283 research outputs found
Chandra & HST Imaging of the Quasars PKS B0106+013 & 3C345: Inverse Compton X-rays and Magnetized Jets
We present results from deep (70 ks) Chandra ACIS observations and Hubble
Space Telescope ACS F475W observations of two highly optically polarized
quasars belonging to the MOJAVE blazar sample, viz., PKS B0106+013 and 1641+399
(3C345). These observations reveal X-ray and optical emission from the jets in
both sources. X-ray emission is detected from the entire length of the 0106+013
radio jet, which shows clear bends or wiggles - the X-ray emission is brightest
at the first prominent kpc jet bend. A picture of a helical kpc jet with the
first kpc-scale bend representing a jet segment moving close(r) to our line of
sight, and getting Doppler boosted at both radio and X-ray frequencies, is
consistent with these observations. The X-ray emission from the jet end however
peaks at about 0.4" (~3.4 kpc) upstream of the radio hot spot. Optical emission
is detected both at the X-ray jet termination peak and at the radio hot spot.
The X-ray jet termination peak is found upstream of the radio hot spot by
around 0.2" (~1.3 kpc) in the short projected jet of 3C345. HST optical
emission is seen in an arc-like structure coincident with the bright radio hot
spot, which we propose is a sharp (apparent) jet bend instead of a terminal
point, that crosses our line of sight and consequently has a higher Doppler
beaming factor. A weak radio hot spot is indeed observed less than 1"
downstream of the bright radio hot spot, but has no optical or X-ray
counterpart. By making use of the pc-scale radio and the kpc-scale radio/X-ray
data, we derive constraints on the jet Lorentz factors (Gamma_jet) and
inclination angles (theta): for a constant jet speed from pc- to kpc-scales, we
obtain a Gamma_jet of ~70 for 0106+013, and ~40 for 3C345. On relaxing this
assumption, we derive a Gamma_jet of ~2.5 for both the sources. Upper limits on
theta of ~13 degrees are obtained for the two quasars. (ABRIDGED)Comment: 46 pages, 11 figures, Accepted for publication in Ap
Very Large Baseline Array observations of Mrk 6 : probing the jet-lobe connection
We present the results of high-resolution VLBI (very long baseline interferometry) observations at 1.6 and 4.9 GHz of the radio-loud Seyfert galaxy, Mrk 6. These observations are able to detect a compact radio core in this galaxy for the first time. The core has an inverted spectral index (Ī±1.6 4.9 = +1.0 Ā± 0.2) and a brightness temperature of 1 Ć 108 K. Three distinct radio components, which resemble jet elements and/or hotspots, are also detected. The position angles of these elongated jet elements point not only to a curved jet in Mrk 6, but also towards a connection between the AGN and the kpc-scale radio lobes/bubbles in this galaxy. Firmer constraints on the star formation rate provided by new Herschel observations (SFR <0.8 Mā yr-1) make the starburst-wind-powered bubble scenario implausible. From plasma speeds, obtained via prior Chandra X-ray observations, and ram pressure balance arguments for the interstellar medium and radio bubbles, the north-south bubbles are expected to take 7.5 Ć 106 yr to form, and the east-west bubbles 1.4 Ć 106 yr. We suggest that the jet axis has changed at least once in Mrk 6 within the last ā107 yr. A comparison of the nuclear radio-loudness of Mrk 6 and a small sample of Seyfert galaxies with a subset of low-luminosity FR I radio galaxies reveals a continuum in radio properties.Peer reviewe
Signatures of large-scale magnetic fields in AGN jets: transverse asymmetries
We investigate the emission properties that a large-scale helical magnetic
field imprints on AGN jet synchrotron radiation. A cylindrically symmetric
relativistic jet and large-scale helical magnetic field produce significant
asymmetrical features in transverse profiles of fractional linear polarization,
intensity, Faraday rotation, and spectral index. The asymmetrical features of
these transverse profiles correlate with one another in ways specified by the
handedness of the helical field, the jet viewing angle (theta_ob), and the bulk
Lorentz factor of the flow (Gamma). Thus, these correlations may be used to
determine the structure of the magnetic field in the jet. In the case of radio
galaxies (theta_ob~1 radian) and a subclass of blazars with particularly small
viewing angles (theta_ob << 1/Gamma), we find an edge-brightened intensity
profile that is similar to that observed in the radio galaxy M87. We present
observations of the AGNs 3C 78 and NRAO 140 that display the type of transverse
asymmetries that may be produced by large-scale helical magnetic fields.Comment: accepted by MNRAS, added reference
Shocks, Seyferts and the SNR connection: a Chandra observation of the Circinus galaxy
We analyse new Chandra observations of the nearest (D=4 Mpc) Seyfert 2 active
galaxy, Circinus, and match them to pre-existing radio, infrared and optical
data to study the kpc-scale emission. The proximity of Circinus allows us to
observe in striking detail the structure of the radio lobes, revealing for the
first time edge-brightened emission both in X-rays and radio. After considering
various other possible scenarios, we show that this extended emission in
Circinus is most likely caused by a jet-driven outflow, which is driving shells
of strongly shocked gas into the halo of the host galaxy. In this context, we
estimate Mach numbers M=2.7-3.6 and M=2.8-5.3 for the W and E shells
respectively. We derive temperatures of 0.74 (+0.06, -0.05) keV and 0.8-1.8 keV
for the W and E shells, and an expansion velocity of ~900-950 km/s. We estimate
that the total energy (thermal and kinetic) involved in creating both shells is
~2x10^55 erg, and their age is ~10^6 years. Comparing these results with those
we previously obtained for Centaurus A, NGC 3801 and Mrk 6, we show that these
parameters scale approximately with the radio power of the parent AGN. The
spatial coincidence between the X-ray and edge-brightened radio emission in
Circinus resembles the morphology of some SNR shocks. This parallel has been
expected for AGN, but has never been observed before. We investigate what
underlying mechanisms both types of systems may have in common, arguing that,
in Circinus, the edge-brightening in the shells may be accounted for by a B
field enhancement caused by shock compression, but do not preclude some local
particle acceleration. These results can be extrapolated to other low-power
systems, particularly those with late type hosts.Comment: 13 pages, 9 figures, and 5 tables. Accepted for publication in Ap
WFPC2 LRF Imaging of Emission Line Nebulae in 3CR Radio Galaxies
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness
emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio
sources. We overlay the emission line images on high resolution VLA radio
images (eight of which are new reductions of archival data) in order to examine
the spatial relationship between the optical and radio emission. We confirm
that the radio and optical emission line structures are consistent with weak
alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS)
radio galaxies where both the radio source and the emission line nebulae are on
galactic scales and strong alignment is seen at all redshifts. There are weak
trends for the aligned emission line nebulae to be more luminous, and for the
emission line nebula size to increase with redshift and/or radio power. The
combination of these results suggests that there is a limited but real capacity
for the radio source to influence the properties of the emission line nebulae
at these low redshifts (z < 0.6). Our results are consistent with previous
suggestions that both mechanical and radiant energy are responsible for
generating alignment between the radio source and emission line gas.Comment: 80 pages, 54 figures. Accepted for publication in ApJ
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