Astronomy and Astrophysics, volume 397, 53-61 (2003/1-1)
The diffuse radio emission from the Coma cluster at 2.675 GHz and 4.85 GHz.
THIERBACH M., KLEIN U. and WIELEBINSKI R.
Abstract (from CDS):
We present new measurements of the diffuse radio halo emission from the Coma cluster of galaxies at 2.675GHz and 4.85GHz using the Effelsberg 100-m telescope. After correction for the contribution from point sources we derive the integrated flux densities for the halo source (Coma C), S2.675GHz=(107±28)mJy and S4.85GHz=(26±12)mJy. These values verify the strong steepening of the radio spectrum of Coma C at high frequencies. Its extent strongly depends on frequency, at 4.85GHz it is only marginally visible. The measurement at 4.85GHz is the first flux density determination for Coma C at this high frequency. In order to quantify the spectral steepening we compare the expectations for the spectrum of Coma C with the observations, resorting to basic models for radio halo formation. The in-situ acceleration model provides the best fit to the data. From equipartition assumptions we estimate a magnetic field strength Beq=0.57(1+k)0.26µG in the intracluster medium of Coma, where k is the energy ratio of the positively and negatively charged particles. As a by-product of the 2.675GHz observation we present a new flux density for the diffuse emission of the extended source 1253+275 (S2.675GHz=112±10). This measurement provides a smaller error range for the power-law fit to the spectrum (α=1.18±0.02) compared to previous investigations and yields an equipartition magnetic field strength of Beq=0.56(1+k)0.24µG.
galaxies: clusters: individual: Coma cluster, 1253+275 - galaxies: intergalactic medium
Extended source 1253+275 = Anon 1253+275 (= NAME COMA RELIC), fig. 2 + t. 4 : Objects in K94 original format HHMMSS.ss+DDMMSS.s, not identified