Is TCP J18010186-2951258 a binary lens?

ATel #11882; Nucita A. A., De Paolis F., Strafella F., & Licchelli D., Department of Mathematics & Physics, Unisalento
on 23 Jul 2018; 14:25 UT
Credential Certification: Achille Nucita (nucita@le.infn.it)

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The transient TCP J18010186-2951258 (at J2000 coordinates RA = 18:01:01.84 Dec=-29:51:23.8) was first discovered by T. Kojima on UT 2018 07 13.494 and the ASAS-SN Sky Patrol light curve (Shappee et al. 2014; Kochanek et al. 2017) resembles that of a microlensing event (Subo Dong et al. ATel #11853). By inspecting the ASAS-SN data around the peak we noticed an anomaly with respect to the Paczinsky best fit profile. Hence, including all currently (and free) archival V band data (AAVSO, and ASAS-SN) together with a few newly remotely acquired data using iTelescope.Net instruments (T17) n Siding Spring, Australia, (https://www.itelescope.net/) we find a best fit solution with a binary lens model with parameters q= 8.3E-3, b=0.66, t_0=113.8 (HJD-2458200), t_E= 19.5 days, u_0=0.027, theta = 2.63 radians, V_0 = 14.5. Subsequent analysis on the characteristics of the lens system parameters and the background source is in progress with the aim to test other possible models (including blending and finite source effects), check the robustness of the solution, confirm the binary lens model and, if so, refine the best fit parameters. Detailed analysis on the possible planetary feature will be presented elsewhere. This work makes use of ASAS-SN data (Shappee et al. 2014 and Kochanek et al. 2017). We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. The use of the Siding Spring Observatory facilities is also acknowledged. We also remind that the BVRI band observations at the T17 Siding Spring iTelescope.Net instrument were performed in occasion of the "Sergio Fonti Summer School for Astronomy" held in Lecce (19-20, July, 2018), see http://www.dmf.unisalento.it/astro/Eventi%20e%20Conferenze/Eventi/ScuolaEstiva_2018.html. We thank all the involved high school students and teachers for their enthusiastic participation in the observations and photometric analyses.

Possible binary lens fit