Variability of emission at scales from fractions of a second to tens of
years is one of characteristic properties of different celestial objects.
Transient events are also the emission variability though not regularly
observed. Such events are difficult to detect for that reason. During
the analysis of the surveys carried out on RATAN-600, it was found that
almost one fifth of the detected sources shows significant radio flux
variations. We discovered three radio transients in our search (Fig.1).
Contact - O.Zhelenkova
The flux variability detected with the telescopes in different ranges
of electromagnetic radiation can be caused by variable processes in
the active galactic nucleus (AGN), the variability of relativistic
jet velocity or its orientation relative to an observer, absorption
variations in the line of sight, and gravitational microlensing. Stars
may also be variable.
Transients are associated with different types of events and objects.
They can be supernovae including radio supernovae, afterglows of gamma-ray
bursts (GRB). Slow radio transients in the Galaxy are generated by different
stellar populations such as outbursts detected from M dwarfs, cataclysmic
variables, and X-ray binaries. The events of interest are also associated
with a sudden increase of accretion rate due to tidal explosion of a star
approached too close to a supermassive object with a mass of millions and
billions of solar masses. This can cause a soft X-ray burst or, probably,
radio emission. In the majority of papers dedicated to radio transients
they usually were found incidentally in archive data but this information,
nevertheless, allows one to estimate the frequency of occurrence of such
objects and to attempt to explain their nature.
We used the data from "Cold" radio surveys carried out with RATAN-600
in 1980-1994 to search for radio sources with significant flux variability.
Seventy-three variable radio sources were detected with considerable
fluctuations (Fig. 1) which are variable at scales of several years
according to different statistical criteria. The long-term variability
for fifty-two radio sources was detected for the first time. Host objects
of the variable radio sources refer to active galaxies. First half of
these objects was determined from the Sloan Digital Sky Survey spectra
and the rest - optically fainter - from the SDSS classification or from
color indices of the WISE infra-red survey.
For the three detected transient events (Fig.2), we searched for
coordinate matching with the lists of supernovae and gamma-ray burst
events, with cataclysmic events in the Galaxy, with Solar system objects,
and space missions. Drawing the data from radio and optical surveys and
also from Vizier, SIMBAD, and NED astronomical databases, we tried to
interpret the nature of transients. Most probably, they refer to three
different events. Radio emission of the first event can be caused by
outburst activity in radioquiet AGN, the second one is linked with
GRB afterglows or radio supernovae. The nature of the third radio
transient is debatable, as it is probably localized in the Solar
system according to the changes of its coordinates.
1. Е.К.Майорова, О.П.Желенкова. On possibility of detection of variable
sources using the data of Cold surveys carried out on RATAN-600.
Astrophysical Bulletin, Vol. 67, Issue 3, pp. 318-339 (2012).
E.Majorova, O.Zhelenkova. Detection of Variable Sources Using the Data
of "Cold" Surveys. Astrophysical Bulletin 68, pp. 371-395 (2013);
3. Majorova E., Zhelenkova O., Temirova A. Search for variable
sources using the data of Cold surveys in the right-ascension interval
Astrophysical Bulletin, Volume 70, Issue 1, pp.33-44 (2015).
4. O.Zhelenkova, E.Majorova. Search for Radio Transients and New Detection
of Radio Sources Using the RATAN-600 Surveys in 1980-1994.
(Astrophysical Bulletin, in press).
5. O.Zhelenkova, E.Majorova. Observational Manifestations and Intrinsic
Properties of the RCR Sources in the Framework of the Normalized Model.
(Astrophysical Bulletin, in press).
Light curves (on the left) and spectra (on the right) of the sources
with detected variations of flux density
Parts of averaged scans with the detected transients (marked with arrows)