An Overview of CTA Science

• Jamie Holder (University of Delaware)

Room: Kerr Grant Lecture Theatre, Physics Building With broader energy coverage, better angular and energy resolution, and an order of magnitude improvement in sensitivity with respect to existing instruments, the Cherenkov Telescope Array (CTA) will revolutionize the study of the Universe at the highest energies. Here we summarize some of the scientific goals of the Observatory, with a focus on the core programme of Key Science Projects proposed by the CTA Consortium. These range from studies of individual objects with unprecedented detail to surveys covering large fractions of the Galactic and extragalactic sky, and address questions including the nature of dark matter, and the mechanisms and impact of relativistic particle acceleration in the Universe.

The Cherenkov Telescope Array: An Observatory Perspective

• Roberta Zanin (CTAO)

Room: Kerr Grant Lecture Theatre, Physics Building The Cherenkov Telescope Array (CTA) is the next generation gamma-ray observatory. It will be open to the entire astronomical and particle physics community as a resource to provide unique observations of the unexplored Universe at very high energies. With its greatly improved sensitivity when compared to the currently running facilities as well as significantly enhanced angular and spectral resolution CTA will bring a significant increase in discovery space, paving the way to new questions, and likely paradigm-changing discoveries. In particular, CTA has an unprecedented sensitivity to short (sub-minute) timescale phenomena, placing it as a key instrument in the future of multi-messenger and multi-wavelength time domain astronomy. In this talk I will present CTA from the design, to the construction, and I will focus on its usage and the observatory policies.

CTA Science Linkages: Needs and Collaboration Opportunities from a MWL Perspective

• Ulisses Barres de Almeida (Centro Brasileiro de Pesquisas Físicas)

Room: Kerr Grant Lecture Theatre, Physics Building The purpose of this talk is to outline the needs for CTA science, and the collaboration opportunities in various research topics provided by CTA, in a multi-instrumental perspective. After providing a general panorama of the MWL synergies for CTA science, we will focus on some potential, specific linkages to Australian Astronomy, regarding, in particular, its large infrastructure of ground-based optical and radio facilities. Australian facilities can play a key role in enabling some of CTA key science goals and in participating on CTA early discoveries and observational planning. From one side, the various radio and optical surveys, and the monitoring programmes carried out with Australian instruments, provide a multi-band view of the Southern Sky that is fundamental for carrying on CTA Galactic science. On the other hand, the longitude covered by the Australian ground-based instruments provide an indispensable complement to the CTA Transients and Multi-Messenger follow-up programmes, particularly in the radio domain. The presentation will aim to outline these most important interfaces that CTA could establish with the Australian Astronomical Community, and provide the necessary data to inform the discussions on possible avenues for collaboration.

The Transient Programme of the Cherenkov Telescope Array

• Daniela Hadasch (ICRR, University of Tokyo)

Room: Kerr Grant Lecture Theatre, Physics Building Transient sources are characterized by their unpredictable emission on timescales spanning milliseconds to years. Many transients are known to be emitters of high-energy gamma rays and are also potential sources of non-photonic signals that include cosmic rays, neutrinos and/or gravitational waves. The next generation observatory for very high energy gamma rays will be the Cherenkov Telescope Array (CTA) covering energies from 20GeV to at least 300TeV. With this energy range and one order of magnitude better sensitivity than the current instruments, CTA will reach high redshifts to detect accelerators like black hole or neutron star mergers and it will have access to the shortest time-scale phenomena. The CTA consortium defined several Key Science Projects for the first 10 years, and the study of transient sources is one of them. In my talk I will present the CTA Transients program. Furthermore, I will report on the current activities in the CTA Transients group studying phenomena like Gamma-ray bursts and on multi-messenger studies related to Gravitational Waves and Neutrino events.

FRB and GW studies at TeV energies

• Fabian Schüssler (IRFU)

Room: Kerr Grant Lecture Theatre, Physics Building The Cherenkov Telescope Array (CTA) is the next generation high-energy gamma-ray observatory. It will improve the sensitivity of current instruments up to an order of magnitude while providing energy coverage for photons from 20 GeV to at least 300 TeV to reach high redshifts and extreme accelerators and will give access to the shortest timescale phenomena. CTA is thus a uniquely powerful instrument for the exploration of the violent and variable universe. The ability to probe short timescales at the highest energies will allow CTA to explore the connection between accretion and ejection phenomena surrounding compact objects, investigate the processes occurring in relativistic outflows and open up significant phase space for serendipitous discoveries. Aiming at playing a central role in the era of multi-messenger astrophysics, the CTA Transient program includes follow-up observations of a broad range of multi-wavelength and multi-messenger alerts, ranging from Galactic compact object binary systems to searches for VHE counterparts to gravitational waves, high-energy neutrinos and to novel phenomena like Fast Radio Bursts. This contribution will summarize the state-of-the-art multi-messenger studies with current VHE gamma-ray facilities. We will focus mainly on searches for VHE counterparts to GWs and FRBs. We will present recent results and discuss the lessons learned and their influence on the preparation of the CTA transient program.

