Using baseline-dependent window functions for data compression and field-of-interest shaping in radio interferometry

In radio interferometry, observed visibilities are intrinsically sampled at some interval in time and frequency. Modern interferometers are capable of producing data at very high time and frequency resolution; practical limits on storage and computation costs require that some form of data compression be imposed. The traditional form of compression is a simple averaging of the visibilities over coarser time and frequency bins. This has an undesired side effect: the resulting averaged visibilities "decorrelate", and do so differently depending on the baseline length and averaging interval. This translates into a non-trivial signature in the image domain known as "smearing", which manifests itself as an attenuation in amplitude towards off-centre sources. With the increasing fields of view and/or longer baselines employed in modern and future instruments, the trade-off between data rate and smearing becomes increasingly unfavourable. In this work we investigate alternative approaches to low-loss data compression. We show that averaging of the visibility data can be treated as a form of convolution by a boxcar-like window function, and that by employing alternative baseline-dependent window functions a more optimal interferometer smearing response may be induced. In particular, we show improved amplitude response over a chosen field of interest, and better attenuation of sources outside the field of interest. The main cost of this technique is a reduction in nominal sensitivity; we investigate the smearing vs. sensitivity trade-off, and show that in certain regimes a favourable compromise can be achieved. We show the application of this technique to simulated data from the Karl G. Jansky Very Large Array (VLA) and the European Very-long-baseline interferometry Network (EVN)

Konsentrasi Asam Lemak Tidak Teresterifikasi (Nonesterified Fatty Acid, NEFA), Albumin, Kalsium Dan Fosfor Dalam Plasma Sebagai Indikator Status Nutrisi Sapi Perah Laktasi

Tujuan penelitian ini adalah untuk mengetahui status gizi sapi perah laktasi didasarkan pada konsentrasi NEFA (nonesterified Asam Lemak), albumin, kalsium, dan fosfor dalam plasma. Tiga puluh dua sapi perah kepala di periode menyusui kedua digunakan untuk up mengambil plasma darah. Uji t dan regresi sama digunakan untuk berbagai penentu dari konsentrasi. Hasil pengamatan yang berarti dan berbagai konsentrasi NEFA 0.17 mEq.L-1 dan 0,11-0,22 mEq.L-1, albumin 2.69 g% dan 2,51-2,87 g%. Kemudian, mean dan berbagai konsentrasi kalsium plasma 9.39 mg% dan 8,90-9,88 mg%, 8.60 dan 8,10-9,10 mg% dari konsentrasi fosfor plasma. Regresi sama berat plasma NEFA (Y) tubuh (X1), produksi susu (X2) adalah Y = 0,163 X1 + 0,215 X2 (R2 = 11,2%, P> 0,05). Regresi sama plasma albumin (Y), berat badan (X1), produksi susu (X2) adalah Y = 0,197 X1 + 0,006 X2 (R2 = 12,3%, P> 0,05). Regresi sama plasma kalsium (Y), berat badan (X1), produksi susu (X2) adalah Y = -0,099 X1 + 0,389 X2 (R2 = 11,9%, P> 0,05), plasma fosfor (Y), berat badan (X1 ), produksi susu (X2) adalah Y = 0.72 X1 + 0,394 X2 (R2 = 19,2%, P> 0,05). Oleh karena itu, cadangan energi (konsentrasi NEFA), kalsium dan fosfor dalam plasma yang paling persyaratan untuk peningkatan produksi susu

Untangling cosmic magnetic fields: Faraday tomography at metre wavelengths with LOFAR

14 pages, 6 figures. Accepted for publication in "The Power of Faraday Tomography" special issue of GalaxiesThe technique of Faraday tomography is a key tool for the study ofmagnetised plasmas in the new era of broadband radio-polarisation observations. In particular, observations at metre wavelengths provide significantly better Faraday depth accuracies compared to traditional centimetre-wavelength observations. However, the effect of Faraday depolarisationmakes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN (Active Galactic Nucleus). The majority of the sources (~64%) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 × 10 26 W Hz -1 (with ~13% of all sources having a linear size > 1 Mpc). In several cases, both hotspots are detected in polarisation at an angular resolution of ~20'. One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least eight blazars. Most sources display simple Faraday spectra, but we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.Peer reviewe

