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A comprehensive study of the nucleus and western hotspot of Pictor A is carried out using AstroSat observations, 13 years of Fermi, and archival Swift observations, along with other published data. We report the first detection of the western hotspot of Pictor A in the far-UV band using observations from AstroSat-UVIT. The broad-band SED of the western hotspot is explained by a multizone emission scenario where X-ray emission is caused by synchrotron emission process in the substructures embedded in the diffuse region, while the emission in radio to optical is caused by synchrotron emission process in the diffuse region. We do not notice any excess in the IR band and an additional zone (beyond 2-zone) is not required to account for the X-ray emission. Our broad-band spectro-temporal study and associated modelling of the core and hotspot of Pictor A suggests that (a) gamma-rays originate in the nuclear jet and not from the hotspot (b) X-ray emission from the core of Pictor A has nuclear jet-origin instead of previously reported disk-origin., 11 pages, 4 figures, Accepted for publication in MNRAS

Measurement of black hole mass for low-$z$ ($z\leq 0.8$) Active Galactic Nuclei (AGNs) is difficult due to the strong contribution from host galaxy stellar light necessitating detailed spectral decomposition to estimate the AGN luminosity. Here, we present an empirical relation to estimate host galaxy stellar luminosity from the optical spectra of AGNs at $z\leq 0.8$. The spectral data were selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalog having a signal-to-noise ratio at 5100 \AA (SNR$_{5100}$) $>$10 containing 11415 quasars. The median total luminosity (log ($L_\text{total}$/[erg s$^{-1}$])), stellar luminosity (log ($L_\text{star}$/[erg s$^{-1}$])), and AGN continuum luminosity (log ($L_\text{cont}$/[erg s$^{-1}$])) in our sample are 44.52, 44.06, and 44.30, respectively. We fit the AGN power-law continuum, host galaxy, and iron blend contribution, simultaneously over the entire available spectrum. We found the host galaxy fraction to anti-correlate with continuum luminosity and can be well-represented by a polynomial function, which can be used to correct the stellar light contribution from AGN spectra. We also found anti-correlation between host galaxy fraction and iron strength, Eddington ratio, and redshift. The empirical relation gives comparable results of host-fraction with the image decomposition method., Comment: 6 pages, 6 figures, published in MNRASL

Active galactic nucleus (AGN) feedback during galaxy merger has been the most favoured model to explain black hole–galaxy co-evolution. However, how the AGN-driven jet/wind/radiation is coupled with the gas of the merging galaxies, which leads to positive feedback, momentarily enhanced star formation, and subsequently negative feedback, a decline in star formation, is poorly understood. Only a few cases are known where the jet and companion galaxy interaction leads to minor off-axis distortions in the jets and enhanced star formation in the gas-rich minor companions. Here, we briefly report one extraordinary case, RAD12, discovered by RAD@home citizen science collaboratory, where for the first time a radio jet–driven bubble (∼ 137 kpc) is showing a symmetric reflection after hitting the incoming galaxy which is not a gas-rich minor but a gas-poor early-type galaxy in a major merger. Surprisingly, neither positive feedback nor any radio lobe on the counter jet side, if any, is detected. It is puzzling if RAD12 is a genuine one-sided jet or a case of radio lobe trapped, compressed and re-accelerated by shocks during the merger. This is the first imaging study of RAD12 presenting follow-up with the Giant Metrewave Radio Telescope, archival MeerKAT radio data and Canada-France-Hawaii Telescope optical data.

We present multiwavelength observations and a model for flat spectrum radio quasar NVSS J141922-083830, originally classified as a blazar candidate of unknown type (BCU II object) in the Third Fermi-LAT AGN Catalog (3LAC). Relatively bright flares (>3 magnitudes) were observed on 21 February 2015 (MJD 57074) and 8 September 2018 (MJD 58369) in the optical band with the MASTER Global Robotic Net (MASTER-Net) telescopes. Optical spectra obtained with the Southern African Large Telescope (SALT) on 1 March 2015 (MJD 57082), during outburst, and on 30 May 2017 (MJD 57903), during quiescence, showed emission lines at 5325\r{A} and at $\approx$3630\r{A} that we identified as the Mg II 2798\r{A} and C III] 1909\r{A} lines, respectively, and hence derived a redshift z = 0.903. Analysis of Fermi-LAT data was performed in the quiescent regime (5 years of data) and during four prominent flaring states in February-April 2014, October-November 2014, February-March 2015 and September 2018. We present spectral and timing analysis with Fermi-LAT. We report a hardening of the gamma-ray spectrum during the last three flaring periods, with a power-law spectral index $\Gamma = 2.0$-$2.1$. The maximum gamma-ray flux level was observed on 24 October 2014 (MJD 56954) at $(7.57 \pm 1.83) \times 10^{-7}$ ph~cm$^{-2}$s$^{-1}$. The multi-wavelength spectral energy distribution during the February-March 2015 flare supports the earlier evidence of this blazar to belong to the FSRQ class. The SED can be well represented with a single-zone leptonic model with parameters typical of FSRQs, but also a hadronic origin of the high-energy emission can not be ruled out., Comment: 15 pages, 11 figures, 8 tables, accepted for publication in MNRAS (29 July 2022)

We study the relativistic, inviscid, advective accretion flow around the black holes and investigate a key feature of the accretion flow, namely the shock waves. We observe that the shock-induced accretion solutions are prevalent and such solutions are commonly obtained for a wide range of the flow parameters, such as energy (${\cal E}$) and angular momentum ($\lambda$), around the black holes of spin value $0\le a_{\rm k} < 1$. When the shock is dissipative in nature, a part of the accretion energy is released through the upper and lower surfaces of the disc at the location of the shock transition. We find that the maximum accretion energies that can be extracted at the dissipative shock ($\Delta{\cal E}^{\rm max}$) are $\sim 1\%$ and $\sim 4.4\%$ for Schwarzschild black holes ($a_{\rm k}\rightarrow 0$) and Kerr black holes ($a_{\rm k}\rightarrow 1$), respectively. Using $\Delta{\cal E}^{\rm max}$, we compute the loss of kinetic power (equivalently shock luminosity, $L_{\rm shock}$) that is enabled to comply with the energy budget for generating jets/outflows from the jet base ($i.e.$, post-shock flow). We compare $L_{\rm shock}$ with the observed core radio luminosity ($L_R$) of black hole sources for a wide mass range spanning $10$ orders of magnitude with sub-Eddington accretion rate and perceive that the present formalism seems to be potentially viable to account $L_R$ of $16$ Galactic black hole X-ray binaries (BH-XRBs) and $2176$ active galactic nuclei (AGNs). We further aim to address the core radio luminosity of intermediate-mass black hole (IMBH) sources and indicate that the present model formalism perhaps adequate to explain core radio emission of IMBH sources in the sub-Eddington accretion limit., Comment: 15 pages, 4 figures, and 3 tables; accepted for publication in MNRAS

