Synergies in Non-Thermal Astrophysics in Southern Africa

29 Jul 2024, 09:00 → 2 Aug 2024, 17:00 Europe/Berlin

Erlangen Centre for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nürnberg

The inaugural workshop on `Synergies in Non-Thermal Astrophysics in Southern Africa’ will be held from 29/7/24 to 2/8/24 at the Erlangen Centre for Astroparticle Physics, Friedrich-Alexander University, Erlangen, Germany. It aims to bring together researchers from collaborations working on current and future multi-wavelength facilities located in southern Africa, such as H.E.S.S., MeerKAT, AMT, and SALT, to discuss multi-wavelength synergies. The workshop is open to all interested researchers. 

Contributed sessions will be held dedicated to both extragalactic and galactic astronomy, as well as transient astrophysical phenomena and stellar intensity interferometry. There will also be a number of breakout sessions to foster new research collaborations.

Hybrid attendance will be possible. For in-person attendees there is a workshop fee of 140 EUR; this covers daily lunches and coffee breaks, as well as a drinks reception and workshop dinner. There is no fee for virtual participation. Registration is capped at 70 in-person participants.

To support attendance by early career researchers from African Nations, we have obtained a significant amount of travel funding (to cover transport, accommodation, meals and workshop fee) courtesy of Friedrich-Alexander-University’s Emerging Talents Initiative. Researchers who wish to apply for this funding should submit an abstract, and a CV with a half-page statement of interest (including a rough budget request) by email to samuel.spencer@fau.de.

 

Important Dates:

Deadline to apply for travel funding: 19/4/24

Final abstract deadline: 17/5/24 Extended until 5/7/24

Final registration deadline: 5/7/24

poster.pdf

Monday 29 July

10:00 → 10:30 Welcome: Registration

10:30 → 11:00 Coffee Break

11:00 → 11:30 Welcome

11:00 Introduction

Speaker: Samuel Spencer (ECAP)

SynergiesIntro.pdf

11:30 → 13:00 Updates from Current Generation Instruments

11:35 Update from gamma-rays

Speaker: Alison Mitchell

Gamma_status_July24_AM.pdf

12:15 Update from CTA Redshift Project

Speaker: Dr Eli Kasai (University of Namibia)

Eli_MultiwavelengthSynergies.pdf

13:00 → 14:00 Lunch

14:00 → 15:00 Updates from Current Generation Instruments

14:00 AMT Status Updates

Speaker: Prof. Michael Backes (University of Namibia)

15:00 → 15:30 Coffee Break

15:30 → 17:10 Updates from Current Generation Instruments

15:30 ERosita Perspective

Speaker: Dr Martin Mayer

NonthermalPhysics_SA.pdf

NonthermalPhysics_SA.pptx

16:10 Transients

Speaker: Dr Lauren Rhodes

17:00 → 19:00 Drinks Reception

Tuesday 30 July

10:00 → 10:30 Transients

10:00 MeerTRAP: Finding short-duration radio transients with MeerKAT

More Transients and Pulsars (MeerTRAP) is an ERC-funded project to search for fast radio transients, including pulsars and Fast Radio Bursts (FRBs), using the MeerKAT telescope in South Africa. To that end, we employ the FBFUSE beamformer combined with a real time, single pulse search pipeline that operates commensally with other MeerKAT users. Thus, in over five years of regular observing, we have amassed more than 30,000 hours on-sky, and have discovered almost 100 new transients within the Galaxy and over 50 extragalactic FRBs. Thanks to MeerKAT’s excellent spatial resolution, we can localise discoveries to sub-arcsecond precision, providing an excellent opportunity for follow-up campaigns using various telescopes in different observing bands. Additionally, the 0.65-m optical telescope that shadows daytime MeerKAT observations, MeerLICHT, is now operational, providing prompt optical follow-up to MeerTRAP discoveries. In this talk, I will give an overview of MeerTRAP, our discoveries, and the role of multi-wavelength follow-up in illuminating questions in transient astronomy such as the still-mysterious origin of FRBs.

