Khagol Bulletin # 132 (Apr 2024) - ENG

| 09 | KHAG L | No. 132 - APRIL 2024 Secondly, the same team has also complemented their results based on polarimetric observations, though using a rather smaller set of 6 WLQs, and found percentage polarization always less than 3 percentage level in contrast to much higher polarization seen in BL Lacs objects. This rule out the possibility of WLQs being radio-quiet counterpart of Bl-lac, and leads to the conclusion that perhaps the cause of the weakness of the emission line more than 3-4% on hour-like time scales and on the other hand stronger optical variability due to relativistic jets is a clear signature of the BL Lacs type of sources. As a result, carrying out intra-night optical variability of a sample of WLQs can be used as an first step to ascertain that weather the variability nature of WLQs are similar to Bl-Lac type (i.e high percentage variation) or like normal quasars (i.e low percentage variation). The monitoring is carried out by using ARIES 1.3m Devasthal Fast Optical Telescope (DFOT) where a sample of about three dozen of RQWLQs is monitored for about 5 dozen sessions with duration 3- 4hrs during a period of 3-4 years led by a PhD student Parveen Kumar in the team. Their detailed investigations as reported in a series of publications (in British Journal MNRAS) revealed that the variability duty cyce of the RQWLQs is about 3-5% which appears similar to the normal quasar, in striking contrast to the expectation of higher variability for qualifying them as radio-quite counterpart of Bl-Lac. strong emission line are the hall-mark of AGNs. Such weak or absence of emission are well understood in another subclass of AGN, known as BL-lac, where a relativistic jet is responsible for doppler boosting of their continuum emission leading to relatively weaker/absent emission lines. The jets' existence is evident from the synchrotron emission observed from them in radio waveband, which is found even more than the total emission in optical waveband. On the other hand the WLQ subs amp l e i s f ound t o be r ad i o - undetected, and hence the cause of the weakness of their emission line poses an intriguing puzzle. Due to this radio- quietness of WLQs they are also proposed as a potential candidate for the radio-quiet counterpart of BL-lac in AGNs unification scheme. The discovery of even aminuscule set of bona-fide radio-quiet BL-Lac among t h e m w o u l d h a v e f u n d a m e n t a l implications for the current understanding of AGNs and their classification scheme. To understand the nature of these newly discovered radio quiet-WLQs (RQWLWQs), a de t a i l ed s y s t ema t i c s t ud y wa s accomplished recently by the team of Prof. Hum Chand along with his students and collaborators. As a first step in their program, they have used the fact that optical variability properties can be used as a tool to discriminate among the various subclasses of AGNs. For instance, it has been established that normal quasars (i.e., non-BL-Lac type) almost never vary by ProfessorRajeshwari Dutta is an observational astronomer working in the field of galaxies. She is currently an Assistant Professor at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, India. After completing her PhD from IUCAA, she held a Humboldt Research Fellowship at European Southern Observatory (ESO) in Garching, Germany, a Postdoctoral Research Associateship at Durham University in the UK, and a Postdoctoral Research Fellowship at the University of Milano-Bicocca in Italy. Her primary research interests are in galaxy formation and evolution, particularly in the connection between gas and galaxies. Her work utilises multi- wavelength (UV to radio) spectroscopic observations to understand the role played bymultiphase gas in galaxy evolution. AGN Exploration Utilizing Data from 1-2mTelescopes: A Study of Weak Emission Line QSOs Active Galactic Nuclei (AGN) are among the mo s t f a s c i n a t i n g a n d e n i gma t i c phenomena in astrophysics. These cosmic powerhouses, harboring supermassive black holes at their cores, emit vast amounts of energy across the entire electromagnetic spectrum. Investigating the AGN environment and central engine provides crucial insights into fundamental astrophysical processes and the evolution of galaxies. While large observatories often dominate AGN research, 1-2m optical t e l escopes p l ay a s i gn i f i cant and complementary role. For instance due to the relatively smaller size of 1-2m class telescopes, it has become economically viable to carry out more frequent observations, enabling astronomers to capture transient events and study their evolution over time. This allows moderate aperture telescopes contribute in many ways such as carrying out (i) Large surveys (ii) Principle Investigator driven science p r o g r a mm e r e q u i r i n g f r e q u e n t observations, so as to compete on a level playing field for publicly available time on large telescopes for further research improvements (iii) Time domain science programs, including those that require telescopes spaced longitudinally for long time coverage. With recent advent of large spectroscopic surveys such as SDSS, a subclass of AGNs is found with Weak (or absent) Emission Lines, known as Weak Emission line quasars, contrary to the expectation as the