cyclotron resonance energies of the binary X-ray pulsar 4U 0115+63 with the Rossi X-ray timing explorer. ApJ 646, 1125–1138, 2006). [Copyright &y& Elsevier]