Speaker: Dr Mechiel Christiaan Bezuidenhout (University of South Africa)

Bezuidenhout_Erlangen_2024.pptx

10:30 → 11:00 Coffee Break

11:00 → 12:00 SII

11:00 HESS SII

Speaker: Mr Andi Zmija

2024-07-30 -- Synergies.pdf

12:00 → 13:00 Tour ECAP

13:00 → 14:00 Lunch

14:00 → 15:00 Galactic

14:00 Fermi + HESS analysis on the Crab nebula

The Crab Nebula serves as a unique laboratory for studying the acceleration of electrons and positrons through their non-thermal radiation. In this contribution, I would like to present the first fully self-consistent analysis of the Crab Nebula’s γ-ray emission over five orders of magnitude in energy (from 1 GeV to ∼100 TeV). By combining 11.4 years of data from the Fermi Large Area Telescope with 80 hours of High Energy Stereoscopic System (H.E.S.S.) data, we provide a measurement of the spatial extension of the nebula and its energy spectrum.

Our findings reveal evidence for a shrinking of the nebula with increasing γ-ray energy. However, none of the phenomenological models we tested can fully describe both the spatial extension and the spectral energy distribution simultaneously. Notably, the extension measured at TeV energies appears larger than expected when compared to the X-ray emission. Our measurements also shed light on the structure of the magnetic field between the pulsar wind termination shock and the dust torus, suggesting that the magnetic field strength decreases with increasing distance from the pulsar.

Speaker: Mr Tim Unbehaun (ECAP)

Crab-Femri-Hess_TimUnbehaun.pdf

14:30 Searching for millisecond pulsar near the Galactic center

Excess of gamma rays with a spherical morphology around the Galactic center (GC) at GeV energies observed in the Fermi-LAT data is one of the most intriguing features in the gamma-ray sky as it is consistent with annihilation of dark matter particles. Astrophysical explanations include a population of millisecond pulsars (MSPs). We use machine learning algorithms to search for MSP candidates among unassociated Fermi-LAT sources near the GC. A search for radio counterparts of the MSP candidates may confirm or disprove the MSP nature of the Galactic center GeV excess.

Speaker: Dmitry Malyshev (ECAP)

2024-07-30_Malyshev_ECAP.pdf

15:00 → 15:30 Coffee Break

15:30 → 17:00 Galactic

15:30 MPIfR-MeerKAT Galactic Plane Survey (MMGPS) I: System setup and early results

Pulsars are highly magnetised, rapidly rotating neutron stars that emit beams of electromagnetic radiation from their magnetic poles and are remarkable laboratories for testing theories of gravity, studying neutron star interiors, and constraining equations of state. Previous surveys searching for such intriguing objects have provided high-impact science results, and new-generation radio telescope sensitivities enable more intriguing discoveries.
The Max-Planck-Institut fur Radioastronomie (MPIfR) MeerKAT galactic plane survey (MMGPS) is an ongoing commensal survey that aims to maximise the scientific return per unit of MeerKAT observing time by covering multiple science cases (pulsars, fast transients, Galactic and extragalactic magnetism and Galactic star formation) simultaneously. The primary science objective of the MMGPS is to find previously undetected compact relativistic binary pulsars along the Galactic plane and use such systems to probe general relativity in the strong field regime. The MMGPS has been partitioned into three parts: the MMGPS-L band (1.4 GHz observations of the Galactic plane), MMGPS-S band (~2.4 GHz observations close to the Galactic plane) and MMGPS-SgrA (high-frequency end of S-Band (~3 GHz) observations centred on Sagittarius A). The L-band portion of the survey has been completed, yielding 74 pulsar discoveries (16 binary systems and 2 double neutron star systems) and the S-band portion of the survey is currently underway.

