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Detection of close periodicities due to orbital and precession modulation of radio emission
from jets in the microquasar LSI+61d303
The RATAN-600 radio telescope monitored the radio emission from a
microquasar, a gamma source, an X-ray optical binary star LSI+61d303,
which includes a Be star and a black hole (BH).
For over a hundred consecutive orbital periods (26.5 days) during 2013-2021,
periodic flares were detected at frequencies of 4.8 and 11.2 GHz,
3-4 days after the closest approach of the components.
As a result of the intense matter flow accreting on the BH, powerful
jet ejections (jets) are formed, in which radio emission and, probably,
gamma rays are generated. It was found from the orbital
light curve averaged over many periods that the radio emission evolves
from an optically thick state at the beginning of the flare to an optically
thin state, when the radio spectrum becomes steepest;
then the system returns to the flat spectrum characteristic of a compact jet.
This process is due to the generation of relativistic electrons in strong
shock waves traveling along the gas flow of a jet and is in good agreement
with the theory of the evolution of synchrotron radiation. A noticeable
shift in the moments of the maximum radio flux of flares was found,
as the phase of the visible 4.6-year period changed, which is easily
explained in the model of precessing jets.
But the main result of many years of research was the discovery in the
power spectrum of the light curves of two close periods, equal to 26.49
and 26.93 days. The first harmonic exactly corresponds to the previously
found orbital period of the system; the second harmonic is due to the
modulation of the radio flux due to the precessional motion of the jet.
It is precisely the beating of close frequencies of these periods that
explains the super-orbital 4.6-year period in the system, and the
model of precessing relativistic jets in LSI+61d303 was unambiguously
confirmed.
Authors:
Trushkin S.A., Shevchenko A.V., Nizhelskij N.A., Tsybulev P.G. (SAO RAS)
Published:
1. Trushkin et al. Long-term multi-frequency studies of flaring activity
from microquasars. Astronomy at the Epoch of Multimessenger Studies,
Proceedings of the BAK-2021 conference, held 23-28 August, 2021 in Moscow.,
pp.471-472 DOI: 10.51194/VAK2021.2022.1.1.196
2. Trushkin et al. Monitoring of Microquasars with RATAN-600 Ground-Based
Astronomy in Russia. 21st Century, Proceedings of the All-Russian Conference
held 21-25 September, 2020 in Nizhny Arkhyz, Russia.
Edited by I.I. Romanyuk, I.A. Yakunin, A.F. Valeev, D.O. Kudryavtsev,
2020, p.351-354.
3. Trushkin et al. The Jets of Microquasars during Giant Flares and Quiet
State. 2017, Galaxies, vol.5, issue 4, p.84
LBV Search Results in Local Volume Galaxies: Study of Four Stars in NGC4449
LBVs (luminous blue variables) make a small type of high luminosity massive
stars with strong spectral and photometric variability. Most LBV were
found in our and nearby galaxies (up to 1 Mpc). In more distant galaxies,
only a few stars of this type are known. The search and study of
LBV stars in galaxies with different metallicities can clarify their nature
and evolutionary status. In this paper, four high luminosity stars
in NGC4449 discovered by the authors were investigated. The spectroscopy
of the three brightest of them, carried out at the BTA (SAO RAS), revealed
emission features characteristic of LBV stars. Noticeable brightness
variations were found in J122809.72+440514.8
(ΔI=0.69±0.13m) and
J122817.83+440630.8 (ΔR=2.15±0.13m),
the variability of the rest does not exceed 0.3m. Estimates
of the bolometric luminosity of stars in the range of
log(LBol/L☉)≈5.24-6.42.
The CMFGEN code was used to simulate the cold state spectrum of
J122809.72+440514.8 (Teff=9300 K), the mass loss rate was
obtained: 5.2x10-3 M☉ yr-1,
which was several times higher than the mass loss rate of η Car.
As a result of the study, the objects J122809.72+440514.8 and
J122817.83+440630.8 were classified as LBVs, and two other stars were
classified as LBV candidates.
Authors:
Solovyeva Yu.N., Vinokurov A.S., Sarkisyan A.N., Oparin D.V.,
Spiridonova O.I. (SAO RAS) in cooperation with Fabrika S.N. (SAO RAS, KFU),
Kostenkov A.E. (SAO RAS, SPBU),
Valeev A.F. (SAO RAS, CrAO RAS), Atapin K.E. (SAI MSU), Bizyaev D.V.
(SAI MSU, APO (USA)), Nedialkov P.B. (Sofia University, Bulgaria)
The work was carried out within the R&D plan No.AAAA-A21-121011890155
and the RFBR grant No. 19-52-18007.
Published:
1. Solovyeva Y.; Vinokurov A.; Sarkisyan A.; Kostenkov A.; Atapin K.;
Fabrika S.; Oparin D.; Valeev A.; Bizyaev D.; Nedialkov,P.; Spiridonova O.
"Search for LBVs in the Local Volume galaxies: study of four stars in
NGC 4449", 2021, MNRAS, 507, 3, pp.4352-4366
Discovery of 10 gas-rich dwarf galaxies with the lowest metallicities with
the BTA and SALT spectroscopy
In previous years, when studying the population of one of the nearest voids,
the authors discovered 5 unusual low-mass dwarfs with the gas metallicity
Z < Z☉/30.
Almost all their baryonic matter is in the form of gas, and the mass of
stars is only a few percents. Their "old" stellar population is blue
indicating an age of about 1-3 billion years. These properties are
consistent with the hypothesis of the initial phase of their evolution.
Since the discovery of the famous galaxy IZw18 with
Z ~ Z☉/30,
over 50 years of searching for such unusual galaxies in the nearby Universe,
only about a dozen of them have been found. In 2018, the authors presented
the "Catalog of nearby voids" (Pustilnik et al. 2019), as well as the
1354 galaxies inhabiting them, which greatly increased the possibilities of
searching for unusual galaxies in voids. According to the results of
spectroscopic observations of 46 selected candidates with the BTA (SAO RAS)
and SALT (RSA) telescopes, 10 new objects with
Z(gas) ~ Z☉/50-Z☉/30,
were found in 3 years, which doubled the number of known galaxies with
such properties. These galaxies form a unique area for studying star
formation and massive stars with record low metallicities. In the future,
it is planned to actively study them in other ranges using
ground-based and space telescopes.
Authors:
S.A. Pustilnik, Y.A. Perepelitsyna, A.L. Tepliakova, A.N. Burenkov,
D.V. Oparin, in cooperation with E.S. Egorova, A.Y. Kniazev (SAI MSU)
Published:
1. Pustilnik S.A., Egorova E.S., Kniazev A.Y., Perepelitsyna Y.A., Tepliakova
A.L., Burenkov A.N., Oparin D.V. XMP gas-rich dwarfs in nearby voids:
results of BTA spectroscopy, 2021, MNRAS, 501, 944-962
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