Status of CTA and Australian Activities

• Gavin Rowell (School of Physical Sciences, University of Adelaide)
• Sabrina Einecke (The University of Adelaide, Australia)

CTA-Pol: Prototyping Polarimetry for CTA Blazars

• Nick Tothill (Western Sydney University)

CTA's survey of blazars will require large-scale polarimetric follow-up, both on-demand and scheduled, using moderate-sized telescopes. The CTA-Oz consortium will prototype a new polarimeter that is optimised for this work, and commission it on local telescopes, leading to a full-scale plan for polarimetric follow-up infrastructure for CTA. I will sketch the landscape for CTA-Oz' polarimetry programme over the timescale of our new LIEF funding and beyond.

The All-Sky Virtual Observatory and CTA: A (Cross-)match made in the Heavens

• Simon O'Toole (AAO Macquarie)

We will give an overview of the All-Sky Virtual Observatory (ASVO), including the services it provides and how it fits into the broader astronomical landscape. We will then focus on how the Data Central node of the ASVO can help CTA by providing fine-grained access control to data products, as well as supporting research teams to collaborate and spend more time on science. Finally we will look at how CTA data products can be cross-matched with data held in Data Central, as well as other data archives using the power of Virtual Observatory standards.

Bayesian Inference for Dark Matter Detection with CTA

• Csaba Balazs (School of Physics and Astronomy, Monash University)

I report on the development of a Bayesian inference software pipeline to determine the sensitivity of CTA to dark matter annihilation events in the Galactic Centre. After highlighting the theoretical foundation of the pipeline I'll describe its components. I'll show predicted limits on the velocity-averaged annihilation cross section as the function of dark matter mass for one of the simplest dark matter scenarios, the scalar singlet model.

Pulsar TeV emission and CTA

• Shi Dai (Western Sydney University)

Rapid-response Radio Follow-up of TeV Gamma-ray Bursts (GRBs)

• Gemma Anderson (ICRAR)

The excitement of the publicly announced 2019 TeV-detected GRBs motivated global multi-wavelength follow-up efforts, reinvigorated this field of transient astrophysics. Such detections have revealed the unexpected: TeV GRB emission may not be generated via synchrotron self-Comptonisation. While high-energy and optical follow-up of these TeV GRBs occurred within minutes of the discovery, most radio follow-up lagged behind by several days. In addition, much of the resulting modelling efforts have disregarded the radio spectrum entirely. However, very early-time radio detections of GRBs can directly probe the emitting population of electrons, the geometry, content and magnetic field structure of the outflows, the burst energetics, and the density structure of the pre-explosion environment. Such radio observations can disentangle other emission components from the forward shock, which is essential for understanding the TeV spectral shape. They will also help us to understand whether the structure of the circumburst medium effects the production of TeV photons. In collaboration with the HESS GRB team, we are triggering rapid and automated radio observations of HESS-detected GRBs using the Australia Telescope Compact Array (ATCA), providing the very earliest radio detections of these events. We have already successfully tested our triggering strategy on the long (TeV faint) GRB 210702A, detecting a rapidly evolving radio flare within 9-14 hrs post-burst. Such emission may arise from a thermally emitting population of electrons that were shock heated but not accelerated into a power law distribution. If this is the case, we would have made the first direct measurement of the fraction of electron accelerated in GRB shocks, providing further insight into the population involved in the TeV emission mechanisms. Such experiments are an excellent demonstration of the transient science that could be achieved via CTA and Square Kilometre Array synergies.

Modeling Particles in the ISM

• Sabrina Einecke (The University of Adelaide, Australia)

ATCA HCO+ Survey

• Nick Tothill (Western Sydney University)

ATCA in single-dish mode is able to map the HCO+ emission from ionised molecular gas. This not only traces ionisation, it can act as a finder chart for DCO+ observations to measure the cosmic-ray ionisation rate. I will present the state of our mapping of HCO+ towards the clouds around the W28 SNR, and outline future developments in molecular gas mapping.

The Isotropic Diffuse Gamma-ray Background and Associated Non-thermal Emission

• Matt Roth (ANU)

Here we present results from a recent study on the origins of the diffuse isotropic gamma-ray background. We tackle the problem using a bottom-up approach by considering cosmic ray diffusion in individual star-forming galaxies, using a single-zone model to obtain an energy dependent calorimetry fraction and associated conversion of cosmic ray energy to gamma-rays in the hadronic scenario. We apply this model to a sample from CANDELS to obtain an estimate for the DIGB. We further present some brief comments on neutrinos produced in SFGs and on non-thermal radio continuum emission and it's relation to the FIR-radio correlation.