Speaker: Ms Denisha Pillay (Max-Planck-Institut für Radioastronomie (MPIfR))

Erlangen presentation (6).pdf

15:50 Probing the Galactic Centre with Pulsars

The Galactic Centre is a region filled with non-thermal astrophysical phenomena, making it a prime target for cutting-edge research using advanced radio telescopes. Using the capabilities of the MeerKAT S-Band receiver, our research is dedicated to finding pulsars within this complex region.
Pulsars, the highly magnetized, rotating neutron stars, are expected to be abundant in the Galactic Centre due to the area's high density of massive stars. However, despite extensive searches, few pulsars have been detected here. This scarcity is largely attributed to the region's extreme interstellar scattering, which obscures radio signals, making it difficult to detect pulsations in blind searches.
Our search aims to overcome these observational challenges to identify previously undiscovered pulsars. When discovered, not only will they allow us to use them as accelerator-meter to study the inner galactic potential, but we can also use them to precisely measure the properties of the supermassive black hole, Sagittarius A*. Moreover, the undetected population of pulsars is hypothesized to play a crucial role in explaining the Galactic Centre excess—a mysterious surplus of gamma rays observed by instruments like the Fermi Gamma-ray Space Telescope, thus further motivating the search.

Speaker: Isabella Rammala (Max-Planck-Institit für Radioastronomie)

Synergies in Non-Thermal Astrophysics-4.pdf

Wednesday 31 July

10:00 → 10:30 Galactic

10:00 Non-thermal Radio Emission from Massive Protostars in the SARAO MeerKAT Galactic Plane Survey

We present an investigation of the L-band emission from known massive young stellar objects (MYSOs) in the SARAO MeerKAT Galactic Plane Survey to search for non-thermal radio emitters from the sample. A total of 398 massive protostars, identified from the Red MSX Source (RMS) survey, are located within the survey region. Among these, 164 fields that host the protostars are isolated from nearby bright HII regions, allowing for the study of any ionized jets present in the fields. Seventy-four of these fields have jets with five-sigma detections or higher, corresponding to a detection rate of 45%. The MeerKAT fluxes of the detections, together with the upper limits of the non-detections and any other fluxes from previous observations, were used to estimate the spectral indices of the jets, to search for the presence of non-thermal radiation. In cases where a source manifests a single emission at a given observation but is resolved into multiple components in observations of higher resolutions, the
sum of the fluxes of the components was used in estimating the indices. Any effects from missing flux in higher resolution observations were incorporated into the uncertainties of the indices. The spectral indices of the sample show that at least 40% of the jets emit non-thermal radiation. Additionally, the spectral energy distribution (SED) of some of the sources, as well as their radio-luminosities exhibit evidence of non-thermal emission, especially in extended sources.

Speaker: Dr Willice Obonyo (University of South Africa)

ECAP_talk_willice.pptx

10:30 → 11:00 Coffee Break

11:00 → 12:20 Extragalactic

11:00 Exploring the Influence of Cosmic Voids on the propagation of TeV Gamma Rays and the Puzzle of GRB 221009A

The recent detection of the gamma-ray burst GRB 221009A has garnered significant attention due to its unprecedented brightness and the first-ever detection of very-high energy (VHE, > 10 TeV) gamma rays from a GRB at the redshift of z=0.151. This redshift indicates a distance at which the gamma-ray flux at these energies would typically undergo severe attenuation due to gamma-gamma pair production with the extragalactic background light (EBL). In my talk, I will explore the possibility that cosmic voids along our line-of-sight to the source might significantly influence the detestability of such VHE gamma-ray photons.