Study of the polarization behaviour in blazars is a powerful tool to discern the role of magnetic field in the variable emission process in their relativistic jets. We present here results of our systematic investigation on the correlation between optical flux and polarization variations for eight flat-spectrum radio quasars on various timescales using data from the Steward Observatory that covers a period of $\sim$10 years. On long time scales ($\sim$several months), from a total of 79 observing cycles, in 34 observing cycles, we found a significant positive correlation between optical flux and optical polarization degree (PD), negative correlation in 3 cycles and no correlation in 42 cycles. On short time scales ($\sim$few days), in 47 out of a total of 55 epochs, we found a positive correlation between optical flux and PD, while, on the remaining 8 epochs, an anti-correlation was detected between the two quantities. Moreover, we noticed a significant positive correlation between optical and $\gamma-$ray fluxes on 14 epochs and a negative correlation between the two on one epoch. While the observed optical flux changes well fit in the shock-in-jet model, the observed changes in PD are not explainable by changes in the power-law spectral index of the relativistic electrons in the jet. Instead, the observed varied correlations between optical flux and PD could be due to multi-zone emission regions or the enhanced flux coinciding with the emergence of a new emission knot with its magnetic field either aligned or misaligned with the large scale magnetic field., Comment: 27 pages, 5 figures, 7 tables, accepted for publication in MNRAS main journal

BL Lacertae, the prototype of the BL Lacertae (BL Lac) category of blazars, underwent a giant $\gamma-$ray flare in April 2021. The Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (hereafter Fermi-LAT) observed a peak $\gamma-$ray (0.1$-$500 GeV) flux of $\sim$2 $\times$ 10$^{-5}$ photons cm$^{-2}$ s$^{-1}$ within a single orbit on 2021 April 27, which is historically the brightest $\gamma-$ray flux ever detected from the source. Here, we report, for the first time, the detection of significant minute-timescale GeV $\gamma-$ray flux variability in the BL Lac subclass of blazars by the Fermi-LAT. We resolved the source variability down to 2-min binned timescales with a flux halving time of $\sim$1 minute, which is the shortest GeV variability timescale ever observed from blazars. The detected variability timescale is much shorter than the light-crossing time ($\sim 14$ minutes) across the central black hole of BL Lac indicating a very compact $\gamma-$ray emission site within the outflowing jet. Such a compact emitting region requires the bulk Lorentz factor of the jet to be larger than 16 so that the jet power is not super Eddington. We found a minimum Doppler factor $\delta_{min}$ of 15 using the $\delta$ function approximation for the $\gamma\gamma$ opacity constraint. For a conical jet geometry, considering $\Gamma = \delta_{min}$, the observed short variability timescale suggests the very compact emission region to lie at a distance of about 8.62 $\times$ 10$^{14}$ cm from the central engine of BL Lac., Comment: 6 pages, 5 figures, 2 tables, accepted for publication in the Astronomy & Astrophysics (A&A) main journal

To understand the mass distribution and co-evolution of supermassive black holes with their host galaxy, it is crucial to measure the black hole mass of AGN. Reverberation mapping is a unique tool to estimate the black hole masses in AGN. We performed spectroscopic reverberation study using long-term monitoring data with more than 100 spectra of a radio-loud quasar PKS 0736+017 to estimate the size of the broad line region (BLR) and black hole mass. The optical spectrum shows strong H$\mathrm{\beta}$ and H$\mathrm{\gamma}$ emission lines. We generated the light curves of 5100{\AA} continuum flux ($f_{5100}$), H$\beta$, and H$\gamma$. All the light curves are found to be strongly variable with fractional variability of 69$\%$, 21$\%$, 30$\%$ for V-band, H$\beta$, and H$\gamma$ light curves, respectively. Along with the thermal contribution, non-thermal emission contributes to the estimated continuum luminosity at 5100\AA. Using different methods, e.g., CCF, {\small JAVELIN}, von-neumann, we estimated the size of the BLR, which is found to be 66.4$^{+6.0}_{-4.2}$ light days in the rest frame. The BLR size combined with the line width of H$\beta$ provides a black hole mass of 7.32$^{+0.89}_{-0.91} \times 10^{7}M_{\odot}$. The source closely follows the BLR size-luminosity relation of AGN., Comment: published in MNRAS, 13 pages, 13 figures

$\require{mediawiki-texvc}$ Supermassive black holes at the centre of active galactic nuclei (AGN) produce relativistic jets that can affect the star formation characteristics of the AGN hosts. Observations in the ultraviolet (UV) band can provide an excellent view of the effect of AGN jets on star formation. Here, we present a census of star formation properties in the Northern Star-forming Region (NSR) that spans about 20 kpc of the large radio source Centaurus A hosted by the giant elliptical galaxy NGC 5128. In this region, we identified 352 UV sources associated with Cen A using new observations at an angular resolution of $, Comment: Accepted for publication by MNRAS. Data and Jupyter notebooks are available at https://github.com/prajwel/Centaurus-A_NSR . 15 pages, 19 figures, 6 tables

We present the results obtained from our campaign to characterize the intra-night-optical variability properties of blazars detected by the {\it Fermi} Large Area Telescope. This involves R-band monitoring observations of a sample of 18 blazars, that includes five flat-spectrum radio quasars (FSRQs) and thirteen BL Lac objects (BL Lacs) covering the redshift range z = 0.085$-$1.184. Our observations, carried out using the 1.3 m J.C. Bhattacharya Telescope cover a total of 40 nights ($\sim$200 hrs) between the period 2016 December and 2020 March. We characterized variability using the power enhanced $F-$test. We found a duty cycle (DC) of the variability of about 11\% for FSRQs and 12\% for BL Lacs. Dividing the sample into different sub-classes based on the position of the synchrotron peak in their broadband spectral energy distribution (SED), we found DC of $\sim$16\%, $\sim$10\% and $\sim$7\% for low-synchrotron peaked (LSP), intermediate synchrotron peaked (ISP) and high synchrotron peaked (HSP) blazars. Such high DC of variability in LSP blazars could be understood in the context of the R-band tracing the falling part (contributed by high energy electrons) of the synchrotron component of the broadband SED. Also, the R-band tracing the rising synchrotron part (produced by low energy electrons) in the case of ISP and HSP blazars, could cause lesser variability in them. Thus, the observed high DC of variability in LSP blazars relative to ISP and HSP blazars is in accordance with the leptonic model of emission from blazar jets., Comment: 18 pages, 9 figures, 4 tables, accepted for publication in The Journal of Astrophysics and Astronomy

We report here results on the analysis of correlated flux variations between the optical and GeV $\gamma$-ray bands in three bright BL Lac objects, namely AO\, 0235+164, OJ 287 and PKS 2155$-$304. This was based on the analysis of about 10 years of data from the {\it Fermi} Gamma-ray Space Telescope covering the period between 08 August 2008 to 08 August 2018 along with optical data covering the same period. For all the sources, during the flares analysed in this work, the optical and $\gamma$-ray flux variations are found to be closely correlated. From broad band spectral energy distribution modelling of different epochs in these sources using the one zone leptonic emission model, we found that the optical-UV emission is dominated by synchrotron emission from the jet. The $\gamma$-ray emission in the low synchrotron peaked sources AO\, 0235+164 and OJ 287 are found to be well fit with external Compton (EC) component, while, the $\gamma$-ray emission in the high synchrotron peaked source PKS 2155$-$304 is well fit with synchrotron self Compton component. Further we note that the $\gamma$-ray emission during the high flux state of AO 0235+164 (epochs A and B) requires seed photons from both the dusty torus and broad line region, while the $\gamma$-ray emission in OJ 287 and during epochs C and D of AO\,0235+164 can be modelled by EC scattering of infra-red photons from the torus., Comment: 17 pages, 26 figures, Accepted for publication in MNRAS (In the previous edition, a minor correction was made.)

