The spectacular cluster chain Abell 781 as observed with LOFAR, GMRT, and XMM-Newton

Abstract Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

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Diffuse radio emission in the galaxy cluster SPT-CL J2031−4037: a steep-spectrum intermediate radio halo?

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa002 ◽

2020 ◽

Vol 493 (1) ◽

pp. L28-L32 ◽

Cited By ~ 1

Author(s):

Ramij Raja ◽

Majidul Rahaman ◽

Abhirup Datta ◽

Jack O Burns ◽

H T Intema ◽

...

Keyword(s):

Radio Emission ◽

Spectral Index ◽

Low Frequency ◽

Galaxy Cluster ◽

Transition System ◽

Cluster Galaxy ◽

Radio Halo ◽

Spectrum Radio ◽

Upper Limits ◽

The Galaxy

ABSTRACT The advent of sensitive low-frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding of the physics of the intracluster medium. Here, we report the discovery of a steep-spectrum radio halo surrounding the central brightest cluster galaxy (BCG) in the galaxy cluster SPT-CL J2031−4037. This cluster is morphologically disturbed yet has a weak cool core, an example of a cool-core/non-cool-core transition system, which harbours a radio halo ∼0.7 Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at the 325 MHz to 1.7 GHz frequencies was found to be −1.35 ± 0.07. Also, P1.4 GHz was found to be 0.77 × 1024 W Hz−1, which falls in the region where radio mini-haloes, halo upper limits and ultra-steep-spectrum (USS) haloes are found in the P1.4 GHz–LX plane. Additionally, simulations presented in the paper provide support for the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep-spectrum ‘intermediate’ or ‘hybrid’ radio halo that is transitioning into a mini-halo.

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Warped diffusive radio halo around the quiescent spiral edge-on galaxy NGC 4565

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936046 ◽

2019 ◽

Vol 628 ◽

pp. L3

Author(s):

V. Heesen ◽

L. Whitler ◽

P. Schmidt ◽

A. Miskolczi ◽

S. S. Sridhar ◽

...

Keyword(s):

Cosmic Rays ◽

Thermal Emission ◽

Low Frequency ◽

Cosmic Ray ◽

Radio Continuum ◽

Continuum Emission ◽

Star Forming ◽

Radio Halo ◽

Gaussian Profile ◽

Pure Diffusion

Context. Cosmic rays play a pivotal role in launching galactic winds, particularly in quiescently star-forming galaxies where the hot gas alone is not sufficient to drive a wind. Except for the Milky Way, not much is known about the transport of cosmic rays in galaxies. Aims. In this Letter, we present low-frequency observations of the nearby edge-on spiral galaxy NGC 4565 using the LOw-Frequency ARray (LOFAR). With our deep 144 MHz observations, we obtain a clean estimate of the emission originating from old cosmic-ray electrons (CRe), which is almost free from contamination by thermal emission. Methods. We measured vertical profiles of the non-thermal radio continuum emission that we fitted with Gaussian and exponential functions. The different profile shapes correspond to 1D cosmic-ray transport models of pure diffusion and advection, respectively. Results. We detect a warp in the radio continuum that is reminiscent of the previously known H I warp. Because the warp is not seen at GHz-frequencies in the radio continuum, its minimum age must be about 100 Myr. The warp also explains the slight flaring of the thick radio disc that can otherwise be well described by a Gaussian profile with an FWHM of 65 arcsec (3.7 kpc). Conclusions. The diffusive radio halo together with the extra-planar X-ray emission may be remnants of enhanced star-forming activity in the past where the galaxy had a galactic wind, as GHz-observations indicate only a weak outflow in the last 40 Myr. NGC 4565 could be in transition from an outflow- to an inflow-dominated phase.

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A low-frequency radio halo survey of the South Pole Telescope SZ-selected clusters with the GMRT

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3432 ◽

2020 ◽

Vol 500 (2) ◽

pp. 2236-2249

Author(s):

Ramij Raja ◽

Majidul Rahaman ◽

Abhirup Datta ◽

Reinout J van Weeren ◽

Huib T Intema ◽

...

