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J. M. Marcaide,
I. Marti-Vidal,
A. Alberdi,
M. A. Perez-Torres,
E Ros,
P. J. Diamond,
J. C. Guirado, L. Lara,
I. I. Shapiro,
C. J. Stockdale,
K. W. Weiler,
F. Mantovani,
R. A. Preston,
R. T. Schilizzi,
R. A. Sramek,
C. Trigilio,
S. D. Van Dyk,
A. R. Whitney
[show abstract]
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ABSTRACT: 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 that day onwards the expansion is different when observed at 6 and 18cm. Indeed, at 18cm, the expansion can be well characterized by the same $m$ as before day 1500, while at 6cm the expansion appears more decelerated, and is characterized by another expansion parameter, $m_{6}= 0.788\pm0.015$. Therefore, since about day 1500 on, the radio source size has been progressively smaller at 6cm than at 18cm. These findings are in stark contrast to previous reports by other authors on the details of the expansion. In our interpretation the supernova expands with a single expansion parameter, $m= 0.845\pm0.005$, and the 6cm results beyond day 1500 are due to physical effects, perhaps also coupled to instrumental limitations. Two physical effects may be involved: (a) a changing opacity of the ejecta to the 6cm radiation, and (b) a radial decrease of the magnetic field in the emitting region. (Long abstract cut. Please, read full abstract in manuscript). Comment: 21 pages, 19 figures, accepted in A&A
03/2009;
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ABSTRACT: We present results from global VLBI and VLA observations of three Fanaroff-Riley type I radio galaxies, 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 find a progressive deceleration of the plasma flow from parsec to kiloparsec scales. We consider another five FR I radio galaxies studied previously by us and find that, in a set of eight FR I objects, the estimated jet bulk velocities and orientation angles with respect to the observer are consistent with the requirements of the unification model for low-power radio sources.
The Astrophysical Journal 01/2009; 474(1):179. · 6.02 Impact Factor
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ABSTRACT: We have observed the radio source in NGC 3862 (3C 264) simultaneously with the European VLBI network and the MERLIN arrays, obtaining detailed images of its radio structure from parsec to subkiloparsec scales. 3C 264 shows a one-sided jet with evident variations in its morphological properties with distance. We have analyzed Hubble Space Telescope optical data of NGC 3862, finding a one-to-one correspondence between radio and optical features in the jet. The radio-to-optical spectral index is approximately constant along the jet. Synchrotron appears as the most plausible mechanism for the observed jet emission at radio and optical wavelengths. Local particle reacceleration or, alternatively, deviation from the condition of equipartition, are plausible mechanisms to explain the low synchrotron cooling and constant spectral index in the jet of 3C 264.
The Astrophysical Journal 01/2009; 513(1):197. · 6.02 Impact Factor
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ABSTRACT: Observations of the core of the giant radio galaxy NGC 315 made with VLBI interferometers are discussed in the context of a relativistic jet. The sidedness asymmetry suggests Doppler favoritism from a relativistic jet. The presence of moving features in the jet, as well as jet counterjet brightness ratios, hint at an accelerating, relativistic jet. An increasing jet velocity is also supported by a comparison of the jet's observed properties with the predictions of an adiabatic expansion model. On the parsec scale, the jet is unpolarized at a wavelength of 6 cm to a very high degree, in clear distinction to the high polarization seen on the kiloparsec scale.
