S. I. Neizvestny

SPECTROPHOTOMETRY OF 83 POSSIBLE BLUE COMPACT DWARF GALAXIES FROM THE SECOND BYURAKAN SURVEY

Spectrophotometric observations of 83 possible blue compact dwarf galaxies (BCDGs) and photoelectric UBVR (Johnson system) observations of 37 galaxies from this list are discussed. The observations have been made with the 6-meter telescope of Special Astrophysical Observatory of Russian Academy of Sciences. The general characteristics of BCDGs are considered. Most galaxies are shown to have very low heavy element abundance.

Photometric investigations of low-mass X-ray binaries with high time resolution

We present the results of a search for ultrafast optical variability among 11 low-mass X-ray binaries (LMXBs). Observations have been carried out with the hard- and soft-ware photometrical complex MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) with the 6-m telescope of SAO RAS and 2.15-m telescope of CASLEO, Argentina, with 10-7 s time resolution. Eight of them showed no short-time variability on the time-scale from 10-7 to 40s. Five extremely short flares of 0.5-5 ms duration, 0.1-1 ms rise times and very high amplitudes (> 40) have been detected from A0620-00. Lower limits for the brightness temperature in the zones of flare generation are 109-1011 K. Two flares of about 0.25 s duration have been recorded from the X-ray burster MXB1735-44; the brightness of the object has increased 15-30 times during these flares. These flashes show fine structure on time-scales of about 5-6 ms (confidence level > 95%). Brightness temperatures for different phases of the above flashes ranged from 5 × 107 K to 1010 K. Stochastic variability was detected from GRO J0422+32 in a wide range of time-scales, from 5 × 10-3 to 102 s, simultaneously in different pairs of bands (U B, B V, B R). The power spectrum of the variations is practically flat. The shortest flashes with rise times of about 5-40 ms have brightness temperature higher than 108 K, for an estimate of the distance to the object of 2.4 kpc. All detected events with high probability can be caused only by non-thermal processes. These results are apparently evidence that there are some departures from the standard model of hydrodynamical accretion on to compact objects.

Superfast photometry with the MANIA complex

Abstract We describe the hard/software MANIA complex for carrying out superfast photometry. A new type of time-code converter Quantochron allows us to measure arrival times of photons registered by a photodetector with time resolution up to 20 ns in 216 channels (space, colours, polarization, etc.) simultaneously. Special software was developed to investigate variability on a time-scale of 2 × 10−8-103 s by statistical analysis of the time inverval distribution between detected photons and classical light curves. The results of some observations are presented.

Investigation of the Optical Variability of Relativistic Objects with High Time Resolution

1. Detection of nonthermal optical flares in low mass X-ray binaries. Eleven low-mass X-ray binaries have been observed with the MA¬NIA (Multichannel Analysis of Nanoseconds Intensity Alteration) complex; X0420+32, A0620-00, X1728-169, X1813-14, X1957+11 in 1986 at the 6 m telescope of SAO [7], and 2S0921-630, 4U1543-475, 4U1636-536, 4U1559-487, MXB1735-44, 4U1822-371 in 1991 at the 2.15 m telescope of CASLEO (Argentina) [1]. Analysis of the data using the special y 2 d 2 function formalism [4], [6] has shown no brightness variations on time-scales of 10-7… 10 s for all objects except A0620-00 and MXB1735-44.

Optical properties of X-ray nova percei 1992 near maximum

Abstract We present spectroscopic and photoelectric optical observations of the X-ray Nova GRO J0422+32 = Nova Persei 1992 obtained with a TV spectrum scanner, UBVR photometer and the soft/hardware MANIA complex at the Special Astrophysical Observatory 6 m telescope and with a fast double-head photometer at the Bologna Observatory. In the early phase after its discovery, the spectrum of the object presented a variable continuum with intensity rising blueward and some weak emissions (H, He, N). Photoelectric data show a modulation on a time scale of about 5 h and stochastic flashes, probably of nonthermal origin, on a time scale from 10–20 ms to 200 s. A unique episode of fading of the object was observed on JD 2448986.52.