Turbulent cosmic ray reacceleration and the curved radio spectrum of the radio relic in the Sausage Cluster

Fujita, Yutaka; Akamatsu, Hiroki; Kimura, Shigeo S.

doi:10.1093/pasj/psw022

Cited by 20 publications

(13 citation statements)

References 55 publications

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“…Such a phenomenon is observed in SNRs (van Adelsberg et al 2008;Yamaguchi et al 2014;Vink et al 2015) -Clumpiness and inhomogeneities in the ICM (Nagai & Lau 2011;Simionescu et al 2011), which will lead to nonlinearity of the shock-acceleration efficiency (Hoeft & Brüggen 2007) -pre-existing low-energy relativistic electrons and/or reaccelerated electrons, resulting in a flat radio spectrum with a rather small temperature jump (Markevitch et al 2005;Kang et al 2012;Pinzke et al 2013;Stroe et al 2016) -a nonuniform Mach number as a results of inhomogeneities in the ICM, which is expected in the periphery of the cluster (Nagai & Lau 2011;Simionescu et al 2011;Mazzotta et al 2011). -shock-drift accelerations, suggested from particle-in-cell simulations (Guo et al 2014a,b) -other mechanisms, for instance turbulence accelerations (e.g., Fujita et al 2015Fujita et al , 2016 Based on our X-ray observational results, we discuss some of the above possibilities.…”

Section: Possible Scenarios For the Discrepancymentioning

confidence: 74%

Suzakuobservations of the merging galaxy cluster Abell 2255: The northeast radio relic

Akamatsu

Mizuno

Ota

et al. 2017

A&A

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We present the results of deep 140 ks Suzaku X-ray observations of the north-east (NE) radio relic of the merging galaxy cluster Abell 2255. The temperature structure of Abell 2255 is measured out to 0.9 times the virial radius (1.9 Mpc) in the NE direction for the first time. The Suzaku temperature map of the central region suggests a complex temperature distribution, which agrees with previous work. Additionally, on a larger-scale, we confirm that the temperature drops from 6 keV around the cluster center to 3 keV at the outskirts, with two discontinuities at r∼5 ′ (450 kpc) and ∼12 ′ (1100 kpc) from the cluster center. Their locations coincide with surface brightness discontinuities marginally detected in the XMM-Newton image, which indicates the presence of shock structures. From the temperature drop, we estimate the Mach numbers to be M inner ∼1.2 and, M outer ∼1.4. The first structure is most likely related to the large cluster core region (∼350-430 kpc), and its Mach number is consistent with the XMM-Newton observation (M ∼1.24: Sakelliou & Ponman 2006). Our detection of the second temperature jump, based on the Suzaku key project observation, shows the presence of a shock structure across the NE radio relic. This indicates a connection between the shock structure and the relativistic electrons that generate radio emission. Across the NE radio relic, however, we find a significantly lower temperature ratio (T 1 /T 2 ∼ 1.44 ± 0.16 corresponds to M X−ray ∼ 1.4) than the value expected from radio wavelengths, based on the standard diffusive shock acceleration mechanism (T 1 /T 2 > 3.2 or M Radio > 2.8). This may suggest that under some conditions, in particular the NE relic of A2255 case, the simple diffusive shock acceleration mechanism is unlikely to be valid, and therefore, more a sophisticated mechanism is required.

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Section: Possible Scenarios For the Discrepancymentioning

confidence: 74%

Suzakuobservations of the merging galaxy cluster Abell 2255: The northeast radio relic

Akamatsu

Mizuno

Ota

et al. 2017

A&A

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“…Several solutions have been proposed to solve this problem using the northern relic in CIZA J2242.8+5301 as a prototype. Kang & Ryu (2016, 2015 proposed that fossil electrons (accelerated by the DSA mechanism) are reaccelerated as the shock runs them over; Fujita et al (2016) suggested that cosmic rays are reaccelerated by turbulence generated behind shocks; Donnert et al (2016) offered another explanation: magnetic turbulence generated by the amplification of the magnetic field is responsi- ble for the particle reacceleration. An alternative solution was suggested by : the curved radio spectrum is a consequence of the SZ effect, which lowers the measured radio flux at the observed radio wavelengths (< 217 GHz).…”

