Kazan Federal University
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GRNTI 41.00 АСТРОНОМИЯ
GRNTI 29.35 Радиофизика. Физические основы электроники
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BISAC SCI004000 Astronomy
BISAC SCI005000 Physics / Astrophysics
We present a study of the flaring radio variability of four microquasars during last ten years with RATAN-600. The main aim of researches is a study of the daily light curves at seven frequencies of 1.2-30 GHz and in multi-azimuthal (MA) mode, when for 5h the fluxes are measured every 5-10 minutes at 4.7 and 8.2 GHz. In SS 433 dozens of bright flares were detected over last ten years. The brightest flare (5.5 Jy at 2.3 GHz) in the total history of GRS 1915+105 research occured in August 2023. In 2024 we have detected five giant radio flares in Cyg X-3 during hypersoft-to-hard X-ray states transits. These flares reached fluxes of 13-18 Jy and have similar properties: optically thick phase in the spectra in the beginning of a flare and the exponential fading for 5-30 days. We relate these events with an efficient formation of relativistic jets during the accretion of matter from a normal star. In the Gamma-ray binary LSI+61d303 with regular flares every 26.5 days, we have detected second period of 26.93 days that can be precession period of jets. We find a clear similarity of bright flares in microquasars.
X-rays: binaries; radio continuum: stars; radiation mechanisms: non-thermal, synchronton radiation
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\title{The flaring activity of microquasars is the key to understanding the processes of accretion and generation of jet emission}%
\titlerunning{Flaring microquasars} % abbreviated title (for running head)
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\author{S.~Trushkin \inst{1,2} \and A.~ Shevchenko\inst{1} \and N. Bursov \inst{1} \and N. Nizhelskij\inst{1} \and P.~ Tsybulev\inst{1} }
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\authorrunning{Trushkin et al.} % abbreviated author list (for running head)
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%%%% list of authors for the TOC (use if author list has to be modified)
%\tocauthor{}
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\institute{Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhny Arkhyz, 369167, Russia
\and Kazan Federal University, 18 Kremlyovskaya St, Kazan 420008, Russia }
\abstract{
We present a study of the flaring radio variability of some microquasars
during last ten years. The main aim of researches is study of the light
radio curves obtained in simultaneous RATAN-600 measurements at frequencies of
1.2-30 GHz in a daily transit mode and in multi-azimuthal (MA) mode, when
the fluxes are measured in every 5-10 minutes during 5 hours at 4.7 and 8.2 GHz.
SS433 is the most flaring microquasar with dozens of detected bright flares
during last ten years.
Over the past three years, we have registered several bright flares
from different microquasars. The brightest flare (5.5 Jy at 2.3 GHz)
in the total history of GRS1915+105 research in August 2023.
Unexpectedly in 2024 we have detected four giant radio flares in Cyg X-3,
reason of which lies in the continuous hyper-soft X-ray state of it.
The flares were at the level of 13-16 Jy, which is in 200 times higher
than the level of quiet state.
These flares have similar property: optically thick
phase of the spectra in the beginning of a flare and the exponential
fading during 5-30 days, when spectra are usual optically thin within range
1-30 GHz like in SS433.
We relate the flaring activity with an efficient formation of
relativistic jets during the accretion of matter from a normal star.
We find a clear similarity bright flares in microquasars.
In the Gamma-ray binary LSI+61d303 with regular flares in
each 26.5 days, we have detected additional close period 26.93 days
that can be precession period of jets.
\keywords{ Stars: X-ray binaries, radio continuum, synchronton radiation}
\doi{10.26119/VAK2024-ZZZZ}
}
\maketitle
\section{Introduction}
Microquasars -- X-ray binary stars with relativistic motions are a rare
type of galactic radio sources of synchrotron radio emission. According
to the traditional scenario, variable radiation is generated gradually
as ejected blobs move along the jet, losing energy of electrons in
matter from the vicinity of black holes or neutron stars under certain
conditions that are not known in all the details, but which are obviously
related to the accretion process of matter coming from a normal star
in the composition of a binary star. This has been proven on a variety
of observational examples of the so-called "disk-jet coupling", which
manifests itself in the "hysteresis" dependence of the evolution of X-ray
radiation on the HID (hardness-intensity-diagram). The radio emission of
the jet on the HID is given the place of the line in the "soft and bright
location". However, the process of jet ejection formation remains unclear,
despite the fact that R. Blandford and colleagues proposed models for the
transfer of matter with momentum and energy from the disk to the jet.
In any case, flares of radio emission remains a critical indicator of
jet formation processes.
