2019ApJ...887L..17C

We present ∼103 ks of Chandra observations of the galaxy cluster SPT-CLJ0528-5300 (SPT0528, z = 0.768). This cluster harbors the most radio-loud (L_1.4GHz = 1.01 x 10³³ erg s^–1 Hz^–1) central active galactic nucleus (AGN) of any cluster in the South Pole Telescope (SPT) Sunyaev-Zeldovich survey with available X-ray data. We find evidence of AGN-inflated cavities in the X-ray emission, which are consistent with the orientation of the jet direction revealed by Australia Telescope Compact Array radio data. The combined probability that two such depressions-each at ∼1.4-1.8σ significance, oriented ∼180° apart and aligned with the jet axis-would occur by chance is 0.1%. At >=10⁶¹ erg, the outburst in SPT0528 is among the most energetic known in the universe, and certainly the most powerful known at z > 0.25. This work demonstrates that such powerful outbursts can be detected even in shallow X-ray exposures out to relatively high redshifts (z ∼ 0.8), providing an avenue for studying the evolution of extreme AGN feedback. The ratio of the cavity power (P_cav=(9.4±5.8)×10⁴⁵ erg s^–1) to the cooling luminosity (L_cool = (1.5 ± 0.5) x 10⁴⁴ erg s^–1) for SPT0528 is among the highest measured to date. If, in the future, additional systems are discovered at similar redshifts with equally high P_cav/L_cool ratios, it would imply that the feedback/cooling cycle was not as gentle at high redshifts as in the low-redshift universe.