SN1998bw: The Case for a Relativistic Shock

SN1998bw shot to fame by claims of association with GRB980425. Independent of its presumed association with a GRB, this SN is unusual in its radio properties. A simple interpretation of the unusually bright radio emission leads us to the conclusion that there are two shocks in this SN: a slow moving shock containing most of the ejecta and a relativistic shock (Gamma=2) which is responsible for the radio emission. This is the first evidence for the existence of relativistic shocks in supernovae. It is quite plausible that this shock may produce high energy emission (at early times and by inverse Compton scattering). As with other supernovae, we expect radio emission at much later times powered primarily by the slow moving ejecta. This expectation has motivated us to continue monitoring this unusual SN.Comment: A&A (in press), Rome GRB Symposium, Nov. 199

Constraints on Off-Axis GRB Jets in Type Ibc Supernovae From Late-Time Radio Observations

It has been suggested that the peculiar properties of the luminous Type Ic supernova SN 1998bw and its low-energy gamma-ray burst GRB 980425 may be understood if they originated in a standard gamma-ray burst explosion viewed far from the axis of the relativistic jet. In this scenario, strong radio emission is predicted from the jet on a timescale 1 to 10 years after the explosion as it decelerates and spreads into our line of sight. To test this hypothesis we have carried out late-time radio observations of SN 1998bw at $t=5.6$ years, yielding upper limits which are consistent with the continued fading of the supernova. We find these limits to be consistent with an off-axis jet only if the progenitor mass loss rate is $\dot{M}\lesssim 4 \times 10^{-7}$ M$_\odot$ yr$^{-1}$ (for a wind velocity $v_w=1000$ km s$^{-1}$) or the fraction of the shock energy in magnetic fields is $\epsilon_B \lesssim 10^{-3}$. These values are low relative to those inferred for cosmological GRBs. We combine the SN 1998bw measurements with existing observations for a sample of 15 local Type Ibc supernovae to estimate that at most 6% produce collimated, relativistic outflows.Comment: Revised version, as it appears in ApJ

HI Emission and Absorption in the Southern Galactic Plane Survey

We present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325.5 deg < l < 333.5 deg; -0.5 deg < b < 3.5 deg) were completed in December 1998. Single dish observations of the full survey region (253 deg < l < 358 deg; |b| <1 deg) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS HI data with particular attention to the smallest and largest scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent HI shells. On the small scale, we note extremely compact, cold clouds seen in HI self-absorption. We explore how these two classes of objects probe opposite ends of the HI spatial power spectrum.Comment: 9 pages, 3 embedded postscript & 4 jpeg figures. Presented at the Astronomical Society of Australia, Hobart, Tasmania, July 4-7 2000. To appear in PASA Vol. 18(1

The ATESP 5 GHz radio survey. II. Physical properties of the faint radio population

One of the most debated issues about sub-mJy radio sources, which are responsible for the steepening of the 1.4 GHz source counts, is the origin of their radio emission. Particularly interesting is the possibility of combining radio spectral index information with other observational properties to assess whether the sources are triggered by star formation or nuclear activity. The aim of this work is to study the optical and near infrared properties of a complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5 GHz as part of the ATESP radio survey. We use deep multi-colour (UBVRIJK) images, mostly taken in the framework of the ESO Deep Public Survey, to optically identify and derive photometric redshifts for the ATESP radio sources. Deep optical coverage and extensive colour information are available for 3/4 of the region covered by the radio sample. Typical depths of the images are U~25, B~26, V~25.4, R~25.5, I~24.3, 19.5<K_s<20.2, J<22.2. Optical/near infrared counterparts are found for ~78% (66/85) of the radio sources in the region covered by the deep multi-colour imaging, and for 56 of these reliable estimates of the redshift and type are derived. We find that many of the sources with flat radio spectra are characterised by high radio-to-optical ratios (R>1000), typical of classical powerful radio galaxies and quasars. Flat-spectrum sources with low R values are preferentially identified with early type galaxies, where the radio emission is most probably triggered by low-luminosity active galactic nuclei. Considering both early type galaxies and quasars as sources with an active nucleus, such sources largely dominate our sample (78%). Flat-spectrum sources associated with early type galaxies are quite compact (d<10-30 kpc), suggesting core-dominated radio emission.Comment: 15 pages, 13 figures, accepted for pubblication in A&