Keyword(s):

Large Scale ◽

Low Frequency ◽

Radio Sources ◽

Synchrotron Emission ◽

Diffuse Emission ◽

Radio Halo ◽

South Pole Telescope ◽

New Radio ◽

Upper Limits ◽

Correlation Line

ABSTRACT The presence of non-thermal electrons and large-scale magnetic fields in the intracluster medium is known through the detection of megaparsec (Mpc) scale diffuse radio synchrotron emission. Although a significant amount of progress in finding new diffuse radio sources has happened in the last decade, most of the investigation has been constrained towards massive low-redshift clusters. In this work, we explore clusters with redshift z > 0.3 in search of diffuse radio emission, at 325 MHz with the Giant Metrewave Radio Telescope. This campaign has resulted in the discovery of two new radio haloes (SPT-CL J0013−4906 and SPT-CL J0304−4401) along with two other detections (SPT-CL J2031−4037 and SPT-CL J2248−4431), previously reported (at 325 MHz) in the literature. In addition, we detect a halo candidate in one cluster in our sample, and upper limits for haloes are placed in eight clusters where no diffuse emission is detected. In the P1.4–LX plane, the detected haloes follow the observed correlation, whereas the upper limits lie above the correlation line, indicating the possibility of future detection with sensitive observations.

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Climatic drivers of seasonal glacier mass balances: an analysis of 6 decades at Glacier de Sarennes (French Alps)

The Cryosphere ◽

10.5194/tc-7-47-2013 ◽

2013 ◽

Vol 7 (1) ◽

pp. 47-66 ◽

Cited By ~ 38

Author(s):

E. Thibert ◽

N. Eckert ◽

C. Vincent

Keyword(s):

Mass Balance ◽

Large Scale ◽

Meteorological Data ◽

Low Frequency ◽

Late Winter ◽

Equilibrium Line Altitude ◽

French Alps ◽

Ice Melt ◽

Main Component ◽

Snow And Ice

Abstract. Refined temporal signals extracted from a winter and summer mass balance series recorded at Glacier de Sarennes (French Alps) using variance decomposition are related to local meteorological data and large-scale North Atlantic Oscillation (NAO) anomalies in terms of interannual variability, trends of the low-frequency signals, and breaks in the time series. The winter balance has increased by &plus;23% since 1976 due to more precipitation in early and late winter. The summer balance has decreased since 1982 due to a 43% increase in snow and ice melt. A 24-day lengthening of the ablation period – mainly due to longer ice ablation – is the main component in the overall increase in ablation. In addition, the last 25 yr have seen increases in ablation rates of 14 and 10% for snow and ice, respectively. A simple degree-day analysis can account for both the snow/ice melt rate rise and the lengthening of the ablation period as a function of higher air temperatures. From the same analysis, the equilibrium-line altitude of this 45° N latitude south-facing glacier has a sensitivity to temperature of &plus;93 m °C−1 around its mean elevation of 3100 m a.s.l. over 6 decades. The sensitivity of summer balance to temperature is −0.62 m w.e. yr−1 °C−1 for a typical 125-day-long ablation season. Finally, the correlation of winter and summer mass balance terms with NAO anomalies is investigated. Singularly, highest values are obtained between winter NAO anomalies and summer balance. Winter NAO anomalies and winter balance and precipitation are almost disconnected. However, these results strongly depend on how the NAO signal is smoothed, so that the link between Sarennes mass balance seasonal terms and NAO signal remains tenuous and hard to interpret.

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4.1. Radio continuum and molecular gas in the Galactic center: large-scale structures

Symposium - International Astronomical Union ◽

10.1017/s0074180900084473 ◽

1998 ◽

Vol 184 ◽

pp. 161-168

Author(s):

Yoshiaki Sofue

Keyword(s):

Radio Emission ◽

Linear Polarization ◽

Large Scale ◽

Galactic Center ◽

Thermal Emission ◽

Radio Continuum ◽

Molecular Gas ◽

Large Scale Structures ◽

Almost Everywhere ◽

Scale Structures

The radio emission from the Galactic Center is a mixture of thermal (free-free) and non-thermal (synchrotron) emissions (Fig. 1a). However, the spectral index in the central 3° region is flat almost everywhere (Sofue 1985), even in regions where strong linear polarization is detected. Therefore, a flat spectrum observed near the galactic center can no longer be taken as an indicator of thermal emission.