Speaker: Hassan Abdalla (Universidad Complutense de Madrid)

Hassan Abdalla.pptx

11:30 The unifying model of Jetted AGNs: the contribution of relativistic and orientation Effects

The unified model of jetted active galactic nuclei (AGNs) based on intrinsic properties presumes that the blazar subtypes of BL Lacertae objects (BLs) and flat-spectrum radio quasars (FSRQs) are aligned equivalents of Fanaroff–Riley type I (FR I) and Fanaroff–Riley type II (FR II) radio galaxies from where their parent sources are obtained. Using compiled radio, X-ray and γ-ray data of 397 blazars and 110 radio galaxies detected by the Fermi Large Area Telescope (Fermi/LAT- 4LAC), We computed the γ-ray core-dominance parameter (Rγ) and γ-ray emission components (beamed and unbeamed) to study the consequences of relativistic beaming and orientation effects on γ-ray properties of radio galaxies, BLs and FSRQs. Analysis of data shows that the distributions of RX and Rγ, on average, are consistent with the prediction of the unified scheme in which FSRQs and BLs are strongly beamed and are inclined at smaller angles than radio galaxies. Through statistical tests with chance probability, p < 0.05, we find that the distributions of RX and Rγ for radio galaxies and the blazar subtypes are not significantly different. There is a regular positive trend (r > +0.60) in the variation of radio core-dominance parameter – X-ray luminosity (Rr - Lx) data from radio galaxies to FSRQs through BLs, which suggests that radio galaxies could be relativistically less beamed population of jetted AGNs. The results are consistent with the unified model for radio galaxies and the conventional blazar subtypes.

Speaker: Dr EVARISTUS IYIDA (UNIVERSITY OF NIGERIA, NSUKKA)

main.pdf

12:00 Searching for high redshift radio galaxies with the MeerKAT Galaxy Cluster Legacy Survey

I present the results of my Master's project to comprehensively search for high-redshift radio galaxies (HzRGs) within 37 fields of the MeerKAT Galaxy Cluster Legacy Survey's first data release. These fields are distinguished by their good dynamic range and comprehensive optical and infrared coverage through the Dark Energy Camera Legacy Survey and the All-sky Wide Infrared Survey Explorer. HzRGs, potentially the precursors of local elliptical galaxies we see today, offer a unique lens for exploring diverse astrophysical phenomena, including large-scale structures, galaxy evolution, and the epoch of reionization. We apply the likelihood multiwavelength cross-matching method, to refine the candidate pool, then determine the in-band spectral indices from MeerKAT data, focusing on ultra-steep spectrum sources. MeerKAT's extreme sensitivity has allowed us to detect a large number of new HzRG candidates, at radio luminosities an order of magnitude lower than other studies, effectively positioning them for follow-up spectroscopic analysis to confirm their redshifts.

Speaker: Vasco Cossa (Rhodes University)

12:20 → 13:00 Extragalactic

12:20 Unveiling The Enigmatic: A Multiwavelength Investigation of Serendipitous Diffuse Radio Emission

Observations of galaxy clusters at low radio frequencies serve as a valuable tool for studying the non-thermal intracluster medium (ICM). Diffuse radio emissions, such as radio halos and relics, assist in probing a cluster’s non-thermal physics and magnetic fields. However, radio observations lack redshift information, rendering it challenging to determine the origin of extended radio emission. In this study, we present a multiwavelength view of diffuse radio emission serendipitously discovered in one of the cluster fields from the MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio Sources (MERGHERS) survey. Although there are no obvious signs of diffuse emission within the cluster itself, to the south of the target lies the newly detected emission, which appears morphologically similar to a pair of cluster radio relics. However, there is no known cluster at a plausible redshift at the source position. We employ a combination of MeerKAT UHF data, Dark Energy Survey (DES) imaging and photometry, and X-ray images to study the properties of the diffuse emission in order to determine its origin. In this talk, I will present our multiwavelength investigation into this intriguing puzzle.

