TY - JOUR
T1 - NICER and Fermi GBM Observations of the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124
AU - Wilson-Hodge, Colleen A.
AU - Malacaria, Christian
AU - Jenke, Peter A.
AU - Jaisawal, Gaurava K.
AU - Kerr, Matthew
AU - Wolff, Michael T.
AU - Arzoumanian, Zaven
AU - Chakrabarty, Deepto
AU - Doty, John P.
AU - Gendreau, Keith C.
AU - Guillot, Sebastien
AU - Ho, Wynn C.G.
AU - Lamarr, Beverly
AU - Markwardt, Craig B.
AU - Özel, Feryal
AU - Prigozhin, Gregory Y.
AU - Ray, Paul S.
AU - Ramos-Lerate, Mercedes
AU - Remillard, Ronald A.
AU - Strohmayer, Tod E.
AU - Vezie, Michael L.
AU - Wood, Kent S.
N1 - Funding Information:
This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program. This work was also supported by NASA through the Fermi Guest Investigator Program. G.K.J. acknowledges support from the Marie Skłodowska-Curie Actions grant no. 713683 (H2020; COFUNDPostdocDTU). This research has made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. Work at the Naval Research Laboratory by M.T.W., P.S.R., and M.K. was supported by NASA. C.M.’s research was supported by the NASA Postdoctoral Program at the MSFC, administered by USRA. Facilities: NICER, Fermi, Swift.
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/8/10
Y1 - 2018/8/10
N2 - Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late 2017 September in a giant outburst with a peak luminosity of 2 × 1039(d/7 kpc)2 erg s-1 (0.1-10 keV), with no formerly reported activity. At this luminosity, Swift J0243.6+6124 is the first known galactic ultraluminous X-ray pulsar. We describe Neutron star Interior Composition Explorer (NICER) and Fermi Gamma-ray Burst Monitor (GBM) timing and spectral analyses for this source. A new orbital ephemeris is obtained for the binary system using spin frequencies measured with GBM and 15-50 keV fluxes measured with the Neil Gehrels Swift Observatory Burst Alert Telescope to model the system's intrinsic spin-up. Power spectra measured with NICER show considerable evolution with luminosity, including a quasi-periodic oscillation near 50 mHz that is omnipresent at low luminosity and has an evolving central frequency. Pulse profiles measured over the combined 0.2-100 keV range show complex evolution that is both luminosity and energy dependent. Near the critical luminosity of L ∼ 1038 erg s-1, the pulse profiles transition from single peaked to double peaked, the pulsed fraction reaches a minimum in all energy bands, and the hardness ratios in both NICER and GBM show a turnover to softening as the intensity increases. This behavior repeats as the outburst rises and fades, indicating two distinct accretion regimes. These two regimes are suggestive of the accretion structure on the neutron star surface transitioning from a Coulomb collisional stopping mechanism at lower luminosities to a radiation-dominated stopping mechanism at higher luminosities. This is the highest observed (to date) value of the critical luminosity, suggesting a magnetic field of B ∼ 1013 G.
AB - Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late 2017 September in a giant outburst with a peak luminosity of 2 × 1039(d/7 kpc)2 erg s-1 (0.1-10 keV), with no formerly reported activity. At this luminosity, Swift J0243.6+6124 is the first known galactic ultraluminous X-ray pulsar. We describe Neutron star Interior Composition Explorer (NICER) and Fermi Gamma-ray Burst Monitor (GBM) timing and spectral analyses for this source. A new orbital ephemeris is obtained for the binary system using spin frequencies measured with GBM and 15-50 keV fluxes measured with the Neil Gehrels Swift Observatory Burst Alert Telescope to model the system's intrinsic spin-up. Power spectra measured with NICER show considerable evolution with luminosity, including a quasi-periodic oscillation near 50 mHz that is omnipresent at low luminosity and has an evolving central frequency. Pulse profiles measured over the combined 0.2-100 keV range show complex evolution that is both luminosity and energy dependent. Near the critical luminosity of L ∼ 1038 erg s-1, the pulse profiles transition from single peaked to double peaked, the pulsed fraction reaches a minimum in all energy bands, and the hardness ratios in both NICER and GBM show a turnover to softening as the intensity increases. This behavior repeats as the outburst rises and fades, indicating two distinct accretion regimes. These two regimes are suggestive of the accretion structure on the neutron star surface transitioning from a Coulomb collisional stopping mechanism at lower luminosities to a radiation-dominated stopping mechanism at higher luminosities. This is the highest observed (to date) value of the critical luminosity, suggesting a magnetic field of B ∼ 1013 G.
KW - X-rays: binaries
KW - accretion, accretion disks
KW - pulsars: individual (SWIFT J0243.6+6124)
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U2 - 10.3847/1538-4357/aace60
DO - 10.3847/1538-4357/aace60
M3 - Article
AN - SCOPUS:85051562528
VL - 863
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 9
ER -