Latest News on FRBs

• Chris Flynn (Swinburne University of Technology)

Room: Kerr Grant Lecture Theatre, Physics Building Likely topics: UTMOST FRB localisation update Localised FRBs with ASKAP -- probing the IGM ASKAP repeaters CHIME finds repeating FRBs

ASKAP FRBs, Radio Transients and MWL Programme

• Clancy James (ICRAR - Curtin University)

Room: Kerr Grant Lecture Theatre, Physics Building The Australian Square Kilometre Array Pathfinder is located in the Murchison Radio-astronomy Observatory (MRO) in outback Western Australia. It's wide-field and survey capabilities make it an excellent instrument for detecting transients, and performing follow-up observations. This talk presents highlights from ASKAP's fast radio burst (FRB) program, CRAFT, and reviews ASKAP's radio, multi-wavelength, and multi-messenger transient programme.

Jets and accretion in X-ray binaries

• James Miller-Jones (ICRAR - Curtin University)

Room: Kerr Grant Lecture Theatre, Physics Building X-ray binaries are accreting stellar-mass black hole and neutron star systems, which are known to launch relativistic jets. Transient X-ray binaries undergo sporadic outbursts in which the accretion rate and jet power both rise by orders of magnitude, occasionally reaching or exceeding the Eddington accretion rate. These spectacular outbursts make good potential targets for CTA observations. The recent discovery of TeV gamma-rays from downstream in the jets of the rapidly-accreting system SS 433 demonstrates that X-ray binaries can in principle accelerate particles to very high energies. However, high-energy gamma-ray detections have been sparse, and previously limited to just two systems with high-mass donor stars. In this talk I will provide an overview of X-ray binaries and their jets, and review previous efforts to detect them at (very) high energy gamma-ray energies. I will outline how Australian facilities are being used to study these systems, and discuss potential synergies with CTA.

Gravitational-Wave Counterpart Searches with GOTO

• Kendall Ackley (Monash University)

Room: Kerr Grant Lecture Theatre, Physics Building The Gravitational-Wave Optical Transient Observer (GOTO) is a wide-field robotic optical instrument currently in operation on La Palma, Canary Islands. The scalable design consists of 8 individual 40 cm diameter astrographs on a single mount to instantaneously image a large 40 square degree field-of-view. The primary aim of GOTO is to detect and study electromagnetic counterparts to gravitational-wave (GW) events from Advanced LIGO and Virgo. We describe the current status of our real-time operation, how we robotically control the instrument, post-process the nightly influx of data, and identify and categorise unique transients using in-house pipeline and control systems. Finally, we will discuss recent results from optical follow-ups of GW events thus far from LIGO's third observing run.

Gamma-Ray Bursts at TeV Energies

• Susumu Inoue (Institute for Cosmic Ray Research, University of Tokyo)

Room: Kerr Grant Lecture Theatre, Physics Building Gamma-ray bursts (GRBs) are the most luminous sources of electromagnetic radiation in the Universe, of which many fundamental aspects remain poorly understood. TeV gamma rays from GRBs are expected to provide crucial new information on the physical mechanisms of energy dissipation, particle acceleration and radiation in these enigmatic objects. After decades of searches, they were finally detected clearly from several recent events by Cherenkov telescopes: GRB 190114C by MAGIC, and GRB 180720B and GRB 190829A by HESS. An intriguing hint has also been seen in the short GRB 160821B by MAGIC. We discuss selected physical inferences from these results, including multi-messenger implications. We also address the prospects for further progress with CTA.

