Using various radio telescopes, an international team of astronomers made deep, low-frequency radio observations of the cluster of compact galaxies Abell 2256. The observation campaign provided further insights into the properties of the cluster’s radio halo. The results are detailed in a paper published September 7 on arXiv.org.
Radio halos are massive regions of diffuse radio emission, usually found in the centers of galaxy clusters. However, diffuse emissions have very low surface brightness, particularly at GHz frequencies, which makes them difficult to detect. Brightens it in lower frequenciesIt revealed the presence of these areas.
With the ability to have high, deep, high and low resolutionrepeat Radio images, LOw Frequency ARray (LOFAR) is an excellent tool for studying radio auras Low frequencies with unprecedented detail and sensitivity. So, a group of researchers led by Kamlesh Rajpurohit of the University of Bologna in Italy, used LOFAR to examine the radio halo of Abell 2256 – a nearby massive cluster of galaxies (at a redshift of 0.058) that exhibits strong emission at all wavelengths. The team also used the Giant Metrewave Radio Telescope (uGMRT) and Karl G. Jansky Very Large Array (VLA) to observe this corona.
“We present the first detailed analysis of the radio corona in the compact galaxy cluster Abell 2256 using the Low Frequency Array (LOFAR), the Giant Metrewave Radio Telescope (uGMRT), and the VLA. Radio observations (120 MHz-2 GHz) combined with archival data Chandra and XMM-Newton X- ray allowed us to study corona emission in unprecedented detail.”
Astronomers were able to obtain the first deep and high-resolution radio images of the radio corona of La Belle 2256. The corona emission was detected by them at all frequencies of 144 MHz, 350 MHz, 675 MHz and 1.5 GHz. The largest linear size of this corona has been measured at about 2.93 million light-years away at 144 MHz and 1.63 million light years at 1.5 GHz, indicating that the outer region has a sharp spectrum.
Overall, the study found that emission from the corona follows a power law spectrum between 144 MHz and 1.5 GHz, and has a very steep spectrum with an integrated spectral index of −1.63. Furthermore, the spatially resolved spectral index maps revealed spectral regression with increasing radius.
The research found that the morphology of the radio corona is remarkably similar to that of X-rays. In particular, the X-ray peak in the main mass component coincides with the radio peak. Furthermore, a point-to-point comparison between the X-ray and radio-surface brightness across the corona indicates a strong sublinear correlation.
The observations also revealed a strong counter-relationship between the spectral index and the X-ray surface brightness across the corona. According to the researchers, this is consistent with radial regression.
Summing up the results, the authors of the paper assert that the properties of the radio corona in Abell 2256 make it a very exotic object, which further investigation may advance our knowledge of particle acceleration mechanisms at very large scales.
K. Rajpurohit et al, Deep, low-frequency radio observations of the Abell 2256 II: the steeply-sloped radio spectrum. arXiv: 2209.03288v1 [astro-ph.CO]And the arxiv.org/abs/2209.03288
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