The broad-band power spectrum of SAX J1808.4-3658

Abstract

We analyzed the rapid aperiodic X-ray variability of the recently discovered millisecond X-ray pulsar SAX J1808.4-3658. The power density spectrum is dominated by a strong band-limited noise component, which follows a power-law with index 1.0-1.3 at high frequencies with a break that varies between 0.25 and 1.6 Hz, below which the spectrum is relatively flat. Superimposed on this, a broad bump is present with a centroid frequency that varies well correlated with the break frequency between 2.4 and 12.0 Hz. These characteristics are very similar to what is commonly seen in other low-luminosity low-mass X-ray binaries. Between 100 and 400 Hz a third broad noise component is present similar to that recently reported in the low-luminosity low-mass X-ray binary 4U 1728-34 (Ford & van der Klis 1998). We find a similar high-frequency noise component also in other low-luminosity neutron star systems. We conclude that at any given epoch the rapid aperiodic X-ray variability of the millisecond X-ray pulsar is indistinguishable from that of other low-luminosity neutron star systems. However, contrary to what has been found in those sources the break frequency of the band-limited noise does not have a strict correlation with mass accretion rate. With decreasing mass accretion rate, the break frequency first decreased, then increased again. This previously unobserved behavior could be typical for the very low mass accretion rates we observe near the end of the outburst of SAX J1808.4-3658, or it could be related to it being a pulsar.

6 pages, including 3 figures. Accepted for publication in ApJ Letters on Aug 26, 1998

References in corpus (5)

• The two-hour orbit of a binary millisecond X-ray pulsar
• Strong Correlation Between Noise Features at Low Frequency and the Kilohertz QPOs in the X-Ray Binary 4U 1728-34
• Soft Phase Lags of Pulsed Emission from the Millisecond X-ray Pulsar SAX J1808.4-3658
• The X-ray Spectrum of SAX J1808.4-3658
• Discovery of Kilohertz QPOs in the Atoll X-Ray Binary 4U 1705-44

Cited by in corpus (44)

• Millisecond Oscillations in X-Ray Binaries
• The flux-dependent amplitude of broadband noise variability in X-ray binaries and active galaxies
• The broad-band power spectra of X-ray binaries
• On the Nature of the X-ray Emission from the Accreting Millisecond Pulsar SAX J1808.4-3658
• Hard X-ray Emission From Low Mass X-ray Binaries
• Propagation of thermonuclear flames on rapidly rotating neutron stars: extreme weather during type I X-ray bursts
• The Disk-Magnetosphere Interaction in the Accretion-Powered Millisecond Pulsar SAX J1808.4-3658
• The atoll source states of 4U 1608-52
• A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U 1728-34
• Relations Between Timing Features and Colors in the X-Ray Binary 4U 0614+09
• X-ray time variability across the atoll source states of 4U 1636--53
• Physics of accretion in the millisecond pulsar XTE J1751-305
• Phase-resolved X-ray spectroscopy of the millisecond pulsar SAX J1808.4-3658
• Relations Between Timing Features and Colors in Accreting Millisecond Pulsars
• Bardeen-Petterson Effect and Quasi-Periodic Oscillations in X-Ray Binaries
• The erratic luminosity behavior of SAX J1808.4-3658 during its 2000 outburst
• Why is it Difficult to Detect a Millisecond Pulsar in Neutron Star X-ray Binaries?
• Transient radio emisison from SAX J1808.4-3658
• A Search for Pulsars in Quiescent Soft X-Ray Transients. I
• SAX J1808.4-3658 and the origin of X-ray variability in X-ray binaries and active galactic nuclei
• Observations of the 599 Hz Accreting X-ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence
• Modelling the cross-spectral variability of the black hole binary MAXI J1659-152 with propagating accretion rate fluctuations
• XMM-Newton Spectroscopy of the Accretion-Driven Millisecond X-ray Pulsar XTE J1751-305 in Outburst
• Discovery of a ~7 Hz Quasi-Periodic Oscillation in the low-luminosity low-mass X-ray binary 4U 1820-30
• Non-interacting black hole binaries with Gaia and LAMOST
• Doppler tomography of the transient X-ray binary Centaurus X-4 in quiescence
• An observational review of accretion-driven millisecond X-ray pulsars
• Rayleigh - Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries
• The Effect of the Mass Accretion Rate on the Burst Oscillations in 4U 1728-34
• The discovery of the 528.6 Hz accreting millisecond X-ray pulsar MAXI J1816-195
• Cross-spectral modelling of the black hole X-ray binary XTEJ1550-564: challenges to the propagating fluctuations paradigm
• Evolution of the hot flow of MAXI J1543-564
• The aperiodic X-ray variability of the accreting millisecond pulsar SAX J1808.4-3658
• Quasi-periodic oscillations and noise in neutron star and black-hole X-ray binaries
• A strongly changing accretion morphology during the outburst decay of the neutron star X-ray binary 4U 1608-52
• The AstroSat observation of accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst
• Coupling Between Periodic and Aperiodic Variability in SAX J1808.4-3658
• The Different Fates of a Low-Mass X-ray Binary. I: Conservative Mass Transfer
• The 2019 outburst of AMXP SAX J1808.4-3658 and radio follow up of MAXI J0911-655 and XTE J1701-462
• The aperiodic timing behaviour of the accretion-driven millisecond pulsar SAX J1808.4-3658
• Testing the transition layer model of quasi-periodic oscillations in neutron star X-ray binarie
• The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence
• Spectral Analysis of the 2019 and 2022 Outbursts of SAX J1808.4-3658
• The stochastic X-ray variability of the accreting millisecond pulsar IGR J17062-6143