WD 1145+017: optical activity during 2016–2017 and limits on the X-ray flux

• Published in: Monthly notices of the Royal Astronomical Society 2018-02, Vol.474 (1), p.933-946
• Main Authors: Rappaport, S., Gary, B. L., Vanderburg, A., Xu(许偲艺), S., Pooley, D., Mukai, K.
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx2663

Abstract WD 1145+017 was observed from 2016 November through 2017 June for the purpose of further characterizing the transit behaviour of the dusty debris clouds orbiting this white dwarf. The optical observations were carried out with a small ground-based telescope run by an amateur astronomer, and covered 53 different nights over the 8-month interval. We have found that the optical activity has increased to the highest level observed since its discovery with Kepler K2, with approximately 17 per cent of the optical flux extinguished per orbit. The source exhibits some transits with depths of up to 55 per cent and durations as long as 2 h. The dominant period of the orbiting dust clouds during 2016–2017 is 4.49126 h. We present ‘waterfall’ images for the entire 2016–2017 and 2015–2016 observing seasons. In addition, the white dwarf was observed with the Chandra X-ray Observatory for 10-ks on each of four different occasions, separated by about a month each. The upper limit on the average X-ray flux from WD 1145+017 is ≃ 5 × 10−15 erg cm−2 s−1 (unabsorbed over the range 0.1–100 keV), which translates to an upper limit on the X-ray luminosity, Lx, of ≃ 2 × 1028 erg s−1. If $L_{\rm x} \simeq G M_{\rm wd} \dot{M}_{\rm acc}/R_{\rm wd}$, where Mwd and Rwd are the mass and radius of the white dwarf, and $\dot{M}_{\rm acc}$ is the accretion rate, then $\dot{M}_{\rm acc} \lesssim 2 \times 10^{11}$ g s−1. This is just consistent with the value of $\dot{M}$ that is inferred from the level of dust activity.