2023ApJ...954...48P -
Astrophys. J., 954, 48 (2023/September-1)
Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013.
PIKE S.N., SUGIZAKI M., VAN DEN EIJNDEN J., COUGHENOUR B., JAODAND A.D., MIHARA T., MOTTA S.E., NEGORO H., SHAW A.W., SHIDATSU M. and TOMSICK J.A.
Abstract (from CDS):
We present Monitor of All-sky X-ray Image (MAXI) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the Be X-ray binary, MAXI J0655-013, in outburst. NuSTAR observed the source once early in the outburst, when spectral analysis yields a bolometric (0.1-100 keV), unabsorbed source luminosity of Lbol = 5.6 × 1036 erg s–1, and a second time 54 days later, by which time the luminosity had dropped to Lbol = 4 × 1034 erg s–1 after first undergoing a dramatic increase. Timing analysis of the NuSTAR data reveals a neutron star spin period of 1129.09 ± 0.04 s during the first observation, which decreased to 1085 ± 1 s by the time of the second observation, indicating spin-up due to accretion throughout the outburst. Furthermore, during the first NuSTAR observation, we observed quasi-periodic oscillations (QPOs) with centroid frequency ν0 = 89 ± 1 mHz, which exhibited a second harmonic feature. By combining the MAXI and NuSTAR data with pulse period measurements reported by Fermi/GBM, we are able to show that apparent flaring behavior in the MAXI light curve is an artifact introduced by uneven sampling of the pulse profile, which has a large pulsed fraction. Finally, we estimate the magnetic field strength at the neutron star surface via three independent methods, invoking a tentative cyclotron resonance scattering feature at 44 keV, QPO production at the inner edge of the accretion disk, and spin-up via interaction of the neutron star magnetic field with accreting material. Each of these result in a significantly different value. We discuss the strengths and weaknesses of each method and infer that MAXI J0655-013 is likely to have a high surface magnetic field strength, Bs > 1013 G.
Abstract Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
Journal keyword(s):
High-mass x-ray binary stars - Neutron stars - Accretion - Pulsars
Simbad objects:
4
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