Discovery of a new subparsec counterjet in NGC 1275: the inclination angle and the environment

TL;DR

This paper reports the discovery of a new counterjet in NGC 1275, providing insights into the jet orientation, environment, and accretion disk properties near the galaxy's central black hole.

Contribution

It presents the first detection of a subparsec counterjet in NGC 1275 and constrains the jet inclination angle and surrounding environment.

Findings

Jet inclination angle estimated at 65°±16°

Counterjet exhibits a strongly inverted spectrum

Central black hole is surrounded by a dense, inhomogeneous accretion disk

Abstract

We report the detection of a new feature at the centre of NGC 1275 in the Perseus cluster, hosting the radio source 3C 84. This feature emerges ~ 2 mas (~ 0.8 pc) north of the central core in recent 15 and 43 GHz VLBA images, and seems to be the counterjet to a known radio jet expanding to the south of the core. Apparently, the two jets were born through an outburst around 2005. From the ratio of the apparent lengths of the two jets from the core, we found that the jet angle to the line of sight is \theta=65^\circ\pm 16^\circ, which is not much different from the angle of the outer jets generated by an activity around 1959 and constrains theories on gamma-ray emission from jets. The new northern jet has a strongly inverted spectrum in contrast with the southern jet. This suggests that the central black hole is surrounded by a subparsec-scale accretion disk with the density of >~ 10^5 cm^-3. The brightness of the counterjet suggests that the disk is highly inhomogeneous. The ambient gas density in the direction of the jet is ~ 8 cm^-3 if the current jet activity is similar to the past average.