PoS(EVN2018)145 http://pos.sissa.it/ ∗ [email protected] [email protected] Speaker. MeerKAT is a South African radio interferometerthe that operation will of be the the Square most Kilometreantennas sensitive Array are in mid-frequency its configured array. class in Like until a SKA1-mid,more dense MeerKAT’s extended core spiral (driven primarily arms by toMeerKAT pulsar provide array and higher into HI angular global science), resolution VLBI asnetworks, imaging. networks well especially would as The add at inclusion significant the of sensitivityrole longest the to of baselines existing the (>7000 VLBI Hartebeesthoek km). Radioimproved Astronomy long-baseline Moreover, Observatory calibration. this (HartRAO) will in MeerKAT-VLBI willern strengthen VLBI hemisphere extend the arrays which VLBI will through coverage be expanded inMeerKAT’s further ability the by to south- the be upcoming split into African several VLBI sub-arraysand Network and tied-array (AVN). simultaneously data generate products interferometric provides thetific opportunity output. to further This increase flexibility its could highmay be commensally expected or utilized scien- independently for participate with VLBI the experimentsis AVN, EVN true where or of a Australian two LBA. or subset The more same of independent, experiments. MeerKAT-only antennas the Through tied-array a and suite interferometric of performance simulations of of MeerKAT sub-arrays,initial this results contribution from presents a project that willtential investigate optimal MeerKAT-VLBI and sub-arraying MeerKAT strategies projects. for a We range aimtechnical, of to and po- systematically processing explore trade-offs the of scientific, MeerKATis sub-array ultimately and aimed commensal at observations, maximising which theit scientific will utility participate of in. both MeerKAT and the VLBI networks ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 14th European VLBI Network Symposium &8-11 Users October Meeting 2018 (EVN 2018) Granada, Spain Roger P. Deane University of Pretoria Rhodes University E-mail: Nkululeko S. Qwabe Exploring Sub-Array Strategies for MeerKAT-VLBI South African Radio Astronomy Observatory (SARAO) University of Pretoria E-mail: PoS(EVN2018)145 1 spatial λ 40 M & Nkululeko S. Qwabe 7000 km. Figure > 10 Jy at 1.4 GHz. This would add significant . 1 parameter in Briggs weighting, Briggs, 1995). In robust increments, demonstrating the major improvement in λ Demonstration of the enhancement of the EVN by MeerKAT (reproduced from -bin in 10 M uv , we show this trade-off for an 8-hour MeerKAT observation, including the contribution 2 The over-arching objective of this project is to maximise the scientific utility of both MeerKAT 110 m single dish antenna, with an SEFD of ∼ Figure and its contribution to existing VLBIof networks. VLBI performance It by aims adding toimplication sub-arrays achieve of of this standalone MeerKAT by MeerKAT antennas, experiments. exploring and enhancement The thetypical compact resultant trade-off core between performance configuration image accentuates sensitivity the andspecified angular imaging resolution which weights is (i.e., controlled the by the user- of confusion noise. Instead of suppressing the statistical power of the vastly more numerous short frequency range with theaccounted addition for). of MeerKAT MeerKAT, sub-arrays despite could thelarge of increase course lack in make sensitivity of could scaled also full improvements be of band made with the overlap MeerKAT above. participation (which in A the is Australian LBA. Figure 1: Deane 2017). Thisformance shows towards a the XMM-LSS comparison extragalactic oftivity field per (Dec. the = VLBA, -4.8 EVN deg). and The EVN+MeerKAT plot 18 shows the cm sensi- per- sensitivity to existing VLBI networks, especially in the longest baselines of illustrates the improvement in sensitivity MeerKAT-VLBI would add to the EVN. MeerKAT sub-arrays for VLBI 1. Introduction and Motivation The dense core of the MeerKATjust array, which over spans two a thirds distance of of theextend about 64 over 1 a antennas. km distance The of in remaining 8 diameter, antennasreflector km includes are in and diameter. located a Each in 3.8 MeerKAT the antenna m spiralarray is diameter will arms composed sub-reflector be of that equipped in a with an 13.5 UHF m Offset (5803500 main Gregorian - MHz) 1015 optical receivers; MHz), and layout. L-band potentially (900 X-band The - (8its MeerKAT 1670 - MHz), high 14.5 and sensitivity GHz), S-band and if (1750 geographic funding - for location,networks these the could is inclusion secured. provide of Given the significant MeerKAT improvementswith array current in into networks global their not VLBI scientific being complete. output,a A despite phased-up band MeerKAT would overlap have an effective area of PoS(EVN2018)145 , is 2 c σ + ) vary as 2 e t We empha- σ σ p shows level of weight parame- 2 ) (assuming 10 = c e σ Nkululeko S. Qwabe σ robust 5), one can conceivably achieve com- . 