PKS 0405−385
Quasar in the constellation Eridanus
From Wikipedia, the free encyclopedia
PKS 0405−385 is a blazar[5] in the constellation of Eridanus. This is a compact radio quasar with a redshift (z) of 1.285, an indicator of its significant distance.[6] The radio spectrum of this source appears flat, making it a flat-spectrum radio quasar (FSRQ).[3]
| PKS 0405−385 | |
|---|---|
The blazar PKS 0405−385 | |
| Observation data (Epoch J2000.0) | |
| Constellation | Eridanus |
| Right ascension | 04h 06m 59.035s[1] |
| Declination | −38° 26′ 28.04″[1] |
| Redshift | 1.285[2] |
| Type | FSRQ[3] |
| Other designations | |
| 4FGL J0407.0−3826[4] | |
| See also: Quasar, List of quasars | |
Description
The visible light spectrum of PKS 0405−385 displays strong, broad emission lines, with an intermediate absorption occurring at a redshift of 0.875.[6] Examination using VLBI shows the radio source spans less than five microarcseconds (μas) in angle.[7] In 1993, this quasar was found to undergo variation in radio flux 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 extreme brightness temperature of about 1021 K.[6] Instead, it was proposed that the variation was the result of interstellar scintillation due to ionized clouds in the Milky Way.[9][10] The radio emission from the quasar underwent rotation of linear polarization during these events, lending support to the idea of scintillation.[11] A scattering medium at a distance of 3–30 pc would explain these observations, bringing the modelled peak brightness temperature down to a more plausible 2.0×1013 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, the gamma ray emission from PKS 0405−385 was found to undergo quasi-periodic oscillation with a period of about 2.8 years. This may be explained by helical motion in a jet originating from the supermassive 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]