PKS 0405–385 is ablazar[5] in theconstellation ofEridanus. This is a compact radioquasar with aredshift (z) of 1.285, an indicator of its significant distance.[6] Theradio spectrum of this source appears flat, making it aflat-spectrum radio quasar (FSRQ).[3]
Thevisible light spectrum of PKS 0405–385 displays strong, broademission lines, with an intermediate absorption occurring at a redshift of 0.875.[6] Examination usingVLBI shows the radio source spans less than five microarcseconds (μas) in angle.[7] In 1993, this quasar was found to undergo variation in radioflux density during time spans of less than an hour. This variability is intermittent during episodes lasting for weeks or months.[6][8] The radio flux was also found to vary on longer timescales for periods of a month or two.[9]
If the short-term variation were due to the quasar, it would imply an extremebrightness temperature of about 1021 K.[6] Instead, it was proposed that the variation was the result ofinterstellar scintillation due to ionized clouds in theMilky Way.[9][10] The radio emission from the quasar underwent rotation oflinear polarization during these events, lending support to the idea of scintillation.[11] A scattering medium at a distance of3–30 pc would explain these observations, bringing the modelled peak brightness temperature down to a more plausible2.0×1013 K.[12][9] The episodic nature of the rapid variations may be explained by changes in the quasar or the interstellar medium.[7] PKS 0405–385 is one of only three known extreme scintillators, the others being PKS 1257−326 and J1819+385.[7]
In 2022, thegamma ray emission from PKS 0405–385 was found to undergoquasi-periodic oscillation with a period of about 2.8 years. This may be explained byhelical motion in ajet originating from thesupermassive black hole (SMBH), or the core SMBH is itself a binary system.[13][5] Enhanced gamma ray activity was observed from this source in 2019 and 2023.[3][14]
^Kedziora-Chudczer, L. L.; et al. (1998), Zensus, J. A.; et al. (eds.), "PKS 0405-385 as Seen by the ISM Telescope",Radio Emission from Galactic and Extragalactic Compact Sources, IAU Colloquium 164, ASP Conference Series, vol. 144, p. 267,Bibcode:1998ASPC..144..267K.
^Rickett, Barney J.; et al. (2002), "Interstellar Scintillation Explains the Intraday Variations in the Linear Polarisation of Quasar PKS 0405-385 at cm-wavelengths",Publications of the Astronomical Society of Australia,19 (1):106–110,Bibcode:2002PASA...19..106R,doi:10.1071/AS01119.
