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Register a new userThe jet of S5 0716+71 at $mu$as scales with RadioAstron
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Added by
Evgeniya Kravchenko V.
Publication date
2019
fields
Physics
and research's language is
English
Authors
E. V. Kravchenko
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Ground-space interferometer RadioAstron provides unique opportunity to probe detail structure of the distant active galactic nuclei at $mu$as scales. Here we report on RadioAstron observations of the BL Lac object S5 0716$+$71, performed in a framework of the AGN Polarization and Survey Key Science Programs at 22 GHz during 2012-2018. We obtained the highest angular resolution image of the source to date, at $57times24 mu$as. It reveals complex structure of the blazar jet in the inner 100 $mu$as, with emission regions that can be responsible for the blazar variability at timescales of a few days to week. Linear polarization is detected in the core and jet areas at the projected baselines up to about $5.6$ Earth diameters. The observed core brightness temperature in the source frame of $geq2.2times10^{13}$ K is in excess of theoretical limits, suggesting the physical conditions are far from the equipartition between relativistic particles and magnetic field.
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We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on January 3-4 2015 at a frequency of 22 GHz (wavelength $lambda=1.3$ cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70 833 km (5.6 Earth diameters) for both, parallel hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 $mu$as, the highest for this source to date. This enabled us to estimate the size of the radio core to be $<12times5~mu$as and to reveal a complex structure and a significant curvature of the blazar jet in the inner 100 $mu$as, which is an indication that the jet viewing angle lies inside the opening angle of the jet conical outflow. Fairly highly (15%) linearly polarized emission is detected in a jet region of 19 $mu$as in size, located 58 $mu$as downstream from the core. The highest brightness temperature in the source frame is estimated to be $>2.2times10^{13}$ K for the blazar core. This implies that the inverse Compton limit must be violated in the rest frame of the source, even for the largest Doppler factor $deltathicksim25$ reported for 0716+714.
Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. We present multiwavelength images made of the radio emission in the powerful quasar S5 0836+710, obtained using a global VLBI array and the antenna Spektr-R of the RadioAstron mission of the Russian Space Agency, with the goal of studying the internal structure and physics of the relativistic jet in this object. The RadioAstron observations at wavelengths of 18cm, 6cm, and 1.3cm are part of the Key Science Program for imaging radio emission in strong AGN. The internal structure of the jet is studied by analyzing transverse intensity profiles and modeling the structural patterns developing in the flow. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02mas to 200mas. Brightness temperatures in excess of $10^{13}$,K are measured in the jet, requiring Doppler factors of $ge 100$ for reconciling them with the inverse Compton limit. Several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin-Helmholtz (KH) instability. The oscillatory patterns are interpreted as the surface and body wavelengths of the helical mode of the KH instability. The interpretation provides estimates of the jet Mach number and of the ratio of the jet to the ambient density, which are found to be $M_mathrm{j}approx 12$ and $etaapprox 0.33$. The ratio of the jet to the ambient density should be conservatively considered an upper limit because its estimate relies on approximations.
We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S5 0716+714 along with Fermi gamma-ray data during a multi-waveband outburst in 2011 October. We analyze total and polarized intensity images of the blazar obtained with the VLBA at 43 GHz during and after the outburst. Monotonic rotation of the linear polarization vector at a rate of >50 degrees per night coincided with a sharp maximum in gamma-ray and optical flux. At the same time, within the uncertainties, a new superluminal knot appeared, with an apparent speed of ~21c. The general multi-frequency behavior of the outburst can be explained within the framework of a shock wave propagating along a helical path in the blazars jet.
The bright radio source S5 0716+714, which is usually classified as a BL Lac object, is one of the most intensively studied blazar. S5 0716+714 demonstrates extremely peculiar properties, such as the shortest time-scale of optical and polarimetric variations observed in blazars. In the given talk, we present the results of 8-h polarimetric monitoring of S5 0716+714 with a $sim70$-sec resolution carried out using the 6-m telescope BTA of the SAO RAS. The observation data analysis reveals the variability both in total and polarized light on the 1.5-hour timescales that specifies the size of the unresolved emitting region. The numerical model of polarization in jet with the helical structure of the magnetic field is suggested, and fitting the model reveals a magnetic field precession with a period of about 15 days.
We have monitored the BL Lacertae object S5 0716+714 simultaneously in the B, R and I bands on three nights in November 2014. The average time resolution is quite high (73s, 34s, 58s for the filters B, R and I), which can help us trace the profile of the variation and search for the short inter-band time delay. Intra-day variability was about 0.1 mag on the first two nights and more than 0.3 mag on the third. A bluer-when-brighter color behavior was found. An clear loop path can be seen on the color-magnitude diagram of the third night, revealing possible time delays between variations at high and low energies. It is the first time that the intra-day spectral hysteresis loop has been found so obviously in the optical band. We used the interpolated cross-correlation function method to further confirm the time delay and calculated the values of lag between light curves at different wavelengths on each night. On the third night, variations in the R and B bands is approximately 1.5 minutes lagging behind the I band. Such optical time delay is probably due to the interplay of different processes of electrons in the jet of the blazar.
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