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The cataclysmic variable SDSS J214354.59+124457.8 (hereafter SDSS J214354) was observed photometrically on sixty one nights between 2012 July 28 and 2019 May 26. The long term variation of this object shows changes between two phases; a dwarf nova type and a novalike. This implies that the object belongs to the group of Z Cam type stars. The timing analysis of the light curve reveals a periodic signal at 0.13902(5) d, which we identify as the superhump period. However, the fractional superhump excess of 10 per cent longer than the orbital period is exceptionally large. We obtained a mass ratio of ∼0.4, which is above the accepted upper limit of q = 0.33 for the formation of superhumps. We suggest that the object contains a secondary with an evolved core. With an orbital period of 0.126 d, SDSS J214354 is situated at the upper border of the period gap. The long term light curve of SDSS J214354 is similar to those of Z Cam type stars which are characterized by recurring standstills, followed by short intervals with DN type outbursts. Therefore, we conclude that SDSS J214354 is a new member of the Z Cam type stars.

We present optical multi-colour photometry of V404 Cyg during the outburst from December, 2015 to January, 2016 together with the simultaneous X-ray data. This outburst occurred less than 6 months after the previous outburst in June–July, 2015. These two outbursts in 2015 were of a slow rise and rapid decay-type and showed large-amplitude (∼2 mag) and short-term (∼10 min–3 hours) optical variations even at low luminosity (0.01–0.1LEdd). We found correlated optical and X-ray variations in two ∼1 hour time intervals and obtained a Bayesian estimate of an X-ray delay against the optical emission, which is ∼30–50 s, during those two intervals. In addition, the relationship between the optical and X-ray luminosity was Lopt ∝ L0.25−0.29 X at that time. These features cannot be easily explained by the conventional picture of tran- sient black-hole binaries, such as canonical disc reprocessing and synchrotron emission related to a jet. We suggest that the disc was truncated during those intervals and that the X-ray delays represent the required time for propagation of mass accretion flow to the inner optically-thin region with a speed comparable to the free-fall velocity.

We present broadband photometric and polarimetric observations of two type II supernovae (SNe) 2013hj and 2014G. SN 2014G is a spectroscopically classified type IIL event, which we also confirm photometrically as its light curve show characteristic features (plateau slope of 2.55 mag (100 d)$ ^{-1} $ in V-band and duration of $ \sim77 $d) of a generic IIL SN. On the other hand SN 2013hj also shows high plateau decline rate of $ 1.5 $ mag (100 d)$ ^{-1} $ in V-band, similar to SNe IIL, but marginally lower than SNe IIL template light curves. Our high cadence photometric observations of SNe 2013hj and 2014G enables us to cover all characteristic phases up to radioactive tail of optical light curves. Broadband polarimetric observations reveal some polarization in SN 2013hj with subtle enhancement as SN evolves towards plateau end, however the polarization angle remains constant throughout the evolution. This characteristic is consistent with the idea that the evolving SN with recombining hydrogen envelope is slowly revealing more asymmetric central region of explosion. Modelling of bolometric light curve yields a progenitor mass of $ \sim11 $M$_{\odot}$ with a radius of $ \sim700 $R$_{\odot}$ for SN 2013hj, while for SN 2014G model estimated progenitor mass is $ \sim9 $M$_{\odot}$ with a radius of $ \sim630 $R$_{\odot}$, both having a typical energy budget of $ \sim2\times10^{51} $ erg., Comment: 22 pages, 10 figures, 9 tables. Accepted for publication in MNRAS

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504, and BL Lacertae) on December 18--21, 2015 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe, and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra- and inter-day time scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio- and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio- and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations., 6 pages, 6 figures, accepted by MNRAS

We report optical photometric and polarimetric observations of the blazar OJ 287 gathered during 2016/17. The high level of activity, noticed after the General Relativity Centenary flare, is argued to be part of the follow-up flares that exhibited high levels of polarization and originated in the primary black hole jet. We propose that the follow-up flares were induced as a result of accretion disk perturbations, travelling from the site of impact towards the primary SMBH. The timings inferred from our observations allowed us to estimate the propagation speed of these perturbations. Additionally, we make predictions for the future brightness of OJ 287. © 2017 by the authors.

We describe the infrared spectrum of the galactic supersoft X-ray source MR Vel (RX J0925.7-4758) in the wave- length range of 1.1−2.6 µm. We find Paschen, Brackett, He I, He II and neutral and ionized oxygen lines in emission. No traces of the secondary star were found. P-Cygni profiles were observed in Paschen β and Brackett γ, from which we conclude that these lines arise in a wind. Fitting the optical and infrared energy distribution with a supercritical disk model, incorporating white dwarf and secondary star contributions, we were able to constrain the distance to 2−5 kpc, which implies an absolute magnitude MV between −2 and 0.

We observed a new dwarf nova, IX Dra, for 46 days between 2000 November 10 and 2001 June 17, and revealed that IX Dra is the fifth member of a peculiar group of SU UMa stars, called ER UMa stars. The light curve is almost perfectly identical to that of V1159 Ori: supercycle, 53 d; interval of normal outbursts, 3–4 d; duty cycle, ∼ 30%; and the outburst amplitude, 2.5mag. From a time-series observation during the superoutbursts, we obtained a presumable superhump period of 0.067 d. We note that some clustering may exist in the period distribution of ER UMa stars. It is needed to confirm this clustering by a larger number of examples.