Rapid-Response Radio Follow-Up of TeV Gamma-Ray Bursts

• Gemma Anderson (ICRAR - Curtin University)

Room: Kerr Grant Lecture Theatre, Physics Building Only recently have radio telescopes been capable of automatically responding to transient alerts and multi-messenger events through the use of a rapid-response observing system. Such systems enable telescopes to automatically repoint and begin observing an event within seconds to minutes of its discovery, responding to transient alerts broadcast by dedicated telescopes or multi-messenger facilities. In this talk, I will present the new rapid-response mode on the Australia Telescope Compact Array (ATCA) and suggest an exciting use case to rapidly follow-up gamma-ray bursts (GRBs) detected by HESS. TeV-detected GRBs are a very new field of high-energy astrophysics with high impact results. Early-time radio detections of such events can provide important and complementary spectral information on these GRBs by allowing us to directly probe the jet physics, energy budgets, magnetic fields, and properties of the surrounding medium. Such an experiment will be an excellent test-bed for transient strategies for both CTA and the SKA.

Follow-up with the Zadko Telescope

• Bruce Gendre (University of Western Australia)

Room: Kerr Grant Lecture Theatre, Physics Building The Zadko Telescope is located on the West coast of Australia, in a unique position at this given latitude and longitude. It is a one meter fully robotic telescope, the only one of this class in Western Australia. Since 2009, it obtained numerous results in the field of high energy (observations of GRBs, GW events and kilonovae). In this presentation, I will present the telescope and its systems, and expose its capacities and abilities.

Linkages between CTA and VLBI

• Chris Phillips (CSIRO)

Room: Kerr Grant Lecture Theatre, Physics Building The gamma-ray sky is dominated by radio sources. Radio observations with milliarcsecond resolution are will be essential to understand new sources detected with the CTA. Studying Active Galactic Nuclei is one of CTA's Key Science Projects. However, the CTA does not have the angular resolution to study the source of relativistic jets - the resolution of VLBI is required to understand the physics of jet sources in AGN (and X-ray binaries in our own Galaxy). The unprecedented sub-minute sensitivity of CTA will undoubtedly review new insights to the transient universe. Very short transients have to be physically compact, again requiring the high angular resolution of VLBI to untangle the origin of Gamma Ray flares.

CTA's Perspectives on AGN Studies and the EBL

• Daniel Mazin (MPI for Physics, Munich & ICRR, University of Tokyo)

Room: Kerr Grant Lecture Theatre, Physics Building CTA is the next generation gamma-ray observatory which will conduct observations from both hemispheres in the energy range from 20 GeV to more than 300 TeV with an unprecedented sensitivity and angular resolution. Several Key Science Projects have been prepared by the CTA consortium to shed light on long standing questions of production mechanisms of gamma rays in extragalactic sources and reasons for the temporal variability in gamma rays which we observe. Also, CTA will allow us to determine the evolution in redshift of the low energy background radiation, the so-called EBL, which provides insights into the evolution of the galaxies as well as an independent measurement of the Hubble constant. In this presentation I will discuss the prospects of some of these studies and possible synergies with other research fields.

The Multi-Messenger View of Active Galactic Nuclei

• Markus Boettcher (North-West University, Potchefstroom)

Room: Kerr Grant Lecture Theatre, Physics Building This talk summarizes recent progress in multi-wavelength and multi-messenger studies of AGN, in particular blazars. Prospects of blazar studies with CTA will be summarized and synergies with Australian and South African facilities (in particular, SKA precursors) will be discussed.

IceCube's Neutrinos and Multi-Messenger Observations of Distant Exotic Environments

• Gary Hill (The University of Adelaide)

Room: Kerr Grant Lecture Theatre, Physics Building The IceCube neutrino alert program led to the observations that suggest that the blazar TXS 0506+056 is a cosmic accelerator, producing high energy cosmic rays, followed by neutrinos and gamma rays from subsequent interactions as these escape the jets. In this talk I will review the motivation for, construction, and science of IceCube, where, the long-sought dream of high-energy neutrino astronomy was finally realised with the observation of a flux of high-energy neutrinos from the Universe. Now that these have been observed, and the first source identified, the goal is to identify more sources, by better analysis methods, or by construction of a larger detector. To this end, the IceCube Upgrade is funded, which will see 7 strings deployed in 2020, and there are plans for IceCube Gen2, which would see another hundred strings deployed to expand the detection volume.

Polarimetry and CTA

• Daniel Cotton (Western Sydney University / University of Southern Queensland)

Room: Kerr Grant Lecture Theatre, Physics Building A new polarimeter is being developed at UNSW and WSU that will have utility for the CTA project. In this talk I will describe the recent development of high precision polarimetry in Australia and the scientific achievements it has enabled, with a focus on understanding the evolution of high mass stars. I will then outline the development of the new polarimeter, how its design differs and how this will enable CTA science.

