Broadband Spectro-temporal Study on Blazar TXS 1700+685

We attempt to present a multiwavelength variability and correlation study as well as detailed multi-waveband spectral characteristics of the May 2021 $\gamma$-ray flare of the blazar source TXS 1700+685. The multi-wavelength observation from \textit{Fermi}-LAT, \textit{Swift}-XRT/UVOT as well as radio archival data are used for our spectro-temporal investigation. We estimate the variability time-scale of the source from the flux doubling time in different flaring regions detected in \textit{Fermi}-LAT observation and the shortest variability time is used to put a constraint on the minimum Doppler factor and on the size of the emission region. We have detected a statistically significant quasi-periodic oscillation feature (QPO) at $\sim$ 17 days. The broad-band emission is satisfactorily represented during its flaring state with a leptonic synchrotron and inverse Compton component. From the broadband spectral modeling, we observe the external Comptonization of the seed photons originating in the broad line region to be dominant compared to the dusty torus. This is further supported by the fact that the emission region is also found to be residing within the BLR. The equipartition value implies the energy density of the magnetic field in the jet comoving frame is weak, and that is also reflected in the magnetic field and low power corresponding to the magnetic field component of the jet. In order to produce the high energy hump, we need the injection of a large population of high energy electrons and/or the presence of strong magnetic field; and we observe the later component to be sub-dominant in our case. The flat rising and steep falling profile in the $\gamma$-ray SED as well as the break or spectral curvature at $\sim$ 1 GeV are in commensuration with the flat-spectrum radio quasar (FSRQ) nature of the source

Quasi-periodic oscillation detected in γ\gamma-rays in blazar PKS 0346-27

We present a variability study of the blazar PKS 0346-27 from December 2018 to January 2022 in its archival $\gamma$-ray observation by Fermi-LAT. We use the Lomb-Scargle periodogram and the weighted wavelet transform methods in order to detect the presence of periodicity/quasi-periodicity and localize this feature in time and frequency space. The significance of the periodicity feature has been estimated using the Monte-Carlo simulation approach. We have also determined the global significance of the periodicity to test the robustness of our claim. To explore the most probable scenario, we modeled the light curve with both a straight jet and a curved jet model. We detect a periodicity feature of $\sim$ 100 days duration for the entire period of observation with a statistical significance of $3\sigma$, which amounts to a 99.7\% confidence level. The global significance of this feature is found to be 96.96\%. Based on the Akaike Information Criteria, the most probable explanation is that the observed emission is enhanced due to the helical motion of a blob within a curved jet. The origin of this QPO is very likely a region of enhanced emission moving helically inside a curved jet. This work presents strong evidence for jet curvature in the source and an independent (albeit a little serendipitous) procedure to estimate the curvature in blazar jets.Comment: 7 pages, 4 figures, Accepted for publication in A&A, in Pres

Similarities and differences in accretion flow properties between GRS 1915+105 and IGR J17091-3624: A case study

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The m, as well as C2 class Rossi X-ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in different energy domains that correspond to different components of the accretion flow and infer the relative dominance of these flow components during the dip/flare events. We correlate the dependence of the dynamic photon index (?) with intensities in different energy bands and comment on the transition of the source to hard/soft phases during soft dips/flares. We also report the presence of sharp QPOs at similar to 7:1 Hz corresponding to both softer and harder domain in the case of v & nbsp;variability class of GRS 1915+105 and discuss the possible accretion flow configuration it suggests. Sharp QPO around similar to 20 mHz is observed in m and C2 classes of IGR J17091-3624 in low and mid energy band (2.0-6.0 keV and 6.0-15.0 keV), but remains undetected in high energy (15.0-60.0 keV). The 2.5-25.0 keV background-subtracted spectra have also been fitted with TCAF along with a Compton reflection component. A plausible accretion flow mechanism in order to explain the observed variability has been proposed.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved

Accretion Flow Properties of GRS 1915+105 During Its theta Class Using AstroSat Data

The Galactic microquasar GRS 1915+105 shows rich variability that is categorized into different classes. In this paper, we report the temporal and spectral analysis of GRS 1915+105 to study the properties of the accretion flow when the light curve shows theta class variability. For this purpose, we use the Large Area X-ray Proportional Counter data from the Target of Opportunity observations of India's first multiwavelength astronomy satellite AstroSat. The theta class is marked by the recurrent appearance of U-shaped regions in the light curve, where the photon count rate first decreases rapidly and then increases slowly. For our analysis, we use U-shaped regions of the first two orbits (02345 and 02346) on 2016 March 4. In both cases, the dynamic power-density spectra (PDS) showed significant power at around 4-5 Hz, suggesting the presence of a low-frequency quasi-periodic oscillation (QPO) around that frequency interval. The QPO frequency is found to increase with time when the energy flux is also enhanced. From the evolution of the spectra, we determine the evolution of the accretion flow parameters in these two observations. Fitting the spectra with the transonic flow solution-based two-component advective flow (TCAF) model in the 4-25 keV energy band shows that the Keplerian disk accretion rate increases with the increase in radiation intensity, while the location of the centrifugal pressure-driven shock front decreases. In both these data, a gradual increment of power-law photon index with intensity is observed, suggesting the progressive softening of the source