Section: Ciza J22428+5301: a Merging Cluster With The Prototype Of Re...mentioning

confidence: 99%

“…Note that the collision axis is also aligned vertically, as in Figure 3. lision is close to the plane of the sky), have been used to test different particle acceleration models, e.g., DSA mechanism (Stroe et al 2016, also analyzed 1RXS J0603.3+4214, the "Toothbrush" cluster); fossil electrons (accelerated by the DSA mechanism) are reaccelerated as the shock runs them over (Kang & Ryu 2015); turbulent cosmic ray reacceleration (Fujita et al 2016); and magnetic turbulence generated by the amplification of the magnetic field (Donnert et al 2016).…”

Section: Bias In Mach Numbers Derived From X-ray Observationsmentioning

confidence: 99%

Shocks and Tides Quantified in the “Sausage” Cluster, CIZA J2242.8+5301 Using N-body/Hydrodynamical Simulations

Molnar

Broadhurst

2017

ApJ

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The colliding cluster, CIZA J2242.8+5301, displays a spectacular, almost 2 Mpc long shock front with a radio based Mach number M 5, that is puzzlingly large compared with the X-ray estimate of M 2.5. The extent to which the X-ray temperature jump is diluted by cooler unshocked gas projected through the cluster currently lacks quantification. Thus, here we apply our self-consistent N-body/hydrodynamical code (based on FLASH) to model this binary cluster encounter. We can account for the location of the shock front and also the elongated X-ray emission by tidal stretching of the gas and dark mater between the two cluster centers. The required total mass is 8.9 ×10 14 M with a 1.3:1 mass ratio favoring the southern cluster component. The relative velocity we derive is 2500 km s −1 initially between the two main cluster components, with an impact parameter of 120 kpc. This solution implies that the shock temperature jump derived from the low angular resolution X-ray satellite Suzaku is underestimated by a factor of two, due to cool gas in projection, bringing the observed X-ray and radio estimates into agreement. We propose that the complex southern relics in CIZA J2242.8+5301, have been broken up as the southerly moving "back" shocked gas impacts the gas still falling in along the collision axis. Finally, we use our model to generate Compton-y maps to estimate the reduction in radio flux caused by the thermal Sunyaev-Zel'dovich (SZ) effect. At 30 Ghz, this amounts to ∆S n = −0.072 mJy/arcmin 2 and ∆S s = −0.075 mJy/arcmin 2 at the locations of the northern and southern shock fronts respectively. Our model estimate agrees with previous empirical estimates that have inferred the measured radio spectra can be significantly affected by the SZ effect, with implications for charged particle acceleration models of the radio relics.

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“…The lack of connection between radio relics and shocks in several merging clusters, together with the low efficiency of DSA for M ∼ 2-3 of these shocks, seems to suggest that in some cases the DSA assumption is not enough for the electron acceleration from the thermal pool (Vink & Yamazaki 2014;Vazza & Brüggen 2014;Skillman et al 2013;Pinzke et al 2013). For this reason, alternative mechanisms have been proposed recently, as for example the re-acceleration of pre-existing cosmic ray electrons (Markevitch et al 2005;Kang et al 2012;Fujita et al 2015;Fujita et al 2016;Kang 2017) and shock drift acceleration (Guo et al 2014a(Guo et al ,b, 2017. However, it is not clear what type of mechanism is involved and whether all relics need additional mechanisms or not.…”

Section: Introductionmentioning

confidence: 99%

X-ray study of the double radio relic Abell 3376 with Suzaku

Urdampilleta

Akamatsu

Mernier

et al. 2018

A&A

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We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 (z = 0.046), observed with the Suzaku XIS instrument. These deep (∼360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (M W = 2.8 ± 0.4) in the western direction at r ∼ 26 , derived from a temperature and surface brightness discontinuity across the radio relic. In the East, we detect a weaker shock (M E = 1.5 ± 0.1) at r ∼ 8 , possibly associated to the 'notch' of eastern relic, and a cold front at r ∼ 3 . Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is ∼0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature.

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Turbulent cosmic ray reacceleration and the curved radio spectrum of the radio relic in the Sausage Cluster

Cited by 20 publications

References 55 publications

Suzakuobservations of the merging galaxy cluster Abell 2255: The northeast radio relic

Suzakuobservations of the merging galaxy cluster Abell 2255: The northeast radio relic

Shocks and Tides Quantified in the “Sausage” Cluster, CIZA J2242.8+5301 Using N-body/Hydrodynamical Simulations

X-ray study of the double radio relic Abell 3376 with Suzaku

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