MWL Studies of AGN - Locating the Emission

• Elina Lindfors (Finnish Centre for Astronomy with ESO / University of Turku)

Room: Kerr Grant Lecture Theatre, Physics Building The location of the blazar zone has been a topic of decades long debate. The only wavelength at which we can spatially resolve the jet is radio, where the jet becomes optically thin several parsecs away from the black hole. It has been generally argued that the main blazar zone is located much closer to the black hole due to the fast variability we see, but also due to lack of seed photons further out. In this talk, I will present recent results from extensive multiwavelength campaigns, demonstrating how the data from radio to VHE gamma-rays was used to pinpoint the location of the blazar zone to the 43GHz VLBI core and possible solutions to the seed photon problem in these cases. I will also discuss why further observations are still needed, also in the CTA era, highlighting the importance of long-term monitoring and multiwavelength support observations, in particular VLBI and optical polarization observations.

Galactic Plane Survey with the Cherenkov Telescope Array (CTA)

• Gavin Rowell (University of Adelaide)

Room: Kerr Grant Lecture Theatre, Physics Building Surveys of the Galactic Plane in TeV gamma rays reveal over 70 TeV sources, most of which are unidentified. The identified sources are associated with supernova remnants, pulsar wind nebulae, compact-stellar binary systems, and diffuse gas. CTA's greatly improved sensitivity is expected to uncover many more sources and the diffuse TeV emission localised around particle accelerators. It may also reveal the large-scale diffuse emission across the Galactic disk. This talk will review the current TeV gamma-ray surveys (e.g from HESS and HAWC), and look at the current efforts within CTA to carry out its Galactic Plane survey and what we might expect. The role of the latest CO ISM surveys will also be covered.

Carbon Monoxide in Our Galaxy and Galactic Centre: Implications for Understanding Gamma-Ray Emission

• Rebecca Blackwell (The University of Adelaide)

Room: Kerr Grant Lecture Theatre, Physics Building Using the Mopra Southern Galactic Plane Carbon Monoxide Survey dataset, comparisons between high resolution molecular gas and current HESS observations of Very High Energy (VHE) gamma-ray sources are presented. In particular, VHE gamma-ray sources in and near the Central Molecular Zone are focused on as case studies. Similar comparisons will be able to be made in the future when CTA provides higher resolution gamma-ray maps, with a greater sensitivity that is expected to detect more diffuse VHE gamma-ray emission. Multiwavelength analysis will be necessary to understand the origin of potentially extremely widespread emission.

The GeV-TeV Interstellar Emission from the Milky Way

• Troy Porter (Stanford University)

Room: Kerr Grant Lecture Theatre, Physics Building The current understanding of the diffuse gamma-ray emission, which is thought to be mainly produced by cosmic ray (CR) particles interacting with the interstellar gas and radiation fields, has a significant basis on advances made with the Fermi Large Area Telescope (Fermi-LAT) over the past decade of its operation. The Fermi-LAT observations are most sensitive at GeV gamma-ray energies, and trace the CRs that have been propagating millions of years through the Milky Way. The gamma-ray distribution on the sky measured by the Fermi-LAT is correspondingly broad and follows the line-of-sight integrated interstellar gas and radiation field densities. However, current generation very high energy instruments, like HESS and HAWC, probe CRs that have been recently accelerated and injected into the nearby interstellar medium (ISM). The corresponding distribution of gamma rays on the sky is more localised, tracing the CR and ISM densities nearby individual the sources. I will talk about recent modelling using the well-known GALPROP code to understand the links between the energy regions covered by these experiments.

Evolutionary Map of the Universe

• Ray Norris (WSU / CSIRO)

Room: Kerr Grant Lecture Theatre, Physics Building The Evolutionary Map of the Universe (EMU), the all-sky radio continuum survey using the Australian Square Kilometre Array Pathfinder (ASKAP), has now completed its "Pilot Survey" ASKAP and is generating science results from the ~200,000 radio sources in that field. We are now planning the full survey to start next year. I will discuss the latest results, and plans for the full EMU survey, and discuss how it can facilitate CTA science.

Data Mining from Radio to TeV

• Sabrina Einecke (The University of Adelaide, Australia)

Room: Kerr Grant Lecture Theatre, Physics Building The scientific branches Big Data and Data Mining are increasingly becoming an integral part in astronomy. Numerous experiments in various energy regimes provide immense amounts of data that need to be accurately combined, analysed and interpreted. Forthcoming experiments of a new era, such as CTA or SKA, will produce mind-blowing data rates of up to multiple Petabytes per second, demanding close collaborations between the branches. This contribution will give an overview of these approaches and their applications in multi-wavelength astronomy.