In supersoft X-ray sources the mass accretion rate is roughly equal to the Eddington rate, and traditional standard disks cannot be adequate. We thus propose a supercritical accretion disk (superdisk) for supersoft X-ray sources. We have found that superdisks exhibit various distinct features, compared with standard thin disks. The continuous spectra of superdisks generally become flat (vSv ~ v O ), which are greatly different from those of disk-blackbody spectra, as expected in the usual accretion disk systems. This flat nature is not so prominent in supersoft X-ray sources, compared with that in the superdisk around a black hole, since the radial extension of the disk is much smaller. Moreover, irradiation becomes important for a smaller accretion rate system. The superdisk picture was applied to RX JOOI9.8+2156, and reproduced its spectra and optical light curves well.

We discovered the optical counterpart about 13 mag of a soft X-ray transient, XTE J1118+480 on 2000 March 30. We perform astrometry and provide the accurate position as R.A. = 11 h 18 m 10 s .85 , Decl. = +48 ◦ 02 ′ 12 ′′ .9. The outbursting object is identified with a 18.8 mag star in USNO catalog. Our prediscovery data shows another outburst during 2000 January, again coinciding with an outburst detected in X-rays. Through the CCD time-series photometry, we found the presence of a periodic variation with the amplitude of 0.055 mag and the period of 0.17078 ± 0.00004d which we consider as promising candidate of orbital period. Because of the high galactic latitude and faint quiescence magnitude of 18.8, XTE J1118+480 is the possible first firmly identified black hole candidate (BHC) X-ray transient in the galactic halo.

We considered the X-ray irradiated accretion disk in the galactic supersoft X-ray source RX J0019.8 +2156, and estimated the contribution in UV and optical fluxes due to the reprocessing effect of X-ray radiation on the surface of the accretion disk and main sequence companion star. In the nuclear-burning white dwarf model of supersoft X-ray sources, radiation near the Eddington luminosity is generated on the white dwarf. For an assumed distance of 2 kpc to the object, however, a simple model with the standard accretion-disk model can not reproduce the observed fluxes in the UV and optical wavelengths of the object. This fact suggests the existence of reprocessing processes by the irradiated components in the binary system at relatively lower frequencies. We thus calculated the irradiation effects on the accretion disk and the mass donor companion in this system, and estimated their contributions to the flux of the lower frequency regions in the energy distribution. As a result, the reprocessed radiation from the irradiated accretion disk and companion star can well reproduce the observed fluxes.

We report time-resolved photometric observations of the first superoutburst confirmed since 1975 in a most enigmatic cataclysmic variable, AL Comae Berenices, during 1995 April-June. We detected double-peaked modulations in the early phase of the outburst, the period of which is slightly shorter than the superhump period. Three possibilities for the mechanism causing these oscillations are discussed. We also refer to similar modulations observed in ER UMa stars. As seen during the 1978 outburst of WZ Sge, a dip of over 2 mag in the light curve occurred in the 1995 outburst. After recovery from this dip, AL Com again declined 0.5 mag and rebrightened, showing modulations with the same period as that of the superhump, which indicates that a "second" superoutburst occurred. These modulations disappeared before the final decline. After decline, AL Com stayed about or over 1 mag brighter than its quiescence level for at least 2 weeks. It is likely that the accretion disk remained in its hot state near the inner edge during the dip and after the end of the outburst.

We report here on time-resolved photometric observations of the superoutburst of a dwarf nova, RZ Leo, which occurred during 2000 December–2001 January. We reveal the following characteristics of the outburst based on our observations: long duration, large amplitude, and the existence of two types of superhumps — “early superhumps” and “normal superhumps”. In addition to the extremely low frequency of the outbursts, the characteristics of the outburst strongly indicate that RZ Leo is the fifth member of the WZ Sge-type dwarf novae. The orbital period of RZ Leo is 0.07651 d, which is remarkably longer than the “canonical” period of other WZ Sge stars (∼ 0.058 d). The longer period indicates a non-degenerate secondary of RZ Leo, which suggests that the idea of a low quiescence viscosity due to a degenerate brown dwarf secondary may not be correct. The present discovery of RZ Leo as being a WZ Sge star provides the first clear indication that the decay of magnetic turbulence in accretion disks of quiescent WZ Sge stars plays an important role in producing the proposed low quiescent viscosity.

Although presently classified as a SU UMa-type dwarf nova, WZ Sge is well known as one of the most peculiar objects in that it shows only superoutbursts with exceptional duration and amplitude, and no normal outbursts. Furthermore, on its decline from the 1978 outburst, WZ Sge showed a deep temporal dip. All of these characteristics have puzzled both theoreticians and observers.

RX J0019.8+2156 (RX J0019) is one of supersoft X-ray sources (SSXSs) which were rarely found in the Galaxy, and the brightest one upto now (Beuermann et al. 1995). Although the binary systems of SSXSs are still not perfectly revealed, if the model with nuclear burning white dwarf (van den Heuvel et al. 1992) is adopted, it is supposed that most of radiative energy are generated on the surface of the white dwarf. The radiation strongly irradiates the accretion disk and companion, and the reprocessing has an influence upon an observed flux of SSXSs in lower frequencies (Popham, DiStefano 1996).