ALBERT

Description: The next Galactic supernova is expected to bring great opportunities for the direct detection of gravitational waves (GW), full flavour neutrinos, and multiwavelength photons. To maximize the science return from such a rare event, it is essential to have established classes of possible situations and preparations for appropriate observations. To this end, we use a long-term numerical simulation of the core-collapse supernova (CCSN) of a 17 M red supergiant progenitor to self-consistently model the multimessenger signals expected in GW, neutrino, and electromagnetic messengers. This supernova model takes into account the formation and evolution of a protoneutron star, neutrino-matter interaction, and neutrino transport, all within a two-dimensional shock hydrodynamics simulation. With this, we separately discuss three situations: (i) a CCSN at the Galactic Center, (ii) an extremely nearby CCSN within hundreds of parsecs, and (iii) a CCSN in nearby galaxies within several Mpc. These distance regimes necessitate different strategies for synergistic observations. In a Galactic CCSN, neutrinos provide strategic timing and pointing information. We explore how these in turn deliver an improvement in the sensitivity of GW analyses and help to guarantee observations of early electromagnetic signals. To facilitate the detection of multimessenger signals of CCSNe in extremely nearby and extragalactic distances, we compile a list of nearby red supergiant candidates and a list of nearby galaxies with their expected CCSN rates. By exploring the sequential multimessenger signals of a nearby CCSN, we discuss preparations for maximizing successful studies of such an unprecedented stirring event.

Description: On-the-fly mapping of cm-wave spectral lines has been implemented at the Tidbinbilla 70-m radio antenna. We describe the implementation and data reduction procedure and present new H92α radio recombination line maps towards Orion A and Sagittarius A. Comparison of the Orion A map to previous observations suggests that the lines arise largely from gas with electron density of 100–200 cm –3 . On-the-fly mapping is very efficient at generating large maps of bright lines (such as radio recombination lines), but will still yield strong efficiency gains for smaller maps of fainter lines, such as the ammonia inversion lines at the 1.3 cm wavelength.

Description: We conducted a three-dimensional traveltime tomographic reconstruction in and around the source region of the 1984 western Nagano Prefecture earthquake to investigate the generation process for the main shock and associated swarm activity. Up to 220 000 high-resolution traveltime records (2 ms error) were compiled from a dense seismic network. From these records, we performed accurate, high-resolution calculations to estimate hypocentre distributions and three-dimensional velocity structure. Most hypocentres aligned along the same path or within the same plane, rather than in three-dimensional clusters. Hypocentres in the swarm region are located in regions with low Vp / Vs ratios, while few earthquakes occurred in regions with high or normal Vp / Vs ratios. We suggest that differences in the number of small fractures and fluid content between these two regions influenced the seismic activity. Rupture propagation associated with the main shock appears to be confined by relatively higher Vp / Vs surroundings, and a low-velocity region which limits its vertical extent.

Description: The photodissociation region in the immediate vicinity of the Trumpler 14 star cluster represents the nearest source (2.3 kpc) to study the physical parameters of a photodissociation region due to feedback from a large population of O-type stars. It resides in the Carina Nebula, a region rich in high-mass stars. We present the first detection and maps of the ammonia inversion emission of the first three metastable lines, ( J , K ) = (1,1), (2,2) and (3,3), in the Carina I dark cloud. These observations, made with the Tidbinbilla 70 m radio telescope, are the initial results of a programme to implement full mapping capability. We also present velocity maps together with the optical depth and rotational ( R 21 ) temperatures. The derived linewidths and rotational temperatures support evidence for an ionization front associated with the Carina I-E and Carina I-W substructures. Detection of the (3,3) metastable line suggests significantly higher kinetic temperatures in the molecular clumps than those derived with CO studies, implying that the CO emission is saturated despite photodissociation. The kinematics of the Carina I-E and Carina I-W ammonia substructures are consistent with studies of radio recombination and molecular lines. The prevailing morphological paradigm for Car I is considered, particularly by comparing the molecular structure traced by the ammonia emission to stellar infrared and radio sources in the region.

Description: Here we report observations of the two lowest inversion transitions of ammonia (NH 3 ) with the 70-m Tidbinbilla radio telescope. The aim of the observations is to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate measures of temperature have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the time-scales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SEST Imaging Bolometer Array 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire 8.0 μm emission to separate the sample into infrared (IR)-bright and IR-faint clumps, we use statistical tests to examine whether our classification shows different populations in terms of mass and temperature. We find that in terms of log clump mass (2.44–4.12 M ) and log column density (15.3–16.6 cm –2 ), that there is no significant population difference between IR-bright and IR-faint clumps, and that kinetic temperature is the best parameter to distinguish between the gravitationally bound state of each clump. The kinetic temperature was the only parameter found to have a significantly low probability of being drawn from the same population. This suggests that clump radii do not have a large effect on the temperature of a clump, so clumps of similar radii may have different internal heating mechanisms. We also find that while the IR-bright clumps have a higher median log virial mass than the IR-faint clumps (IR-bright: 2.88 M ; IR-faint: 2.73 M ), both samples have a similar range for both virial mass and full width at half-maximum (FWHM; IR-bright: log virial mass = 2.03–3.68 M , FWHM = 1.17–4.50 km s –1 ; IR-faint: log virial mass = 2.09–3.35 M , FWHM = 1.05–4.41 km s –1 ). There are 87 per cent (40 of 46) of the clumps with masses larger than the virial mass, suggesting that they will form stars or are already undergoing star formation.