The Milky Way at Low Frequencies

• Natasha Hurley-Walker (ICRAR - Curtin University)

Room: Kerr Grant Lecture Theatre, Physics Building Recent years have seen a resurgence in radio astronomy at sub-GHz frequencies, with the construction and operation of telescopes such as the LOw-Frequency ARray (LOFAR) and the Murchison Widefield Array (MWA), as well as the upgrade of existing facilities such as the Giant Metrewave Radio Telescope (GMRT). Radio astronomy at low frequencies offers a valuable window into objects and processes in the Milky Way, revealing details of objects as diverse as pulsars, supernova remnants, the cold interstellar medium, ionised regions around young stars, and the nearby magnetic ISM. I will present recent results in this field, explore some of the synergies with CTA, and discuss the potential for the future with the advent of SKA_Low.

The GASKAP Survey: Mapping the Milky Way ISM in HI and OH

• Katie Jameson (CSIRO)

Room: Kerr Grant Lecture Theatre, Physics Building The Australian Square Kilometre Array Pathfinder (ASKAP) is a new radio array that allows us to map atomic hydrogen (HI) and hydroxide (OH) at unprecedented resolution and sensitivity. I will present an overview of the Galactic ASKAP Survey (GASKAP), which aims to map HI and OH throughout the Galactic Plane and Magellanic System. I will highlight how the HI and OH data from GASKAP will help provide the large-scale ISM context for the roles high energy particles and cosmic rays play in shaping the ISM and star formation.

Supernova Remnants in the Multi-Messenger Era

• Miroslav Filipovic (Western Sydney University)

Room: Kerr Grant Lecture Theatre, Physics Building We are currently carrying out observational studies of SNRs and superbubbles using today’s gamma-ray, X-ray and radio telescopes and will continue our efforts with upcoming telescopes like eROSITA, Cherenkov Telescope Array, HESS and the SKA precursors, including synergistic programmes such as ASKAP-eROSITA. SKA pathfinders' observations in radio at low frequencies with high sensitivity will detect new SNRs in our Galaxy and the MCs, which are either old and too faint, young and too small, or located in a too confusing environment and have thus not been detected yet. In addition, the SKA pathfinders' observations will also allow high-resolution polarimetry and are key to the study of the energetics of accelerated particles as well as the magnetic field strength and configurations. Gamma-ray studies provide answers to the long-standing question in high energy astrophysics: Where do cosmic rays come from? The gamma-ray emission seen from some middle-aged supernova remnants (SNRs) is now known to be from distant populations of cosmic-rays (probably accelerated locally) interacting with gas, but there is still much work to be done in accounting for the Galactic cosmic-ray flux. Young PeV gamma-ray supernova remnants require different techniques to address the question of cosmic-ray acceleration. The Cherenkov Telescope Array will allow us to do this. I will present an overview of our ongoing multi-messenger studies of the young (and some not-so-young) SNRs.

Supernova Remnant Tomography

• Ivo Seitenzahl (UNSW-Canberra)

Room: Kerr Grant Lecture Theatre, Physics Building I report on the discovery of optical emission from the non-radiative shocked ejecta of three young Type Ia supernova remnants (SNRs): SNR 0519-69.0, SNR 0509-67.5, and N103B. Deep integral field spectroscopic observations reveal broad and spatially resolved [Fe XIV] 5303A emission. The width of the broad line reveals, for the first time, the reverse shock speeds. For two of the remnants we can constrain the underlying supernova explosions with evolutionary models. SNR 0519-69.0 is well explained by a standard near-Chandrasekhar mass explosion, whereas for SNR 0509-67.5 our analysis suggests an energetic sub-Chandrasekhar mass explosion. With [S XII], [Fe IX], and [Fe XV] also detected, we can uniquely visualize different layers of the explosion. We refer to this new analysis technique as "supernova remnant tomography".

