31 research outputs found
The ruff of equatorial emission around the SS433 jets: its spectral index and origin
We present unique radio observations of SS433, using MERLIN, the VLBA, and
the VLA, which allow us to, for the first time, properly image and derive a
meaningful spectral index for the `ruff' of equatorial emission which surrounds
SS433's jet. We interpret this smooth ruff as a wind-like outflow from the
binary.Comment: 4 pages, 4 figures, to appear in Proceedings of the 4th Microquasar
Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodrigue
Resolving the masers in M82
Despite first being detected in the 1970s, surprisingly little is known about
the OH main line maser population in the nearby starburst galaxy M82. Sometimes
referred to as 'kilomasers', they have isotropic luminosities intermediate
between Galactic masers and those found in more distant megamasers. Several
observations have been carried by this group over the last ten years in an
attempt to get a better handle on their nature. High velocity resolution VLA
observations in 2006 showed that almost all of the maser spots, distributed
across the central arcminute of the galaxy, were apparently coincident with
background continuum features, and a handful displayed multiple velocity
components. The majority of those with velocity structure are located on a
blue-shifted arc in the pv-plane, spatially located on an arc northward of the
peculiar source known as B41.95+57.5. Now, new results from high spatial and
spectral resolution observations with the EVN have resolved several of these
masers into multiple spatial components for the first time. The maser emission
is compared with known continuum sources in the galaxy, and we conclude that at
least some of the maser emission is from high-gain maser action.Comment: Six pages, one table, one figure. To appear in proceedings of the
11th EVN Symposium (Bordeaux, 9-12 October 2012
Multi-source self-calibration: Unveiling the microJy population of compact radio sources
Context. Very Long Baseline Interferometry (VLBI) data are extremely
sensitive to the phase stability of the VLBI array. This is especially
important when we reach {\mu}Jy r.m.s. sensitivities. Calibration using
standard phase referencing techniques is often used to improve the phase
stability of VLBI data but the results are often not optimal. This is evident
in blank fields that do not have in-beam calibrators. Aims. We present a
calibration algorithm termed Multi-Source Self-Calibration (MSSC) which can be
used after standard phase referencing on wide-field VLBI observations. This is
tested on a 1.6 GHz wide-field VLBI data set of the Hubble Deep Field-North and
the Hubble Flanking Fields. Methods. MSSC uses multiple target sources detected
in the field via standard phase referencing techniques and modifies the
visibili- ties so that each data set approximates to a point source. These are
combined to increase the signal to noise and permit self-calibration. In
principle, this should allow residual phase changes caused by the troposphere
and ionosphere to be corrected. By means of faceting, the technique can also be
used for direction dependent calibration. Results. Phase corrections, derived
using MSSC, were applied to a wide-field VLBI data set of the HDF-N comprising
of 699 phase centres. MSSC was found to perform considerably better than
standard phase referencing and single source self-calibration. All detected
sources exhibited dramatic improvements in dynamic range. Using MSSC, one
source reached the detection threshold taking the total detected sources to
twenty. 60% of these sources can now be imaged with uniform weighting compared
to just 45% with standard phase referencing. The Parseltongue code which
implements MSSC has been released and made publicly available to the
astronomical community (https://github.com/jradcliffe5/multi_self_cal).Comment: 7 pages, 4 figures, accepted to A&
CU Virginis - The First Stellar Pulsar
CU Virginis is one of the brightest radio emitting members of the magnetic
chemically peculiar (MCP) stars and also one of the fastest rotating. We have
now discovered that CU Vir is unique among stellar radio sources in generating
a persistent, highly collimated, beam of coherent, 100% polarised, radiation
from one of its magnetic poles that sweeps across the Earth every time the star
rotates. This makes the star strikingly similar to a pulsar. This similarity is
further strengthened by the observation that the rotating period of the star is
lengthening at a phenomenal rate (significantly faster than any other
astrophysical source - including pulsars) due to a braking mechanism related to
its very strong magnetic field.Comment: 10 pages including 2 figure
Images of an equatorial outflow in SS433
We have imaged the X-ray binary SS433 with unprecedented Fourier-plane
coverage at 6cm using simultaneously the VLBA, MERLIN, and the VLA, and also at
20cm with the VLBA. At both wavelengths we have securely detected smooth,
low-surface brightness emission having the appearance of a `ruff' or collar
attached perpendicularly to the well-studied knotty jets in this system,
extending over at least a few hundred AU. We interpret this smooth emission as
a wind-like outflow from the binary, and discuss its implications for the
present evolutionary stage of this system.Comment: Accepted by ApJ Letter
Searching for the signatures of jet-ISM interactions in X-ray binaries
Jets from X-ray binaries are continuously injecting matter and energy into
the surrounding interstellar medium (ISM). However, there exist to date
relatively few cases where jet-ISM interactions have been directly observed. We
review the current examples, and go on to present new data on the proposed
hotspots of GRS1915+105, finding no concrete evidence for any association
between the hotspots and the central source, in agreement with previous
findings in the literature. We also present preliminary results on radio and
H-alpha searches for jet-ISM interactions around known X-ray binaries, and
discuss strategies for future searches.Comment: 7 pages, 3 figures; to be published in proceedings of "A Population
Explosion: The Nature and Evolution of X-ray Binaries in Diverse
Environments", 28 Oct. - 2 Nov. 2007, St. Petersburg Beach, FL (R.M.
Bandyopadhyay, S. Wachter, D. Gelino, & C.R. Gelino, eds.
Ring-Like Structure in the Radio Lobe of MG0248+0641
We present radio and optical observations of MG0248+0641, which contains a
kiloparsec-scale ring-like structure in one of its radio lobes. The radio
observations show a typical core-double morphology: a central core between two
lobes, each of which has a hotspot. The western radio lobe appears as a nearly
continuous ring, with linear polarization electric field vectors which are
oriented in a radial direction from the ring center. We consider several
different interpretations for the nature of this ring, including gravitational
lensing of a normal jet by a foreground galaxy. Even though simple lensing
models can describe the ring morphology reasonably well, the high linear
polarization seen around the ring cannot be easily explained. The chance
interposition of a galactic supernova remnant, nova, planetary nebula, or H II
region, has been ruled out. The highly polarized ring of MG0248+0641 is much
like the prominent ring seen in 3C219, and the multiple ones in 3C310 and
Hercules A, suggesting that similar physical processes are producing shell
structures in these radio galaxies. The ring in MG0248+0641 may be caused by
the formation of ``bubbles'', as a result of instabilities in the energy flow
down the western radio jet. It may also be possible that the required
instabilities are triggered by the infall of gas, via tidal interaction of the
central source with a nearby galaxy. This scenario may be indicated by our
marginal detection of an optical source close to the western hotspot.Comment: 21 pages. Submitted to AJ Aug 15, 1997; Accepted Sep 30, 1997. Minor
changes in conten