Three fields in the outskirts of the Small Magellanic Cloud were observed by the UltraViolet Imaging Telescope (UVIT) on board AstroSat, between 2017 December 31 and 2018 January 1. The observations were carried out on a total of seven filters, three in the far-ultraviolet (FUV; 1300–1800 Å) band and four in the near-ultraviolet (NUV; 2000–3000 Å) band. We carried out photometry of these observations that have a spatial resolution better than 1.″5. We present here the first results of this work, which is a matched catalog of 11,241 sources detected in three FUV and four NUV wavelengths. We make the catalog available online, which would be of use to the astronomical community to address a wide variety of astrophysical problems. We provide an expression to estimate the total count rate in the full point-spread function of UVIT that also incorporates the effect of saturation.

The blazar OQ 334 displayed a {\gamma}-ray flare in 2018, after being in the long quiescent {\gamma}-ray state since 2008. Subsequent to the flare, the source was in a higher {\gamma}-ray flux state and again flared in 2020. We present here the first spectral and timing analysis of the source at its various flaring states. During the higher {\gamma}-ray state, we found four major peaks identified as P1, P2, P3, and P4. From timing analysis, we found the rise and decay time of the order of hours with the fastest variability time of 9.01+/-0.78 hr. We found the highest {\gamma}-ray photon of 77 GeV during P4, which suggests the location of the {\gamma}-ray emitting region at the outer edge of the broad-line region or the inner edge of the torus. The {\gamma}-ray spectral analysis of the source indicates that during P4, the {\gamma}-ray spectrum clearly deviates from the power-law behavior. From cross-correlation analysis of the {\gamma}-ray and radio lightcurves, we found that the two emission regions are separated by about 11 pc. Our broadband spectral energy distribution modeling of the source during quiescent and active phases indicates that more electron and proton power are required to change the source from low flux to high flux state. The Anderson-Darling test and histogram fitting results suggest that the three days binned {\gamma}-ray fluxes follow a lognormal distribution., Comment: 15 pages, 12 figures, 5 tables, Accepted for publication in MNRAS

The observed nuclear X-ray emission in the radio-quiet category of active galactic nuclei (AGN) is believed to be from a compact region, the corona situated in the vicinity of the central supermassive black holes (SMBH). The shape of the X-ray continuum, among other factors, depends on the temperature of the corona ($\rm{kT_{e}}$). The launch of the Nuclear Spectroscopic Telescope Array (NuSTAR) has led to the determination of the high energy cut-off ($\rm{E_{cut}}$; and thereby $\rm{kT_{e}}$) in many AGN. In a handful of sources, multiple observations with NuSTAR have also revealed changes in $\rm{E_{cut}}$. In this work we aimed to investigate the variation in $\rm{kT_{e}}$ in three AGN, namely NGC 3227, NGC 5548 and MR 2251$-$178 using more than one epoch of data on a source from NuSTAR. We carried out spectral analysis of multiple epochs of data acquired using NuSTAR on the three sources including a few new observations not published so far. By fitting Comptonization model to the data we determined the temperature of the corona and also investigated changes in $\rm{kT_{e}}$ if any in these sources. In NGC 3227, we found evidence for variation in $\rm{kT_{e}}$. We found no correlation of $\rm{kT_{e}}$, photon index ($\Gamma$), reflection fraction ($R$) and optical depth ($\tau$) with flux, while, $\tau$ is found to anti-correlate with $\rm{kT_{e}}$. These could be due to more than one physical process at work in the source that causes the change in $\rm{kT_{e}}$. Conclusive evidence for the variation in $\rm{kT_{e}}$ is not found in MR 2251$-$178 and NGC 5548., Comment: 18 pages, 18 figures, Accepted for publication in Astronomy & Astrophysics (A&A)

Blazars, a class of active galactic nuclei, emit over the entire accessible electromagnetic spectrum and modelling of their broad-band spectral energy distribution (SED) is the key to constrain the underlying emission mechanisms. Here we report the results on the one-zone leptonic emission modelling carried out on the blazar 4C+21.35 using multiwavelength data spanning over the period 2008–2018. Broad-band SED modelling using γ-ray data from Fermi-Large Area Telescope, X-ray data from Swift-XRT and AstroSat, and UV–optical data from Swift-UVOT, AstroSat, and Catalina Real-Time Transient Survey was carried out at seven different epochs, including three γ-ray flaring episodes and four quiescent periods (three long-term averaged ones and one during AstroSat observing period). Our SED modelling suggests that two compact emission regions originating at a different time outside the broad-line region and moving away from the core with variation primarily in the jet electron spectra can explain the emission from the high-, moderate-, and low-activity periods. The emissions from high- and first low-activity states are likely to have originated in the first region. The moderate- and second low-activity states are likely due to the second emission region with fresh particle acceleration/injection at a later time.

Blazars are known to show flux variations over a range of energies from low energy radio to high energy gamma-rays. Cross-correlation analysis of the optical and $\gamma$-ray light curves in blazars shows that flux variations are generally correlated in both bands, however, there are exceptions. We explored this optical-GeV connection in four flat spectrum radio quasars (FSRQs) by a systematic investigation of their long term optical and $\gamma$-ray light curves. On analysis of the four sources, namely 3C 273, 3C 279, PKS 1510$-$089 and CTA 102 we noticed different behaviours between the optical and GeV flux variations. We found instances when (i) the optical and GeV flux variations are closely correlated (ii) there are optical flares without $\gamma$-ray counterparts and (iii) $\gamma$-ray flares without optical counterparts. To understand these diverse behaviours, we carried out broad band spectral energy distribution (SED) modelling of the sources at different epochs using a one-zone leptonic emission model. The optical-UV emission is found to be dominated by emission from the accretion disk in the sources PKS 1510$-$089, CTA 102 and 3C 273, while in 3C 279, the synchrotron radiation from the jet dominates the optical-UV emission. Our SED analysis indicates that (i) correlated optical and $\gamma$-ray flux variations are caused by changes in the bulk Lorentz factor ($\Gamma$), (ii) $\gamma$-ray flares without optical counterparts are due to increase in $\Gamma$ and/or the electron energy density and (iii) an optical flare without $\gamma$-ray counterpart is due to increase in the magnetic field strength., Comment: 22 pages, 32 figures, accepted to MNRAS

Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energy, which also shows variations. We present here our results on the correlation analysis between optical flux and polarization degree (PD) variations in a sample of 11 BL Lac objects using $\sim$ 10 years of data from the Steward Observatory. We carried out the analysis on long-term ($\sim$ several months) as well as on short-term timescales ($\sim$ several days). On long-term timescales, for about 85% of the observing cycles, we found no correlation between optical flux and PD. On short-term timescales, we found a total of 58 epochs with a significant correlation between optical flux and PD, where both positive and negative correlation were observed. In addition, we also found a significant correlation between optical flux and $\gamma$-ray flux variations on long-term timescales in 11% of the observing cycles. The observed PD variations in our study cannot be explained by changes in the power-law spectral index of the relativistic electrons in the jets. The shock-in-jet scenario is favoured for the correlation between optical flux and PD, whereas the anti-correlation can be explained by the presence of multi-zone emission regions. The varying correlated behaviour can also be explained by the enhanced optical flux caused by the newly developed radio knots in the jets and their magnetic field alignment with the large scale jet magnetic field., Comment: 20 pages, 6 figures, accepted for publication in MNRAS

