PDS 456 is a relatively nearby radio-quiet quasar located in the constellation of Serpens. This is a luminous active galactic nucleus (AGN) with a redshift of (z) 0.184, first discovered by astronomers conducting the Pico dos Dias survey in 1997. The object is known to have prototypical ionized ultra-fast X-ray outflows and a bolometric luminosity value of 10<sup>47</sup> erg s<sup>âÂÂ1</sup>.
An extremely bright X-ray flare was detected from PDS 456 in September 2018. Based on observations, it showed a flux increase by a factor 4, including its time-scale doubling and a high level of flare energy, exceeding 10<sup>51</sup> erg. In addition, PDS 456 also displayed X-ray emission hardening following the flare. Radio images by very long baseline interferometry (VLBI) found PDS 456 has a complex nucleus described to be radio-emitting, an extended structure and a jet.
In 2019, observations by the Atacama Large Millimeter Array (ALMA) found PDS 456 to contain kiloparsec-scale molecular outflows. The molecular outflows are estimated to have a mass of 2.5 x 10<sup>8</sup> M<sub>ÃÂ</sub> while a value of 290 M<sub>ÃÂ</sub> yr<sup>âÂÂ1</sup> was calculated for its outflow mass rate. Given its short depletion time, it is estimated the star-formation in PDS 456 would be quenched.
Additionally, disk wind from the accretion disk and signatures of highly ionized gas detected via X-ray broadband spectra of PDS 456, was also present. A supermassive black hole mass of 10<sup>9.2ñ0.2</sup> M<sub>ÃÂ</sub> was estimated for the object.