The Intensity Modulation of Fluorescent Line by a Finite Light Speed Effect in Accretion-Powered X-ray Pulsars

Abstract

The X-ray line diagnostic method is a powerful tool for an investigation of plasma around accretion-powered X-ray pulsars. We point out an apparent intensity modulation of emission lines with their rotation period of neutron stars, due to the finite speed of light (we call this effect "finite light speed effect"), if the line emission mechanism is a kind of reprocessing, such as fluorescence or recombination after ionization by X-ray irradiation from pulsars. The modulation amplitude is determined by the size of the emission region, in competition with the smearing effect by the light crossing time in the emission region. This is efficient if the size of the emission region is roughly comparable to that of the rotation period multiplied by the speed of light. We apply this effect to a symbiotic X-ray pulsar, GX 1+4, a spin modulation of the intense iron line of which has been reported. The finite light speed effect can explain the observed intensity modulation, if its fluorescent region has a size of $\sim 10^{12}$ cm.

arXiv comment6 pages, 5 figures, published in publication in the Astrophysical Journal

References in corpus (16)

• The Symbiotic Neutron Star Binary GX 1+4/V2116 Ophiuchi
• Double-Peaked X-Ray Lines from the Oxygen/Neon-Rich Accretion Disk in 4U1626-67
• X-ray Spectroscopy of the High Mass X-ray Binary Pulsar Centaurus X-3 over its Binary Orbit
• Broadband spectroscopy using two Suzaku observation of the HMXB GX 301-2
• Study of the many fluorescent lines and the absorption variability in GX 301-2 with XMM-Newton
• Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE
• Short-Term Variability of X-rays from Accreting Neutron Star Vela X-1: I. Suzaku Observations
• The Orbital Period of the Accreting Pulsar GX1+4
• XMM-Newton EPIC & OM observations of Her X-1 over the 35 day beat period
• Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114
• ASCA and Ginga Observations of GX 1+4
• A Compton reflection dominated spectrum in a peculiar accreting neutron star
• Pulse phase dependence of emission lines in the X-ray pulsar 4U 1626-67
• Photoionized Lines in the X-ray Spectra of SMC X-1
• Spectral variation in the X-ray pulsar GX 1+4 during a low-flux episode
• A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4

Cited by in corpus (2)

• Pulsating iron spectral features in the emission of X-ray pulsar V0332+53
• The Modulating Optical Depth of Photoelectric Absorption Edge with Pulse Phase in Accretion-Powered X-ray Pulsars