We present the timing and spectral analysis of the Compton Thick Seyfert 2 active galactic nuclei NGC 1068 observed using {\it NuSTAR} and {\it XMM-Newton}. In this work for the first time we calculated the coronal temperature ($\rm{kT_{e}}$) of the source and checked for its variation between the epochs if any. The data analysed in this work comprised of (a) eight epochs of observations with {\it NuSTAR} carried out during the period December 2012 to November 2017, and, (b) six epochs of observations with {\it XMM-Newton} carried out during July 2000 to February 2015. From timing analysis of the {\it NuSTAR} observations, we found the source not to show any variations in the soft band. However, on examination of the flux at energies beyond 20 keV, during August 2014 and August 2017 the source was brighter by about 20\% and 30\% respectively compared to the mean flux of the three 2012 {\it NuSTAR} observations as in agreement with earlier results in literature. From an analysis of {\it XMM-Newton} data we found no variation in the hard band (2 $-$ 4 keV) between epochs as well as within epochs. In the soft band (0.2 $-$ 2 keV), while the source was found to be not variable within epochs, it was found to be brighter in epoch B relative to epoch A. By fitting physical models we determined $\rm{kT_{e}}$ to range between 8.46$^{+0.39}_{-0.66}$ keV and 9.13$^{+0.63}_{-0.98}$ keV. From our analysis, we conclude that we found no variation of $\rm{kT_{e}}$ in the source., Comment: 13 pages, 14 figures, accepted for publication in MNRAS

The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by the corona. Moreover, the observed X-ray variability can also originate in the disc, and gets propagated and amplified by the jet. Here, we present results on the BL Lac object Mrk 421 using the NuSTAR data acquired during 2017 when the source was in a moderate X-ray brightness state. For comparison with high jet activity, we also considered one epoch data in April 2013 during a very high X-ray brightness state. Our aim is to explore the possibility of the signature of accretion disc emission in the overall X-ray emission from Mrk 421. The spectral fitting of the data using the two component advective flow model shows gives (a) the size of the dynamic corona at the base of the jet from ~28 to 10 r$_s$, (b) the disc mass accretion rate from 0.021 to 0.051 $\dot M_{\rm Edd}$, (c) the halo mass accretion rate from 0.22 to 0.35 $\dot M_{\rm Edd}$, and (d) the viscosity parameter of the Keplerian accretion disc from 0.18 $-$ 0.25. In the assumed model, the total flux, disc and jet flux correlate with the radio flux observed during these epochs. We conclude that the spectra of all the epochs of Mrk 421 in 2017 are well described by the accretion disc based two component advective flow model. The estimated disc and jet flux relations with radio flux show that accretion disc can contribute to the observed X-ray emission, when X-ray data (that covers a small portion of the broad band spectral energy distribution of Mrk 421) is considered in isolation. However, the present disc based models are disfavoured with respect to the relativistic jet models when considering the X-ray data in conjunction with data at other wavelengths., Comment: 15 pages, 9 figures, 9 tables, accepted for publication in A&A, comments welcome

The orientation of the jet axis to the line of sight of the observer plays a major role in explaining the phenomena observed from blazars and radio galaxies. In the gamma-ray band, only a handful of radio galaxies have been identified, all being located in the nearby Universe (z, MNRAS Letters, in press

We present the far ultraviolet (FUV) imaging of the nearest Jellyfish or Fireball galaxy IC3418/VCC 1217, in the Virgo cluster of galaxies, using Ultraviolet Imaging Telescope (UVIT) onboard the ASTROSAT satellite. The young star formation observed here in the 17 kpc long turbulent wake of IC3418, due to ram pressure stripping of cold gas surrounded by hot intra-cluster medium, is a unique laboratory that is unavailable in the Milkyway. We have tried to resolve star forming clumps, seen compact to GALEX UV images, using better resolution available with the UVIT and incorporated UV-optical images from Hubble Space Telescope archive. For the first time, we resolve the compact star forming clumps (fireballs) into sub-clumps and subsequently into a possibly dozen isolated stars. We speculate that many of them could be blue supergiant stars which are cousins of SDSS J122952.66+112227.8, the farthest star (~17 Mpc) we had found earlier surrounding one of these compact clumps. We found evidence of star formation rate (4 - 7.4 x 10^-4 M_sun per yr ) in these fireballs, estimated from UVIT flux densities, to be increasing with the distance from the parent galaxy. We propose a new dynamical model in which the stripped gas may be developing vortex street where the vortices grow to compact star forming clumps due to self-gravity. Gravity winning over turbulent force with time or length along the trail can explain the puzzling trend of higher star formation rate and bluer/younger stars observed in fireballs farther away from the parent galaxy., Comment: 12 pages, 9 figures. Accepted for publication in the Special Issue of the Journal of Astrophysics and Astronomy on ASTROSAT

Performance of the Level-2 pipeline, which translates the UVIT data created by the ISRO's ground segment processing systems (Level-1) into astronomer ready scientific data products, is described. This pipeline has evolved significantly from experiences during the in orbit mission. With time, the detector modules of UVIT developed certain defects which led to occasional corruption of imaging and timing data. This article will describe the improvements and mitigation plans incorporated in the pipeline and report its efficacy and quantify the performance., Comment: Accepted for publication in Journal of Astrophysics & Astronomy, 6 pages, 4 figures

Blazars show optical and $\gamma$-ray flux variations that are generally correlated, although there are exceptions. Here we present anomalous behaviour seen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data at optical, UV, X-ray and $\gamma$-ray energies, spanning about 9 years from August 2008 to February 2017. We have identified four time intervals (epochs), A, B, D and E, when the source showed large-amplitude optical flares. In epochs A and B the optical and $\gamma$-ray flares are correlated, while in D and E corresponding flares in $\gamma$-rays are weak or absent. In epoch B the degree of optical polarization strongly correlates with changes in optical flux during a short-duration optical flare superimposed on one of long duration. In epoch E the optical flux and degree of polarization are anti-correlated during both the rising and declining phases of the optical flare. We carried out broad-band spectral energy distribution (SED) modeling of the source for the flaring epochs A,B, D and E, and a quiescent epoch, C. Our SED modeling indicates that optical flares with absent or weak corresponding $\gamma$-ray flares in epochs D and E could arise from changes in a combination of parameters, such as the bulk Lorentz factor, magnetic field and electron energy density, or be due to changes in the location of the $\gamma$-ray emitting regions., Comment: accepted in mnras, 17 pages, 31 figures

Changing look active galactic nuclei (CLAGNs) show complex nature in their X-ray spectral shape and line of sight column density variation. The physical mechanisms responsible for these variations are unclear. Here, we study the spectral properties of a CLAGN, NGC\,1365 using combined {\it XMM-Newton} and {\it NuSTAR} observations to understand the CL behavior. The model fitted mass accretion rate varied between $0.003\pm 0.001$ and $0.009\pm0.002$ $\dot M_{\rm Edd}$ and the dynamic corona changed from $28\pm 3$ to $10\pm1$ $r_g$. We found that the variable absorption column density correlates with the mass accretion rate and the geometry of the corona. The derived wind velocity was sufficiently low compared to the escape velocity to drive the wind away from the disc for the epochs when column densities were high. This suggests that the high and variable absorption can be due to failed winds from the disc. Our estimated ratio of mass outflow to inflow rate from the inner region of the disc lies between $0.019\pm0.006$ and $0.12\pm0.04$. From spectral fitting of the combined data, we found the mass of the central black hole to be constant $4.38\pm0.34 - 4.51\pm0.29 \times10^{6} M_\odot$, consistent with earlier findings. The confidence contours of $N_H$ with other model parameters show that the model fitted parameters are robust and non-degenerate. Our study construed that the changing accretion rate, which is a fundamental physical quantity and the geometry of the corona driving the CL phenomena in NGC\,1365. The physical picture considered in this work connects both variable continuum and variable absorbing medium scenarios., Comment: 8 pages, 7 figures, 1 table, accepted for publication in A&A, comments welcome

