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Additional photometric observations of Gaia17dce

ATel #11123; V. Reshetnyk (National Taras Shevchenko University of Kyiv, Ukraine), V. Godunova (ICAMER Observatory, Ukraine), A. Simon (National Taras Shevchenko University of Kyiv, Ukraine), I. Sokolov (INASAN RAS, Russia)
on 3 Jan 2018; 05:18 UT
Credential Certification: Andrew Simon (skazhenijandrew@gmail.com)

Subjects: Optical, Transient

We have continued to monitor the optical transient Gaia17dce which was detected by Gaia on 2017-11-27 at magnitude G = 16.67. This hostless transient was already confirmed with our images taken on 2017-12-01 (JD 2458089.21) with the 2-m RCC telescope at the Terskol Observatory (ATel #11044). The photometric measurements have shown that Gaia 17dce started to decline shortly after its discovery.

A forced photometry of this unclassified object (candidate CV?) was performed from 2017-12-13 to 2017-12-17 with the 2-m telescope at the Terskol Observatory. The data acquired, especially R-band observations, indicate that Gaia17dce has faded by more than 4 magnitudes within these four days (Fig. 1). Using the NOMAD catalog for photometric calibration we measured the following magnitudes (not corrected for the Galactic foreground extinction):

JD R mag R err
2458089.2124 17.13 0.05
2458101.1548 18.12 0.04
2458102.1581 18.61 0.09
2458104.1795 21.1 0.3
2458105.1668 >22.0
A light curve shown in Fig.2 presents the photometric data which were obtained on 2017-12-13 and 2017-12-14 using R filter. The plot depicts the general decline of the curve with small brightness variations within 0.2 mag on a time scale of hours.

In addition, our measurements on 2017-12-16 (JD 2458104.18) yielded magnitudes of V = 21.4 ± 0.4, B = 20.8 ± 0.3. It is significant to note that we did not detect Gaia17dce in CCD images taken on 2017-12-17 through B, V, R, I filters (limiting mag > 22.0).

We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts).