ABSTRACT
We present a detailed photometric study of the bright cataclysmic variable, BG Triangulum (BG Tri), using ground-based observations mainly from the Rozhen Observatory, the All-Sky Automated ...Survey for Supernovae (ASAS-SN), the Transiting Exoplanet Survey Satellite (TESS) and the Wide Angle Search for Planets (WASP). We report on the discovery of a negative superhump with P−sh = 0.1515(2) d and a co-existing superorbital variation with P = 3.94(53) d in data from 2019 and 2020. A positive superhump with P+sh = 0.1727(14) d is also discovered in data from 2006. The obtained negative superhump deficit ε− = 0.044(1) and the positive superhump excess ε+ = 0.090(9) give us an independent photometric evaluation of the mass ratio (q) of the system, which we find to be q− = 0.37(2) and q+ = 0.40(5), respectively. We also present a study of the quasi-periodic oscillations and stochastic variability (flickering) in BG Tri. The light curves show a rich mixture of simultaneously overlapping quasi-periods ranging from 5 to 25 min. The multicolour (UBVRI) photometric observations from the Rozhen Observatory reveal the typical increase of the flickering amplitudes to the shorter wavelengths. The recently introduced A60 amplitude of the flickering light source in all studied photometric bands is systematically lower when the negative superhump is gone in season 2021.
We report observations of the flickering variability of the symbiotic recurrent nova RS Oph at quiescence in five bands (UBVRI). We find evidence of a correlation between the peak-to-peak flickering ...amplitude (ΔF) and the average flux of the hot component (F
av). The correlation is highly significant, with a correlation coefficient of 0.85 and a p-value of ∼10−20. Combining the data from all wavebands, we find a dependence of the type
$\Delta F \propto F_{{\rm av}}^k$
, with power-law index k = 1.02 ± 0.04 for the UBVRI flickering of RS Oph. Thus, the relationship between the amplitude of variability and the average flux of the hot component is consistent with linearity. The rms amplitude of flickering is on average 8 per cent (±2 per cent) of F
av. The detected correlation is similar to that found in accreting black holes/neutron stars and cataclysmic variables. The possible reasons are briefly discussed. The data are available upon request from the authors.
We present recent optical photometric observations of the blazar OJ 287 taken during 2015 September-2016 May. Our intense observations of the blazar started in 2015 November and continued until 2016 ...May and included detection of the large optical outburst in 2015 December that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of nine ground-based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in 2016 March. In addition, we investigated multiband flux variations, colour variations, and spectral changes in the blazar on diverse time-scales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour, and spectral variability.
Abstract
We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, ...and by the Swift and Fermi satellites. We study the source behaviour in the period 2007–2015, characterized by several extreme flares. The ratio between the optical, X-ray and γ-ray fluxes is very variable. The γ-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of ∼50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.
We performed optical photometry and spectral observations of the symbiotic stars 4U1954+319 and ZZ CMi. For 4U1954+319, using high-resolution spectra, we, measure the equivalent widths of diffuse ...interstellar bands (DIBs) and estimate the interstellar reddening E(B-V ) = 0:83?0:09. Using the GAIA distances and our photometry, we find: (1) the absolute V -band magnitude MV =-5:23 ? 0:08 of 4U1954+319 and that the mass donor is a supergiant of luminosity class Ib, and (2) MV = -0:27?0:2 for ZZ CMi and that the mass donor is a giant of luminosity class III.
We analyse optical photometric data of short term variability (flickering) of accreting white dwarfs in cataclysmic variables (KR Aur, MV Lyr, V794 Aql, TT Ari, V425 Cas), recurrent novae (RS Oph and ...T CrB) and jet-ejecting symbiotic stars (CH Cyg and MWC 560). We find that the amplitude–flux relationship is visible over four orders of magnitude, in the range of fluxes from 1029 to 1033 erg s−1 Å−1, as a ‘statistically perfect correlation with correlation coefficient 0.96 and p-value ∼10−28. In the above range, the amplitude of variability for any of our 9 objects is proportional to the flux level with (almost) one and the same factor of proportionality for all nine accreting white dwarfs with ΔF = 0.36(±0.05)Fav, σrms = 0.086(±0.011)Fav, and σrms/ΔF = 0.24 ± 0.02. Overall, our results indicate that the viscosity in the accretion discs is practically the same for all nine objects in our sample, in the mass accretion rate range 2 × 10−11 − 2 × 10−7 M⊙ yr−1.
We report optical spectroscopic observations of the Be/γ-ray binaries LSI+61303, MWC 148 and MWC 656. The peak separation and equivalent widths of prominent emission lines (Hα, Hβ, Hγ, HeI, and FeII) ...are measured. We estimated the circumstellar disc size, compared it with separation between the components, and discussed the disc truncation. We find that in LSI+61°303 the compact object comes into contact with the outer parts of the circumstellar disc at periastron, in MWC 148 the compact object goes deeply into the disc during the periastron passage, and in MWC 656 the black hole is accreting from the outer parts of the circumstellar disc along the entire orbit. The interstellar extinction was estimated using interstellar lines. The rotation of the mass donors appears to be similar to the rotation of the mass donors in Be/X-ray binaries. We suggest that X-ray/optical periodicity ~1 day deserves to be searched for.
We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, ...we determine the temperature (~55 000 K) and the luminosity (~5.3 L⨀) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10(exp -12) erg cm(exp -2) s(exp -1), which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise, we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4±0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.
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