Description: The BICEP 2 results, when interpreted as a gravitational wave signal and combined with other cosmic microwave background data, suggest a roll-off in power towards small scales in the primordial matter power spectrum. Among the simplest possibilities is a running of the spectral index. Here we show that the preferred level of running alleviates small-scale issues within the CDM model, more so even than viable WDM models. We use cosmological zoom-in simulations of a Milky Way-sized halo along with full-box simulations to compare predictions among four separate cosmologies: a BICEP 2-inspired running index model (α s  = –0.024), two fixed-tilt CDM models motivated by Planck , and a 2.6 keV thermal WDM model. We find that the running BICEP 2 model reduces the central densities of large dwarf-sized haloes ( V max  ~ 30–80 km s –1 ) and alleviates the too-big-to-fail problem significantly compared to our adopted Planck and WDM cases. Further, the BICEP 2 model suppresses the count of small subhaloes by ~50 per cent relative to Planck models, and yields a significantly lower ‘boost’ factor for dark matter annihilation signals. Our findings highlight the need to understand the shape of the primordial power spectrum in order to correctly interpret small-scale data.

Description: Mapping supernovae to their progenitors is fundamental to understanding the collapse of massive stars. We investigate the red supergiant problem, which concerns why red supergiants with masses ~16–30 M have not been identified as progenitors of Type IIP supernovae, and the supernova rate problem, which concerns why the observed cosmic supernova rate is smaller than the observed cosmic star formation rate. We find key physics to solving these in the compactness parameter, which characterizes the density structure of the progenitor. If massive stars with compactness above 2.5  ~ 0.2 fail to produce canonical supernovae, (i) stars in the mass range 16–30 M populate an island of stars that have high 2.5 and do not produce canonical supernovae, and (ii) the fraction of such stars is consistent with the missing fraction of supernovae relative to star formation. We support this scenario with a series of two- and three-dimensional radiation hydrodynamics core-collapse simulations. Using more than 300 progenitors covering initial masses 10.8–75 M and three initial metallicities, we show that high compactness is conducive to failed explosions. We then argue that a critical compactness of ~0.2 as the divide between successful and failed explosions is consistent with state-of-the-art three-dimensional core-collapse simulations. Our study implies that numerical simulations of core collapse need not produce robust explosions in a significant fraction of compact massive star initial conditions.

Description: Sterile neutrinos comprise an entire class of dark matter models that, depending on their production mechanism, can be hot, warm, or cold dark matter (CDM). We simulate the Local Group and representative volumes of the Universe in a variety of sterile neutrino models, all of which are consistent with the possible existence of a radiative decay line at ~3.5 keV. We compare models of production via resonances in the presence of a lepton asymmetry (suggested by Shi & Fuller 1999 ) to ‘thermal’ models. We find that properties in the highly non-linear regime – e.g. counts of satellites and internal properties of haloes and subhaloes – are insensitive to the precise fall-off in power with wavenumber, indicating that non-linear evolution essentially washes away differences in the initial (linear) matter power spectrum. In the quasi-linear regime at higher redshifts, however, quantitative differences in the 3D matter power spectra remain, raising the possibility that such models can be tested with future observations of the Lyman-α forest. While many of the sterile neutrino models largely eliminate multiple small-scale issues within the CDM paradigm, we show that these models may be ruled out in the near future via discoveries of additional dwarf satellites in the Local Group.

Description: We report the detection of four water masers within the Small Magellanic Cloud (SMC): two discovered with the 70-m Tidbinbilla radio telescope, and two discovered with the Australia Telescope Compact Array (ATCA). Precise positions of all four masers have been derived from ATCA observations, and the characteristics of each water maser have been monitored over a period of several years. Sensitive observations towards two previously detected water masers reported in the literature failed to detect any emission. The detected water masers show evidence of higher levels of temporal variability than equivalent Galactic sources, and one of the features associated with NGC 346 IR1 shows an acceleration of 9.6 km s –1 yr –1 over a 31 d period. Sensitive targeted observations for methanol and OH masers failed to detect any accompanying emission – in the case of methanol perhaps highlighting an under abundance in the SMC, consistent with expectations due to lower metallicity. The water masers are both bright and compact making them excellent targets for Very Long Baseline Interferometry (VLBI) observations, which can potentially measure the proper motion of the SMC (~1–2 mas yr –1 ) with temporal baselines of ~12 months. Such observations would utilize sources associated with only the current epoch of star formation and hence have several advantages over alternative methods.

Description: We present new detections of cyanodiacetylene (HC 5 N) towards hot molecular cores, observed with the Tidbinbilla 34 m radio telescope (DSS–34). In a sample of 79 hot molecular cores, HC 5 N was detected towards 35. These results are counter to the expectation that long chain cyanopolyynes, such as HC 5 N, are not typically found in hot molecular cores, unlike their shorter chain counterpart HC 3 N. However, it is consistent with recent models which suggest HC 5 N may exist for a limited period during the evolution of hot molecular cores.