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