# Research Section
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) Maarten 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)
### 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.
## 1. Resolving the accretion disk structure in AGN.
As the innermost regions of AGN are too difficult to resolve spatially, a technique known as *Reverberation Mapping* is used to resolve these innermost regions. As the light travels from the inner to our regions, the fluctuations in the two regions can be recorded, with a lag which is understood as the light travel time. This technique yields the size of the accretion disk. We perform simultaneosu monitoring in the multiple wavelengths to obtain this *lag* through the flux variations over a period of time. Currently, our analysis is based on the multi epoch observations in optical bands (UBVRI) using a network of robotic telescopes around the world. We have also proposed space based observations in order to understand the accretion disk structure for a handful of AGN.
## 2. Understanding the dynamics of gas in the inner regions of AGN:
We don't know what is the structure and the dynamics of gas in the broad line region (BLR) of AGN. To understand the dynamics of matter in these regions, we use spectroscopy as a tool. The various emission lines (H$\alpha$, H$\beta$, MgII, CIV etc. ) originating from these regions can be resolved using ground based spectroscopic measurements and these lines provide clues to the structure and dynamics of matter in these regions. We have used the spectra from Sloan Digital Sky Survey (SDSS) to understand the properties for a large sample (250+) of AGN, a majority of which consist of the peculiar class of Active Galaxies: The Narrow Line Seyfert 1 galaxies. We already have exciting results from this project and we will be communicating this paper very soon.
## 3. Microvariability study for a handful of interesting AGN:
AGN are known to be variable at all time scales. In this project, we use a handful of peculiar Narrow Line Seyfert 1 (NLSy1) Galaxies, and perform microvariability study in order to check for the variability at smallest time scales. We also try to relate the phenomenon of jet launching with the microvariability observed in this sample of AGN as in the previous works, many of them have been reported to have jets. Microvariability has indeed been observed in some of the AGN in our sample at a statistically significant level.
## 4. Changing look Active Galaxies: Unraveling the AGN host and the role of environment in triggering AGN activity:
Discovery of changing look active galaxies has recently challenged the unified model of active galaxies, however, the possible underlying physical mechanism responsible for the changing-look phenomena is still unclear. We use multi-band polarimetric observations of these changing look AGNs (CLAGN) with the aim of constraining the polarization state and angle of these CLAGNs, which allows us to understand the AGN host galaxies with respect to the general population of galaxies.
## 5. Searching for very high redshift quasars:
High redshift quasars, being the most luminous non-transient objects, hold the keys to the understanding of the universe during and immediately after the epoch of cosmic re-ionization and the growth of Super Massive Black Holes (SMBH) in that era. However, studying the properties of these systems at redshift (z) beyond 5 remains challenging. Using the instruments installed at our facility, the Devasthal Optical Telescope (DOT), we are studying a sample of quasars with photometric redshift z > 5. We seek to constrain their accurate redshifts and quasar properties determined by the Gunn Peterson trough signatures and utilize the prominent emission lines to estimate the SMBH mass. The presence or absence of the Gunn Peterson trough indicates whether the Intergalactic medium (IGM) is already ionized at such redshifts and thus provide clues about the quasar neighborhoods. Using the subset of IR bright quasars, the quasar properties which include the SMBH mass can be studied using the CIV and MgII emission lines arising out of the Broad-line region of these quasars which are detected in the IR wavelength at these high redshifts.
# Conference Proceedings:
1. *[Properties of Broad and Narrow Line Seyfert galaxies selected from SDSS](https://ui.adsabs.harvard.edu/abs/2020CoBAO..67..219J/abstract)*. Vivek Kumar Jha, Hum Chand, and Vineet Ojha. Communications of the Byurakan Astrophysical Observatory (ComBAO), Volume 67, Issue 2, December 2020.
# Talks presented so far.
This page is a collection of talks I have presented so far during my Ph.D. research work. [Click here](https://hackmd.io/@research-page/talks-presented) to know more.
# 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. )
2. Astropy and its affiliated packages: (astropy 4.0 and above)
3. Photutils (photutils 0.6 and above)
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.