Speaker: Ms Mikaela Webber (Rhodes University)

13:00 → 14:00 Lunch

14:00 → 14:20 Future Prospects

14:00 Namibian Astronomy: Exploiting Favorable Conditions for Multi-Wavelength Observatories

Namibia, renowned for its pristine night skies and minimal light pollution, has emerged as a significant hub for astronomical research. Hosting the first International Dark Sky Association (IDA) Dark Sky Reserve in Africa, the NamibRand Nature Reserve, Namibia boasts ideal conditions for astronomical observations. This work delves into measurements of night-sky brightness proximal to the world-leading High Energy Stereoscopic System (H.E.S.S.). Leveraging its arid climate, Namibia experiences a scarcity of rainfall, leading to an abundance of cloudless nights—a phenomenon conducive to extended observation hours for astronomical facilities like H.E.S.S. With this, Namibia’s skies offer vast opportunities for uninterrupted exploration of the Universe. Moreover, Namibia’s sparse population density, ranking as the third least densely populated country globally, further mitigates light pollution, enhancing its appeal for astronomical endeavors. In addition to the dark sky quality of the Namibian night sky and optimal weather conditions including favorable altitudes, recent studies on radio frequency interference (RFI) conducted at the two proposed sites (close to the H.E.S.S. site and on the Gamsberg) for the Africa Millimeter Telescope (AMT) showed that the two sites are relatively radio quiet with a few potential interference in intermediate frequency (IF) bands. Due to the low population density of the country, interference in most astronomical observational radio bands is unlikely due to low industrial and commercial utilization of these observation bands and the high free-space path loss. Building upon these advantageous conditions, Namibia is poised to pioneer the establishment of the world’s first multi-wavelength observatory. This ambitious endeavor envisions incorporating telescopes operating across a spectrum of wavelengths, including cm-wave and mm-wave radio, optical wavelengths, and gamma rays. The proposed Namibian Multi-Wavelength Observatory aims to consolidate the capabilities of existing facilities such as H.E.S.S. and the planned Africa Millimeter Telescope, thereby solidifying Namibia’s position as a front-runner in astronomical research and exploration.

Speaker: Mr Hiiko Katjaita (University of Namibia)

Dark_Sky_Measurements.pptx

14:20 → 15:00 Galactic

14:20 Investigating the origin of the TeV γ-rays in HESS J1640-465

HESS J1640-465 is a powerful source of very high energy γ-rays and possibly the most luminous
TeV source in the Milky Way. It is also associated with a radio supernova remnant (SNR) and an
X-ray PWN powered by an energetic pulsar. Determining the origin of the VHE γ-rays requires
measuring, and modeling the broadband non-thermal emission of this source. My recent analysis
of the X-ray PWN and associated γ-ray emission indicates that a PWN powered by the energetic
pulsar could produce the observed γ-rays under some peculiar conditions; a conclusion testable
by measuring the previously undetected radio properties of this PWN. I was recently awarded a
MeerKAT observation to do that, and in this talk, I will present the properties of the detected PWN
and the additional information it provides.

15:00 → 15:30 Coffee Break

15:30 → 17:00 Breakout Sessions

Thursday 1 August

10:00 → 10:20 Galactic

10:00 Deriving Pulsar Properties from Pulsar Wind Nebulae Using H.E.S.S. and LHAASO Data

A significant fraction of the highest energy gamma-ray astrophysical sources observed are associated with Pulsar Wind Nebulae (PWNe). Given recent observations, the postulated, but unverified, hadronic component from PWNe requires renewed attention in the long search for PeVatrons. We estimate possible ranges for the average pulsar pair production multiplicity on 31 sources in the Australia Telescope National Facility (ATNF) catalogue. We then use the latest gamma-ray data from H.E.S.S. and LHAASO in combination with radio data available in the literature to further constrain associated pulsar properties for a set of well-known PWNe. These include lower limits for the pulsar birth period and average pair production multiplicity. Based on these, for all but one source, we cannot exclude the possibility of these systems being hadronic PeVatrons.

