Cessation of X-ray Pulsation of GX 1+4

Abstract

We report results from our weekly monitoring campaign on the X-ray pulsar GX 1+4 with the {\em Rossi X-ray Timing Explorer} satellite. The spin-down trend of GX 1+4 was continuing, with the pulsar being at its longest period ever measured (about 138.7 s). At the late stage of the campaign, the source entered an extended faint state, when its X-ray (2-60 keV) flux decreased significantly to an average level of $\sim 3\times 10^{-10}ergsc{m}^{-2}{s}^{-1}$. It was highly variable in the faint state; the flux dropped to as low as $\sim 3\times 10^{-11}ergsc{m}^{-2}{s}^{-1}$. In several observations during this period, the X-ray pulsation became undetectable. We can, therefore, conclude conservatively that the pulsed fraction, which is normally $\gtrsim$ 70% (peak-to-peak), must have decreased drastically in those cases. This is very similar to what was observed of GX 1+4 in 1996 when it became similarly faint in X-ray. In fact, the flux at which the cessation of X-ray pulsation first occurred is nearly the same as it was in 1996. We suggest that we have, once again, observed the propeller effect in GX 1+4, a phenomenon that is predicted by theoretical models of accreting X-ray pulsars.

arXiv comment13 pages, 9 figures (available at http://www.physics.purdue.edu/~cui/ftp/cuifigs.tar.gz). To appear in ApJ

References in corpus (8)

• Observations of Accreting Pulsars
• Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
• Evidence for "Propeller" Effects In X-ray Pulsars GX 1+4 And GROJ1744-28
• The Symbiotic Neutron Star Binary GX 1+4/V2116 Ophiuchi
• Magnetic propeller outflows
• The transient X-ray pulsar 4U 0115+63 from quiescence to outburst through the centrifugal transition
• ASCA and Ginga Observations of GX 1+4
• Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114

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• Detection of hard X-ray pulsations and a strong iron K_beta emission line during an extended low state of GX 1+4
• The Soft X-ray Spectrum of the High Mass X-Ray Binary V0332+53 in Quiescence
• Discovery of radio emission from the symbiotic X-ray binary system GX 1+4
• Comprehensive Timing and X-ray Spectral Analysis of GX 1+4
• A curious case of the accretion-powered X-ray pulsar GX 1+4
• A Two-Stage Kick Scenario for the Peculiar LMXB GX 1+4