0000000000114561
AUTHOR
L. Lara
Magnetic Field Configuration in 4C 39.25
AbstractWe have performed simultaneous multi-frequency polarization VLBA observations of the compact radio sources 3C 395 and 4C 39.25 which show both stationary and superluminal components in their parsec-scale structures. Those of 3C 395 have been reported elsewhere. Here we report on high resolution maps of the total intensity and polarized radio emission of 4C 39.25, trace the magnetic field configuration along the jet, and explore different possibilities for the nature of the components within the framework of the bent shocked relativistic jet model.
The broad-line radio galaxy J2114+820
In the frame of the study of a new sample of large angular size radio galaxies selected from the NRAO VLA Sky Survey, we have made radio observations of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio structure basically consists of a prominent core, a jet directed in north-west direction and two extended S-shaped lobes. We have also observed the optical counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved central component. The optical spectrum shows broad emission lines. This fact, together with its low radio power and FR-I type morphology, renders J2114+820 a non-trivial object from the point of view of the current unification schemes of…
High-resolution observations of SN 2001gd in NGC 5033
We report on 8.4 GHz VLBI observations of SN2001gd in the spiral galaxy NGC5033 made on 26 June 2002 and 8 April 2003. Our data nominally suggests a relatively strong deceleration for the expansion of SN2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 8 April 2003, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of E_min =(0.3-14) 10^{47} ergs, and a corresponding equipartition average magnetic field of B_min = (50--350) mG. We also present multiwavelength VLA measurements of SN2001gd, which are well fit by an optically thin, synchrotron spectrum, partially absorbed by thermal p…
A new sample of large angular size radio galaxies II. The optical data
We constructed and presented in the first paper of this series a new sample of 84 large angular size radio galaxies by selecting from the NRAO VLA Sky Survey objects with angular size > 4', declination above +60 degrees and total flux density at 1.4 GHz > 100 mJy. In this paper we present optical spectra and images of those galaxies associated with the radio emission for which no redshift was known prior to our observations. Optical counterparts have been identified for all (but one) members of the sample. After our observations, a reliable spectroscopic redshift is available for 67 objects (80%) from the sample. This paper, second of a series of three, contributes to increase the num…
A new sample of large angular size radio galaxies
We present in this paper a detailed study of a new sample of large angular size FR I and FR II radio galaxies and compare the properties of the two classes. As expected, a pure morphology based distinction of FR Is and FR IIs corresponds to a break in total radio power. The radio cores in FR Is are also weaker than in FR IIs, although there is not a well defined break power. We find that asymmetry in the structure of the sample members must be the consequence of anisotropies in the medium where the lobes expand, with orientation playing a minor role. Moreover, literature data and our observations at kiloparsec scales suggest that the large differences between the structures of FR I and FR I…
VLBI Observations of a Complete Sample of Radio Galaxies. VII. Study of the FR I Sources 3C 31, 4C 35.03, and 3C 264
We present results from global VLBI and VLA observations of three FanaroU-Riley type I radio gal- axies, 3C 31, 4C 35.03, and 3C 264, at a frequency of 5 GHz. In all three cases, we observe asymmetric parsec-scale structures consisting of a compact core and a single jet pointing in the direction of the more prominent kiloparsec jet. We interpret such alignment as evidence for the relativistic nature of FR I radio jets at parsec scales. Comparing the VLBI and VLA images of these sources, we —nd a progressive deceleration of the plasma —ow from parsec to kiloparsec scales. We consider another —ve FR I radio galaxies studied previously by us and —nd that, in a set of eight FR I objects, the es…
Restarting activity in radio galaxies
We present observations of two radio galaxies, J1835+620 and 3C338, both with signs of having passed through different stages of core activity. The former presents two symmetric and bright components within a typical FR II structure, possibly resulting from two distinct phases of activity; the latter is a FR I radio galaxy with two separated regions with different age properties, possibly due to a switch-off and -on cycle in its core. In both sources, the optical counterpart lies in a group of galaxies with indications of mutual interaction, a scenario often invoked to explain triggering of core activity.
High-Resolution Radio Observations of Supernova SN1986J
We present high-resolution observations of the supernova SN1986J in the galaxy NGC891 at the frequency of 5 GHz, more than 15 years after its explosion. The image shows a highly distorted shell of radio emission, suggesting that the shock front has been strongly deformed. The brightness distribution within the shell is also highly asymmetric, and we propose that such asymmetry could be due to the collision of the supernova ejecta with an anisotropic, clumpy medium. The average speed of the shell has decreased from about 7400 km s−1 in 1988.74 down to ~ 6300 km s−1 in 1999.14, pointing to a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor…
High-resolution radio imaging of young supernovae
The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.