Speaker: Dr Spencer Samuel (Erlangen Centre for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nürnberg )

Properties_Synergies.pdf

10:20 → 11:00 Coffee Break

11:00 → 12:00 Extragalactic

11:00 HI Asymmetries and deficiencies in ALFALFA

Galaxies exhibit a wide variety of observable properties. The environment in which a galaxy resides is known to significantly impact its characteristics. A galaxy's cold gas component (usually a disk for late-type systems) is particularly sensitive to environmental conditions. Neutral atomic hydrogen (HI) as we know it, makes up the large majority of a galaxy's gas content.

Galaxies are often observed to be HI-deficient if they are located in dense environments such as galaxy clusters, or towards the centres of groups. There are  several processes that can lead to HI-deficiency in a galaxy, each of which affects the asymmetry of the galaxy's spatially integrated (i.e., global) HI profile. Some of these processes include tidal interactions, galaxy mergers, interactions with satellite galaxies, flyby interactions as well as ram-pressure stripping.

Therefore, by studying the properties of asymmetric HI galaxy spectra, we learn more about the important environmental processes that influence the ways galaxies evolve with time.
HI is particularly well-suited as a tracer of environmental processes given that a galaxy's HI disk is typically >2 times more extended than its stellar disk, and is therefore less gravitationally bound.

In this work, we aim to use HI line data from the Arecibo Legacy Fast Alfa (ALFALFA) survey to study the prevalence of HI spectral asymmetries in the context of galaxy environment.
From the full ALFALFA sample, we define 2 samples so as to quantify environment.
We define as merger candidates those galaxies that have a neighbouring galaxy within 25 kpc spatially and 750 km/s spectrally. A sample of well-isolated galaxies is also procured. A galaxy is said to be isolated if it has no neighboring galaxies within 750 kpc spatially and 7500 km/s spectrally. The goal is to quantify the asymmetries in these two galaxy samples in order to generate quantifiable evidence of the environment-induced effects. From our results, we find that on average, the merger sample does show enhanced asymmetries compared to the isolated sample. This tells us that the HI gas of galaxies in denser environments (merger sample) is interacting with other galaxies in the environment and thus perturbing the distribution of gas within the galaxy. This results in a disturbed HI profile morphology or rather in simple terms, an asymmetric HI profile. This thus alludes to the idea that environment is indeed one of the drivers of asymmetries observed in the HI profiles of galaxies.

Speaker: Ms Reshoketswe Thobejane (University of the Western Cape)

11:20 The properties of radio relics and the connection with radio halos in galaxy clusters and their correlation with non-thermal phenomena at multi-frequency

We present an investigation of the properties of radio relics (RRs), one type of diffuse emission located at the outskirts of some Galaxy Clusters (GCs), and a search for information about the origin of non-thermal processes taking place in the cluster atmospheres. We adopt a new approach to constrain models for the origin of RRs according to the following steps: i) Instead of working on a single relic, we worked on a large sample of RRs, by performing the compilation of one of the largest reference cluster relic sample (77 relics) available; ii) We perform a study of statistical properties of RRs and the hosting clusters by evaluating the relationship between the radio power of relics at 1.4 GHz and: radio halos power, cluster X-rays bolometric luminosity, integrated Compton parameter, cooling time, and Mach number of the shock associated to the relic; iii) We perform morphological analysis of the connection between RRs and the population of fossil particles coming from radio galaxies jets and lobes in the cluster. The results obtained show that relics know about halos because they scale together in their radio powers, galaxy activity in the cluster centre, and cluster properties like X-ray luminosity and Integrated Compton parameter. Examination of relics in other clusters, as well as optical/infrared spectroscopic studies of candidate radio galaxies as possible origins of the relics, and deep radio studies of their jets and lobes, will be necessary to derive solid results.

