Perpustakaan Digital ITB

Extragalactic jets are high-energy astrophysical phenomena that are found in the radio-loud active galactic nuclei (AGN). The jet is a collimated ow of plasma that propagates at nearly the speed of light. The AGN jet is emanated from the center of the galaxy, and ultimately powered by the accretion onto the supermassive black hole (SMBH) and propagates through the intergalactic medium beyond its host galaxies. The jet can expand until kilo-parsecs (kpc) to Mpc. Relativistic astrophysical jets are seen not only in the radio galaxies and quasars but also in supernovae and smaller black hole systems like microquasars. This thesis will be focused on the jet from a radio galaxy. The study of relativistic jets has been a great eort from multi-messenger astronomy. How the jet is produced, accelerated, and collimated is one of the most important but dicult questions in astronomy, and over the past decades, extensive studies have been made from theory/simulations to observations. To better understand the formation of relativistic jets from SMBH, Very Long Baseline Interferometry (VLBI) is especially a powerful observational technique since one can directly resolve the jet formation scales near SMBH at very high angular resolution. In this thesis, we study the collimation prole of the jets in the nearby radio galaxy M84 using Very Long Baseline Array observations and Very Large Array data. We revealed a detailed collimation prole of the M84 jet over distances from 103 rs to 108 rs. We found that the jet geometry shows a transition from a semi-parabolic shape to a conical/hyperbolic shape at a distance of 104 Schwarzschild radii (rs). We further compared the obtained M84 jet prole with M87 whose jet collimation prole is well established in the literature. We found that the M84 jet is less collimated than the M87 jet with a parabolic power-law index of a = 0:72 and a = 0:56, respectively. The collimation break occurs about one order smaller than the Bondi radius at 3:8 105 rs. This case is dierent from the M87 jet where the collimation break was found near the Bondi radius. The closer transition of the jet is to the SMBH means that the jet is not well collimated. This may be caused by the low accretion rate, low jet power, and the low intergalactic medium in the environment of M84.