0 − . ), the confusion noise, ( t σ 2 parameters ( robust parameters < 0 and it increases sharply for values > 0. image weighting parameter. The effective noise, robust robust 1 km) through low A plot of how the thermal noise ( . experiments Figure 2: mostly uniform for the thermal noise, the confusion noise,ters. and effective noise with different beams/source and source counts from Bonaldi et al., 2019) and the effective noise ( MeerKAT sub-arrays for VLBI baselines ( function of the While SARAO will decide the policy,ations capabilities, in and the priority future, of potential we(1) MeerKAT-VLBI can oper- envision dedicated three MeerKAT-VLBI experiments potential "primary withinmensal MeerKAT-VLBI observing the VLBI modes": Open with approved Time Large proposal SurveyOpen Projects allocation; (LSPs, Time (2) e.g. projects com- MIGHTEE, with LADUMA)sub-arraying pre-coordination and in other between Open the Time with relevantobserving the principal modes same is investigators; required the main and pre-coordination. focus (3) (and of The this commensal) third study. of MeerKAT-VLBI, In it these order to is potential quantify illustrate the necessary the effect potential to of for removing develop sub-arraying specific antennas appropriate from tools the MeerKAT to array. Figure visualize and parable performance through the removalexperiment’s a imaging few weights antennas appropriately. in Similarly, theperiment one core could in and conceive Open adjusting of Time the a thatbeamforming MeerKAT pulsar processing discards search load. ex- a If subset either ofjectives of (or these the a cases outermost has favourable antennas a impact totion, negligible on impact the reduce processing removed on considerations) the antennas the of could real-time scientific be the ob- be used relevant used in to MeerKAT observa- an participate in independent a MeerKAT experiment VLBIsize or experiment here with, that alternatively for this example, is the not AVN,point approved EVN SARAO in or policy/priority, time. LBA. but rather an exploratory exercise at this 2. Quantifying the impact of sub-arraying for MeerKAT and MeerKAT-VLBI PoS(EVN2018)145 Right: Nkululeko S. Qwabe 3 shows heat maps of the effective noise and PSF size as a function 4 The MeerKAT projected baseline length distribution for a 8-hour track of a source imaging parameter for 64 hypothetical sub-arrays of MeerKAT. Each sub-array has Left: illustrates the antenna configuration in terms of baseline lengths (towards Dec = -30 deg, 8- 3 robust One of the ways that we can visualize the effect of removing certain antennas from the of the MeerKAT array is to plot thetracting effective those noise antennas. and Figure PSF sizes of the sub-arrays that resultall from antennas sub- included except forare that sorted one by indicated their distance on from thewith the y-axis array antennas tick core. removed label. Antennas from towards the The theouter top core, y-axis antenna. correspond tick while to This labels the sub-arrays assumes bottoms an correspond 8-hour to L-band observation the of sub-arrays a without source an at Declination = -30 deg. Figure 3: MeerKAT antenna distances from the array centre.which The spans majority about of 1.2 the antennas km are from within the the array core centre. with Dec = -30 deg. The firstsituated. peak represents the The core-core second baselines where smaller most peak of the represents antennas baseline are lengths for "core-outlier" baselines hour observation) and antenna distance from core, which could be used to guide sub-array selection. MeerKAT sub-arrays for VLBI 3. Sub-Arraying Strategies In order to systematically explore differentinto sub-arraying sub-arrays strategies, using we several will different seek approaches.distances to from split The the MeerKAT most array simple core, which isFigure is selecting what antennas we by illustrate their at this point, the very start of this project. PoS(EVN2018)145 shows robust robust parameters Nkululeko S. Qwabe Left panel: robust parameter. parameter. We exclude robust robust 4 shows the PSF size (color-scale) for Right panel: ). 2 Effective noise and PSF size as a function of the I would like to acknowledge the funding from SARAO and the time they have allowed for 7 (6.8 - 8.4) arcsec for all sub-arrays for robust weight parameters less than 0.1. This serves 4. Conclusion This new era of flexible backendspresents and opportunities interferometers for comprised intelligent of sub-arraying large strategies numbersof that of these can antennas highly increase over-subscribed the telescopes. scientific Inrequire yield order quantification to of find the optimal relevant sub-arraying parameters,contribution, strategies, which we we is present the an primary initial focus effort ofMeerKAT-VLBI opportunities toward this as that project. a goal In possible for this beneficiary. MeerKAT, with Amethods potential more will complete be analysis directly with applicable these tosuch current as and the future SKA1-mid cm-wave and and ALMA. mm-wavenot This interferometers all is antennas particularly would true have of the arrays full such suite as of SKA1-mid receiver where bands installed. Acknowledgments me to further my studies.Deane for A the great guidance appreciation and topatience extra the and effort contribution love of to of my my geteven lovely supervisor the though wife Prof. project it Mrs takes to Malebo Roger time where Qwabe away it from for our supporting is. family. me Thank I in you. also pursuing my acknowledge MSc. the the Effective noise (color-scale) as a function of the for the same region covered on∼ the left plot. The PSFto size illustrate remains at that an removing averagenegligible of a effect approximately single for certain antenna science from cases, if the the 64 imaging weights MeerKAT are array appropriately can adjusted. potentially have a Figure 4: MeerKAT sub-arrays for VLBI parameters above 0.1 because the effective noisethe increases increase dramatically above in this confusion value, driven noiseparameters by (see at Figure the lower angular resolution that results from higher PoS(EVN2018)145 Nkululeko S. Qwabe 5 Mexico Institute of Mining and Technology, Socorro, New Mexico. 482, 2 Pathway to the SKA. Stellenbosch, South Africa: Proceedings of Science. MeerKAT sub-arrays for VLBI References [1] Briggs, D. (1995). High Fidelity Deconvolution of Moderately Resolved Sources. Ph.D. The[2] New Bonaldi et al.(2019). 2019MNRAS.482....2B Bonaldi, A., Bonato, M., Galluzzi, V., et al.[3] 2019, mnras, Deane, R. (2016). Extragalctic VLBI surveys in the MeerKAT era. In: MeerKAT Science: On the