Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuzaku observations of the merging galaxy cluster Abell2255: The northeast radio relic
167
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the results of deep 140 ks Suzaku X-ray observations of the north-east (NE) radio relic of the merging galaxy cluster Abell2255. The temperature structure of Abell2255 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 {it r}$sim$5arcmin~(450 kpc) and $sim$12arcmin~(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 ${cal M}_{rm inner}sim$1.2 and, ${cal M}_{rm outer}sim$1.4. The first structure is most likely related to the large cluster core region ($sim$350--430 kpc), and its Mach number is consistent with the XMM-Newton observation (${cal M}sim$1.24: Sakelliou & Ponman 2006). Our detection of the second temperature jump, based on the Suzaku key project observation, shows the presence of a shock structure across the NE radio relic. This indicates a connection between the shock structure and the relativistic electrons that generate radio emission. Across the NE radio relic, however, we find a significantly lower temperature ratio ($T_1/T_2sim1.44pm0.16$ corresponds to~${cal M}_{rm X-ray}sim1.4$) than the value expected from radio wavelengths, based on the standard diffusive shock acceleration mechanism ($T_1/T_2>$ 3.2 or ${cal M}_{rm Radio}>$ 2.8).
rate research
Read More
We present LOFAR $120-168$ MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT $595-629$ MHz and VLA $2-4$ GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of $mathcal{M}=2.4$ and $2.3$ for the northern and southern shocks, respectively. For $mathcal{M}lesssim3$ shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high ($>10$ per cent) particle acceleration efficiency required. However, for $mathcal{M}gtrsim4$ shocks the required efficiency is $gtrsim1%$ and $gtrsim0.5%$, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to $geqslant(53pm3)^circ$ and $geqslant(39pm5)^circ$ for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics ($sim1.8,text{Mpc}$) our upper limit on the power is $P_text{1.4 GHz}=(1.4pm0.6)times10^{23},text{W}text{Hz}^{-1}$ which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.
We present the results of Suzaku observations of the galaxy cluster 1RXS J0603.3+4214 with toothbrush radio relic. Although a shock with Mach number $M simeq 4$ is expected at the outer edge of the relic from the radio observation, our temperature measurements of the intracluster medium indicate a weaker temperature difference than what is expected. The Mach number estimated from the temperature difference at the outer edge of the relic is $M simeq 1.5$, which is significantly lower than the value estimated from the radio data even considering both statistical and systematic errors. This suggests that a diffusive shock acceleration theory in the linear test particle regime, which is commonly used to link the radio spectral index to the Mach number, is invalid for this relic. We also measured the temperature difference across the western part of the relic, where a shock with $M simeq 1.6$ is suggested from the X-ray surface brightness analysis of the XMM-Newton data, and obtained consistent results in an independent way. We searched for the non-thermal inverse Compton component in the relic region and the resultant upper limit on the flux is $2.4 times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3-10 keV band. The lower limit of the magnetic field strength becomes 1.6 $mu$G, which means that magnetic energy density could be more than a few $% $ of the thermal energy.
The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is $sim$50$$ or $sim$ 3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of $langle J rangle_{1,{rm GHz}}< 1.2 times 10^{-44} {rm W}, {rm Hz}^{-1} {rm m}^{-3}$. A non-detection of diffuse radio emission in the X-ray bridge between these two clusters has implications for particle-acceleration mechanisms in cosmological large-scale structure. We also report extended or otherwise noteworthy radio sources in the 30 deg$^2$ field around Abell 3391-Abell 3395. We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected sizes greater than 1 Mpc. The sky density of field radio galaxies with largest linear sizes of $>0.7$ Mpc is $approx 1.7$ deg$^{-2}$, three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos.
We present the results of Suzaku and Chandra observations of the galaxy cluster RXC J1053.7+5453 ($z=0.0704$), which contains a radio relic. The radio relic is located at the distance of $sim 540$ kpc from the X-ray peak toward the west. We measured the temperature of this cluster for the first time. The resultant temperature in the center is $ sim 1.3$ keV, which is lower than the value expected from the X-ray luminosity - temperature and the velocity dispersion - temperature relation. Though we did not find a significant temperature jump at the outer edge of the relic, our results suggest that the temperature decreases outward across the relic. Assuming the existence of the shock at the relic, its Mach number becomes $M simeq 1.4 $. A possible spatial variation of Mach number along the relic is suggested. Additionally, a sharp surface brightness edge is found at the distance of $sim 160$ kpc from the X-ray peak toward the west in the Chandra image. We performed X-ray spectral and surface brightness analyses around the edge with Suzaku and Chandra data, respectively. The obtained surface brightness and temperature profiles suggest that this edge is not a shock but likely a cold front. Alternatively, it cannot be ruled out that thermal pressure is really discontinuous across the edge. In this case, if the pressure across the surface brightness edge is in equilibrium, other forms of pressure sources, such as cosmic-rays, are necessary. We searched for the non-thermal inverse Compton component in the relic region. Assuming the photon index $ Gamma = 2.0$, the resultant upper limit of the flux is $1.9 times 10^{-14} {rm erg s^{-1} cm^{-2}}$ for $4.50 times 10^{-3} {rm deg^{2}}$ area in the 0.3-10 keV band, which implies that the lower limit of magnetic field strength becomes $ 0.7 {rm mu G}$.
We examine the possible acceleration mechanisms of the relativistic particles responsible for the extended radio emission in Abell 520. We used new LOFAR 145 MHz, archival GMRT 323 MHz and VLA 1.5 GHz data to study the morphological and spectral properties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. In Abell 520, we confirm the presence of extended synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming DSA, the radio data are suggestive of a shock of $mathcal{M}_{SW}=2.6_{-0.2}^{+0.3}$ that is consistent with the X-ray derived estimates. This is in line with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of $mathcal{M}_{NE}^{X}=1.52pm0.05$. This is lower than the value predicted from the radio emission ($mathcal{M}_{NE}=2.1pm0.2$). Our observations indicate that the SW radio emission in Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