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Murchison Widefield Array rapid-response observations of the short GRB 180805A

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.15 ◽

2021 ◽

Vol 38 ◽

Author(s):

G. E. Anderson ◽

P. J. Hancock ◽

A. Rowlinson ◽

M. Sokolowski ◽

A. Williams ◽

...

Keyword(s):

Radio Emission ◽

Gamma Ray ◽

Response Times ◽

Low Frequency ◽

Rapid Response ◽

Gamma Ray Burst ◽

Upper Limit ◽

Emission Models ◽

Murchison Widefield Array ◽

Prompt Emission

Abstract Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a $3\sigma$ persistent flux density upper limit of 40.2 mJy beam–1. Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3\sigma$ limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam–1, respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a $6\sigma$ fluence upper-limit range from 570 Jy ms at DM $=3\,000$ pc cm–3 ( $z\sim 2.5$ ) to 1 750 Jy ms at DM $=200$ pc cm–3 ( $z\sim 0.1)$ , corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.

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Diffuse Extragalactic Emission at Low Frequencies within the Epoch of Reionization 0-hour Field

10.26686/wgtn.17060021.v1 ◽

2021 ◽

Author(s):

◽

Stefan Duchesne

Keyword(s):

Radio Emission ◽

Sample Size ◽

Galaxy Clusters ◽

Low Frequency ◽

Small Sample ◽

Point Sources ◽

Scaling Relations ◽

Low Frequencies ◽

Cluster Emission ◽

Radio Halo

<p>Low-frequency radio imaging of the southern sky has become available with the advent of the Murchison Widefield Array (MWA). The topic of this thesis is the study of extended, low-frequency radio emission, with a primary focus on the non-thermal synchrotron emission associated with the intra-cluster medium (ICM) of galaxy clusters. We do not limit the study to such emission, however, and investigate a small sample of other interesting and extended radio emission from objects in the southern sky. A significant portion of this work is invested in detecting, and characterising, extended, diffuse radio emission from galaxy clusters within a 45 degree by 45 degree region of the southern sky centred on R.A. = 0 hours, decl. = -27 degrees. This field is chosen as a deep MWA image has been made available which is sensitive to extended structures. Within the field we search for low-frequency, diffuse cluster emission, previously detected or otherwise. In doing so we find 34 diffuse radio sources, 3 of which are newly detected haloes, 1 newly detected relic with many new candidates of each. Further, we detect a new phoenix candidate as well as 2 candidate dead radio galaxies at the centre of clusters. We confirm previous observations of such emission as well, and measure properties such as their integrated flux densities, spectral indices, and sizes where possible. We compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power with the cluster X-ray luminosity and mass. We find that both scaling relations are consistent with previous findings despite the increase in sample size, though note that the raw scatter in the data for best-fitting parameters increases with increase in sample size. In this, we demonstrate the utility of low-frequency radio telescopes like the MWA in detecting such emission, showing that the MWA is pushing into higher-redshift, lower-mass systems, though we caution that the low resolution of the MWA can work against us. We follow-up on two galaxy clusters found to host extended emission - Abell S1136 and Abell S1063. In the case of Abell S1136 we observe the emission at its centre with the Australia Telescope Compact Array (ATCA) and determine the presence of a core, suggesting the emission to be that of an ancient episode of an active galactic nucleus in the central elliptical of the cluster, ESO 470-G020. After reducing archival ATCA data for Abell S1063 we find no evidence of a halo and consider the source to be constructed of blended point sources. We close with a description of a strong double-lobed radio source associated with a non-elliptical host ESO 472-G013, likely a spiral or irregular galaxy, that was found serendipitously whilst searching for diffuse cluster emission. We explore the host within the context of star-formation, and consider the possible origins of the AGN and lobes due to interaction with either the nearby spiral, ESO 472-G012, or a past or ongoing merger event.</p>

