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Abstract:

We present optical and infrared monitoring data of SN2012hn collected by the Public European Southern Observatory Spectroscopic Survey for Transient Objects. We show that SN 2012hn has a faint peak magnitude (MR ~ -15.65) and shows no hydrogen and no clear evidence for helium in its spectral evolution. Instead, we detect prominent Ca II lines at all epochs, which relates this transient to previously described 'Ca-rich' or 'gap' transients. However, the photospheric spectra (from -3 to +32 d with respect to peak) of SN 2012hn show a series of absorption lines which are unique and a red continuum that is likely intrinsic rather than due to extinction. Lines of Ti II and Cr II are visible. Thismay be a temperature effect,which could also explain the red photospheric colour. A nebular spectrum at +150 d shows prominent Ca II, OI, CI and possibly MgI lines which appear similar in strength to those displayed by core-collapse supernovae (SNe). To add to the puzzle, SN 2012hn is located at a projected distance of 6 kpc from an E/S0 host and is not close to any obvious star-forming region. Overall SN 2012hn resembles a group of faint H-poor SNe that have been discovered recently and for which a convincing and consistent physical explanation is still missing. They all appear to explode preferentially in remote locations offset from a massive host galaxy with deep limits on any dwarf host galaxies, favouring old progenitor systems. SN 2012hn adds heterogeneity to this sample of objects.We discuss potential explosion channels including He-shell detonations and double detonations of white dwarfs as well as peculiar core-collapse SNe. © 2013 The Authors.

Abstract:

In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return. © 2013 Astronomical Society of Australia.

Abstract:

We present optical and near-infrared (NIR) photometry and NIR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M82. These demonstrate that SN 2004am was a highly reddened Type II-P SN similar to the low-luminosity Type II-P events such as SNe 1997D and 2005cs.We show that SN 2004am was located coincident with the obscured super star cluster M82-L, and from the cluster age infer a progenitor mass of 12+7 -3M. In addition to this, we present a high spatial resolution Gemini-North Telescope K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival datafrom the Hubble Space Telescope, we are able to recover a NIR transient source coincident with both objects. We find the likely extinction towards SN 2008iz to be not more than AV~10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M82 as the most plausible scenario. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

In this paper, we investigate the properties of a sample of six BL Lacs by fitting their spectra using our inhomogeneous jet model with an accelerating, magnetically dominated, parabolic base, which transitions to a slowly decelerating conical jet with a geometry based on observations of M87. Our model is able to fit very well to the simultaneous multiwavelength spectra of all the BL Lacs including radio observations. We find that the BL Lacs have lower jet powers and bulk Lorentz factors than the sample of Compton-dominant blazars investigated in Paper III, consistent with the blazar sequence. Excitingly, we find a correlation between the radius at which the jet first comes into equipartition and the jet power, in agreement with our prediction from Paper III.We interpret this result as one of two physical scenarios: a universal jet geometry which scales linearly with black hole mass or a dichotomy in Eddington accretion rates between flat-spectrum radio quasars (FSRQs) and BL Lacs. If we assume that the jet geometry of all blazars scales linearly with black hole mass, then we find a plausible range of masses (~107-1010M⊙).We find that the quiescent gamma-ray spectrum ofMarkarian 421 is best fitted by scattering of external cosmic microwave background photons. We are unable to fit the spectrum using synchrotron self-Compton emission due to strong gamma-ray absorption via pair production even using a compact, rapidly decelerating, jet with a very large bulk Lorentz factor (50), as has been suggested recently. This is because the ratio of synchrotron to inverse-Compton emission requires a high density of synchrotron photons to scatter which makes the region opaque to TeV gamma-rays even with large bulk Lorentz factors. Finally, we fit to the spectral energy distributions of the four high power high synchrotron peak frequency BL Lacs recently found by Padovani et al. We find that their high peak frequency emission is caused by high maximum electron energies whilst the rest of their jet properties are typical of relatively high power BL Lacs and consistent with our predictions. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.