The Astrophysical Journal 01/2009; 519(1):108. · 6.02 Impact Factor
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J M Marcaide,
I Martí-Vidal,
A Alberdi,
M A Pérez-Torres,
E Ros,
P J Diamond,
J C Guirado, L Lara,
I I Shapiro,
C J Stockdale,
K W Weiler,
F Mantovani,
R A Preston,
R T Schilizzi,
R A Sramek,
C Trigilio,
S D Van Dyk,
A R Whitney
[show abstract]
[hide abstract]
ABSTRACT: We studied the growth of the shell-like radio structure of supernova SN 1993J in M 81 from September 1993 to October 2003 with very-long-baseline interferometry (VLBI) observations at the wavelengths of 3.6, 6, and 18 cm. We developed a method to accurately determine the outer radius (R) of any circularly symmetric compact radio structure such as SN 1993J. The source structure of SN 1993J remains circularly symmetric (with deviations from circularity under 2%) over almost 4000 days. We characterize the decelerated expansion of SN 1993J until approximately day 1500 after explosion with an expansion parameter m = 0.845 ± 0.005 (R ∝ t m). However, from that day onwards the expansion differs when observed at 6 and 18 cm. Indeed, at 18 cm, the expansion can be well characterized by the same m as before day 1500, while at 6 cm the expansion appears more decelerated, and is characterized by another expansion parameter, m 6 = 0.788 ± 0.015. Therefore, since about day 1500 onwards, the radio source size has been progressively smaller at 6 cm than at 18 cm. These findings differ significantly from those of other authors in the details of the expansion. In our interpretation, the supernova expands with a single expansion parameter, m = 0.845 ± 0.005, and the 6 cm results beyond day 1500 are caused by physical effects, perhaps also coupled to instrumental limitations. Two physical effects may be involved: (a) a changing opacity of the ejecta to the 6 cm radiation; and (b) a radial decrease of the magnetic field in the emitting region. We also found that at 6 cm about 80% of the radio emission from the backside of the shell behind the ejecta is absorbed (our average estimate, since we cannot determine any possible evolution of the opacity), and the width of the radio shell is (31 ± 2)% of the outer radius. The shell width at 18 cm depends on the degree of assumed absorption. For 80% absorption, the width is (33.5 ± 1.7)%, and for 100% absorption, it is (37.8 ± 1.3)%. A comparison of our VLBI results with optical spectral line velocities shows that the deceleration is more pronounced in the radio than in the optical. This difference might be due to a progressive penetration of ejecta instabilities into the shocked circumstellar medium, as also suggested by other authors.
A&A. 01/2009; 505:927-945.
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I {Mart'i}-Vidal,
J ~M Marcaide,
A Alberdi,
J ~C Guirado, L Lara,
M ~A Pérez-Torres,
E Ros,
M ~K Argo,
R ~J Beswick,
T ~W ~B Muxlow,
A Pedlar,
I ~I Shapiro,
C ~J Stockdale,
R ~A Sramek,
K ~W Weiler,
J Vinko
åp. 08/2007; 470:1071-1077.
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I. Marti-Vidal,
J. M. Marcaide,
A. Alberdi,
J. C. Guirado, L. Lara,
M. A. Perez-Torres,
E Ros,
M. K. Argo,
R. J. Beswick,
T. W. B. Muxlow,
A. Pedlar,
I. I. Shapiro,
C. J. Stockdale,
R. A. Sramek,
K. W. Weiler,
J. Vinko
[show abstract]
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ABSTRACT: We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20 February 2005 (151 days after explosion). The Very Large Array (VLA) flux density was 1.23$\pm$0.07 mJy, corresponding to an isotropic luminosity at 8.4GHz of (4.45$\pm$0.3)$\times10^{25}$ erg s$^{-1}$ Hz$^{-1}$ and a brightness temperature of (1.3$\pm$0.3)$\times10^{8}$ K. We also provide an improved source position, accurate to about 0.5 mas in each coordinate. The VLBI image shows a clear asymmetry. From model fitting of the size of the radio emission, we estimate a minimum expansion velocity of 15,700$\pm$2,000 km s$^{-1}$. This velocity is more than twice the expected mean expansion velocity estimated from a synchrotron self-absorbed emission model, thus suggesting that synchrotron self-absorption is not relevant for this supernova. With the benefit of an optical spectrum obtained 12 days after explosion, we favor an emission model which consists of two hot spots on an underlying expanding shell of width comparable to that of SN 1993J. Comment: Accepted for publication in A&A (22/05/07)
05/2007;
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Miguel A. Perez-Torres,
A. Alberdi,
J. M. Marcaide,
M. A. Guerrero,
P. Lundqvist,
I. I. Shapiro,
E Ros, L. Lara,
J. C. Guirado,
K. W. Weiler,
C. J. Stockdale
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ABSTRACT: 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 plasma. We obtain a supernova flux density of (1.02 +/- 0.05) mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0 +/- 0.3) * 10^{36} ergs between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM-Newton X-ray detection of SN2001gd on 18 December 2002. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of L_X = 1.4 +/- 0.4 * 10^{39} ergs/s in the (0.3-5) keV band. We suggest that both radio and X-ray observations of SN2001gd indicate that a circumstellar interaction similar to that displayed by SN1993J in M81 is taking place. Comment: 9 pages, 6 figures, 2 tables, accepted for publication in MNRAS
04/2005;
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M.A. Pérez-Torres,
J.M. Marcaide,
A. Alberdi,
E. Ros,
J.C. Guirado, L. Lara,
F. Mantovani,
C.J. Stockdale,
K.W. Weiler,
P.J. Diamond,
S.D. Van Dyk,
P. Lundqvist,
N. Panagia,
I.I. Shapiro,
R. Sramek
[show abstract]
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ABSTRACT: 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.