The majority of the γ-ray sources detected by the Fermi Gamma-ray Space Telescope belong to the blazar class of active galactic nuclei (AGNs). In addition to blazars, a minority of non-blazar AGNs is also found to be γ-ray emitters. A class of AGNs with large jet to line-of-sight angle are termed as misaligned AGNs (MAGNs). A significant fraction of γ-ray emitting non-blazar AGNs belong to this class. The detection of these sources in γ-rays suggests that most of their emission originate in the jet. Considering jet origin of intra-night optical variability (INOV), one thus can expect to observe strong presence of INOV in these γ-ray detected MAGN. However, no observations exist on their INOV nature. We therefore, have carried out a first search for INOV on a sample of six MAGN, that comprises three FR I, two Steep Spectrum Radio Quasars (SSRQs)/Compact Steep Spectrum (CSS) and one FR II galaxy. Our observations carried out on a total of eight nights for a duration of ∼29 h, reveal that MAGNs show large amplitude (between 2 and 10 per cent) INOV with a duty cycle of about 50 per cent, including both variable and probably variable sources, which is similar to that shown by blazars. Though INOV has been detected in MAGNs, differences if any between the INOV characteristics of FR I, SSRQs/CSS, and FR II types of MAGNs could not be unambiguously established owing to limited observations. Nevertheless, the first detection of INOV in MAGNs points to their jet based origin.

Radio and $\gamma$-ray loud narrow-line Seyfert 1 galaxies (NLS1s) are unique objects to study the formation and evolution of relativistic jets, as they are believed to have high accretion rates and powered by low mass black holes contrary to that known for blazars. However, only about a dozen $\gamma$-ray detected NLS1s ($\gamma$-NLS1s) are known to date and all of them are at $z\le1$. Here, we report the identification of a new $\gamma$-ray emitting NLS1 TXS 1206+549 at $z=1.344$. A near-infrared spectrum taken with the Subaru telescope showed H$\beta$ emission line with FWHM of $1194\pm77$ km s$^{-1}$ and weak [O III] emission line but no optical Fe II lines, due to the limited wavelength coverage and poor signal-to-noise ratio. However, UV Fe II lines are present in the SDSS optical spectrum. The source is very radio-loud, unresolved, and has a flat radio spectrum. The broadband SED of the source has the typical two hump structure shown by blazars and other $\gamma$-NLS1s. The source exhibits strong variability at all wavelengths such as the optical, infrared, and $\gamma$-ray bands. All these observed characteristics show that TXS 1206+549 is the most distant $\gamma$-NLS1 known to date., Comment: Accepted in MNRAS Letter

The scaling relations between the black hole (BH) mass and soft lag properties for both active galactic nuclei (AGNs) and BH X-ray binaries (BHXRBs) suggest the same underlying physical mechanism at work in accreting BH systems spanning a broad range of mass. However, the low-mass end of AGNs has never been explored in detail. In this work, we extend the existing scaling relations to lower-mass AGNs, which serve as anchors between the normal-mass AGNs and BHXRBs. For this purpose, we construct a sample of low-mass AGNs ($M_{\rm BH}, 11 pages, 5 figures, 4 tables, Published in MNRAS

Curvit is an open-source Python package that facilitates the creation of light curves from the data collected by the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat, India's first multi-wavelength astronomical satellite. The input to Curvit is the calibrated events list generated by the UVIT-Payload Operation Center (UVIT-POC) and made available to the principal investigators through the Indian Space Science Data Center. The features of Curvit include (i) automatically detecting sources and generating light curves for all the detected sources and (ii) custom generation of light curve for any particular source of interest. We present here the capabilities of Curvit and demonstrate its usability on the UVIT observations of the intermediate polar FO Aqr as an example. Curvit is publicly available on GitHub at https://github.com/prajwel/curvit., Accepted for publication in Journal of Astrophysics & Astronomy, 11 pages, 5 figures

Understanding the geometry and kinematics of the broad line region (BLR) of active galactic nuclei (AGN) is important to estimate black hole masses in AGN and study the accretion process. The technique of reverberation mapping (RM) has provided estimates of BLR size for more than 100 AGN now, however, the structure of the BLR has been studied for only a handful number of objects. Towards this, we investigated the geometry of the BLR for a large sample of 57 AGN using archival RM data. We performed systematic modeling of the continuum and emission line light curves using a Markov Chain Monte Carlo method based on Bayesian statistics implemented in PBMAP (Parallel Bayesian code for reverberation-MAPping data) code to constrain BLR geometrical parameters and recover velocity integrated transfer function. We found that the recovered transfer functions have various shapes such as single-peaked, double-peaked and top-hat suggesting that AGN have very different BLR geometries. Our model lags are in general consistent with that estimated using the conventional cross-correlation methods. The BLR sizes obtained from our modeling approach is related to the luminosity with a slope of 0.583 (+/-) 0.026 and 0.471 (+/-) 0.084 based on H{\beta} and H{\alpha} lines, respectively. We found a non-linear response of emission line fluxes to the ionizing optical continuum for 93\% objects. The estimated virial factors for the AGN studied in this work range from 0.79 to 4.94 having a mean at 1.78 (+/-) 1.77 consistent with the values found in the literature., Comment: 20 pages, 16 figures, 5 tables, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS), 30 December 2020

We present the results of photometric reverberation mapping observations on the changing look active galactic nucleus Mrk 590 at z = 0.026. The observations were carried out from July to December, 2018 using broad band B, R and narrow band H{\alpha} and S II filters. B-band traces the continuum emission from the accretion disk, R-band encompasses both the continuum emission from the accretion disk and the redshifted H{\alpha} line from the broad line region (BLR), S II band contains the redshifted H{\alpha} emission and the H{\alpha} band traces the continuum emission underneath the S II band. All the light curves showed strong variation with a fractional root-mean-square variation of 0.132 (+/-) 0.001 in B-band and 0.321 (+/-) 0.001 in H{\alpha} line. From cross-correlation function analysis, we obtained a delayed response of H{\alpha} line emission to the optical B-band continuum emission of 21.44(+1.49/-2.11) days in the rest-frame of the source, corresponding to a linear size of the BLR of 0.018 pc. This is consistent with previous estimates using H{\beta}. By combining the BLR size with the H{\alpha} line full width at half maximum of 6478 (+/-) 240 km/s measured from a single-epoch spectrum obtained with the Subaru telescope, we derived a black hole mass of 1.96 (+0.15 / -0.21) X 10^8 Msun., Comment: 16 pages, 12 figures, 4 tables, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS), 5 October 2021

