Wilson-Hodge Colleen A, Malacaria Christian, Jenke Peter A, Jaisawal Gaurava K, Kerr Matthew, Wolff Michael T, Arzoumanian Zaven, Chakrabarty Deepto, Doty John P, Gendreau Keith C, Guillot Sebastien, Ho Wynn C G, LaMarr Beverly, Markwardt Craig B, Özel Feryal, Prigozhin Gregory Y, Ray Paul S, Ramos-Lerate Mercedes, Remillard Ronald A, Strohmayer Tod E, Vezie Michael L, Wood Kent S
ST12 Astrophysics Branch, NASA Marshall Space Flight Center, Huntsville, AL 35812, USA.
Universities Space Research Association, NSSTC, Huntsville, AL 35805, USA.
Astrophys J. 2018 Aug 6;863(1). doi: 10.3847/1538-4357/aace60.
Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late September 2017 in a giant outburst with a peak luminosity of 2 × 10(/7 kpc) erg s (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 and 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 Burst Alert Telescope to model the system's intrinsic spin-up. Power spectra measured with show considerable evolution with luminosity, including a quasi-periodic oscillation (QPO) 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 ~ 10 erg s, 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 and GBM show a turn-over 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 ~ 10 G.
斯威夫特J0243.6+6124是一颗新发现的银河系Be/X射线双星，于2017年9月底在一次巨大爆发中被发现，峰值光度为2×10⁷ erg s⁻¹（0.1 - 10 keV），此前没有该天体活动的报道。在这个光度下，斯威夫特J0243.6+6124是已知的第一颗银河系超亮X射线脉冲星。我们描述了该源的费米伽马射线暴监测仪（GBM）计时和光谱分析。利用GBM测量的自旋频率和爆发警报望远镜测量的15 - 50 keV流量，为该双星系统获得了一个新的轨道历表，以模拟系统的固有自旋加速。费米测量的功率谱显示出随光度有显著变化，包括在50 mHz附近的一个准周期振荡（QPO），它在低光度时普遍存在且中心频率不断变化。在0.2 - 100 keV组合能量范围内测量的脉冲轮廓显示出复杂的变化，这既与光度有关也与能量有关。在约10⁸ erg s⁻¹的临界光度附近，脉冲轮廓从单峰转变为双峰，所有能带中的脉冲分数达到最小值，费米和GBM中的硬度比随着强度增加呈现出转向变软的趋势。这种行为在爆发上升和下降时重复出现，表明存在两种不同的吸积状态。这两种状态表明中子星表面的吸积结构从低光度时的库仑碰撞停止机制转变为高光度时的辐射主导停止机制。这是（迄今为止）观测到的临界光度的最高值，表明磁场约为10¹³ G。