Speaker: Prof. Claudio Paulo (Universidade Eduardo Mondlane, Faculdade de Ciências, Departamento de Física, Grupo de Astrofísica, Ciências Espaciais e Inteligência Artificial)

11:40 Chemical abundances of type-2 AGN in different environments

The chemical abundance of active galaxies, which host active galactic nuclei (AGN) at their centre, remains poorly studied, most often due to the difficulty of removing the effect of AGN in metallicity measurements. In particular, the chemical abundance of active galaxies in different environments, including clusters and groups of galaxies, is still unknown. In this work, we use a novel HCm code (HII-CHI-mistry) adapted to measure the chemical abundance of type-2 AGN. We measure the
oxygen abundance (12 + log(O/H)), the nitrogen abundance (log(N/O)), and the ionisation parameter (logU) for ~ 12000 type-2 AGN selected from the SDSS survey. We analyse the metallicity properties of type-2 AGNs in relation to other properties of AGN host galaxies, such as morphology, stellar mass and star formation rate (SFR), and in terms of the environment. In addition, for galaxies in groups and clusters, we study the metallicity properties in relation to the properties of the galaxy groups/clusters (e.g., the cluster-centric distance and the number of galaxies in the group/cluster). We do not observe a clear and strong mass-metallicity relation, although, we do observe that in groups and clusters, the 12 + log(O/H) abundance is higher in galaxies with higher stellar mass. We find that the 12 + log(O/H) abundance decreases with increasing SFR in all environments. We do not find a fundamental plane of type-2 AGN, suggesting more complex scenarios in the behaviour of stellar mass, SFR and metallicity when AGN are present, compared to pure star-forming galaxies. We find that type-2 AGN hosts, both early- and late-type, have on average higher 12 + log(O/H) abundances in groups and clusters compared to field galaxies, independent of redshift. Our results indicate that, although type-2 AGN in groups and clusters have on average higher metallicities for a given stellar mass, neither simple group or cluster membership nor cosmic-centric distance seems to drive this effect. Finally, with this work, we provide the largest catalogue of chemical abundances of type-2 AGN to date.

Speaker: Ms Mehbuba Ahmed (Space Science and Geospatial Institute (SSGI))

12:00 → 13:00 Extragalactic

12:00 The MERGHERS survey

The MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio Sources (MERGHERS) survey is targeting a homogeneously selected sample of SZ-detected galaxy clusters with the aim of probing the cosmic and mass evolution of diffuse cluster radio emission. Almost all statistical cluster samples studied for diffuse radio emission are restricted to low-redshift, high-mass clusters due to historical telescope sensitivity limitations. MERGHERS is designed in mass-complete tiers, to build up to a large statistically significant cluster sample across wide redshift and mass ranges, as yet unprobed at mid-MHz and GHz ranges. The initial tier of the MERGHERS project focuses on mid-to-high redshift clusters (0.4 < z < 0.6) from the Atacama Cosmology Telescope DR5 cluster catalogue, providing the first mass-selected statistical sample in this redshift range. I will present the MERGHERS survey and some early results, and discuss the critical multiwavelength synergies required to classify detected diffuse emission, probe the non-thermal physics, and study the extragalactic radio sources in the fields.

Speaker: Kenda Knowles (Rhodes University / SARAO)

Knowles_Synergies2024.pdf

12:20 Estimating observation times for monitoring observations of Radio Galaxies using the Africa Millimeter Telescope

cores, provides valuable insights into supermassive black holes, galaxy evolution, and cosmic environments. The Africa Millimetre Telescope (AMT) that will be constructed in the Khomas Highlands in Namibia will be designed to add to the Event Horizon Telescope (EHT) network. With the AMT, the EHT will be able to produce colour movies of black holes, allowing us to better determine their properties, including their spin. The AMT is poised to become a significant asset in millimetre-wave astronomy in Africa. Beyond observations with the EHT, the AMT will have a single-dish science programme focused on transients, including monitoring of gamma-ray blazars. This study will be using flux density estimates from Lepto-hadronic multi-messenger models of 324 gamma-ray blazars. The source catalogue will be used to analyze the optimized AMT observational circumstances, create optimal observation times based on source positions, and establish observation periods for data acquisition. This study aims to contribute to the performance of the upcoming AMT by optimising the use of telescope time, minimising the impact of atmospheric conditions to facilitate long-term monitoring of gamma-ray blazars at mm-wavelength.