We carried out a detailed study of the temporal and broadband spectral behaviour of one of the brightest misaligned active galaxies in gamma-rays, NGC 1275 utilising 11 years of Fermi, and available Swift and AstroSat observations. Based on the cumulative flux distribution of the gamma-ray lightcurve, we identified four distinct activity states and noticed an increase in the baseline flux during the first three states. Similar nature of the increase in the average flux was also noticed in X-ray and UV bands. A large flaring activity in gamma-rays was noticed in the fourth state. The source was observed twice by AstroSat for shorter intervals (~days) during the longer observing periods (~years) state 3 and 4. During AstroSat observing periods, the source gamma-ray flux was higher than the average flux observed during longer duration states. The increase in the average baseline flux from state 1 to state 3 can be explained considering a corresponding increase of jet particle normalisation. The inverse Comptonisation of synchrotron photons explained the average X-ray and gamma-ray emission by jet electrons during the first three longer duration states. However, during the shorter duration AstroSat observing periods, a shift of the synchrotron peak frequency was noticed, and the synchrotron emission of jet electrons well explained the observed X-ray flux., Comment: Corrected AstroSat-SXT and LAXPC instrument description in Section 2.2.2 and updated references to match the published version. Results unchanged

The study of narrow-line Seyfert 1 galaxies (NLS1s) is now mostly limited to low redshift ($z0.8$. We studied the correlation between the properties of H$\beta$ and Mg II lines of a large sample of SDSS DR14 quasars to find high-$z$ NLS1 candidates. Based on the strong correlation of $\mathrm{FWHM(MgII)=(0.880\pm 0.005) \times FWHM(H\beta)+ (0.438\pm0.018)}$, we present a sample of high-$z$ NLS1 candidates having FWHM of Mg II $, Comment: Published in ApJS on March 2021. Catalog is available on Zenodo (https://doi.org/10.5281/zenodo.4405039)

The astrophysical journal 903(1), L8 (2020). doi:10.3847/2041-8213/abbc06, One of the major challenges in studying the cosmic evolution of relativistic jets is the identification of the high-redshift (z > 3) BL Lacertae objects (BL Lacs), a class of jetted active galactic nuclei characterized by their quasi-featureless optical spectra. Here we report the identification of the first γ-ray emitting BL Lac, 4FGL J1219.0+3653 (J1219), beyond z = 3, i.e., within the first two billion years of the age of the universe. The optical and near-infrared spectra of J1219 taken from 10.4 m Gran Telescopio Canarias exhibit no emission lines down to an equivalent width of ∼3.5 Å supporting its BL Lac nature. The detection of a strong Lyα break at ∼5570 Å, on the other hand, confirms that J2119 is indeed a high-redshift (z ∼ 3.59) quasar. Based on the prediction of a recent BL Lac evolution model, J1219 is one of the only two such objects expected to be present within the comoving volume at z = 3.5. Future identifications of more z > 3 γ-ray emitting BL Lac sources, therefore, will be crucial to verify the theories of their cosmic evolution., Published by Univ.11032, Chicago, Ill. [u.a.]

We present long term optical and near infrared flux variability analysis of 37 blazars detected in the $\gamma$-ray band by the {\it Fermi Gamma-Ray Space Telescope}. Among them, 30 are flat spectrum radio quasars (FSRQs) and 7 are BL Lac objects (BL Lacs). The photometric data in the optical (BVR) and infrared (JK) bands were from the Small and Moderate Aperture Research Telescope System acquired between 2008$-$2018. From cross-correlation analysis of the light curves at different wavelengths, we did not find significant time delays between variations at different wavelengths, except for three sources, namely PKS 1144$-$379, PKS B1424$-$418 and 3C 273. For the blazars with both B and J-band data, we found that in a majority of FSRQs and BL Lacs, the amplitude of variability ($\sigma_m$) in the J-band is larger than B-band consistent with the dominance of the non-thermal jet over the thermal accretion disc component. Considering FSRQs and BL Lacs as a sample, there are indications of $\sigma_m$ to increase gradually towards longer wavelengths in both, however, found to be statistically significant only between B and J-bands in FSRQs. In the B$-$J v/s J colour magnitude diagram, we noticed complicated spectral variability patterns. Most of the objects showed a redder when brighter (RWB) behaviour. Few objects showed a bluer when brighter (BWB) trend, while in some objects both BWB and RWB behaviours were noticed. These results on flux and colour characteristics indicate that the jet emission of FSRQs and BL Lacs is indistinguishable., Comment: Accepted for publication in MNRAS

We used the data from the Fermi Gamma-ray Space Telescope to characterise the {\gamma}-ray flux variability of blazars on month-like time scales. Our sample consists of 1120 blazars of which 481 are flat spectrum radio quasars (FSRQs) and 639 are BL Lac objects (BL Lacs). We generated monthly binned light curves of our sample for a period of approximately nine years from 2008 August to 2017 December and quantified variability by using excess variance (F_var). On month-like time scales, 371/481 FSRQs are variable ( 80%), while only about 50% (304/639) of BL Lacs are variable. This suggests that FSRQs are more variable than BL Lac objects. We find a mean F_var of 0.55 +/- 0.33 and 0.47 +/- 0.29 for FSRQs and BL Lacs respectively. Large F_var in FSRQs is also confirmed from the analysis of the ensemble structure function. By Dividing our sample of blazars based on the position of the synchrotron peak in their broad-band spectral energy distribution, we find that the low synchrotron peaked (LSP) sources have the largest mean F_var value of 0.54 +/- 0.32 while the intermediate synchrotron peaked (ISP) and high synchrotron peaked (HSP) sources have mean F_var values of 0.45 +/- 0.25 and 0.47 +/- 0.33 respectively. On month-like time scales, we find FSRQs to show a high duty cycle (DC) of variability of 66% relative to BL Lacs that show a DC of 36%. We find that both the F_var and time scale of variability ({\tau}) do not correlate with the black hole mass. We note that F_var is found to be weakly correlated with Doppler factor ({\delta}) and {\tau} is also weakly correlated with {\delta}. Most of the sources in our sample have {\tau} of the order of days, which might be related to processes in the jet. We find marginal difference in the distribution of {\tau} between FSRQs and BL Lacs., Comment: 8 pages, 14 figures, Accepted for publication in A&A

We report the analysis of simultaneous multi-wavelength data of the high energy peaked blazar RGB J0710+591 from the LAXPC, SXT and UVIT instruments on-board AstroSat. The wide band X-ray spectrum (0.35 -- 30 keV) is modelled as synchrotron emission from a non-thermal distribution of high energy electrons. The spectrum is unusually curved, with a curvature parameter $\beta_p \sim 6.4$ for a log parabola particle distribution, or a high energy spectral index $p_2 > 4.5$ for a broken power-law distribution. The spectrum shows more curvature than an earlier quasi-simultaneous analysis of Swift-XRT/NuSTAR data where the parameters were $\beta_p \sim 2.2$ or $p_2 \sim 4$. It has long been known that a power-law electron distribution can be produced from a region where particles are accelerated under Fermi process and the radiative losses in acceleration site decide the maximum attainable Lorentz factor, $\gamma_{max}$. Consequently, this quantity decides the energy at which the spectrum curves steeply. We show that such a distribution provides a more natural explanation for the AstroSat data as well as the earlier XRT/NuSTAR observation, making this as the first well constrained determination of the photon energy corresponding to $\gamma_{max}$. This in turn provides an estimate of the acceleration time-scale as a function of magnetic field and Doppler factor. The UVIT observations are consistent with earlier optical/UV measurements and reconfirm that they plausibly correspond to a different radiative component than the one responsible for the X-ray emission., Comment: 9 pages, 3 figures. Accepted for publication in MNRAS

