14 research outputs found
A cosmic microscope to probe the Universe from Present to Cosmic Dawn - dual-element low-frequency space VLBI observatory
A space-based very long baseline interferometry (VLBI) programme, named as
the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space
working together with giant ground-based telescopes (e.g., Square Kilometre
Array, FAST, Arecibo) to image the low radio frequency Universe with the
purpose of unraveling the compact structure of cosmic constituents including
supermassive black holes and binaries, pulsars, astronomical masers and the
underlying source, and exoplanets amongst others. The operational frequency
bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission
plans to launch two 30-m-diameter radio telescopes into 2,000 km x 90,000 km
elliptical orbits. The two telescopes can work in flexibly diverse modes: (i)
space-ground VLBI. The maximum space-ground baseline length is about 100,000
km; it provides a high-dynamic-range imaging capacity with unprecedented high
resolutions at low frequencies (0.4 mas at 1.67 GHz and 20 mas at 30 MHz)
enabling studies of exoplanets and supermassive black hole binaries (which emit
nanoHz gravitational waves); (ii) space-space single-baseline VLBI. This unique
baseline enables the detection of flaring hydroxyl masers, and more precise
position measurement of pulsars and radio transients at milli-arcsecond level;
(iii) single dish mode, where each telescope can be used to monitor transient
bursts and rapidly trigger follow-up VLBI observations. The large space
telescope will also contribute in measuring and constraining the total angular
power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope
offers astronomers the opportunity to conduct novel, frontier science.Comment: Accepted for publication in Chinese Journal of Space Science, 10
pages, 2 figure
Radio Sources Segmentation and Classification with Deep Learning
Modern large radio continuum surveys have high sensitivity and resolution,
and can resolve previously undetected extended and diffuse emissions, which
brings great challenges for the detection and morphological classification of
extended sources. We present HeTu-v2, a deep learning-based source detector
that uses the combined networks of Mask Region-based Convolutional Neural
Networks (Mask R-CNN) and a Transformer block to achieve high-quality radio
sources segmentation and classification. The sources are classified into 5
categories: Compact or point-like sources (CS), Fanaroff-Riley Type I (FRI),
Fanaroff-Riley Type II (FRII), Head-Tail (HT), and Core-Jet (CJ) sources.
HeTu-v2 has been trained and validated with the data from the Faint Images of
the Radio Sky at Twenty-one centimeters (FIRST). We found that HeTu-v2 has a
high accuracy with a mean average precision () of 77.8%,
which is 15.6 points and 11.3 points higher than that of HeTu-v1 and the
original Mask R-CNN respectively. We produced a FIRST morphological catalog
(FIRST-HeTu) using HeTu-v2, which contains 835,435 sources and achieves 98.6%
of completeness and up to 98.5% of accuracy compared to the latest 2014 data
release of the FIRST survey. HeTu-v2 could also be employed for other
astronomical tasks like building sky models, associating radio components, and
classifying radio galaxies
Status and progress of China SKA Regional Centre prototype
The Square Kilometre Array (SKA) project consists of delivering two largest
radio telescope arrays being built by the SKA Observatory (SKAO), which is an
intergovernmental organization bringing together nations from around the world
with China being one of the major member countries. The computing resources
needed to process, distribute, curate and use the vast amount of data that will
be generated by the SKA telescopes are too large for the SKAO to manage on its
own. To address this challenge, the SKAO is working with the international
community to create a shared, distributed data, computing and networking
capability called the SKA Regional Centre Alliance. In this model, the SKAO
will be supported by a global network of SKA Regional Centres (SRCs)
distributed around the world in its member countries to build an end-to-end
science data system that will provide astronomers with high-quality science
products. SRCs undertake deep processing, scientific analysis, and long-term
storage of the SKA data, as well as user support. China has been actively
participating in and promoting the construction of SRCs. This paper introduces
the international cooperation and ongoing prototyping of the global SRC
network, the construction plan of the China SRC and describes in detail the
China SRC prototype. The paper also presents examples of scientific
applications of SKA precursor and pathfinder telescopes completed using
resources from the China SRC prototype. Finally, the future prospects of the
China SRC are presented.Comment: T. An, et al. Status and progress of China SKA Regional Centre