Keywords: Radio galaxies, flux density, observation period, AMT

Speaker: Mrs Sigrid Shilunga (University of Namibia)

12:40 Measuring the cosmic radio dipole with the MeerKAT Absorption Line Survey

We present the second data release of the MeerKAT Absorption Line Survey (MALS), consisting of wideband continuum catalogues of 391 pointings observed by MALS at L band. The full wideband catalogue covers 4344 deg$^2$ of sky with a depth down to $10\ \mu \mathrm{Jy\ beam}^{-1}$, and contains 971,980 sources. With its balance between survey depth and sky coverage, MALS DR2 covers five orders of magnitude of flux density, presenting a robust view of the extragalactic radio source population down to $200\ \mu$Jy. Using this catalogue, we perform a measurement of the cosmic radio dipole, an anisotropy in the number counts of radio sources with respect to the cosmic background, analogous to the dipole found in the cosmic microwave background. We present the characterisation of completeness and noise properties of the catalogue, as well as novel dipole estimators developed for this measurement. We discuss the challenges that came along with a measurement of the dipole on MALS in the form of some persistent systematics. We discuss some of these systematic effects present in the MeerKAT data and their possible causes, and how these could be addressed for MALS and other surveys that aim to do large scale cosmology.

Speaker: Dr Jonah Wagenveld (Max Planck Institute for Radio Astronomy)

SNTASA talk-1.pdf

13:00 → 14:00 Lunch

14:00 → 15:00 Breakout Sessions

15:00 → 15:35 Coffee Break

15:35 → 17:00 Breakout Sessions

17:00 → 21:00 Workshop Dinner

Friday 2 August

10:00 → 10:30 Extragalactic

10:00 Magnetic reconnection driven particle acceleration to understand the non-thermal emission in galaxy clusters

From observations, we see non-thermal radio emission with emissivity ranging from 1 to 3, extended over a large region (∼ megaparsec) in galaxy clusters, which contain largely collisionless plasma. To explain this, the electrons should be energized or accelerated. One explanation is that the energy released during a merger event could be channeled to accelerate electrons through turbulence or shock. However, the efficiency of these mechanisms are very low.

We, therefore, will look for another particle acceleration mechanism: magnetic reconnection in collisionless plasma. Reconnection sites form naturally due to fluctuation dynamo operating in the intra-cluster medium (ICM), producing strong magnetic fields that reverse on short length scales. The plasma in the ICM being non-relativistic (temperature ∼ 10^8 K ), we aim to explore particle acceleration due to reconnection using PIC simulation for non-relativistic, electron-positron plasma. We use the publicly available PIC code WarpX for that.

Driven by the tearing instability, magnetic reconnection begins by giving rise to magnetic islands and x-points, where the inductive electric field gets generated and accelerate the particles. Thus, magnetic energy gets converted to particles’ kinetic energy. As reconnection proceeds, secondary current sheets appear and they give rise to plasmoids, which grow in size, coalesce to form one big island and eventually shuts down the reconnection. In the due process, the particles, which were thermal initially, end up having a non-thermal distribution with a power law index ~-4, which explains the observed radio emission in galaxy clusters.

Speaker: Subham Ghosh (International Centre for Theoretical Sciences)

10:30 → 11:00 Coffee Break

11:00 → 12:30 Breakout Sessions

12:30 → 13:00 Breakout Sessions

13:00 → 14:00 Lunch

14:00 → 15:00 Future Prospects

15:00 → 15:30 Coffee Break