# Research Section :::info This page is a brief collection of all my present research activities. Here I put the results obtained from the various research projects, few talks/posters that I present related to those results and the resulting publications out of these projects. I will also attempt to write *popular science* level articles related to various aspects of my work. ::: --- <iframe width="660" height="415" src="https://www.youtube.com/embed/FPF1X13wbDI" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> > *This animation is an artistic impression of the inner regions of an active galaxy. The animation starts with the optical image of 3C273, a very well known quasar and zooms in up to the sub-parsec scale, where the clumps of gas known as the Broad Line Region (BLR) clouds exist embedded beneath a torus of dust.* (video Courtesy: ESO YouTube channel) --- In early [February 1963](https://earthsky.org/space/this-date-in-science-maartin-schmidt-discovers-first-known-quasar) Martin Schmidt at the California Institute of Technology, recognized that the spectrum of a radio detected source 3C 273 could be interpreted as if the source is located at red-shift 0.16. This was the first ever discovered *quasar*, short for *quasi stellar source* as it was initially known. Within a few years, a lot of such extra-galactic sources were discovered which since then are known as Active galactic Nuclei or AGN. The term quasar is now commonly used for AGN with high luminosity. Active galaxies differ from normal galaxies by the fact that they are luminous objects which outshine their own host galaxies and the high luminosity arises due to the actively accreting Super massive Black Hole (SMBH) residing at the centre. This activity provides us observational signature in all the energy bands. The accretion of matter can be described in the form of optically thick, geometrically thin accretion disk formed in the vicinity of the SMBH. Click here to [know more.](https://ned.ipac.caltech.edu/level5/Cambridge/frames.html) --- :::success ### My Ph.D. thesis is based on resolving the inner regions of these AGN through multiple wave band observations to understand the nature, structure and dynamics of matter there. ::: # Ongoing projects: This is a list of ongoing research projects I am involved in currently. - Resolving the accretion disk structure in AGN. - Understanding the dynamics of gas in the inner regions of AGN: - Microvariability study for a handful of interesting AGN: - Changing look Active Galaxies: Unraveling the AGN host and the role of environment in triggering AGN activity: - Searching for very high redshift quasars: # Other things: ## A collection of review papers: Written by eminent experts in the field, I have put together a collection of books and review papers aimed at beginner student in the field of AGN astronomy. I also go through these papers from time to time in order to understand and revise the concepts and terminology involved in the fiele of AGN research. [Click here](https://hackmd.io/@research-page/agn-review) to see these papers. ## Aperture photometry script to make things faster: We are developing a [code](https://github.com/viveikjha/aperture_photometry) to perform aperture photometry on data obtained through the 1.3m Devasthal fast optical Telescope. We are in the process of developing a photometry pipeline and this code is an integral part of the same. We aim to make this package work on data from any telescope with minor tweaks here and there. The salient features are: 1. This is being developed as a pure PYTHON software. 2. None of the operations depend on IRAF tasks. We reiterate here that the aim is not to discourage IRAF and/or related pacakges, but with time since the packages have become unsupported and PYTHON packages have developed enough to perform all related tasks. For image display and related purposes, we use the GINGA package instead of DS9. 3. To reduce the images we use CCDPROC alongwith our custom written tools. 4. The PYTHON package PHOTUTILS is being used for the aperture photometry. We built all our codes on Python 3.6+. The required packages are: (It is recommended to install packages though pip and keep them to the latest versions. We execute the code mostly through Google Colab, so the latest versiosn of these packages are automatically picked. ) 1. Numpy 2. Astropy and its affiliated packages: (astropy 4.0 and above) 3. Photutils (photutils 0.6 and above) 4. CCDProc 5. Astroalign 6. astroquery 7. Matplotlib 8. Ginga We aim it to develop it as a fast and easy to handle alternative to the users dependent on IRAF/DAOPHOT kind of software. Currently, the work is slow on this as I have been busy with other projects. I hope to pick it up soon.
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Some review papers which must be read by every beginner student in quasar astronomy.

This is a list of papers related to Active Galactic Nuclei. This list is not aimed to be comprehensive as new knowledge keeps getting on every few days. I'll keep updating this list time and again to keep this list current and meaningful. I am including the paper title and abstracts as well, to save some of my time and efforts. All the articles have links to the full articles available online. 1. The emission lines of quasars and similar objects Kris Davidson, Hagai Netzer (1979) link for full paper. Much of our information about quasars is derived from their emission-line spectra. The analysis of such spectra has become an intricate subject which differs considerably from traditional, low-density nebular astrophysics. This review is intended to explain our present understanding of the situation, including some aspects of galactic nuclei whose luminosities are more modest than quasars. Quasars line-emitting regions are probably photoionized (even if supplementary heating processes also occur). So far, models have been constructed which include ionization and thermal equilibria, the transfer of resonance-line and related photons, and the likely effects of absorption and scattering by dust grains. From comparisons between emission-line intensities produced in these models and observed quasars spectra, it appears that certain densities and pressures and size scales occur in or around quasars. The relative abundances of nitrogen, and oxygen in particular —are moderately "overabundant" elements are not very far from solar values, although it is suspected that heavy elements carbon, in quasars. The emission-line intensities also provide indirect information about quasars ultraviolet and soft-x-ray continua; there are hints that photons with energies between 20 and 300 eV which are not directly observable may even represent the peak of the luminous output of a typical quasar. Finally, some gas-dynamical questions, while extremely important, are very difficult to answer, because of a lack of observables. 2. An introduction to active galactic nuclei: Classification and unification

2/10/2021
Talks presented so far.

This page is a collection of various talks I have presented at my home institute and/or national/international seminars, conferences or workshops. ARIES annual research scholars' review , Spetember 2020: BAO meeting, Armenia, Spetember 2020: ARIES online seminar series, April 2020: Poster presented in Guilin, China, September 2019.

10/11/2020
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