The ATESP Radio Survey II. The Source Catalogue

This paper is part of a series reporting the results of the Australia Telescope ESO Slice Project (ATESP) radio survey obtained at 1400 MHz with the Australia Telescope Compact Array (ATCA) over the region covered by the ESO Slice Project (ESP) galaxy redshift survey. The survey consists of 16 radio mosaics with ~8"x14" resolution and uniform sensitivity (1sigma noise level ~79 microJy) over the whole area of the ESP redshift survey (~26 sq. degrees at decl. -40 degr). Here we present the catalogue derived from the ATESP survey. We detected 2960 distinct radio sources down to a flux density limit of ~0.5 mJy (6sigma), 1402 being sub-mJy sources. We describe in detail the procedure followed for the source extraction and parameterization. The internal accuracy of the source parameters was tested with Monte Carlo simulations and possible systematic effects (e.g. bandwidth smearing) have been quantified.Comment: 14 pages, 14 Postscript figures, Accepted for publication in A&A Suppl. Corrected typos and added Journal Referenc

The Role of Deontic Logic in the Specification of Information Systems

In this paper we discuss the role that deontic logic plays in the specification of information systems, either because constraints on the systems directly concern norms or, and even more importantly, system constraints are considered ideal but violable (so-called `soft¿ constraints).\ud To overcome the traditional problems with deontic logic (the so-called paradoxes), we first state the importance of distinguishing between ought-to-be and ought-to-do constraints and next focus on the most severe paradox, the so-called Chisholm paradox, involving contrary-to-duty norms. We present a multi-modal extension of standard deontic logic (SDL) to represent the ought-to-be version of the Chisholm set properly. For the ought-to-do variant we employ a reduction to dynamic logic, and show how the Chisholm set can be treated adequately in this setting. Finally we discuss a way of integrating both ought-to-be and ought-to-do reasoning, enabling one to draw conclusions from ought-to-be constraints to ought-to-do ones, and show by an example the use(fulness) of this

Surface Grafting of Poly(L-glutamates). 3. Block Copolymerization

This paper describes for the first time the synthesis of surface-grafted AB-block copolypeptides, consisting of poly(γ-benzyl L-glutamate) (PBLG) as the A-block and poly(γ-methyl L-glutamate) (PMLG) as the B-block. Immobilized primary amine groups of (γ-aminopropyl)triethoxysilane (APS) on silicon wafers initiated the ring-opening polymerization of N-carboxyanhydrides of glutamic acid esters (NCAs). After removal of the BLG-NCA monomer solution after a certain reaction time, the amine end groups of the formed PBLG blocks acted as initiators for the second monomers. This method provides the possibility of making layered structures of surface-grafted block copolymers with tuned properties. Ellipsometry and small-angle X-ray reflection (SAXR) measurements revealed the thickness of the polypeptide layers ranging from 45-100 Å of the first block to 140-270 Å for the total block copolypeptides. The chemical composition of the blocks was determined by X-ray photoelectron spectroscopy (XPS). In addition, Fourier transform infrared transmission spectroscopy (FT-IR) revealed that the polypeptide main chains of both blocks consisted of pure R-helices. The average orientation of the helices ranging from 22-42° with respect to the substrate within the first block to 31-35° in the second block could be derived with FT-IR as well.

A year in the life of GW170817: the rise and fall of a structured jet from a binary neutron star merger

We present the results of our year-long afterglow monitoring of GW170817, the first binary neutron star (NS) merger detected by advanced LIGO and advanced Virgo. New observations with the Australian Telescope Compact Array (ATCA) and the Chandra X-ray Telescope were used to constrain its late-time behavior. The broadband emission, from radio to X-rays, is well-described by a simple power-law spectrum with index ~0.585 at all epochs. After an initial shallow rise ~t^0.9, the afterglow displayed a smooth turn-over, reaching a peak X-ray luminosity of ~5e39 erg/s at 160 d, and has now entered a phase of rapid decline ~t^(-2). The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ~22 deg from its axis. Within such model, the properties of the explosion (such as its blastwave energy E_K~2E50 erg, jet width theta_c~4 deg, and ambient density n~3E-3 cm^(-3)) fit well within the range of properties of cosmological short GRBs.Comment: 11 pages, 8 figures, 2 tables, MNRAS, in press. Final version, minor changes only relative to original submission dated 21 August 201

A Coordinated Radio Afterglow Program

We describe a ground-based effort to find and study afterglows at centimeter and millimeter wavelengths. We have observed all well-localized gamma-ray bursts in the Northern and Southern sky since BeppoSAX first started providing rapid positions in early 1997. Of the 23 GRBs for which X-ray afterglows have been detected, 10 have optical afterglows and 9 have radio afterglows. A growing number of GRBs have both X-ray and radio afterglows but lack a corresponding optical afterglow.Comment: To appear in Proc. of the 5th Huntsville Gamma-Ray Burst Symposium, 5 pages, LaTe