prototype. Sci. China-Phys. Mech. Astron. 65: 129501 (2022
DALiuGE: A Graph Execution Framework for Harnessing the Astronomical Data Deluge
The Data Activated Liu Graph Engine - DALiuGE - is an execution framework for
processing large astronomical datasets at a scale required by the Square
Kilometre Array Phase 1 (SKA1). It includes an interface for expressing complex
data reduction pipelines consisting of both data sets and algorithmic
components and an implementation run-time to execute such pipelines on
distributed resources. By mapping the logical view of a pipeline to its
physical realisation, DALiuGE separates the concerns of multiple stakeholders,
allowing them to collectively optimise large-scale data processing solutions in
a coherent manner. The execution in DALiuGE is data-activated, where each
individual data item autonomously triggers the processing on itself. Such
decentralisation also makes the execution framework very scalable and flexible,
supporting pipeline sizes ranging from less than ten tasks running on a laptop
to tens of millions of concurrent tasks on the second fastest supercomputer in
the world. DALiuGE has been used in production for reducing interferometry data
sets from the Karl E. Jansky Very Large Array and the Mingantu Ultrawide
Spectral Radioheliograph; and is being developed as the execution framework
prototype for the Science Data Processor (SDP) consortium of the Square
Kilometre Array (SKA) telescope. This paper presents a technical overview of
DALiuGE and discusses case studies from the CHILES and MUSER projects that use
DALiuGE to execute production pipelines. In a companion paper, we provide
in-depth analysis of DALiuGE's scalability to very large numbers of tasks on
two supercomputing facilities.Comment: 31 pages, 12 figures, currently under review by Astronomy and
Computin
Radio Variable and Transient Sources on Minute Timescales in the ASKAP Pilot Surveys
We present results from a radio survey for variable and transient sources on
15-min timescales, using the Australian SKA Pathfinder (ASKAP) pilot surveys.
The pilot surveys consist of 505 h of observations conducted at around 1 GHz
observing frequency, with a total sky coverage of 1476 deg. Each
observation was tracked for approximately 8-10h, with a typical rms sensitivity
of 30 jy/beam and an angular resolution of 12 arcsec. The
variability search was conducted within each 8-10h observation on a 15-min
timescale. We detected 38 variable and transient sources. Seven of them are
known pulsars, including an eclipsing millisecond pulsar, PSR J20395617.
Another eight sources are stars, only one of which has been previously
identified as a radio star. For the remaining 23 objects, 22 are associated
with active galactic nuclei or galaxies (including the five intra-hour
variables that have been reported previously), and their variations are caused
by discrete, local plasma screens. The remaining source has no multi-wavelength
counterparts and is therefore yet to be identified. This is the first
large-scale radio survey for variables and transient sources on minute
timescales at a sub-mJy sensitivity level. We expect to discover 1 highly
variable source per day using the same technique on the full ASKAP surveys.Comment: 20 pages, 11 figures; accepted for publication in MNRA
Interactions between the jet and disk wind in a nearby radio intermediate quasar III Zw 2
Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how
these two components interact remains an open question. We study the radio
properties of a radio-intermediate quasar III Zw 2. We detect two jet knots J1
and J2 on parsec scales, which move at a mildly apparent superluminal speed of
. Two -ray flares were detected in III Zw 2 in 2009--2010,
corresponding to the primary radio flare in late 2009 and the secondary radio
flare in early 2010. The primary 2009 flare was found to be associated with the
ejection of J2. The secondary 2010 flare occurred at a distance of 0.3
parsec from the central engine, probably resulting from the collision of the
jet with the accretion disk wind. The variability characteristics of III Zw 2
(periodic radio flares, unstable periodicity, multiple quasi-periodic signals
and possible harmonic relations between them) can be explained by the global
instabilities of the accretion disk. These instabilities originating from the
outer part of the warped disk propagate inwards and can lead to modulation of
the accretion rate and consequent jet ejection. At the same time, the wobbling
of the outer disk may also lead to oscillations of the boundary between the
disk wind and the jet tunnel, resulting in changes in the jet-wind collision
site. III Zw 2 is one of the few cases observed with jet-wind interactions, and
the study in this paper is of general interest for gaining insight into the
dynamic processes in the nuclear regions of AGN.Comment: accepted by Ap