Characterization of the decametre sky at subarcminute resolution
arXiv:2405.05311 · doi:10.1038/s41550-024-02266-z
Abstract
The largely unexplored decameter radio band (10-30 MHz) provides a unique window for studying a range of astronomical topics, such as auroral emission from exoplanets, inefficient cosmic ray acceleration mechanisms, fossil radio plasma, and free-free absorption. The scarcity of low-frequency studies is mainly due to the severe perturbing effects of the ionosphere. Here we present a calibration strategy that can correct for the ionosphere in the decameter band. We apply this to an observation from the Low Frequency Array (LOFAR) between 16 to 30 MHz . The resulting image covers 330 square degrees of sky at a resolution of 45", reaching a sensitivity of 12 mJy/beam. Residual ionospheric effects cause additional blurring ranging between 60 to 100". This represents an order of magnitude improvement in terms of sensitivity and resolution compared to previous decameter band observations. In the region we surveyed, we have identified four fossil plasma sources. These rare sources are believed to contain old, possibly re-energised, radio plasma originating from previous outbursts of active galactic nuclei. At least three of them are situated near the center of low-mass galaxy clusters. Notably, two of these sources display the steepest radio spectral index among all the sources detected at 23 MHz. This indicates that fossil plasma sources constitute the primary population of steep-spectrum sources at these frequencies, emphasising the large discovery potential of ground-based decameter observations.
19 pages, 9 figures, 1 table. Submitted version, full version is published by Nature Astronomy
References in corpus (21)
- The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
- WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
- The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
- GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
- The LOFAR Two-metre Sky Survey -- V. Second data release
- Diffuse Radio Emission from Galaxy Clusters
- The Very Large Array Low-frequency Sky Survey Redux (VLSSr)
- LOFAR observations of galaxy clusters in HETDEX
- Coherent radio emission from a quiescent red dwarf indicative of star-planet interaction
- Gentle re-energisation of electrons in merging galaxy clusters
- The LOFAR LBA Sky Survey I. survey description and preliminary data release
- The LOFAR radio environment
- A snapshot of the oldest AGN feedback phases
- Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
- Extremely deep 150 MHz source counts from the LoTSS Deep Fields
- Revived Fossil Plasma Sources in Galaxy Clusters
- The LOFAR LBA Sky Survey II. First data release
- LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources
- The merging galaxy cluster Abell 3266 at low radio frequencies
- Pushing subarcsecond resolution imaging down to 30 MHz with the trans-European International LOFAR Telescope
- The LOFAR LBA Sky Survey: Deep Fields I. The Boötes Field