GMRT observations of the Ophiuchus galaxy cluster
M. Murgia, D. Eckert, F. Govoni, C. Ferrari, M. Pandey-Pommier, J., Nevalainen, S. Paltani

TL;DR
This study uses GMRT radio observations at multiple low frequencies to analyze the spectral properties of the mini-halo in the Ophiuchus galaxy cluster, revealing a steepening spectral index with radius and consistent non-thermal electron models.
Contribution
First low-frequency GMRT observations of the Ophiuchus cluster mini-halo, providing detailed spectral index measurements and modeling of non-thermal electron populations.
Findings
Mini-halo detected at 153 and 240 MHz, not at 610 MHz.
Spectral index increases from 1.3 at the center to 2.0 at the outskirts.
Electron energy spectrum extends from gamma_min < 700 to gamma_max = 3.8 x 10^4.
Abstract
VLA observations at 1477 MHz revealed the presence of a radio mini-halo surrounding the faint central point-like radio source in the Ophiuchus cluster of galaxies. In this work we present a study of the radio emission from this cluster of galaxies at lower radio frequencies. We observed the Ophiuchus cluster at 153, 240, and 614 MHz with the GMRT. The mini-halo is clearly detected at 153 and 240 MHz while it is not detected at 610 MHz. The most prominent feature at low frequencies is a patch of diffuse steep spectrum emission located at about 5' south-east from the cluster center. By combining these images with that at 1477 MHz, we derived the spectral index of the mini-halo. Globally, the mini-halo has a low-frequency spectral index of alpha_240^153 ~1.4 +/- 0.3 and an high-frequency spectral index of alpha_1477^240 ~ 1.60 +/- 0.05. Moreover, we measure a systematic increase of the…
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