Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342

Abstract

We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multi-frequency Very Long Baseline Array observations. This source is known as the nearest γ-ray emitting radio-loud narrow line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating the jet being continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical-like shape. The location of the "collimation break" is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance of the order of ∼100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting the coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy γ-ray flares detected by the F ermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile between the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial on this source and NLS1s in general.

Mapping the Narrow-Line Seyfert 1 Galaxy 1H 0323+342

“…The structure of the relativistic jet from J0324 + 3410 has been studied at high-resolution radio frequencies [3,4,5,6,7]. Here we summarise their results.…”

“…The inner region of the jet has a parabolic shape, while the outer region has a conical shape (see Fig. 2 in [6]). At the collimation break, the jet width is squeezed to half its value (see Fig.…”

“…Indeed, J0324 + 3410 has been the target of many studies at high-resolution radio frequencies [3,4,5,6,7], and is currently under monitoring in the framework of the MOJAVE program 2 [8]. It was found that the jet from J0324 + 3410 is one sided with a change in shape at about ∼ 7 mas from the core, being parabolic close to the central black hole, and becoming conical as the distance increases [5,6,7]. This quasi-stationary feature is similar to HST-1 in M87, although the radial distance from the central singularity is ∼ 10 7−8 r g , two orders of magnitudes farther than HST-1 from M87 [5,6,7].…”

“…It was found that the jet from J0324 + 3410 is one sided with a change in shape at about ∼ 7 mas from the core, being parabolic close to the central black hole, and becoming conical as the distance increases [5,6,7]. This quasi-stationary feature is similar to HST-1 in M87, although the radial distance from the central singularity is ∼ 10 7−8 r g , two orders of magnitudes farther than HST-1 from M87 [5,6,7]. Both Hada [6] and Kovalev [7] proposed that one solution could be to have a greater mass for the central black hole in J0324 + 3410, of the order of 10 8 M as suggested by [9].…”

Relativistic Jets in Gamma-Ray-Emitting Narrow-Line Seyfert 1 Galaxies

“…On pc scale a core-jet structure has observed for SBS 0846+513 [56] (Figure 5, left panel), PKS 2004−447 [102,142], 1H 0323+342 [143,144], FBQS J1644+2619 [36,145], B3 1441+476 [146], PKS 1502+036 [147], and PMN J0948+0022 ( Figure 5, right panel) [103,148], although the jet in the two latter sources is significantly fainter than that observed in the other sources. The pc scale morphology of γ-ray-emitting NLSy1 seems to be a reminiscent of blazars, suggesting Doppler boosting effect due to small jet viewing angles.…”