Predicting the 4th caustic crossing in Gaia16aye binary microlensing event

ATel #9770; P. Mroz (Warsaw), L. Wyrzykowski (Warsaw), K. Rybicki (Warsaw), G. Altavilla (INAF Bologna), V. Bakis (Akdeniz Univ.), P. Bendjoya (C2PU-Omicron), G. Birenbaum (Wise Obs.), N. Blagorodnova (Caltech), S. Blanco-Cuaresma (Geneva), A. Bonanos (NOA Athens), V. Bozza (Salerno), N. Britavskiy (Odessa), U. Burgaz (Ege Univ.), T. Butterley (Durham Univ.), P. Capuozzo (Ardingly College), J. M.Carrasco (Barcelona Univ.), M. Chruslinska (Warsaw), G. Damljanovic (Belgrade), M. Dennefeld (IAP), V. S.Dhillon (Sheffield Univ.), M. Dominik (St. Andrews Univ.), H. Esenoglu (TUG), S. Fossey (UCL), A. Gomboc (Nova Gorica Univ.), N. Hallokoun (Wise Obs.), A. Hamanowicz (Warsaw), L. K.Hardy (Sheffield Univ.), R. Hudec (Ondrejov), I. Khamitov ("TUG Antaluya), J. Klencki (Warsaw), Z. Kolaczkowski (Wroclaw), U. Kolb (Open Univ.), S. Leonini (Montarrenti Obs), G. Leto (INAF OACT), F. Lewis (Cardiff Univ.), A. Liakos (NOA Athens), S. P.Littlefair (Sheffield Univ.), D. Maoz (Wise Obs.), J. R.Maund (Sheffield Univ.), P. Mikolajczyk (Wroclaw), L. Palaversa (Geneva/Cambridge), M. Pawlak (Warsaw), M. Penny (Ohio State), A. Piascik (Liverpool JMU), P. Reig (Crete Univ.), L. Rhodes (Sheffield Univ.), D. Russell (New York Univ.), R. Z.Sanchez (INAF OACT), B. Shappee (Ohio State), Y. Shvartzvald (Wise Obs.), M. Sitek (Warsaw), M. Sniegowska (Warsaw), K. Sokolovsky (IAASARS NOA/SAI/ASC Lebedev), I. Steele (Liverpool JMU), R. Street (LCOGT), L. Tomasella (INAF OAPD), L. Trascinelli (Ardingly College), K. Wiersema (Leicester), R. W.Wilson (Durham Univ.), I. Zharkov (Ardingly College), S. Zola (Jagiellonian Univ.), A. Zubareva (SAI)
on 18 Nov 2016; 21:06 UT
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)

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Gaia16aye, nicknamed Ayers Rock (19:40:01.13 +30:07:53.4, J2000) is a spectacular binary microlensing event in the Northern Galactic Plane. The event has been observed by Gaia, ASAS-SN survey and a network of follow-up telescopes, coordinated by the Time Domain WP of the EC's OPTICON grant.

The combined photometry has already exhibited a complex light curve with three caustic crossing (see ATELs #9376, #9507, #9753). Here we present the binary microlensing model, which predicts the fourth and final caustic crossing to occur on around 2016 Nov 20.8 UT (JD~2457713.3).

The light curve can be fit by a binary-lens model with parallax with the following parameters: t0 = 2457678.14 +/- 0.30, u0 = 0.109 +/- 0.003, tE = 122.92 +/- 1.82 d, q = 0.155 +/- 0.009, s = 0.903 +/- 0.003, alpha = 0.411 +/- 0.009, piEN = 0.156 +/- 0.012, piEE = 0.145 +/- 0.012. Please note that the best-fit microlensing parameters (and the caustic crossing moment) can still change slightly, as the new data are being collected and included in the modelling. The graphical representation of the current model, updated daily, based on the part of the incoming data, can be found here.

The final caustic crossing will last only a couple of hours, therefore, due to short visibility of the target, we strongly encourage the astronomical community from around the globe to conduct the photometric observations of the last moments of this spectacular event. The source is going to be very bright (around 12 mag in I-band) and will be accessible also for small-aperture telescopes.

The photometric calibrations were obtained in an automated fashion using the Cambridge Photometric Calibration Server (CPCS), designed and maintained by Sergey Koposov and Lukasz Wyrzykowski. We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team.

Current binary microlensing model