We present imaging and photometric studies of the radio galaxy NGC 1316 (Fornax A) using high spatial resolution near-ultraviolet (NUV) and far-ultraviolet (FUV) imaging telescopes of the first Indian multi-wavelength space observatory AstroSat. The residual maps of UV emission obtained from the subtraction of smooth models witness peculiar features within the central few kpc (1–2 kpc) region. The spatial correspondence between the radio emission maps and FUV imaging study reveal that the UV emitting sources are displaced away from the centre by the AGN outburst (radio jet). The presence of rims andclumpy structures in the outskirt of this galaxy delineate that the galaxy has acquired a large fraction of gas through merger-like events and is still in the process of settling. The estimates of the star formation rates (SFR) using FUV and NUV luminosities are found to be 0.15 $M_{\odot}$ yr$^{-1}$ and 0.36 $M_{\odot}$ yr$^{-1}$, respectively, and provide the lower limit due to the screen effect. The estimated lower rates of SFR in this galaxy probablyrepresent its quenching due to the AGN driven outflows emanating from the central engine of NGC 1316.

We study the multi-wavelength variability of the blazar Mrk 421 at minutes to days timescales using simultaneous data at c-rays from Fermi, 0.7–20 keV energies from AstroSat, and optical and near infrared (NIR) wavelengths from ground based observatories. We compute the shortest variability timescalesat all of the above wave bands and find its value to be $\sim$1.1 ks at the hard X-ray energies and increasingly longer at soft X-rays, optical and NIR wavelengths as well as at the GeV energies. We estimate the value ofthe magnetic field to be 0.5 Gauss and the maximum Lorentz factor of the emitting electrons $\sim 1.6 \times 10^5$ assuming that synchrotron radiation cooling drives the shortest variability timescale. Blazars vary at a largerange of timescales often from minutes to years. These results, as obtained here from the very short end of the range of variability timescales of blazars, are a confirmation of the leptonic scenario and in particular the synchrotron origin of the X-ray emission from Mrk 421 by relativistic electrons of Lorentz factor as high as $10^5$. This particular mode of confirmation has been possible using minutes to days timescale variability data obtained from AstroSat and simultaneous multi-wavelength observations.

We present a detailed timing and spectral study of an extremely variable narrow-line Seyfert 1 galaxy NGC 4748 using observations in the year 2017 and 2014 performed with AstroSat and XMM-Newton, respectively. Both observations show extremely variable soft and hard X-ray emission that are correlated with each other. In the 2014 data set, the source retains its general behaviour of ‘‘softer when brighter’’ while the 2017 observation exhibits a ‘‘harder when brighter’’ nature. Such changing behaviour is rare in AGNs and is usually observed in the black hole binary systems. The ‘‘harder when brighter’’ is confirmed with the anticorrelation between the photon index and the 0.3–10 keV power-law flux. This suggests a possible change in the accretion mode from standard to the advection-dominated flow. Additionally, both the observations show soft X-ray excess below 2 keV over the power-law continuum. This excess was fitted with a single or multiple blackbody component(s). The origin of soft excess during the 2017 observation is likely due to the cool Comptonization as the photon index changes with time. On the other hand, the broad iron line anddelayed UV emission during the 2014 observation strongly suggest that X-ray illumination onto the accretion disk and reflection and reprocessing play a significant role in this AGN.

We present the results obtained from timing and spectral studies of the highly obscured low luminosity active galactic nucleus NGC 4941 using data obtained from the nuclear spectroscopic telescope array and the Neil Gehrels Swift observatories. We find similar variability in 3–10 keV and 10–60 keVenergy ranges with fractional rms variability of $\sim$14%. We investigate broad-band spectral properties of the source in 3–150 keV range, using data from NuSTAR and Swift/BAT, with phenomenological slab model and physically motivated mytorus model. From the spectral analysis, we find heavy obscuration with global average column density of the obscured material as $3.09^{+1.68}_{-1.01}\times 10^{-24}$ cm$^{-2}$. Evidence of a strong reflectioncomponent is observed in the spectrum. We detect a strong iron line with equivalent width of $\sim$1 keV. From the slab model, we obtain the exponential cutoff energy as $177^{+92}_{-16}$ keV. From this, we estimate the Comptoncloud properties with the hot electron temperature $kT_e= 59^{+31}_{-5}$ keV and the optical depth s $\tau=2.7^{+0.2}_{-1.6}$.

We present an estimation and analysis of Near Infrared (NIR) background for the astronomical site at Mount Abu. Mount Abu Observatory is situated at Gurushikhar, Rajasthan, India, operated by the Physical Research Laboratory. Data obtained from the NIR observations of various sources using the Near Infrared Camera/Spectrograph (NICS) on the 1.2-m telescope are used to derive the NIR background estimates. We notice seasonal variations in these values, with the summer months showing brighter background compared to the winter. We also present a comparison of synthetic atmospheric transmission at Mount Abu with otherIndian observatories at various altitudes. We identify the plausible contributors to the NIR background in our observations and discuss the potential ones that can contribute to the noticed seasonal variations. Overall, we found that the NIR background does not show any systematic variation over the period of observations from 2010 to 2019. The results reported here are specific to the NICS instrument on the 1.2-m telescope.