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Author Patruno, Alessandro ♦ King, Andrew R. ♦ Jaodand, Amruta ♦ Hessels, Jason W. T. ♦ Kuiper, Lucien ♦ Bult, Peter ♦ Wijnands, Rudy ♦ Van der Klis, Michiel ♦ Knigge, Christian
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ BLACK HOLES ♦ FLUX DENSITY ♦ GHZ RANGE ♦ L-S COUPLING ♦ MAGNETIC FIELDS ♦ MASS TRANSFER ♦ MOMENT OF INERTIA ♦ NEUTRON STARS ♦ NEUTRONS ♦ ORBITS ♦ PULSARS ♦ PULSATIONS ♦ ROTATION ♦ SMALL ANGLE SCATTERING ♦ STELLAR WINDS ♦ TELESCOPES ♦ X RADIATION ♦ X-RAY DIFFRACTION
Abstract The accreting millisecond X-ray pulsar SAX J1808.4−3658 shows a peculiar orbital evolution that proceeds at a very fast pace. It is important to identify the underlying mechanism responsible for this behavior because it can help to understand how this system evolves and which physical processes (such as mass loss or spin–orbit coupling) are occurring in the binary. It has also been suggested that, when in quiescence, SAX J1808.4−3658 turns on as a radio pulsar, a circumstance that might provide a link between accreting millisecond pulsars and black-widow (BW) radio pulsars. In this work, we report the results of a deep radio pulsation search at 2 GHz using the Green Bank Telescope in 2014 August and an X-ray study of the 2015 outburst with Chandra , Swift XRT, and INTEGRAL . In quiescence, we detect no radio pulsations and place the strongest limit to date on the pulsed radio flux density of any accreting millisecond pulsar. We also find that the orbit of SAX J1808.4−3658 continues evolving at a fast pace. We compare the orbital evolution of SAX J1808.4−3658 to that of several other accreting and nonaccreting binaries, including BWs, redbacks, cataclysmic variables, black holes, and neutron stars in low-mass X-ray binaries. We discuss two possible scenarios: either the neutron star has a large moment of inertia and is ablating the donor, generating mass loss with an efficiency of 40%, or the donor star has a strong magnetic field of at least 1 kG and is undergoing quasi-cyclic variations due to spin–orbit coupling.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-06-01
Publisher Place United States
Journal Astrophysical Journal
Volume Number 841
Issue Number 2


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