Particle Escape in Supernova Remnants and Related Gamma-Ray Emission

• Silvia Celli (GSSI)

Room: Kerr Grant Lecture Theatre, Physics Building Abstract The escape process of particles accelerated at supernova remnant (SNR) shocks is one of the poorly understood aspects of the shock acceleration theory. In this talk I will describe a phenomenological approach to study the particle escape and its impact on the gamma-ray spectrum resulting from hadronic collisions both inside and outside of a middle-aged SNR. Under the assumption that in the spatial region immediately outside of the remnant diffusion is suppressed with respect to the average Galactic one, I will show that a significant fraction of particles are still located inside the SNR long time after their nominal release from the acceleration region. This fact results into a gamma-ray spectrum that resembles a broken power law, similar to those observed in several middle-aged SNRs. Above the break, the spectral steepening is determined by the diffusion coefficient outside of the SNR and by the time dependency of the maximum energy. Consequently, the comparison between the model prediction and actual data will contribute to determining these two quantities, the former being particularly relevant within the predictions concerning the gamma-ray emission from the halo of escaping particles around SNRs which could be detected with future Cherenkov telescope facilities.

Pulsar Wind Nebulae at TeV Energies

• Alison Mitchell (University of Zürich)

Room: Kerr Grant Lecture Theatre, Physics Building Pulsar Wind Nebulae (PWNe), regions dynamically dominated by highly energetic particles accelerated in the vicinity of pulsars, are the most populous Galactic source class identified at TeV energies in the H.E.S.S. Galactic Plane Survey. Recently, the first views of the Galactic plane at energies > 100 TeV from HAWC have unveiled a source population exclusively associated with energetic pulsars, known lepton factories. Gamma-ray emission beyond 100 TeV provides evidence for the presence of PeV particles, reaching the cosmic ray knee, whilst current data is consistent with a leptonic scenario for the emission. The detection of highly extended TeV emission around less energetic, nearby pulsars with ages > 100 kyr has prompted discussion of a distinct “halo" phenomenon, associated with particle escape from the PWN in later evolutionary stages. Multi-wavelength data provides an opportunity for further insights into the nature of halos and how their properties differ from those PWNe. Radio observations in particular, are key to morphological studies and in identifying molecular cloud regions that could act as targets for hadronic emission, enabling constraints on the presence of hadronic particles within pulsar environments to be made. In this talk, I will outline the prospects for future studies of PWNe and halos with CTA, emphasising how multi-wavelength data will play a vital role in advancing our understanding of PWNe at TeV energies.

Gamma-ray Pulsars in the CTA Era

• Arache Djannati-Atai (APC-CNRS)

Room: Kerr Grant Lecture Theatre, Physics Building I'll give an overview of current research and results on gamma-ray pulsars from ground and discuss the prospects with CTA, including some considerations on multi-wavelength coordination.

A Broadband View of the Galactic Centre in Anticipation of CTA

• Roland Crocker (Australian National University)

Room: Kerr Grant Lecture Theatre, Physics Building The inner few hundred parsecs of the Galaxy host its resident supermassive black hole and a surrounding region of intense star formation. In addition, this region of the Milky Way is where its dark matter density is expected to peak. Moreover, a number of mysterious signals emanate or peak in this part of the sky: the `GC Excess' gamma-ray signal, the `Fermi Bubbles', and the positron annihilation signal. I will review this phenomenology and what it might be telling us about the processes occurring at the Galaxy's heart, anticipating insights that CTA may bring when it is fully operational.

Cosmic-Ray Models of the Ridge-Like Excess of Gamma Rays in the Galactic Centre

• Chris Gordon (University of Canterbury)

Room: Kerr Grant Lecture Theatre, Physics Building The High-Energy Stereoscopic System (HESS) has detected diffuse TeV emission correlated with the distribution of molecular gas along the Ridge at the Galactic Centre. Diffuse, non-thermal emission is also seen by the Fermi large area telescope (Fermi-LAT) in the GeV range and by radio telescopes in the GHz range. Additionally, there is a distinct, nearly spherically symmetric excess of gamma rays seen by Fermi LAT in the GeV range. A cosmic ray flare, occurring in the Galactic Centre, 10 000 years ago has been proposed to explain the TeV Ridge. An alternative, steady-state model explaining all three data sets (TeV, GeV, and radio) invokes purely leptonic processes. We show that the flare model from the Galactic Centre also provides an acceptable fit to the GeV and radio data, provided the diffusion coefficient is energy independent. However, if Kolmogorov-type turbulence is assumed for the diffusion coefficient, we find that two flares are needed, one for the TeV data (occurring approximately 10 000 years ago) and an older one for the GeV data (approximately 100 000 years old). We also show that a range of single-zone, steady-state models are able to explain all three spectral data sets. Large gas densities equal to the volumetric average in the region can be accommodated by an energy-independent diffusion or streaming based steady-state model. Additionally, we investigate how the flare and steady-state models may be distinguished with future gamma-ray data looking for a spatial dependence of the gamma-ray spectral index.