Low-frequency Radio Absorption in Tycho’s Supernova Remnant

Arias, María Laura; Vink, Jacco; Zhou, Ping; Gasperin, F. de; Hardcastle, M. J.; Shimwell, T. W.

doi:10.3847/1538-3881/ab4f80

Cited by 25 publications

(55 citation statements)

References 58 publications

(89 reference statements)

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“…Heesen et al 2018), properties of supernova remnants and the interstellar medium through absorption (e.g. Arias et al 2018) and radio-recombination lines (e.g. Emig et al 2019), and possibly the characterisation of new classes of astronomical objects.…”

Section: Discussionmentioning

confidence: 99%

Reaching thermal noise at ultra-low radio frequencies

Gasperin

Brunetti

Brüggen

et al. 2020

A&A

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Context. Ultra-low frequency observations (< 100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature and because of ionospheric disturbances whose effects are inversely proportional to the observing frequency. Nonetheless, these observations are crucial for studying the emission from low-energy populations of cosmic rays. Aims. We aim to obtain the first thermal-noise limited (∼1.5 mJy beam−1) deep continuum radio map using the Low Frequency Array’s Low Band Antenna (LOFAR LBA) system. Our demonstration observation targeted the galaxy cluster RX J0603.3+4214 (known as the Toothbrush cluster). We used the resulting ultra-low frequency (39–78 MHz) image to study cosmic-ray acceleration and evolution in the post shock region considering the presence of a radio halo. Methods. We describe the data reduction we used to calibrate LOFAR LBA observations. The resulting image was combined with observations at higher frequencies (LOFAR 150 MHz and VLA 1500 MHz) to extract spectral information. Results. We obtained the first thermal-noise limited image from an observation carried out with the LOFAR LBA system using all Dutch stations at a central frequency of 58 MHz. With eight hours of data, we reached an rms noise of 1.3 mJy beam−1 at a resolution of 18″ × 11″. Conclusions. The procedure we developed is an important step towards routine high-fidelity imaging with the LOFAR LBA. The analysis of the radio spectra shows that the radio relic extends to distances of 800 kpc downstream from the shock front, larger than what is allowed by electron cooling time. Furthermore, the shock wave started accelerating electrons already at a projected distance of < 300 kpc from the crossing point of the two clusters. These results may be explained by electrons being re-accelerated downstream by background turbulence, possibly combined with projection effects with respect to the radio halo.

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Section: Discussionmentioning

confidence: 99%

Reaching thermal noise at ultra-low radio frequencies

Gasperin

Brunetti

Brüggen

et al. 2020

A&A

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“…The combination of LoLSS and LoTSS data will be important in identifying emission from Hii regions whose morphology is similar to that of SNRs, whilst having a flatter spectrum. Additionally, LoLSS data will enable the measure the low-frequency spectral curvature of supernova remnants as a diagnostic of shock acceleration and the foreground free-free absorption (Arias et al 2018).…”

Section: The Milky Waymentioning

confidence: 99%

The LOFAR LBA Sky Survey

Gasperin

Williams

Best

et al. 2021

A&A

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Context. The LOw Frequency ARray (LOFAR) is the only radio telescope that is presently capable of high-sensitivity, high-resolution (i.e. < 1 mJy beam −1 and < 15) observations at ultra-low frequencies (< 100 MHz). To utilise these capabilities, the LOFAR Surveys Key Science Project is undertaking a large survey to cover the entire northern sky with Low Band Antenna (LBA) observations. Aims. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire northern sky with 3170 pointings in the frequency range between 42 − 66 MHz, at a resolution of 15 and at a sensitivity of 1 mJy beam −1 (1σ). In this work, we outline the survey strategy, the observational status, and the calibration techniques. We also briefly describe several of our scientific motivations and present the preliminary public data release. Methods. The preliminary images were produced using a fully automated pipeline aimed at correcting all direction-independent effects in the data. Whilst the direction-dependent effects, such as those from the ionosphere, have not yet been corrected, the images presented in this work are still ten times more sensitive than previous available surveys at these low frequencies. Results. The preliminary data release covers 740 deg 2 around the HETDEX spring field region at an angular resolution of 47 with a median noise level of 5 mJy beam −1. The images and the catalogue of 25,247 sources have been publicly released. We demonstrate that the system is capable of reaching a root mean square (rms) noise of 1 mJy beam −1 and an angular resolution of 15 once directiondependent effects are accounted for. Conclusions. LoLSS will provide the ultra-low-frequency information for hundreds of thousands of radio sources, providing critical spectral information and producing a unique data set that can be used for a wide range of science topics, such as the search for high redshift galaxies and quasars, the study of the magnetosphere of exoplanets, and the detection of the oldest populations of cosmic-rays in galaxies, clusters of galaxies, as well as those produced by active galactic nuclei (AGN).

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“…To date, with this approach, the LOFAR surveys have facilitated numerous scientific studies 1 in core areas of radio astronomy such as the physics of active galactic nuclei, particle acceleration in galaxy clusters, large scale structure and star formation. Furthermore, the breadth of scientific studies continues to expand to include topics ranging from cosmological studies (Siewert et al 2020) through to pulsars (Tan et al 2018), supernovae remnants (Arias et al 2019) and even exoplanets (Vedantham et al 2020). Meanwhile, valuable synergies are being established such as those with the LOFAR Magnetism Key Science Project 2 , APERTIF imaging surveys, Extended Baryon Oscillation Spectroscopic Survey (eBOSS; Dawson et al 2016), extended ROentgen Survey with an Imaging Telescope Array (eROSITA; Predehl et al 2021) and the William Herschel Telescope Enhanced Area Velocity Explorer survey of LOFAR selected sources (WEAVE-LOFAR; Smith et al 2016) which are each enabling new scientific studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

The LOFAR Two-metre Sky Survey

Shimwell

Hardcastle

Tasse

et al. 2022

A&A

239

108

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In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) we present 120-168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44 • 30 and 1h00m +28 • 00 and spanning 4178 and 1457 square degrees respectively. The images were derived from 3,451 hrs (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4,396,228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6 resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 µJy/beam; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2 ; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy/beam. By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of > ±0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20 resolution 120-168 MHz continuum images have a median rms sensitivity of 95 µJy/beam, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480 × 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy/beam at 4 and 2.2 mJy/beam at 20 ; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data to facilitate the thorough scientific exploitation of this unique dataset.

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Low-frequency Radio Absorption in Tycho’s Supernova Remnant

Cited by 25 publications

References 58 publications

Reaching thermal noise at ultra-low radio frequencies

Reaching thermal noise at ultra-low radio frequencies

The LOFAR LBA Sky Survey

The LOFAR Two-metre Sky Survey

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