Title:Qatar-1: indications for possible transit timing variations

Abstract:Variations in the timing of transiting exoplanets provide a powerful tool detecting additional planets in the system. Thus, the aim of this paper is to discuss the plausibility of transit timing variations on the Qatar-1 system by means of primary transit light curves analysis. Furthermore, we provide an interpretation of the timing variation. We observed Qatar-1 between March 2011 and October 2012 using the 1.2 m OLT telescope in Germany and the 0.6 m PTST telescope in Spain. We present 26 primary transits of the hot Jupiter Qatar-1b. In total, our light curves cover a baseline of 18 months. We report on indications for possible long-term transit timing variations (TTVs). Assuming that these TTVs are true, we present two different scenarios that could explain them. Our reported $\sim$ 190 days TTV signal can be reproduced by either a weak perturber in resonance with Qatar-1b, or by a massive body in the brown dwarf regime. More observations and radial velocity monitoring are required to better constrain the perturber's characteristics. We also refine the ephemeris of Qatar-1b, which we find to be \mbox{$T_0 = 2456157.42204 \pm 0.0001$ \bjdtdb} and \mbox{$P = 1.4200246 \pm 0.0000007$ days}, and improve the system orbital parameters.