Managing Research Data in Big Science

The project which led to this report was funded by JISC in 2010--2011 as part of its 'Managing Research Data' programme, to examine the way in which Big Science data is managed, and produce any recommendations which may be appropriate. Big science data is different: it comes in large volumes, and it is shared and exploited in ways which may differ from other disciplines. This project has explored these differences using as a case-study Gravitational Wave data generated by the LSC, and has produced recommendations intended to be useful variously to JISC, the funding council (STFC) and the LSC community. In Sect. 1 we define what we mean by 'big science', describe the overall data culture there, laying stress on how it necessarily or contingently differs from other disciplines. In Sect. 2 we discuss the benefits of a formal data-preservation strategy, and the cases for open data and for well-preserved data that follow from that. This leads to our recommendations that, in essence, funders should adopt rather light-touch prescriptions regarding data preservation planning: normal data management practice, in the areas under study, corresponds to notably good practice in most other areas, so that the only change we suggest is to make this planning more formal, which makes it more easily auditable, and more amenable to constructive criticism. In Sect. 3 we briefly discuss the LIGO data management plan, and pull together whatever information is available on the estimation of digital preservation costs. The report is informed, throughout, by the OAIS reference model for an open archive

Towards a uniform evaluation of the science quality of SKA technology options: Polarimetrie aspects

We discuss how to evaluate SKA technology options with regard to science output quality. In this work we will focus on polarimetry. We review the SKA specification for polarimetry and assess these requirements. In particular we will use as a illustrative case study a comparison of two dish types combined with two different feeds. The dish types we consider are optimized axi-symmetric prime-focus and offset Gregorian reflector systems; and the two feeds are the Eleven-feed (wideband) and a choked horn (octave band). To evaluate the imaging performance we employ end-to-end simulations in which given sky models are, in software, passed through a model of the telescope design according to its corresponding radio interferometrical measurement equation to produce simulated visibilities. The simulated visibilities are then used to generate simulated sky images. These simulated sky images are then compared to the input sky models and various figures-of-merit for the imaging performance are computed. A difficulty is the vast parameter space for observing modes and configurations that exists even when the technology is fixed. However one can fixed certain standard benchmark observation modes that can be applied across the board to the various technology options. The importance of standardized, end-to-end simulations, such as the one presented here, is that they address the high-level science output from SKA as a whole rather than low-level specifications of its individual parts

A Compact Dual-Polarized 4-Port Eleven Feed with High Sensitivity for Reflectors over 0.35-1.05 GHz

We present significant improvements to the circular Eleven feed technology for a dual-reflector system operating over 0.35-1.05 GHz as a backup for the square kilometer array (SKA) project Band 1. In this work, the number of the feed ports is reduced to 4 from the previous 8 for dual polarization using a novel geometry at the center. The design is carried out by optimizing with a social civilization algorithm. The resulting improvements include a reflection coefficient below -12dB, an aperture efficiency above 70% at the upper end of the band, a maximum cross-polar level under -15dB, and an ohmic loss about 0.05 dB. A prototype based on this design has been manufactured and the design simulations have been verified against measurements. A simulated sensitivity of the dual-reflector receiver system for the SKA project based on the measured data is also presented in this communication

Sensitivity simulation and measurement of the SKA Band 1 wideband feed package on MeerKAT

Advances in wideband feed technology for radio telescopes enable high sensitivity observations over large bandwidths. The wideband quad-ridge flared horn (QRFH) feed package for Band 1 of the Square Kilometre Array (SKA) was optimized for high sensitivity. The 3:1 feed package covers 350-1050 MHz and is a complete room temperature system with low-noise amplifiers integrated inside the ridges of the horn. The QRFH is dual-linear polarized and designed with spline-defined profiles for the horn and ridge shape. Measured feed s-parameters show input reflection less than -11 dB across the band with good port isolation. In this paper we present the first measured sensitivity levels of the Band 1 feed package, which was tested on the SKA precursor reflector MeerKAT. We also present measured aperture efficiency and intrinsic cross-polarization (IXR). The measured results show good agreement with simulations

A Simultaneous Dual-site Technosignature Search Using International LOFAR Stations

The Search for Extraterrestrial Intelligence aims to find evidence of technosignatures, which can point toward the possible existence of technologically advanced extraterrestrial life. Radio signals similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at 110-190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations took place simultaneously with two international stations (noninterferometric) of the Low Frequency Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrowband transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 10 17 W, for 0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multisite simultaneous observations for rejecting anthropogenic signals in the search for technosignatures.Comment: 15 Pages, 16 Figures, 2 Machine Readable Table

The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries

The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119-151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles, radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries have on average steeper radio spectra and longer spin periods (1.4 7), as well as lower spin-down rates (3.1 7) compared to the known pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra

New definition for dual-polarized antenna sensitivity

Sensitivity is arguably the single most important defining characteristic of a radio telescope. This is because it sets the threshold for what sources can reasonably be detected. Intuitively, sensitivity is the noise level of an antenna referenced to measurements on the sky. So the lower it is, the easier one would expect to make detections of weak sources, and from this it would make sense to call it loosely the \u27detection power\u27 of telescopes. But this sensitivity concept does not take into account the polarization of the source or the polarization of the antenna itself, and could thus lead to problems. The traditionally used definition of sensitivity is namely based on single antennas. This antenna based sensitivity is derived assuming that the two polarized antennas that make up radio polarimeters are orthogonal and have identical amplitude gains. In practice these dual-polarized antennas will have different gains and exhibit polarization leakage due to nonorthogonality. To address these more realistic dual-polarized antennas, I introduce a new definition of dual-polarized (or full-polarization) antenna sensitivity. This new definition of sensitivity is a polarimetric generalization of the scalar, system equivalent flux density (SEFD). The new definition generalizes the total sensitivity, and also provides a quantity that represents sensitivity to purely polarized flux. Based on the new SEFD definition, I find that the intuitive notion that identical and orthogonal antennas should typically have better sensitivity than dissimilar, leaky antennas