12/2004: pages 97-103;
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ABSTRACT: We present a new, complete, sample of 95 radio sources selected from the B2 and 3CR catalogues, with z < 0.1. Since no selection effect on the core radio power, jet velocity, or source orientation is present, this sample is well suited for statistical studies. In this first paper we present the observational status of all sources on the parsec (mas) and kiloparsec (arcsec) scale; we give new parsec-scale data for 28 sources and discuss their parsec-scale properties. Combining these data with those in the literature, information on the parsec-scale morphology is available for a total of 53 radio sources with different radio power and kpc-scale morphology. We investigate their properties. We find a dramatically higher fraction of two-sided sources in comparison to previous flux limited VLBI surveys. Comment: 29 pages, 21 figures - ApJ in press (10 Jan 2005 issue)
09/2004;
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M. A. Perez-Torres,
J. M. Marcaide,
A. Alberdi,
E Ros,
J. C. Guirado, L. Lara,
F. Mantovani,
C. J. Stockdale,
K. W. Weiler,
P. J. Diamond,
S. D. Van Dyk,
P. Lundqvist,
N. Panagia,
I. I. Shapiro,
R. Sramek
[show abstract]
[hide abstract]
ABSTRACT: 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.
04/2004;
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ABSTRACT: We present the results of a high angular resolution study of the BL Lac object Markarian 501 in the radio band. We consider data taken at 14 different epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We study the kinematics of the parsec-scale jet and estimate its bulk velocity and orientation with respect to the line of sight. Limb brightened structure in the jet is clearly visible in our data and we discuss its possible origin in terms of velocity gradients in the jet. Quasi-simultaneous multi-wavelength observations allow us to map the spectral index distribution and to compare it to the jet morphology. Finally, we estimate the physical parameters of the parsec-scale jet. Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and fig. 2 available only as .jpg files)
09/2003;
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ABSTRACT: We report on the results of a two epoch study of the low power Compact Symmetric Object 4C 31.04. Observations performed with the VLBA at 5 GHz in 1995 and 2000 have yielded images of this source at milliarcsecond angular resolution. A central core is detected, with bright compact hot spots and extended lobes on both sides. Model-fitting and other analysis of the data (brightness profile, difference map) clearly indicate that the source is expanding. We estimate the velocity of this expansion to be (0.085 +/- 0.016) mas/yr, i.e. (0.33 +/- 0.06) c in both hot spots. Assuming a constant expansion velocity, we estimate the kinematic age of the source at 550 yrs. We also study the spectral index using VLBA observations at 1.3 GHz and MERLIN at 22 GHz. The derived spectral age is 3000-5000 years in equipartition conditions. The two estimates are discussed and found to be in agreement, given present uncertainties. Comment: 9 pages, 8 .eps figures; accepted for publication in Astronomy & Astrophysics
12/2002;
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ABSTRACT: We present a new complete sample of radio sources selected from the B2 and 3CR catalogues, with no bias respect to the jet velocity and orientation. Using preliminary data we investigate the parsec scale properties of radio sources with different radio power and kpc scale morphology. We stress the evidence for high velocity pc scale jets in all sources and conclude that the properties of parsec scale jets are similar regardless of the source total power and large scale morphology. Moreover we show two epoch images of two nearby radio galaxies: a low power compact source and a CSO. The comparison of the two epoch images suggests that in both sources the size is increasing with time. We derive a possible advance speed and estimate their dynamic age.
