Post-correlation RFI detection

Offringa, A. R.; Bruyn, de Antonius; Zaroubi, Saleem; Biehl, Michael

doi:10.22323/1.107.0036

Cited by 121 publications

(169 citation statements)

References 15 publications

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“…To summarize, the data were calibrated for the antenna position offsets, elevation dependent gains, global delay, cross-hand delay, bandpass, polarization leakage and angles, and temporal gain variations using the primary and secondary calibrator sources. RFI was identified and flagged with the AOFlagger (Offringa et al 2010). The calibration solutions from the primary and secondary calibrator sources were applied to the target field and several rounds of self-calibration were carried out to refine the gain solutions.…”

Section: Jvla Observationsmentioning

confidence: 99%

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

Weeren

Ogrean

Jones

et al. 2017

ApJ

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To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandraobservations of the HST Frontier Fields cluster MACSJ0717.5+3745. The Chandraimage shows a complex merger event, with at least four components belonging to different merging subclusters. Northwestof the cluster, ∼0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. We detect a density discontinuity north-northeastof this core, which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100-300kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleuslead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for reacceleration (revival) of fossil electrons. The presence of hot 20 keV ICM gas detected by Chandranear the relic location provides additional support for this re-acceleration scenario.

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Section: Jvla Observationsmentioning

confidence: 99%

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

Weeren

Ogrean

Jones

et al. 2017

ApJ

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“…Flagging for RFI is performed in a standard and automatic fashion using the AOFlagger (Offringa et al 2010). This program has been shown to provide excellent RFI excision with minimal false positives.…”

Section: Pre-processing Stepsmentioning

confidence: 99%

“…This program has been shown to provide excellent RFI excision with minimal false positives. Details of the typical performance of the implemented algorithm on LOFAR data, along with representative RFI statistics, are presented by Offringa et al (2013).…”

Section: Pre-processing Stepsmentioning

confidence: 99%

The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

Heald

Pizzo

Orrù

et al. 2015

A&A

105

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We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky Low Frequency Array (LOFAR) imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR's multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the MSSS Verification Field (MVF), a region of 100 square degrees centered at (α, δ) J2000 = (15 h , 69 • ). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108 resolution, and 550 mJy at 50 MHz with 166 resolution. Images and catalogs for the full survey, expected to contain 150 000-200 000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.

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“…Because of the major increase in resolution and bandwidth of observatories, leading to observations of tens of terabytes, manual data flagging is no longer feasible. Automated RFI flagging pipelines can solve this problem (Flöer et al 2010;Offringa et al 2010b). Alternative RFI strategies might be required for the detection of transients (Ryabov et al 2004;Kocz et al 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, new algorithms and a pipeline have been implemented to automatically detect RFI with a high accuracy (Offringa et al 2010a,b). Preliminary results have shown that by using these algorithms, only a few percent of the data is lost due to RFI (Offringa et al 2010b).…”

Section: Introductionmentioning

confidence: 99%

The LOFAR radio environment

Offringa

Bruyn

Zaroubi

et al. 2012

A&A

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Aims. This paper discusses the spectral occupancy for performing radio astronomy with the Low-Frequency Array (LOFAR), with a focus on imaging observations. Methods. We have analysed the radio-frequency interference (RFI) situation in two 24-h surveys with Dutch LOFAR stations, covering 30−78 MHz with low-band antennas and 115-163 MHz with high-band antennas. This is a subset of the full frequency range of LOFAR. The surveys have been observed with a 0.76 kHz/1 s resolution. Results. We measured the RFI occupancy in the low and high frequency sets to be 1.8% and 3.2% respectively. These values are found to be representative values for the LOFAR radio environment. Between day and night, there is no significant difference in the radio environment. We find that lowering the current observational time and frequency resolutions of LOFAR results in a slight loss of flagging accuracy. At LOFAR's nominal resolution of 0.76 kHz and 1 s, the false-positives rate is about 0.5%. This rate increases approximately linearly when decreasing the data frequency resolution. Conclusions. Currently, by using an automated RFI detection strategy, the LOFAR radio environment poses no perceivable problems for sensitive observing. It remains to be seen if this is still true for very deep observations that integrate over tens of nights, but the situation looks promising. Reasons for the low impact of RFI are the high spectral and time resolution of LOFAR; accurate detection methods; strong filters and high receiver linearity; and the proximity of the antennas to the ground. We discuss some strategies that can be used once low-level RFI starts to become apparent. It is important that the frequency range of LOFAR remains free of broadband interference, such as DAB stations and windmills.

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Post-correlation RFI detection

Cited by 121 publications

References 15 publications

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

The LOFAR radio environment

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