PKS 0805−07

PKS 0805−07, also cataloged as PMN J0808−0751 and 4FGL J0808.2−0751, is a quasar in the constellation Monoceros. Its light has traveled at least 10 billion years to reach Earth, given a redshift of 1.83. This object is a high-redshift blazar, meaning it is a powerful, radio-loud active galactic nucleus whose relativistic jet is aimed nearly directly at our planet.

The quasar emits radiation across the electromagnetic spectrum, with strong gamma-ray detections (above roughly 100 MeV) by the Large Area Telescope, and shows extreme variability in all wavelengths. Based on its optical spectral lines—where the equivalent width is either above or below 5 Å—it is classified as a flat-spectrum radio quasar (FSRQ) with prominent emission lines. Like other FSRQs, it has high bolometric luminosity and thermal activity linked to an accretion disk, visible in its optical and ultraviolet spectra. It also displays radio polarization above 1% at 1.4 GHz and hosts a spinning black hole.

Compared to BL Lacertae objects, PKS 0805−07 has lower electron energy (γ p ≲ 1.6 × 10³) and a stronger magnetic field, with a smaller ratio of electron energy to magnetic energy. In the gamma-ray luminosity versus photon index plane, it separates from BL Lacs by the relation Γ = -0.127 log ly + 8.18, with an 88.6% success rate. Very Long Baseline Array observations at 15 GHz across five epochs from January 1996 to August 2019 reveal a core-jet morphology. The source is core-dominated and asymmetric, unlike lobe-dominated sources, due to modest relativistic motion (β ≈ 0.20) within its radio lobes.

Since April 2009, the Large Area Telescope has detected high gamma-ray activity from PKS 0805−07, and it was noted as having one of the fastest superluminal motions among quasars at that time. Between November 17 and 19, 2022, the AGILE satellite observed an ongoing bright gamma-ray flare from this source, with a flux of F(>100 MeV) = (2.7 ± 0.8) × 10⁻⁶ photons/cm²/s at about 6 sigma significance.