11/2002;
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J. M. Marcaide,
A. Alberdi,
M. A. Perez-Torres,
J. C. Guirado, L. Lara,
E Ros,
P. J. Diamond,
F. Mantovani,
I. I. Shapiro,
K. W. Weiler,
R. A. Preston,
R. T. Schilizzi,
R. A. Sramek,
C. Trigilio,
S. D. Van Dyk,
A. R. Whitney
[show abstract]
[hide abstract]
ABSTRACT: 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 structure in the expansion curve. The results by the two VLBI groups carrying out this research show general agreement, but also some differences. A comparison of the optical and VLBI results about the details of the deceleration show some discrepancies.
08/2002;
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ABSTRACT: We report here on 5 GHz global very-long-baseline interferometry (VLBI) observations of SN 1986J, 16 yr after its explosion. We obtained a high-resolution image of the supernova, which shows a distorted shell of radio emission, indicative of a deformation of the shock front. The angular size of the shell is $\sim4.7 {\rm mas}$, corresponding to a linear size of $\sim6.8 \times 10^{17} {\rm cm}$ for a distance of 9.6 Mpc to NGC 891. The average speed of the shell has decreased from $\sim$7400 \kms in 1988.74 down to about $6300 {\rm km s^{-1}}$ in 1999.14, indicative of a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor wind ($\rho_{\rm cs} \propto r^{-s}, s=2$), the swept-up mass by the shock front is $\sim$2.2\Ms. This large swept-up mass, coupled with the mild deceleration suffered by the supernova, suggests that the mass of the hydrogen-rich envelope ejected at explosion was $\ga12$ \Ms. Thus, the supernova progenitor must have kept intact most of its hydrogen-rich envelope by the time of explosion, which favours a single, massive star progenitor scenario. We find a flux density for SN 1986J of $\sim$7.2 mJy at the observing frequency of 5 GHz, which results in a radio luminosity of $\sim1.4 \times 10^{37} {\rm erg s^{-1}}$ for the frequency range $10^7$--$10^{10}$ Hz ($\alpha =-0.69; S_\nu \propto \nu^{\alpha})$. We detect four bright knots that delineate the shell structure, and an absolute minimum of emission, which we tentatively identify with the centre of the supernova explosion. If this is the case, SN 1986J has then suffered an asymmetric expansion. We suggest that this asymmetry is due to the collision of the supernova ejecta with an anisotropic, clumpy (or filamentary) medium. Comment: To appear in MNRAS (pink pages)
02/2002;
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ABSTRACT: 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 number of well defined samples of radio galaxies with ample spectroscopic information. Comment: Accepted in Astronomy & Astrophysics. Fig 1 is supplied as low resolution gif files. Contact L. Lara for better quality postscript files
09/2001;
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ABSTRACT: 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 for the first time. Comment: Accepted in A&A. Due to file size limitations, Fig.2 with is provided as 28 low quality gif files. High quality ps files available upon request at lucas@iaa.csic.es
02/2001;
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ABSTRACT: We present new results on the parsec-scale jet of the quasar 3C395, derived from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at 8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending up to 20 mas, with a projected magnetic field essentially aligned with the radio jet. The emission is strongly dominated, in total intensity and polarization, by the core and the inner jet region (of ~3 mas length). We have studied the details of this dominant region finding clear structural variations during this ~2.5 years period, in contrast with the apparent quietness of the jet structure inferred from lower resolution VLBI observations. We observe the ejection of a new component from the core and variations in the degree of polarization of the inner jet components. We estimate a high Faraday Rotation Measure close to the core, with a strong decrease along the inner jet. Comment: 7 pages, 4 figures, A&A in press
01/2001;
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ABSTRACT: A complete sample of 27 radio galaxies was selected from the B2 and 3CR catalogs, in order to study their properties on the milliarcsecond scale. In the Appendix of this paper we present new radio images for 12 of them. Thanks to the present data, all the sources in this sample have been imaged at mas resolution. We discuss the general results. In particular we stress the evidence for high velocity jets in low power radio galaxies, we compare high and low power sources, and discuss the source properties in the light of the unified scheme models. We derive that the properties of parsec scale jets are similar in sources with different total radio power and kpc scale morphology. From the core - total radio power correlation, we estimate that relativistic jets with Lorentz factor $\gamma$ in the range 3 - 10 are present in high and low power radio sources. We discuss also the possible existence of a two velocity structure in the jets (fast spine and lower velocity external shear layer). Comment: 38 pages, 18 figures with an Appendix; ApJ in press (vol. 551, Apr. 20, 2001 issue)
01/2001;