\section{Observations}
Observations of the sample were conducted with the RATAN-600 radio
telescope during 2011-2024 at frequencies of 1.24, 2.3, 4.7, 8.2, 11.2,
21.7 and 30 GHz simultaneously. The flux densities were measured with
a typical error of about 3--5\% at 4.7, 8.2, 11.2 GHz and 5-10\% at 1.2, 2.3, 21.7, 30 GHz.
The receivers equipped by the modern HEMT amplifiers can measure fluxes of cosmic
sources on a levels 5-30 mJy in the conditions of the absence of interference.
Usually we use the standard calibrators: 3C48, 3C138, 3C161, 3C286, NGC7027, DR21,
known from the commonly accepted radio scales (Baars+ 1977 and Ott+ 1994),
and additional stable sources J0240-23, J1347+12, J1850-01, and others.
Observations of these calibrators are included in all astronomical programs.
Usually observations are carried out with the Northern sector and with the Southern sector
paired with the Flat mirror of telescope in the mode of transit of sources
through fixed antenna beams. Thus we obtain the daily points of measured fluxes
at different frequencies. Also we use multi-azimuthal mode, when during
$\pm$2.5 hours from culmination time of sources we can produce up to 63
(usually 31) measurements of the fluxes at frequencies 4.7 and 8.2 GHz,
receivers of which established on the special secondary mirror cabin, capable of change
of focus and azimuth of the three-mirror antenna "Southern sector +
Flat mirror". Thus we can obtain the flux points every 5-10 minutes.
\section{Long-term light curves of microquasars }
\subsection{SS433}
SS433 is the well-known bright X-ray, optical binary having the precessing
jets, visible in X-rays, and on the VLA and VLBI maps.
In the fig.1 (left) we give the total light curves at three frequencies during more
then 13 years. In the fig.1 (right) the example of the recent bright
flare are shown with exponential fitting of the fading of the flare.
The flares are usually optically thin in the range 1-20 GHz.
\begin{figure*}
\hbox{
\centerline{
\includegraphics[width=0.5\textwidth]{fig1_SS433_lc_2011-2024.eps}
\includegraphics[width=0.47\textwidth]{fig1_SS433_lc_2024.eps}
}
}
\caption{
{\it Left:} The light curves of the SS433 at different frequencies during 2011-2024.
{\it Right:} The light curves of the SS433 at different frequencies in 2024.
}
\label{fig:SS}
\end{figure*}
\subsection{Cyg X-3}
Cyg X-3 is the famous flaring source of the X-ray binary, consisted
of the Wolf-Rayet star and low mass black hole. In this microquasar
the relativistic jets were detected with VLBI mapping.
The jets are as a rule one-side during the flares, while in a quiet state
images could be double-side. Thus radio images expose boosting according
to the Doppler effect along line of sight.
In the fig.2 (Left) the light curves of the Cyg X-3 are shown for
radio range (RATAN) and for X-ray band of the Swift/BAT at 15-50 keV.
Obviously the hyper-soft X-ray states, being marked by blue ellipses
coincided with the giant radio flaring events. In the fig.2 (right)
and we show the characteristic light curves of the some flaring
events. In order to emphasize the "disk-jets-coupling"\ in the fig.3
we show the radio flaring light curves together with X-ray light (Swift) and
gamma-ray curves (Fermi). We confirm that the high energy Gamma-ray
emission correlated this radio flares.
\begin{figure*}
\hbox{
\centerline{
\includegraphics[width=0.5\textwidth]{fig2_CygX-3_lc_2010-24.eps}
\includegraphics[width=0.5\textwidth]{fig2_C3_lc_2019.eps}
}
}
\caption{
{\it Left:} The radio light curves of the Cyg X-3 measured with RATAN-600 at 4.7, 8.2 and 11.2 GHz
and X-ray light curves with Swift/BAT at 15-50 keV during 2010-2024.
{\it Right:} The radio light curves of the Cyg X-3 measured with RATAN-600
at 4.7, 8.2 and 11.2, 21.7 GHz in 2019.
}
\label{fig:C3a}
\end{figure*}
\begin{figure*}
\hbox{
\centerline{
\includegraphics[width=0.5\textwidth]{fig3_CygX-3_lc_rat_sw_fer_2021.eps}
\includegraphics[width=0.5\textwidth]{fig3_C3_lc_fermi+ratan.eps}
}
}
\caption{
{\it Left}: The radio light curves of the Cyg X-3 measured with RATAN-600 at 4.7, 8.2, 11.2, 21.7 GHz during 2021.
{\it Right}: The radio light curves of the Cyg X-3 measured with RATAN-600 at 4.7, 8.2, 11.2, 21.7 GHz during 2024.
