The substellar companion in the eclipsing white dwarf binary SDSS J141126.20+200911.1

We present high time resolution SDSS-g ′ and SDSS-z ′ light curves of the primary eclipse in SDSS J141126.20+200911.1, together with time-resolved X-Shooter spec-troscopy and near-infrared JHKs photometry. Our observations confirm the substel-lar nature of the companion, making SDSS J141126.20+200911.1 the first eclipsing white dwarf/brown dwarf binary known. We measure a (white dwarf model depen-dent) mass and radius for the brown dwarf companion of M2 = 0.050 ± 0.002M and R2 = 0.072 ± 0.004M, respectively. The lack of a robust detection of the companion light in the z′-band eclipse constrains the spectral type of the companion to be later than L5. Comparing the NIR photometry to the expected white dwarf flux reveals a clear Ks-band excess, suggesting a spectral type in the range L7–T1. The radius measurement is consistent with the predictions of evolutionary mod-els, and suggests a system age in excess of three Gyr. The low companion mass is inconsistent with the inferred spectral type of L7–T1, instead predicting a spectral type nearer T5. This indicates that irradiation of the companion in SDSS J1411 could be causing a significant temperature increase, at least on one hemisphere