An estimation of the white dwarf mass in the Dwarf Nova GK Persei with NuSTAR observations of two states

作者：Wada Yuuki^*; Yuasa Takayuki; Nakazawa Kazuhiro; Makishima Kazuo; Hayashi Takayuki; Ishida Manabu

来源：Monthly Notices of the Royal Astronomical Society, 2018, 474(2): 1564-1571.

DOI：10.1093/mnras/stx2880

• stars: dwarf novae
• X-rays: individual: GK Persei

We report on X-ray observations of the Dwarf Nova GK Persei performed by NuSTAR in 2015. GK Persei, behaving also as an Intermediate Polar, exhibited a Dwarf Nova outburst in 2015 March-April. The object was observed with NuSTAR during the outburst state, and again in a quiescent state wherein the 15-50 keV flux was 33 times lower. Using a multitemperature plasma emission and reflection model, the highest plasma temperature in the accretion column was measured as 19.7(-1.0)(+1.3) keV in outburst and 36.2(-3.2)(+3.5) keV in quiescence. The significant change of the maximum temperature is considered to reflect an accretion-induced decrease of the inner-disc radius R-in, where accreting gas is captured by the magnetosphere. Assuming this radius scales as Rin proportional to M-2/7, where. M is themass accretion rate, we obtain R-in = 1.9(-0.2)(+0.4) R-WD and R-in = 7.4(-1.2)(+2.1) R-WD in outburst and quiescence, respectively, where R-WD is the white-dwarf (WD) radius of this system. Utilizing the measured temperatures and fluxes, as well as the standard mass-radius relation ofWDs, we estimate the WD mass as M-WD = 0.87 +/- 0.08M(circle dot) including typical systematic uncertainties by 7 per cent. The surface magnetic field is also measured as B similar to 5 x 10(5) G. These results exemplify a new X-ray method of estimating M-WD and B of WDs by using large changes in (M) over dot.

• 出版日期2018-2
• 单位RIKEN