Quasars are ideal targets to use for astrometric calibration of large scale astronomical surveys as they have negligible proper motion and parallax. The forthcoming 4-m International Liquid Mirror Telescope (ILMT) will survey the sky that covers a width of about 27 arcminute. To carry out astrometric calibration of the ILMT observations, we aimed to compile a list of quasars with accurate equatorial coordinates and falling in the ILMT stripe. Towards this, we cross-correlated all the quasars that are known till the present date with the sources in the Gaia-DR2 catalogue, as the Gaia-DR2 sources have position uncertainties as small as a few milli arcsec (mas). We present here the results of this cross-correlation which is a catalogue of 6738 quasars that is suitable for astrometric calibration of the ILMT fields. In this work, we present this quasar catalogue. This catalogue of quasars can also be used to study quasar variability over diverse time scales when the ILMT starts its observations. While preparing this catalogue, we also confirmed that quasars in the ILMT stripe have proper motion and parallax lesser than 20 mas/yr and 10 mas, respectively., Comment: 9 pages, 9 figures, Accepted in Journal of Astrophysics & Astronomy

We report results of the dust reverberation mapping (DRM) on the Seyfert 1 galaxy Z229-15 at z = 0.0273. Quasi-simultaneous photometric observations for a total of 48 epochs were acquired during the period 2017 July to 2018 December in B, V, J, H and Ks bands. The calculated spectral index ({\alpha}) between B and V bands for each epoch was used to correct for the accretion disk (AD) component present in the infrared light curves. The observed {\alpha} ranges between -0.99 and 1.03. Using cross correlation function analysis we found significant time delays between the optical V and the AD corrected J, H and Ks light curves. The lags in the rest frame of the source are 12.52 (+10.00/-9.55) days (between V and J), 15.63 (+5.05/-5.11) days (between V and H) and 20.36 (+5.82/-5.68) days (between V and Ks). Given the large error bars, these lags are consistent with each other. However, considering the lag between V and Ks bands to represent the inner edge of the dust torus, the torus in Z229-15 lies at a distance of 0.017 pc from the central ionizing continuum. This is smaller than that expected from the radius luminosity (R-L) relationship known from DRM. Using a constant {\alpha} = 0.1 to account for the AD component, as is normally done in DRM, the deduced radius (0.025 pc) lies close to the expected R-L relation. However, usage of constant {\alpha} in DRM is disfavoured as the {\alpha} of the ionizing continuum changes with the flux of the source., Comment: 12 pages, 13 figures, 3 tables, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS), 08 December 2020

Results of the initial calibration of the Ultra-Violet Imaging Telescope (UVIT) were reported earlier by Tandon et al. (2017). The results reported earlier were based on the ground calibration as well as the first observations in orbit. Some additional data from the ground calibration and data from more in-orbit observations have been used to improve the results. In particular, extensive new data from in-orbit observations have been used to obtain (a) new photometric calibration which includes (i) zero-points (ii) flat fields (iii) saturation, (b) sensitivity variations (c) spectral calibration for the near Ultra Violet (NUV; 2000 - 3000 Angstroms) and far Ultra-Violet (FUV; 1300 - 1800 Angstroms) gratings, (d) point spread function and (e) astrometric calibration which included distortion. Data acquired over the last three years show continued good performance of UVIT with no reduction in sensitivity in both the UV channels., Comment: 15 pages, 8 figures, Accepted for publication in Astronomical Journal

Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their H$\alpha$ images reveal ionized gas tails up to 100 kpc, which could be hosting ongoing star formation. Here we report the ultraviolet (UV) imaging observation of the jellyfish galaxy JO201 obtained at a spatial resolution $\sim$ 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of the present study. JO201 is the "UV-brightest cluster galaxy" in Abell 85 ($z \sim$ 0.056) with knots and streams of star formation in the ultraviolet. We identify star forming knots both in the stripped gas and in the galaxy disk and compare the UV features with the ones traced by H$\alpha$ emission. Overall, the two emissions remarkably correlate, both in the main body and along the tentacles. Similarly, also the star formation rates of individual knots derived from the extinction-corrected FUV emission agree with those derived from the H$\alpha$ emission and range from $\sim$ 0.01 -to- 2.07 $M_{\odot} \, yr^{-1}$. The integrated star formation rate from FUV flux is $\sim$ 15 $M_{\odot} \, yr^{-1}$. The unprecedented deep UV imaging study of the jellyfish galaxy JO201 shows clear signs of extraplanar star-formation activity due to a recent/ongoing gas stripping event.

The origin of gamma-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two gamma-ray bright blazars 3C 279 (z=0.54) and 3C 454.3 (z=0.86), using near-simultaneous radio-to-gamma-ray observations. For both sources, the gamma-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population and/or enhancement of the Doppler factor can naturally explain these observations. In both cases, magnetic reconnection may play a pivotal role in powering the luminous gamma-ray flares., Comment: ApJS, in press

We examine the long-term (∼ 10 years) γ-ray variability of blazars observed by EGRET and Fermi and find that 10 EGRET-detected flat spectrum radio quasars (FSRQs) were not present in any of the Fermi catalogue (during the first four years of Fermi observation). Six of these 10 EGRET sources show possible Fermi counterparts based on overlap with error circles given in 3 r d Fermi catalogue. A seventh EGRET source is positionally consistent with a newly discovered Fermi source from our analysis. Unlike the high luminosity state exhibited during 1991 to 1995, our analysis using seven years of Fermi data showed that five of these are at its low luminosity state in the GeV band. This result indicates that FSRQs exhibit a long-term quiescent state (more than 7 years). In addition, 37 new γ-ray sources are also detected during the course of this analysis. On the basis of AGN being the most dominant source class in γ-rays, many of these new sources could be associated with AGN and may exhibit long-term variabilities in γ-rays.

We report evidence for star formation quenching in the central 8.6 kpc region of the jellyfish galaxy JO201 which hosts an active galactic nucleus, while undergoing strong ram pressure stripping. The ultraviolet imaging data of the galaxy disk reveal a region with reduced flux around the center of the galaxy and a horse shoe shaped region with enhanced flux in the outer disk. The characterization of the ionization regions based on emission line diagnostic diagrams shows that the region of reduced flux seen in the ultraviolet is within the AGN-dominated area. The CO J$_{2-1}$ map of the galaxy disk reveals a cavity in the central region. The image of the galaxy disk at redder wavelengths (9050-9250 $\overset{\lower.5em\circ}{\mathrm{A}}$) reveals the presence of a stellar bar. The star formation rate map of the galaxy disk shows that the star formation suppression in the cavity occurred in the last few 10$^8$ yr. We present several lines of evidence supporting the scenario that suppression of star formation in the central region of the disk is most likely due to the feedback from the AGN. The observations reported here make JO201 a unique case of AGN feedback and environmental effects suppressing star formation in a spiral galaxy., Author's accepted manuscript