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Diffuse Extragalactic Emission at Low Frequencies within the Epoch of Reionization 0-hour Field

10.26686/wgtn.17060021 ◽

2021 ◽

Author(s):

◽

Stefan Duchesne

Keyword(s):

Radio Emission ◽

Sample Size ◽

Galaxy Clusters ◽

Low Frequency ◽

Small Sample ◽

Point Sources ◽

Scaling Relations ◽

Low Frequencies ◽

Cluster Emission ◽

Radio Halo

<p>Low-frequency radio imaging of the southern sky has become available with the advent of the Murchison Widefield Array (MWA). The topic of this thesis is the study of extended, low-frequency radio emission, with a primary focus on the non-thermal synchrotron emission associated with the intra-cluster medium (ICM) of galaxy clusters. We do not limit the study to such emission, however, and investigate a small sample of other interesting and extended radio emission from objects in the southern sky. A significant portion of this work is invested in detecting, and characterising, extended, diffuse radio emission from galaxy clusters within a 45 degree by 45 degree region of the southern sky centred on R.A. = 0 hours, decl. = -27 degrees. This field is chosen as a deep MWA image has been made available which is sensitive to extended structures. Within the field we search for low-frequency, diffuse cluster emission, previously detected or otherwise. In doing so we find 34 diffuse radio sources, 3 of which are newly detected haloes, 1 newly detected relic with many new candidates of each. Further, we detect a new phoenix candidate as well as 2 candidate dead radio galaxies at the centre of clusters. We confirm previous observations of such emission as well, and measure properties such as their integrated flux densities, spectral indices, and sizes where possible. We compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power with the cluster X-ray luminosity and mass. We find that both scaling relations are consistent with previous findings despite the increase in sample size, though note that the raw scatter in the data for best-fitting parameters increases with increase in sample size. In this, we demonstrate the utility of low-frequency radio telescopes like the MWA in detecting such emission, showing that the MWA is pushing into higher-redshift, lower-mass systems, though we caution that the low resolution of the MWA can work against us. We follow-up on two galaxy clusters found to host extended emission - Abell S1136 and Abell S1063. In the case of Abell S1136 we observe the emission at its centre with the Australia Telescope Compact Array (ATCA) and determine the presence of a core, suggesting the emission to be that of an ancient episode of an active galactic nucleus in the central elliptical of the cluster, ESO 470-G020. After reducing archival ATCA data for Abell S1063 we find no evidence of a halo and consider the source to be constructed of blended point sources. We close with a description of a strong double-lobed radio source associated with a non-elliptical host ESO 472-G013, likely a spiral or irregular galaxy, that was found serendipitously whilst searching for diffuse cluster emission. We explore the host within the context of star-formation, and consider the possible origins of the AGN and lobes due to interaction with either the nearby spiral, ESO 472-G012, or a past or ongoing merger event.</p>

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The corona of GJ 1151 in the context of star–planet interaction

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1982 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1015-1019

Author(s):

G Foster ◽

K Poppenhaeger ◽

J D Alvarado-Gómez ◽

J H M M Schmitt

Keyword(s):

Radio Emission ◽

Low Frequency ◽

Mass Star ◽

Coronal Temperature ◽

X Ray ◽

Upper Limit ◽

Radio Signals ◽

Low Mass ◽

Time Periods

ABSTRACT The low-mass star GJ 1151 has been reported to display variable low-frequency radio emission, which has been interpreted as a signpost of coronal star–planet interactions with an unseen exoplanet. Here we report the first X-ray detection of GJ 1151’s corona based on the XMM–Newton data. We find that the star displays a small flare during the X-ray observation. Averaged over the observation, we detect the star with a low coronal temperature of 1.6 MK and an X-ray luminosity of LX = 5.5 × 1026 erg s−1. During the quiescent time periods excluding the flare, the star remains undetected with an upper limit of $L_{\mathrm{ X},\, \mathrm{ qui}} \le 3.7\times 10^{26}$ erg s−1. This is compatible with the coronal assumptions used in a recently published model for a star–planet interaction origin of the observed radio signals from this star.

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