A search for steep spectrum radio relics and halos with the GMRT

Weeren, R. J. van; Röttgering, H. J. A.; Brüggen, M.; Cohen, A. S.

doi:10.1051/0004-6361/200912501

Cited by 63 publications

(85 citation statements)

References 101 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We take the values at the front of the relic as the injection spectral indices. This then gives Mach numbers of 2.2 +0.2 −0.1 and 2.4 +0.4 −0.2 for relics RE and RW, respectively (van Weeren et al 2009a). The uncertainties in the Mach number are based on the variation in spectral index at the front of the relics of about −0.15 units.…”

Section: Origin Of the Double Radio Relicmentioning

confidence: 98%

“…We use the same procedure as described in van Weeren et al (2009a) and take k = 100, i.e., the ratio of energy in relativistic protons to that in electrons. For relic RW, we have a spectral index of −1.49, and a surface brightness of 1.2 μJy arcsec −2 .…”

Section: Equipartition Magnetic Field Strengthmentioning

confidence: 99%

“…Hydrodynamical models of structure formation, including particle acceleration mechanisms (e.g., Hoeft & Brüggen 2007;Hoeft et al 2008;Pfrommer 2008;Battaglia et al 2009) make predictions about the location, orientation and radio power of relics in merging clusters. Amongst the several dozen radio relics known to date (e.g., van Weeren et al 2009b;Rudnick & Lemmerman 2009;Pizzo & de Bruyn 2009;Giacintucci et al 2008;Brentjens 2008;Kempner & Sarazin 2001;Giovannini et al 1999Giovannini et al , 1991, there are a few rare double relic systems, with two relics located symmetrically on opposite sites of the cluster center (e.g., van Weeren et al 2009avan Weeren et al , 2010Brown et al 2010;Bonafede et al 2009;Venturi et al 2007;Bagchi et al 2006;Röttgering et al 1997). These double relics can be used to constrain the merger geometry and timescales involved (Roettiger et al 1999).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

Weeren

Hoeft

Röttgering

et al. 2011

A&A

Self Cite

100

View full text Add to dashboard Cite

Context. Some merging galaxy clusters host diffuse elongated radio sources, also called radio relics. It is proposed that these radio relics trace shock waves in the intracluster medium (ICM) created during a cluster merger event. Within the shock waves particles are accelerated to relativistic energies, and in the presence of a magnetic field synchrotron radiation will be emitted. Here we present giant metrewave radio telescope (GMRT) and Westerbork synthesis radio telescope (WSRT) observations of a new double relic in the galaxy cluster ZwCl 0008.8+5215. Aims. The aim of the observation is to understand the phenomenon of radio relics. Methods. We carried out radio continuum observations at 241 and 610 MHz with the GMRT, and 1.3−1.8 GHz observations with the WSRT in full polarization mode. Optical V, R, and I band images of the cluster were taken with the 2.5 m Isaac Newton Telescope (INT). An optical spectrum, to determine the redshift of the cluster, was taken with the William Herschel Telescope (WHT). Results. Our observations show the presence of a double radio relic in the galaxy cluster ZwCl 0008.8+5215, for which we find a spectroscopic redshift of z = 0.1032 ± 0.0018 from an optical spectrum of one of the cD galaxies. The spectral index of the two relics steepens inwards to the cluster center. For part of the relics, we measure a polarization fraction in the range ∼5−25%. A ROSAT X-ray image displays an elongated ICM and the large-scale distribution of galaxies reveals two cluster cores, all pointing towards a binary cluster merger event. The radio relics are located symmetrically with respect to the X-ray center of the cluster, along the proposed merger axis. The relics have a linear extent of 1.4 Mpc and 290 kpc. This factor of five difference in linear size is unlike that of previously known double relic systems, for which the sizes do not differ by more than a factor of two. Conclusions. We conclude that the double relics in ZwCl 0008.8+5215 are best explained by two outward moving shock waves in which particles are (re)accelerated trough the diffusive shock acceleration (DSA) mechanism.

show abstract

Section: Origin Of the Double Radio Relicmentioning

confidence: 98%

Section: Equipartition Magnetic Field Strengthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

Weeren

Hoeft

Röttgering

et al. 2011

A&A

Self Cite

100

View full text Add to dashboard Cite

show abstract

“…In van Weeren et al (2009b), we presented observations of a sample of 26 diffuse steep-spectrum sources, with α ≤ −1.15, selected from the 1.4 GHz NVSS (Condon et al 1998) and 74 MHz VLSS (Cohen et al 2007) surveys. These sources were either resolved out in the VLA B-array 1.4 GHz snapshot observations or 1.4 GHz FIRST survey (Becker et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Diffuse steep-spectrum sources from the 74 MHz VLSS survey

