Dramatic broadening of emission lines in TCP J21040470+4631129

ATel #13297 (19 Nov 2019): V. Neustroev, A. E. Watkins, P. E. Kvist, E. P. Halsio, A. E. N. Ruokanen, M. M. Anetjarvi (U. Oulu), T. Tordai (MCSE), K. L. Page, J. P. Osborne (U. Leicester), G. Sjoberg (AAVSO), D. Boyd (ARAS), T. R. Marsh, B. T. Gaensicke (U. Warwick), C. Knigge (U. Southampton), S. Zharikov (UNAM), R. P. V. Rautio, T. A. Rikkola; L. Poranen; E. Sarkar (U. Oulu), N. P. M. Kuin (UCL-MSSL)

We report on new optical and X-ray observations of the WZ Sge-type dwarf nova TCP J21040470+4631129 (hereafter TCP2104) discovered on 2019 July 12. The object experienced two superoutbursts and three rebrightenings, and now is slowly declining (ATel #12936, #12947, #13009, #13122). Our new optical spectroscopic data were obtained on November 6, 50 days after the most recent rebrightening observed on September 15-17 (ATel #13122). We used the ALFOSC spectrograph at the Nordic Optical Telescope (NOT) on La Palma.

This observation shows a remarkable change in TCP2104’s emission line profiles. All the Balmer and He I lines are now much broader than they were during the superoutbursts and rebrightenings. For example, the FWHM of the Halpha line is now ~1550 km/s, 3-4 times larger than it was during the superoutburst (350-500 km/s). In the blue part of the spectrum, the Balmer emission lines are now superposed on the broad absorption lines of the white dwarf.

Time-resolved optical photometric observations show that after the last rebrightening TCP2104 has been declining at a rate of ~0.006 mag/day, and has been showing double-wave periodic modulations with an amplitude of ~0.08 mag. Their period of 77.09+/-0.01 min is consistent with the spectroscopic orbital period of 77.07+/-0.02 min (ATel #13009). TCP2104 is currently at the level of V~15.25 mag.

On November 3, we obtained another observation of TCP2104 with Swift. The observation showed no significant change in both the X-rays or UV compared to previous observations. The XRT count rate was 0.088 +/- 0.011 count/sec, while the UV magnitudes were: w2 = 12.64 +/-0.02, m2 = 12.75 +/- 0.03, and w1 = 12.97 +/- 0.02.

The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA. We thank the Swift PI, Brad Cenko, for approving the observations, and the Swift planning and operations teams for their ongoing support.

NOT spectra
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