Radio halo in galaxy cluster Abell 2256: Using varied radio telescopes, a world workforce of astronomers has carried out deep low-frequency radio observations of a merging galaxy cluster Abell 2256. The observational marketing campaign delivered extra insights into the properties of the cluster’s radio halo. The findings had been detailed in a paper revealed September 7 on arXiv.org.
Radio halos are monumental areas of diffuse radio emission, often discovered on the facilities of galaxy clusters. However, diffuse emissions typically have very low floor brightness, notably at GHz frequencies, which makes them onerous to detect. Their brightness will increase at lower frequencies, unveiling the presence of those areas.
With the aptitude of acquiring deep, high-resolution, high-fidelity and low-frequency radio photos, the LOw Frequency ARray (LOFAR) is a wonderful instrument for finding out radio halos at low frequencies with unprecedented element and sensitivity.
Therefore, a gaggle of researchers led by Kamlesh Rajpurohit of the University of Bologna in Italy, has employed LOFAR to be able to examine radio halo in Abell 2256—a close-by (at a redshift of 0.058) large galaxy cluster exhibiting sturdy emission in any respect wavelengths.
The workforce additionally used the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Karl G. Jansky Very Large Array (VLA) to watch this halo.
“We present the first detailed analysis of the radio halo in the merging galaxy cluster Abell 2256 using the LOw Frequency ARray (LOFAR), the upgraded Giant Metrewave Radio Telescope (uGMRT) and the VLA. Radio observations (120 MHz-2 GHz) combined with archival Chandra and XMM-Newton X-ray data allowed us to study the halo emission with unprecedented detail,” the researchers wrote within the paper.
The astronomers managed first deep, excessive spatial decision radio photos of Abell 2256’s radio halo. The halo emission was detected by them in any respect frequencies, specifically 144 MHz, 350 MHz, 675 MHz and 1.5 GHz. The largest linear measurement of this halo was measured to be about 2.93 million mild years at 144 MHz and 1.63 million light years at 1.5 GHz, which means that its outermost area has a steep spectrum.
In basic, the research discovered that emission from the halo follows a power-law spectrum between 144 MHz and 1.5 GHz, and has an extremely steep spectrum with an built-in spectral index of −1.63. Moreover, the spatially resolved spectral index maps revealed a spectral steepening with growing radius.
The analysis discovered that the morphology of the radio halo is remarkably just like that in X-rays. In explicit, the X-ray peak in the primary mass part coincides with the radio peak. Furthermore, the point-to-point comparability between the radio and X-ray floor brightness throughout the halo signifies a robust sublinear correlation.
The observations additionally revealed a robust anti-correlation between the spectral index and the X-ray floor brightness throughout the halo. According to the researchers, that is in keeping with radial steepening.
Summing up the outcomes, the authors of the paper underlined that the properties of radio halo in Abell 2256 make it a really peculiar object, whose additional investigation could advance our data about particle acceleration mechanisms on very massive scales.
More info:
Ok. Rajpurohit et al, Deep low-frequency radio observations of Abell 2256 II: The ultra-steep spectrum radio halo. arXiv:2209.03288v1 [astro-ph.CO], arxiv.org/abs/2209.03288
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