Research

Magnetic field in relativistic jets of supermassive black holes

Master Thesis Supervised by Dr. José Luis Gómez

Instituto de Astrofísica de Andalucía (IAA-CSIC), Granada, Spain

Aim: To analyse the multi-frequency VLBA polarimetric observations from the BG216 program to determine the structure of the magnetic field in the jet of AGN. The observations include quasars (3C 273, CTA 102), BL Lac objects (BL Lac, 0716+714) and radio galaxies (3C 111, 3C 120). Additionally, we will also analyse some VLBA archival polarimetric data of different AGN. Total intensity and linearly polarized images, and rotation measure (RM) maps will be produced to determine the structure of the magnetic field from the analysis of Faraday rotation and the polarization angle. This will allow us to the analyse the magnetic field in the jets of different AGN at different spatial scales and hence allow us to understand the jet formation and stability.

Elementary statistical analysis of all the sources analysed will be performed which will allow us to understand the qualitative differences in the different sources. The output of this will be useful in conducting a large-scale studies of jets in AGN like the MOJAVE and the VLBA-BU-BLAZAR programs. The results will be published in a research paper in a peer-reviewed journal.

Status: For 0716 +714, the initial phase and amplitude calibration are performed on the AIPS using ParselTongue following the standard procedure for polarimetric observations. The data is cleaned, self- calibrated, and imaged both in total and polarized intensity with Difmap. The analysis for rest of the sources will be completed by January 2022.

Skills obtained (till October 2021): Understanding of VLBI, calibration using AIPS and ParselTongue, self-calibration, cleaning and imaging of data using Difmap and eht-imaging.

Unravelling the origin of extended radio emission in narrow-line Seyfert 1 galaxies with JVLA

Publication: arXiv:2109.07841 , Accepted for publication in Astronomy & Astrophysics, 16 Sep 2021.

Supervisor: Dr. Emilia Järvelä

European Space Agency, European Space Astronomy Centre, Spain

Aim: To determine the predominant source of radio emission in a sample of 44 NLS1s, selected based on their extended kpc-scale radio morphologies at 5.2 GHz.

Analysis: We accomplish this by analysing their spatially resolved radio spectral index maps, centred at 5.2 GHz, as the spectral index carries information about the production mechanisms of the emission. The data is calibrated using the EVLA pipeline and the radio maps and spectral index maps are produced using the CASA tclean task to do multi-term (multi-scale) multi-frequency synthesis, mt-mfs. Additionally tapered maps are produced to enhance the sensitivity to extended structures. Post-imaging, several correction steps were performed to achieve the final spectral index maps.

Results: We find an extraordinary diversity among our sample. Due to the variety seen in NLS1s simple proxies, such as the star formation diagnostics also employed in this paper, and the radio loudness parameter, are not ideal tools for characterising NLS1s. We emphasise the necessity of examining NLS1s as individuals, instead of making assumptions based on their classification.

Skills obtained: Understanding of interferometry technique and AGN, calibration and imaging using CASA, producing and understanding spectral index maps.

QSO PG 1630+377 Lyman edge polarisation

First Author Paper, Manuscript in Preparation

Collaboration: R. Antonucci, D. Hines, M. Kishimoto, A. Acharya

According to Koratkar A. et al., 1995, the polarisation of the quasar measured with the HST/FOS showed a steep rise below the Lyman edge, values reaching above ∼ 20%, never seen before in non-blazar active galaxies. The aim of this paper was to verify this result using the HST/FOC observations in optical/uv by determining the polarisation on both sides of the Lyman edge. The photutils package of AstroPy was used to analyse the data to find that the polarisation is only ~ 3%. We also followed up with the same set of FOS observations in Koratkar A. et al., 1995 to find that the results are incorrect. We have just completed the manuscript to be submitted to a peer-reviewed journal.