Weeren

Röttgering

Brüggen

2011

A&A

Self Cite

View full text Add to dashboard Cite

Context. Galaxy clusters grow by a sequence of mergers with other clusters and galaxy groups. During these mergers, shocks and/or turbulence are created within the intracluster medium (ICM). In this process, particles could be accelerated to highly relativistic energies. The synchrotron radiation from these particles is observed in the form of radio relics and halos that are generally characterized by a steep radio spectral index. Shocks can also revive fossil radio plasma from a previous episode of AGN activity, creating a socalled radio "phoenix". Here we present multi-frequency radio observations of diffuse steep-spectrum radio sources selected from the 74 MHz VLSS survey. Previous Giant Metrewave Radio Telescope (GMRT) observations showed that some of these sources had filamentary and elongated morphologies, which are expected for radio relics. Aims. We attempt to understand the nature of diffuse steep-spectrum radio sources and characterize their spectral index and polarization properties. Methods. We carried out radio continuum observations at 325 MHz with the GMRT. Observations with the Very Large Array (VLA) and Westerbork Synthesis Radio Telescope (WSRT) were taken at 1.4 GHz in full polarization mode. Optical images around the radio sources were taken with the William Herschel and Isaac Newton Telescope (WHT, INT). Results. Most of the sources in our sample consist of old radio plasma from AGNs located in small galaxy clusters. The sources can be classified as AGN relics or radio phoenices. The spectral indices across most of the radio sources display large variations. Conclusions. We conclude that diffuse steep-spectrum radio sources are not only found in massive X-ray luminous galaxy clusters but also in smaller systems. Future low-frequency surveys will uncover large numbers of steep-spectrum radio relics related to previous episodes of AGN activity.

show abstract

“…This trend suggests that the outer, extended, regions of the source are composed of aged plasma. We have fitted a synchrotron aging model including a period of activity and a period during which the AGN was switched off (KGJP; Komissarov & Gubanov 1994;Van Weeren et al 2009) to the integrated flux density measurements at four different frequencies (images listed in Table 1) for the central region of the source (labeled C in Fig. 6).…”

Section: Spectral Analysismentioning

confidence: 99%

The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?

Shulevski

Morganti

Barthel

et al. 2015

A&A

Self Cite

View full text Add to dashboard Cite

Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (∼4 ), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). At 62 MHz, we detect the radio emission of this structure extending out to 210 kpc. At 1.4 GHz and intermediate spatial resolution (∼30 ), the structure appears to have a helical morphology. We have derived the characteristics of the radio spectral index across the source. We show that the source morphology is most likely the result of at least two episodes of AGN activity separated by a dormant period of around 35 Myr. The outermost regions of radio emission have a steep spectral index (α < −1), indicative of old plasma. We connect the spectral index properties of the resolved source structure with the integrated flux density spectral index of 4C 35.06 and suggest an explanation for its unusual integrated flux density spectral shape (a moderately steep power law with no discernible spectral break), possibly providing a proxy for future studies of more distant radio sources through inferring their detailed spectral index properties and activity history from their integrated spectral indices. The AGN is hosted by one of the galaxies located in the cluster core of Abell 407. We propose that it is intermittently active as it moves in the dense environment in the cluster core. In this scenario, the AGN turned on sometime in the past, and has produced the helical pattern of emission, possibly a sign of jet precession/merger during that episode of activity. Using LOFAR, we can trace the relic plasma from that episode of activity out to greater distances from the core than ever before. Using the the WSRT, we detect H I in absorption against the center of the radio source. The absorption profile is relatively broad (FWHM of 288 km s −1 ), similar to what is found in other clusters. The derived column density is N HI ∼ 4 × 10 20 cm −2 for a T spin = 100 K. This detection supports the connection -already suggested for other restarted radio sources -between the presence of cold gas and restarting activity. The cold gas appears to be dominated by a blue-shifted component although the broad H I profile could also include gas with different kinematics. Understanding the duty cycle of the radio emission as well as the triggering mechanism for starting (or restarting) the radio-loud activity can provide important constraints to quantify the impact of AGN feedback on galaxy evolution. The study of these mechanisms at low frequencies using morphological and spectral information promises to bring new important insights in this field.

show abstract

A search for steep spectrum radio relics and halos with the GMRT

Cited by 63 publications

References 101 publications

A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215

Diffuse steep-spectrum sources from the 74 MHz VLSS survey

The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?

Contact Info

Product

Resources

About