Detection of Gamma-Ray Emission from the Sagittarius Dwarf Spheroidal Galaxy

• Roland Crocker (Research School of Astronomy and Astrophysics, Australian National University)

The Fermi Bubbles are giant, γ-ray emitting lobes emanating from the nucleus of the Milky Way discovered in∼1-100 GeV data collected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. Previous work has revealed substructure within the Fermi Bubbles that has been interpreted as a signature of collimated outflows from the Galaxy’s super-massive black hole. I will show that much of the γ-ray emission associated to the brightest region of substructure – the so-called cocoon– is actually due to the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. This large Milky Way satellite is viewed through the Fermi Bubbles from the position of the Solar System. As a tidally and ram-pressure stripped remnant, the Sgr dSph has no on-going star formation, but I will demonstrate that its γ-ray signal is naturally explained by inverse Compton scattering of cosmic microwave back-ground photons by high-energy electron-positron pairs injected by the dwarf’s millisecond pulsar (MSP) population, combined with these objects’ magnetospheric emission.

Towards a Network of Cherenkov Telescopes

• Simon Lee (School of Physical Sciences, University of Adelaide)

The extreme and often varying nature of Active Galactic Nuclei, along with gamma-ray bursts and other transients, can be investigated with observations of very-high-energy gamma rays. Studying them requires uninterupted availability and the capacity to take continuous observations over large spans of time. The Cherenkov Telescope Ring is thus an idea to establish a worldwide network of Imaging Air Cherenkov Telescopes (IACT). This would allow for long-term continuous observations and 24-hour follow-up availability in case of transient events. Establishing an IACT site in Australia would be crucial to obtain full-sky coverage, and would be able to trigger other telescopes such as CTA to take observations of their own. The performance of an IACT site depends on factors such as its altitude, number of telescopes, the layout, and telescope design. To investigate possibilities for an Australian site simulations have been made, analysed, and compared. In this talk the concept and science cases of a Cherenkov Telescope Ring will be briefly introduced, and comparisons of simulated site performance will be presented. Lightcurves and spectrum reconstruction from simulated source observations will also be shown.

Quantifying Australian Site for IACT

• Paddy McGee (School of Physical Sciences, University of Adelaide)
• Sabrina Einecke (The University of Adelaide, Australia)

Student Updates

• Kirsty Feijen (School of Physical Sciences, University of Adelaide)
• Adnaan Thakur (University of Adelaide)
• Peter Marinos (University of Adelaide)
• Rami Alsulami (University of Adelaide)

Peter Marinos aims to simulate the Galactic TeV diffuse gamma-ray emission with GALPROP for a variety of model parameters, and to make comparisons between these models and the diffuse emission estimated by the H.E.S.S. telescope array in their Galactic plane survey. Kirsty Feijen aims to reveal the origin of HESS J1804−216 by modelling both the spectral and spatial gamma-ray morphology from SNRs in the hadronic scenario. Adnaan Thakur: SNR RXJ1713.7-3946 is a one of the brightest young supernova remnants detected by the HESS Galactic Plane Survey. We have studied the C[II], HI and H_2 emission from the region and will provide an update on our analysis. Rami Alsulami: I investigate the optical outflow towards the Scutum Supershell using multi-wavelength observations (X-rays, TeV gamma rays and optical H alpha. I also investigate possible scenarios for the origin of such an extended outflow.

Fink Broker and High-energy Transients

• Anais Moller (Swinburne University)

During the next decade, the Vera C. Rubin Observatory will obtain high-resolution optical images of the Southern Sky at unprecedented depths. It will detect every night, millions of potential transient objects. I will introduce Fink, a broker developed on high-end technology and designed for fast and efficient analysis of Rubin big data. Fink will receive and process all transients detected by Rubin over 10 years of LSST. It enables the selection of promising transients by providing preliminary classifications and combining information from multiple channels (multi-messenger and multi-wavelength surveys and catalogues). Within minutes, Fink is able to communicate these candidates to teams and follow-up facilities. Fink opens a new way of combining data from LSST and other time-domain surveys and will be key to study the most extreme astrophysical transients in the next decade.