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Gaia17bfi: a WZ Sge-type dwarf nova in the rising phase of superoutburst

ATel #10389; M. Gromadzki (Warsaw Observatory), L. Wyrzykowski (Warsaw Observatory), P. Mroz (Warsaw Observatory), K. Rybicki (Warsaw Observatory), A. Hamanowicz (Warsaw Observatory), D. Buckley (SALT, SAAO), S. B. Potter (SAAO) and P. A. Woudt (U. of Cape Town)
on 18 May 2017; 09:53 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)

Subjects: Optical, Binary, Cataclysmic Variable, Nova, Variables

The optical transient Gaia17bfi (AT2017ebe, 09:24:52.36, -35:59:00.24) was discovered on 2017-05-11 with G=15.4 by Gaia Science Alerts programme. There is no previous detections of this object by the Gaia mission and there is no progenitor object detected on archival photographic plates. This suggests the amplitude was larger than 5 magnitudes.

SALT/RSS spectroscopy on 2017-05-16 reveals a steep blue continuum with very broad absorption Balmer lines. FWHM of these lines corresponds to velocity around 2800 km/s. He I absorption lines are also present. This spectrum is reminiscent of those observed in a WZ Sge-type dwarf novae in the rising phase of superoutburst.

We encourage further spectroscopic and photometric follow up.

We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (ATel #6593).