VLBI Observations of a Complete Sample of Radio Galaxies V. 3C346 and 4C31.04: two Unusual CSS Sources
We present observations at 1.7 and 8.4 GHz of two Compact Steep Spectrum (CSS) sources from a complete sample of low-intermediate power radio galaxies. 3C346 shows an asymmetric structure with a one-sided ``jet'' and ``hot spot''. Present observations suggest that the classification of this source as a CSS is inappropriate, and that it is a common radio galaxy at a small angle to the line of sight. Its properties are in agreement with the predictions of unified schemes models. 4C31.04 shows more complex structure with the possibility of a centrally located flat spectrum core in between two close lobes. We suggest that this source could be a low redshift Compact Symmetric Object.
A new sample of large angular size radio galaxies I. The radio data
We present a new sample of 84 large angular size radio galaxies selected from the NRAO VLA Sky Survey. Radio sources with declination above +60 degrees, total flux density greater than 100 mJy at 1.4 GHz and angular size larger than 4 arcmin have been selected and observed with the VLA at 1.4 and 4.9 GHz. The radio observations attempt to confirm the large angular size sources and to isolate the core emission for optical identification. In this paper, the first of a series of three, we present radio maps of 79 sources from the sample and discuss the effects of the selection criteria in the final sample. 37 radio galaxies belong to the class of giants, of which 22 are reported in this paper …
A Decade of SN1993J: Discovery of Wavelength Effects in the Expansion Rate
We have studied the growth of the shell-like radio structure of supernova SN1993J in M81 from September 1993 through October 2003 with very-long-baseline interferometry (VLBI) observations at the wavelengths of 3.6, 6, and 18cm. For this purpose, we have developed a method to accurately determine the outer radius (R) of any circularly symmetric compact radio structure like SN1993J. The source structure of SN1993J remains circularly symmetric (with deviations from circularity under 2%) over almost 4000 days. We characterize the decelerated expansion of SN 1993J through approximately day 1500 after explosion with an expansion parameter $m= 0.845\pm0.005$ ($R \propto t^{m}$). However, from tha…
How is really decelerating the expansion of SN1993J?
SN1993J is to date the radio supernova whose evolution has been monitored in greatest detail and the one which holds best promise for a comprehensive theoretical-observational analysis. The shell-like radio structure of SN1993J has expanded in general accord with models of shock excited emission, showing almost circular symmetry for over 8 years, except for a bright feature at the south-eastern region of the shell that has been observed at every epoch. The spectrum of SN1993J has flattened from alpha =-1 to alpha =-0.67 (S_(\nu) propto nu**(alpha)). The decelerated expansion can be modeled well with a single slope but apparently better with two slopes. There are also intriguing hints of str…
Space-VLBI observations of the twisted jet in 3C395
We present Space-VLBI observations of the quasar 3C395 which show evidence of the existence of a large bend in the inner parts of its jet, close to the core. This bend would explain why previous Earth-based cm-VLBI observations could not detect the ejection of new moving components, as expected from flux density variability in this source. In general, the observational properties of the jet in 3C395 are heavily marked by the existence of bends on different scales.
On the SN 1993J Radio Shell Structure
An accurate measurement of the expansion deceleration of SN 1993J depends on how well the shell size and its emission structure are known. With the goal of determining the emission structure of the shell, we have developed a new approach, which we call “Green Function Deconvolution” (GFD), based on iterative use of Green functions on the sky plane to reconstruct the radial emission profiles of spherically symmetric sources. This approach works reasonably well in the case of optically thin emitting sources, which is not the case for SN 1993J since, as we find, the emission from the central part of SN 1993J further away from us is strongly or totally absorbed. We describe the GFD method and p…
An Astronomical Observatory in the Classroom
We describe a project developed at the University of Granada in collaboration with the Instituto de Astrofisica de Andalucia aimed at using a remote telescope for live astronomical observations from the classroom. Available instrumentation, software and activities are presented.
High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd
The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.
New sample of large angular size radio galaxies. I.
We present a new sample of 84 large angular size radio galaxies selected from the NRAO VLA Sky Survey. Radio sources with declination above +60{deg}, total flux density greater than 100mJy at 1.4GHz and angular size larger than 4' have been selected and observed with the VLA at 1.4 and 4.9GHz. The radio observations attempt to confirm the large angular size sources and to isolate the core emission for optical identification. In this paper, the first of a series of three, we present radio maps of 79 sources from the sample and discuss the effects of the selection criteria in the final sample. 37 radio galaxies belong to the class of giants, of which 22 are reported in this paper for the firs…