Performans Ayam Kampung Super Pada Pakan Yang Disubttusi Dedak Padi Fermentasi Dengan Fermentor Berbeda

Penelitian bertujuan untuk mengetahui pengaruh dedak padi fermentasi dengan fermentor berbeda terhadap performans ayam kampung super. Penelitian dilaksanakan di kandang Kelompok Permata Kota Kendari. Penelitian menggunakan Rancangan Acak Lengkap (RAL) yang terdiri dari 4 perlakuan pakan yaitu R0 = ransum kontrol tanpa dedak padi fermentasi (DP), R1 = 10% dedak padi fermentasi cairan rumen (DPFCR), R2 = 10% dedak padi fermentasi ragi tempe (DPFRTe), R3 = 10% dedak padi fermentasi ragi tape (DPFRTa), dengan 4 kali ulangan. Setiap satuan percobaan terdiri dari 5 ekor ayam kampung super. Parameter yang diukur adalah konsumsi pakan, pertambahan bobot badan, konversi pakan, bobot potong, bobot karkas dan persentase karkas. Data dianalisis dengan analysis of variance (ANOVA) sesuai dengan RAL dan bila terdapat perbedaan antar perlakuan akan dilakukan uji lanjut dengan Uji Tukey (Steel and Toriee, 1991). Hasil penelitian menunjukkan bahwa pemberian dedak padi fermentasi dengan fermentor berbeda tidak berpengaruh nyata (P>0,05) terhadap Konsumsi Pakan, PBB, Bobot Potong, Bobot Karkas dan Persentase karkas. Penggunaan dedak padi fermentasi dengan fermentor berbeda berpengaruh nyata (P<0,05) terhadap konversi ransum. Dari hasil penelitian ini, maka dedak padi fermentasi dapat digunakan 10% dalam ransum untuk mensubtitusi pakan basal.Kata kunci : Ayam Kampung Super, Dedak Padi Fermentasi, Konsumsi Pakan, Konversi Pakan

Remnant radio-loud AGN in the Herschel-ATLAS field

Only a small fraction of observed active galactic nuclei (AGN) display large-scale radio emission associated with jets, yet these radio-loud AGN have become increasingly important in models of galaxy evolution. In determining the dynamics and energetics of the radio sources over cosmic time, a key question concerns what happens when their jets switch off. The resulting ‘remnant' radio-loud AGN have been surprisingly evasive in past radio surveys, and therefore statistical information on the population of radio-loud AGN in their dying phase is limited. In this paper, with the recent developments of Low-Frequency Array (LOFAR) and the Very Large Array, we are able to provide a systematically selected sample of remnant radio-loud AGN in the Herschel-ATLAS field. Using a simple core-detection method, we constrain the upper limit on the fraction of remnants in our radio-loud AGN sample to 9 per cent, implying that the extended lobe emission fades rapidly once the core/jets turn off. We also find that our remnant sample has a wide range of spectral indices (−1.5 ⩽ α1400150 ⩽ −0.5), confirming that the lobes of some remnants may possess flat spectra at low frequencies just as active sources do. We suggest that, even with the unprecedented sensitivity of LOFAR, our sample may still only contain the youngest of the remnant population

