Intra-Night Flickering Of T Coronae Borealis: Flickering Parameters And Quasi-Period Modes. Comparison With Rs Ophiuchi

We analyze 40 U-band light curves (LCs) of the flickering source (FS) of the symbiotic recurrent nova T CrB, observed over 1993-2018. The light contribution of the red giant is removed. The LCs are linearized, flattened and processed by a method, created earlier for the case of RS Oph. The method is described and results for T CrB and RS Oph are compared.Over the period 2009-2017 the average flux of the FS increased by 2.5 mag or 10.1 times. Simultaneously, the standard deviation and amplitude deviation of the LC increased about 2.7 and 3.7 times, respectively, which is evidence that the average and scatter of the flickering are connected.The statistics of the skewness, kurtosis, structure gradient and Hurst gradient of the LCs of T CrB are similar to these of RS Oph, giving a hint that the flickering of T CrB contains larger fraction of single shots. This fraction increases toward the short time scale of the flickering. In comparison with a Gaussian distribution, the FS of T CrB shows some excess of large positive deviations while FS of RS Oph shows some deficit of short deviations.As in the case of RS Oph, all LCs of T CrB show time structures, sometimes repeatings, with quasi-periods (QPs) from minutes to tens of minutes. Using the minima of the structure function and the maxima of the auto-correlation function we detected 84 QPs - 48 in 40 whole LCs and 36 in 32 partial high resolution LCs. The distribution of the revealed QPs shows modes at 4.7, 11.8, 19.0, 42.1 and 81.7 min. The QP modes of T CrB and RS Oph follow the power functions QP(M) = 5.1 x 2.0(M) and QP(M) = 3.47 x 1.55(M), respectively, where M is the mode number. It seems that these power functions describe regularities corresponding to 2:1 and 3:2 resonances, with unknown reason.