TCP J21040470+4631129

The bright WZ Sge-type dwarf nova TCP J21040470+4631129 was discovered on July 12, 2019. We are monitoring this object since the discovery. Our optical spectroscopic data are obtained with the 2.1-m telescope at the OAN-SPM, the 2.5-m Isaac Newton Telescope on La Palma, and other smaller telescopes, while photometric observations are mostly performed using 30-cm class telescopes. The observations show that the object is exhibiting remarkable behaviour. After the end of the plateau stage on August 3,  TCP J21040470+4631129 experienced 2 short rebrightenings and possibly another, stunted rebrightening, after which the object underwent the second superoutburst with a relatively short plateau stage of about 9 days. After the second plateau has ended on September 3, TCP J21040470+4631129 showed another short rebrightening on September 16. We note that the fading after the rebrightening has again decelerated suggesting that another rebrightening is possible. Moreover, superhump modulations are still present in a light curve.

Our extensive optical spectroscopic monitoring showed a notable difference between the spectra obtained during the first and the second plateau stages. During the second plateau, the flux in the emission lines was much reduced, and especially higher-order Balmer lines were significantly weakened. But the most dramatic spectral changes were observed during the recent rebrightening. The spectrum obtained just before the rebrightening maximum shows only Balmer absorption lines, while all the emission lines completely disappeared. However, another spectrum obtained 10 hours later shows very strong emission lines again.

We are also monitoring TCP J21040470+4631129 with Swift. The observations obtained between rebrightenings showed a very stable XRT count rate at the level of 0.11+/-0.02 cts/s. However, during rebrightenings it has dropped by about 10 times.