Revived Fossil Plasma Sources in Galaxy Clusters

© 2020 ESO.It is well established that particle acceleration by shocks and turbulence in the intra-cluster medium can produce cluster-scale synchrotron emitting sources. However, the detailed physics of these particle acceleration processes is still not well understood. One of the main open questions is the role of fossil relativistic electrons that have been deposited in the intracluster medium (ICM) by radio galaxies. These synchrotron-emitting electrons are very difficult to study as their radiative lifetime is only tens of Myr at gigahertz frequencies, and they are therefore a relatively unexplored population. Despite the typical steep radio spectrum due to synchrotron losses, these fossil electrons are barely visible even at radio frequencies well below the gigahertz level. However, when a pocket of fossil radio plasma is compressed, it boosts the visibility at sub-gigahertz frequencies, creating what are known as radio phoenices. This compression can be the result of bulk motion and shocks in the ICM due to merger activity. In this paper we demonstrate the discovery potential of low-frequency radio sky surveys to find and study revived fossil plasma sources in galaxy clusters. We used the 150 MHz TIFR GMRT Sky Survey and the 1.4 GHz NVSS sky survey to identify candidate radio phoenices. A subset of three candidates was studied in detail using deep multi-band radio observations (LOFAR and GMRT), X-ray obserations (Chandra or XMM-Newton), and archival optical observations. Two of the three sources are new discoveries. Using these observations, we identified common observational properties (radio morphology, ultra-steep spectrum, X-ray luminosity, dynamical state) that will enable us to identify this class of sources more easily, and will help us to understand the physical origin of these sources.Peer reviewedFinal Accepted Versio

LOFAR early-time search for coherent radio emission from GRB 180706A

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio flare from magnetic re-connection events might be expected with the prompt gamma-ray emission. There are two competing models for the central engines of GRBs; a black hole or a newly formed milli-second magnetar. If the central engine is a magnetar it is predicted to produce coherent radio emission as persistent or flaring activity. In this paper, we present the deepest limits to date for this emission following LOFAR rapid response observations of GRB 180706A. No emission is detected to a 3$\sigma$ limit of 1.7 mJy beam$^{-1}$ at 144 MHz in a two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger. A forced source extraction at the position of GRB 180706A provides a marginally positive (1 sigma) peak flux density of $1.1 \pm 0.9$ mJy. The data were time-sliced into different sets of snapshot durations to search for FRB like emission. No short duration emission was detected at the location of the GRB. We compare these results to theoretical models and discuss the implications of a non-detection.Peer reviewedFinal Accepted Versio

The triggering probability of radio-loud AGN: A comparison of high and low excitation radio galaxies in hosts of different colors

Low luminosity radio-loud active galactic nuclei (AGN) are generally found in massive red elliptical galaxies, where they are thought to be powered through gas accretion from their surrounding hot halos in a radiatively inefficient manner. These AGN are often referred to as "low-excitation" radio galaxies (LERGs). When radio-loud AGN are found in galaxies with a young stellar population and active star formation, they are usually high-power radiatively-efficient radio AGN ("high-excitation", HERG). Using a sample of low-redshift radio galaxies identified within the Sloan Digital Sky Survey (SDSS), we determine the fraction of galaxies that host a radio-loud AGN, $f_{RL}$, as a function of host galaxy stellar mass, $M_*$, star formation rate, color (defined by the 4000 \angstrom break strength), radio luminosity and excitation state (HERG/LERG). We find the following: 1. LERGs are predominantly found in red galaxies. 2. The radio-loud AGN fraction of LERGs hosted by galaxies of any color follows a $f^{LE}_{RL} \propto M^{2.5}_*$ power law. 3. The fraction of red galaxies hosting a LERG decreases strongly for increasing radio luminosity. For massive blue galaxies this is not the case. 4. The fraction of green galaxies hosting a LERG is lower than that of either red or blue galaxies, at all radio luminosities. 5. The radio-loud AGN fraction of HERGs hosted by galaxies of any color follows a $f^{HE}_{RL} \propto M^{1.5}_*$ power law. 6. HERGs have a strong preference to be hosted by green or blue galaxies. 7. The fraction of galaxies hosting a HERG shows only a weak dependence on radio luminosity cut. 8. For both HERGs and LERGs, the hosting probability of blue galaxies shows a strong dependence on star formation rate. This is not observed in galaxies of a different color.[abridged]Comment: 7 pages, 6 figure