Narrow line Seyfert 1 galaxies (NLS1s) are believed to be powered by accretion of matter onto low mass black holes (BHs) in spiral host galaxies with BH masses M_BH of 10^6 - 10^8 M_sun . However, the broad band spectral energy distribution of the gamma-ray emitting NLS1s are found to be similar to flat spectrum radio quasars. This challenges our current notion of NLS1s having low M_BH . To resolve this tension of low M_BH values in NLS1s, we fitted the observed optical spectrum of a sample of radio-loud NLS1s (RL-NLS1s), radio-quiet NLS1s (RQ-NLS1s) and radio-quiet broad line Seyfert 1 galaxies (RQ-BLS1s) of about 500 each with the standard Shakura-Sunyaev accretion disk (AD) model. For RL-NLS1s we found a mean log(M_ADBH/M_sun) of 7.98 +/- 0.54. For RQ-NLS1s and RQ-BLS1s we found mean log(M_ADBH/M_sun) of 8.00 +/- 0.43 and 7.90 +/- 0.57, respectively. While the derived M_BH values of RQ-BLS1s are similar to their virial masses, for NLS1s the derived M_ADBH values are about an order of magnitude larger than their virial estimates. Our analysis thus indicates that NLS1s have M_BH similar to RQ-BLS1s and their available virial M_BH values are underestimated influenced by their observed relatively small emission line widths. Considering Eddington ratio as an estimation of the accretion rate and using M_ADBH, we found the mean accretion rate of our RQ-NLS1s, RL-NLS1s and RQ-BLS1s as 0.06 (+0.16, -0.05), 0.05 (+0.18, -0.04) and 0.05 (+0.15, -0.04) respectively. Our results therefore suggest that NLS1s have BH masses and accretion rates similar to BLS1s., Comment: 8 pages, 3 Figures, 2 Tables; Accepted for publication in Astrophysical Journal Letters

The primary X-ray emission in active galactic nuclei (AGN) originates in a compact region called the corona located very close to the super-massive black hole and the accretion disk. The knowledge of the cut-off energy ($E_{cut}$) of the primary X-ray continuum in an AGN is very important as it carries information on the physical characteristics of the hot X-ray emitting corona. We present here the results of our investigation on the spectral properties of a sample of 10 nearby AGN (0.005 $, Comment: 17 pages, 13 figures; Accepted for publication in Monthly Notices of the Royal Astronomical Society(MNRAS)

We present measurements of the spectral properties for a total of 526,265 quasars, out of which 63% have continuum S/N$>3$ pixel$^{-1}$, selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalog. We performed a careful and homogeneous analysis of the SDSS spectra of these sources, to estimate the continuum and line properties of several emission lines such as H${\alpha}$, H${\beta}$, H${\gamma}$, Mg \textsc{ii}, C \textsc{iii]}, C \textsc{iv} and Ly${\alpha}$. From the derived emission line parameters, we estimated single-epoch virial black hole masses ($M_{\mathrm{BH}}$) for the sample using H${\beta}$, Mg \textsc{ii} and C \textsc{iv} emission lines. The sample covers a wide range in bolometric luminosity ($\log L_{\mathrm{bol}}$; erg s$^{-1}$) between 44.4 and 47.3 and $\log M_{\mathrm{BH}}$ between 7.1 and 9.9 $M_{\odot}$. Using the ratio of $L_{\mathrm{bol}}$ to the Eddington luminosity as a measure of the accretion rate, the logarithm of the accretion rate is found to be in the range between $-$2.06 and 0.43. We performed several correlation analyses between different emission line parameters and found them to match with that known earlier using smaller samples. We noticed that strong Fe \textsc{ii} sources with large Balmer line width, and highly accreting sources with large $M_{\mathrm{BH}}$ are rare in our sample. We make available online an extended and complete catalog that contains various spectral properties of 526,265 quasars derived in this work along with other properties culled from the SDSS-DR14 quasar catalog., Comment: Accepted by ApJS. Catalogs and supplementary materials are available at https://www.utu.fi/sdssdr14/

Precise measurement of the coronal properties of Active Galactic Nuclei (AGN) requires the availability of high signal-to-noise ratio data covering a wide range of X-ray energies. The Nuclear Spectroscopic Telescope Array (NuSTAR) which is highly sensitive to earlier missions in its operational energy range of 3–79 keV, allows us to arrive at precise estimates of the coronal parameters such as cut-off energy ( $$E_\mathrm{cut}$$ ), coronal temperature ( $$\textit{kT}_e$$ ) and geometry of the corona at least for sources that have $$E_\mathrm{cut}$$ within the energy range of NuSTAR. In this paper, we present our preliminary results on the spectral analysis of two Seyfert galaxies namely 3C 120 and NGC 4151 using NuSTAR observations in the 3–79 keV band. We investigated the continuum and coronal parameters, the photon index $$\Gamma $$ , $$E_\mathrm{cut}$$ and $$\textit{kT}_{e}$$ . By fitting the X-ray spectrum of 3C 120 and NGC 4151 with a simple phenomenological model, we found that both the sources showed a clear cut-off in their spectrum.

We report the first results obtained from our campaign to characterize the intranight-optical variability (INOV) properties of {\it Fermi}~detected blazars, using the observations from the recently commissioned 1.3 m J C Bhattacharya telescope (JCBT). During the first run, we were able to observe 17 blazars in the Bessel $R$ filter for $\sim$137 hrs. Using $C$ and scaled $F$-statistics, we quantify the extent of INOV and derive the duty cycle (DC) which is the fraction of time during which a source exhibits a substantial flux variability. We find a high DC of 40\% for BL Lac objects and the flat spectrum radio quasars are relatively less variable (DC $\sim15$\%). However, when estimated for blazars sub-classes, a high DC of $\sim$59\% is found in low synchrotron peaked (LSP) blazars, whereas, intermediate and high synchrotron peaked objects have a low DC of $\sim$11\% and 13\%, respectively. We find evidences about the association of the high amplitude INOV with the $\gamma$-ray flaring state. We also notice a high polarization during the elevated INOV states (for the sources that have polarimetric data available), thus supporting the jet based origin of the observed variability. We plan to enlarge the sample and utilize the time availability from the small telescopes, such as 1.3 m JCBT, to strengthen/verify the results obtained in this work and those existed in the literature., Comment: 9 figures, 5 tables, published in the Astrophysical Journal

The time delay between flux variations in different wavelength bands can be used to probe the inner regions of active galactic nuclei (AGN). Here, we present the first measurements of the time delay between optical and near-infrared (NIR) flux variations in H0507+164, a nearby Seyfert 1.5 galaxy at z = 0.018. The observations in the optical V -band and NIR J, H and Ks bands carried over 35 epochs during the period October 2016 to April 2017 were used to estimate the inner radius of the dusty torus. From a careful reduction and analysis of the data using cross-correlation techniques, we found delayed responses of the J, H and Ks light curves to the V -band light curve. In the rest frame of the source, the lags between optical and NIR bands are found to be $27.1^{+13.5}_{-12.0}$ days (V vs. J), $30.4^{+13.9}_{-12.0}$ days (V vs. H) and $34.6^{+12.1}_{-9.6}$ days (V vs. K ). The lags between the optical and different NIR bands are thus consistent with each other. The measured lags indicate that the inner edge of dust torus is located at a distance of 0.029 pc from the central UV/optical AGN continuum. This is larger than the radius of the broad line region of this object determined from spectroscopic monitoring observations thereby supporting the unification model of AGN. The location of H0507+164 in the {\tau} - MV plane indicates that our results are in excellent agreement with the now known lag-luminosity scaling relationship for dust in AGN., Comment: 8 pages, 4 figures, accepted by MNRAS main journal