First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

Savini, F.; Bonafede, A.; Brüggen, M.; Weeren, R. J. van; Brunetti, G.; Intema, H. T.; Botteon, A.; Shimwell, T. W.; Wilber, A.; Rafferty, D. A.; Giacintucci, S.; Cassano, R.; Cuciti, V.; Gasperin, F. de; Röttgering, H. J. A.; Hoeft, M.; White, G. J.

doi:10.1093/mnras/sty1125

Cited by 54 publications

(61 citation statements)

References 41 publications

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“…At 1.28 GHz, we used a 5 ′′ -resolution image (not shown here) to measure the minihalo flux and obtained S 1.28 GHz = 0.65±0.08 mJy. A flux density of 12 mJy (with 15% uncertainty) is reported at 144 MHz by Savini et al (2018). A spectral index of α = 1.33 ± 0.08 is inferred between 144 MHz and 1.28 GHz, consistent with the index in the 144-610 MHz range (Savini et al 2018).…”

Section: A 2667supporting

confidence: 67%

“…A flux density of 12 mJy (with 15% uncertainty) is reported at 144 MHz by Savini et al (2018). A spectral index of α = 1.33 ± 0.08 is inferred between 144 MHz and 1.28 GHz, consistent with the index in the 144-610 MHz range (Savini et al 2018). The flux density of the minihalo at 1.4 GHz, extrapolated from the lower-frequency measurements with α = 1.33±0.08, is S 1.4 GHz = 0.6±0.1 mJy.…”

Section: A 2667supporting

confidence: 67%

“…(c) Chandra X-ray image, same as in (b). White lines mark the position of an X-ray cold front (Savini et al 2018).…”

Section: A 2667mentioning

confidence: 99%

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Expanding the Sample of Radio Minihalos in Galaxy Clusters

Giacintucci

Markevitch

Cassano

et al. 2019

ApJ

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Radio minihalos are diffuse synchrotron sources of unknown origin found in the cool cores of some galaxy clusters. We use GMRT and VLA data to expand the sample of minihalos by reporting three new minihalo detections (A 2667, A 907 and PSZ1 G139.61+24.20) and confirming minihalos in five clusters (MACS J0159.8-0849, MACS J0329.6-0211, RXC J2129.6+0005, AS 780 and A 3444). With these new detections and confirmations, the sample now stands at 23, the largest sample to date. For consistency, we also reanalyze archival VLA 1.4 GHz observations of 7 known minihalos. We revisit possible correlations between the non-thermal emission and the thermal properties of their cluster hosts. Consistently with our earlier findings from a smaller sample, we find no strong relation between the minihalo radio luminosity and the total cluster mass. Instead, we find a strong positive correlation between the minihalo radio power and X-ray bolometric luminosity of the cool core (r < 70 kpc). This supplements our earlier result that most if not all cool cores in massive clusters contain a minihalo. Comparison of radio and Chandra X-ray images indicates that the minihalo emission is typically confined by concentric sloshing cold fronts in the cores of most of our clusters, supporting the hypothesis that minihalos arise from electron reacceleration by turbulence caused by core gas sloshing. Taken together, our findings suggest that the origin of minihalos should be closely related to the properties of thermal plasma in cluster cool cores.

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Section: A 2667supporting

confidence: 67%

Section: A 2667supporting

confidence: 67%

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Expanding the Sample of Radio Minihalos in Galaxy Clusters

Giacintucci

Markevitch

Cassano

et al. 2019

ApJ

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“…On the other hand, MHs are formed due to the turbulence caused by the later stage of a minor merger event i.e., sloshing core (Mazzotta & Giacintucci 2008). An "intermediate" state between these was also proposed by Brunetti & Jones (2014) where a radio halo transitioning into a mini-halo or vice-versa and recent discoveries of ∼ Mpc scale radio halos in cool core and semi-relaxed clusters seems to favour this scenario (e.g., Bonafede et al 2014;Sommer et al 2017;Savini et al 2018;Kale et al 2019).…”

Section: Introductionmentioning

confidence: 70%

“…In comparison with other clusters hosting intermediate halos (e.g., Bonafede et al 2014;Sommer et al 2017;Savini et al 2018;Kale et al 2019, hereafter Halos Minihalos USS SPT-CL J2031-4037 Figure 3. The distribution of halos, mini-halos, USS halos and halo upper limits (black arrows) in the L X −P 1.4GHz plane (Cassano et al 2013;Kale et al 2015) is presented here.…”

Section: Discussionmentioning

confidence: 91%

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

Raja

Rahaman

Datta

et al. 2020

Monthly Notices of the Royal Astronomical Society: Letters

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The advent of sensitive low frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding about 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 cool core/non-cool core transition system, which harbours a radio halo of ∼ 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 325 MHz to 1.7 GHz frequencies was found to be −1.35 ± 0.07. Also, P 1.4 GHz was found to be 0.77 × 10 24 W Hz −1 which falls in the region where radio mini-halos, halo upper limits and ultra-steep spectrum (USS) halos are found in the P 1.4 GHz − L X plane. Additionally, simulations presented in the paper provide support to the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep spectrum "intermediate" or "hybrid" radio halo which is transitioning into a mini-halo.

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Diffuse Radio Emission from Galaxy Clusters

et al. 2019

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In a growing number of galaxy clusters diffuse extended radio sources have been found. These sources are not directly associated with individual cluster galaxies. The radio emission reveal the presence of cosmic rays and magnetic fields in the intracluster medium (ICM). We classify diffuse cluster radio sources into radio halos, cluster radio shocks (relics), and revived AGN fossil plasma sources. Radio halo sources can be further divided into giant halos, mini-halos, and possible "intermediate" sources. Halos are generally positioned at cluster center and their brightness approximately follows the distribution of the thermal ICM. Cluster radio shocks (relics) are polarized sources mostly found in the cluster's periphery. They trace merger induced shock waves. Revived fossil plasma sources are characterized by their radio steep-spectra and often irregular morphologies. In this review we give an overview of the properties of diffuse cluster radio sources, with an emphasis on recent observational results. We discuss the resulting implications for the underlying physical acceleration processes that operate in the ICM, the role of relativistic fossil plasma, and the properties of ICM shocks and magnetic fields. We also compile an updated list of diffuse cluster radio sources which will be available on-line (http://galaxyclusters.com).

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First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

Cited by 54 publications

References 41 publications

Expanding the Sample of Radio Minihalos in Galaxy Clusters

Expanding the Sample of Radio Minihalos in Galaxy Clusters

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

Diffuse Radio Emission from Galaxy Clusters

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