}
\label{fig:C3b}
\end{figure*}
\subsection{GRS1915+105}
Its maximum flow reached 5.5 Jy at 2.3 GHz, which is 3-4 times
higher than previous record measurements. We followed this flare between
August 1-9, 2023 simultaneously on two frequencies 4.7 GHz and 8.2 GHz
in the daily MA-mode observations on RATAN-600, when
flux were measured every 8.6 minutes within interval $\pm$ 2.5 hours from the local
culmination time. In the synchrotron optically thin radio spectrum,
the spectral index changed smoothly from +0.15 to $-$0.95 from August 1
to August 9, and within the interval of MA observations, the spectra
(4.7-8.2 GHz) also changed noticeably. In the MA observations, flux
variability was found at times from 30 to 300 minutes. We estimated the
presence of quasi-periodic oscillations (QPO) in the light curves. Can it
can be argued that in eight MA measurements, QPOs (less than 10% of the
average flow) were detected on time scales from 30 to 100 minutes at both
4.7 GHz and 8.2 GHz frequencies. We related the flare activity GRS1915+105
with a more efficient formation of relativistic jet emissions during the
accretion of matter from a normal star. We find a clear similarity of the
flare events in GRS1915+105 with giant flares in Cyg X-3 microquasars,
four of which were detected in February and April, June and July 2024.
\begin{figure}
\centerline{
\includegraphics[width=0.5\textwidth]{fig4_1915_lc_flare2023.eps}
\includegraphics[width=0.5\textwidth]{fig4_1915_sp_tot_10d.eps}
}
\caption{ {\it Left}:The radio light curves of the giant flare of
GRS1915+105 in 2023. {\it Right}: Evolution of spectra during this flare.
}
\label{fig:GRS}
\end{figure}
The brightness of the flares increased linearly with time,
and their decay went exponentially ($\exp{-t/\tau}$),
where the parameter $\tau$ slowly changed from 4.3 to 2.7
days with the increase of frequency from 2.3 to 30 GHz. The spectrum in
the optically thin zone was determined by a spectral index in the range
from $-$0.7 to $-$0.4. In the second outburst, the exponential decline was
generally maintained, but the $\tau$ at the beginning of the fading
was noticeably higher than later.
\subsection{LSI+61d303}
The case of the X-ray binary LSI+61d303 with detected radio pulsar as
a relativistic component lies apart from the main sample of microquasars,
although it is the single Galactic radio source showing the clear
flaring periodicity (26.5 days).
The nature of these flares remains the subject of intense debate, and it
cannot yet be firmly established that renewable jets are in action.
Based on the data we have obtained, we confirm that there
are two characteristic periods of 26.49 days (equal orbital period)
and 26.93 days in the light curves, which speaks rather in favor of jets.
Last one could be the precession period of the hypothetical jets.
Thus the detected super-orbital SO) period of 1660 days could be explained
by usual beating of close frequencies.
Indeed we can clearly see the modulation of the flares by SO-period.
The repeated flares (2022) of LSI+61d303 are well visible in fig.5 (Right),
where the orbit phase 0.6 are marked by triangles.
\begin{figure}
\hbox{
\centerline{
\includegraphics[width=0.5\textwidth]{fig5_lsi_lc_2013-2023.eps}
\includegraphics[width=0.5\textwidth]{fig5_lsi_lc_2022.eps}
}
}
\caption{
{\it Left}: The radio light curves of the LSI+61d303 measured with RATAN-600
at 4.7 and 11.2 GHz during 2013-2023.
{\it Right}: The radio light curves of the LSI+61d303 measured with RATAN-600
at 4.7 and 11.2 GHz during 2022.
}
\label{fig:LSI}
\end{figure}
%\subsection{V404 Cyg}
\section{Discussion}
We have studied the variability of the four microquasars during
long-term period and found a lot of special properties of the radio
emission together with optical and X-ray bands (see [1-8] for details).
Using the example of the many flares we have detected from
different microquasars, we can briefly list the main properties of
radio emission:
\begin{enumerate}
\item the synchrotron spectrum, often having one index from 2 GHz to 200
GHz, is optically thick at the beginning of the flare, and optically
thin after the maximum, while spectra become steeper ;
\item the grow up of flux is linear in time;
\item flares fade follows an exponential law;
\item The flares in BH binaries are random in nature, but are definitely related to the
X-ray state of the binary system, following after hyper-soft X-ray state.
\end{enumerate}
Any models should take into account these properties of flares. In close
future we will discuss the finite jet segment model in application of
Cyg X-3 [9] and the hollow conical jet emission model for SS 433 [10].
%\acknowledgements{}
\section*{Funding}
This work was supported in the framework of the national project
"Science"\ by the Ministry of Science and Higher Education of
the Russian Federation under the contract Nxxx.
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