Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHard X-ray Observation of Abell 496
71
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the results of hard X-ray observations of Abell 496 (A496), a nearby relaxed cluster, using the Rossi X-ray Timing Explorer (RXTE). The 3-20 keV spectrum of this cluster is well-modeled by a thermal component of kT ~ 4.1 keV plus a cooling flow with mass accretion rate of dot{M} ~ 285 M_{odot} yr^{-1}. The spectrum is equally well-modeled by a multi-temperature plasma component with a Gaussian temperature distribution of mean temperature 3.8 keV and sigma_{kT} ~ 0.9 keV. The metallicity is found to be approximately 1/3 solar; however, the Ni/Fe ratio is about 3.6. No significant nonthermal emission at hard X-rays was detected for this cluster. We discuss the implications of the models presented here and compare them with the temperature profiles derived for this cluster using the Advanced Satellite for Cosmology and Astrophysics (ASCA). Our results are inconsistent with declining temperature profiles.
rate research
Read More
We present a long BeppoSAX observation of Abell 754 that reports a nonthermal excess with respect to the thermal emission at energies greater than ~45 keV. A VLA radio observation at 1.4 GHz definitely confirms the existence of diffuse radio emission in the central region of the cluster, previously suggested by images at 74 and 330 MHz (Kassim et al 2001), and reports additional features. Besides, our observation determines a steeper radio halo spectrum in the 330-1400 MHz frequency range with respect to the spectrum detected at lower frequencies, indicating the presence of a spectral cutoff. The presence of a radio halo in A754, considered the prototype of a merging cluster, reinforces the link between formation of Mpc-scale radio regions and very recent or current merger processes. The radio results combined with the hard X-ray excess detected by BeppoSAX give information on the origin of the electron population responsible for nonthermal phenomena in galaxy clusters. We discuss also the possibility that 26W20, a tailed radio galaxy with BL Lac characteristics located in the field of view of the PDS, could be responsible for the observed nonthermal hard X-ray emission.
We present the results of Suzaku observation of the radio halo cluster Abell 2319. The metal abundance in the central cool region is found to be higher than the surrounding region, which was not resolved in the former studies. We confirm that the line-of-sight velocities of the intracluster medium in the observed region are consistent with those of the member galaxies of entire A2319 and A2319A subgroup for the first time, though any velocity difference within the region is not detected. On the other hand, we do not find any signs of gas motion relevant to A2319B subgroup. Hard X-ray emission from the cluster is clearly detected, but its spectrum is likely thermal. Assuming a simple single temperature model for the thermal component, we find that the upper limit of the non-thermal inverse Compton component becomes $2.6 times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ in the 10-40 keV band, which means that the lower limit of the magnetic field is 0.19 $mu$G with the radio spectral index 0.92. Although the results slightly depend on the detailed spectral modeling, it is robust that the upper limit of the power-law component flux and lower limit of the magnetic field strength become $sim 3 times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and $sim 0.2 mu$G, respectively. Considering the lack of a significant amount of very hot ($sim 20$ keV) gas and the strong bulk flow motion, it is more likely that the relativistic non-thermal electrons responsible for the radio halo are accelerated through the intracluster turbulence rather than the shocks.
Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell 496 confirms there are mild metal abundance enhancements near the center, as previously found by White et al. (1994) in a joint analysis of Ginga LAC and Einstein SSS spectra. Simultaneous analysis of spectra from all ASCA instruments (SIS + GIS) shows that the iron abundance is 0.36 +- 0.03 solar 3-12 from the center of the cluster and rises ~50% to 0.53 +- 0.04 solar within the central 2. The F-test shows that this abundance gradient is significant at the >99.99% level. Nickel and sulfur abundances are also centrally enhanced. We use a variety of elemental abundance ratios to assess the relative contribution of SN Ia and SN II to the metal enrichment of the intracluster gas. We find spatial gradients in several abundance ratios, indicating that the fraction of iron from SN Ia increases toward the cluster center, with SN Ia accounting for ~50% of the iron mass 3-12 from the center and ~70% within 2. The increased proportion of SN Ia ejecta at the center is such that the central iron abundance enhancement can be attributed wholly to SN Ia; we find no significant gradient in SN II ejecta. These spatial gradients in the proportion of SN Ia/II ejecta imply that the dominant metal enrichment mechanism near the center is different than in the outer parts of the cluster. We show that the central abundance enhancement is unlikely to be due to ram pressure stripping of gas from cluster galaxies, or to secularly accumulated stellar mass loss within the central cD. We suggest that the additional SN Ia ejecta near the center is the vestige of a secondary SN Ia-driven wind from the cD (following a more energetic protogalactic SN II-driven wind phase), which was partially smothered in the cD due to its location at the cluster center.
Wide-band Suzaku data on the merging cluster Abell 3667 were examined for hard X-ray emission in excess to the known thermal component. Suzaku detected X-ray signals in the wide energy band from 0.5 to 40 keV. The hard X-ray (> 10 keV) flux observed by the HXD around the cluster center cannot be explained by a simple extension of the thermal emission with average temperature of ~7 keV. The emission is most likely an emission from a very hot (kT > 13.2 keV) thermal component around the cluster center, produced via a strong heating process in the merger. In the north-west radio relic, no signature of non-thermal emission was observed. Using the HXD, the overall upper-limit flux within a 34x34 field-of-view around the relic is derived to be 5.3e-12 erg s-1 cm-2 in the 10-40 keV band, after subtracting the ICM contribution estimated using the XIS or the XMM-Newton spectra. Directly on the relic region, the upper limit is further tightened by the XIS data to be less than 7.3e-13 erg s-1 cm-2, when converted into the 10--40 keV band. The latter value suggest that the average magnetic field within the relic is higher than 1.6 uG. The non-thermal pressure due to magnetic fields and relativistic electrons may be as large as ~20% of the thermal pressure in the region.
Chandra ACIS-S observations of the galaxy cluster A3112 feature the presence of an excess of X-ray emission above the contribution from the diffuse hot gas, which can be equally well modeled with an additional non-thermal power-law model or with a low-temperature thermal model of low metal abundance. We show that the excess emission cannot be due to uncertainties in the background subtraction or in the Galactic HI column density. Calibration uncertainties in the ACIS detector that may affect our results are addressed by comparing the Chandra data to XMM MOS and PN spectra. While differences between the three instruments remain, all detect the excess in similar amounts, providing evidence against an instrumental nature of the excess. Given the presence of non-thermal radio emission near the center of A3112, we argue that the excess X-ray emission is of non-thermal nature and distributed throughout the entire X-ray bandpass, from soft to hard X-rays. The excess can be explained with the presence of a population of relativistic electrons with ~7% of the clusters gas pressure. We also discuss a possible thermal nature of the excess, and examine the problems associated with such interpretation.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
