7 citations · 27 across the 24 of their papers we have counts for
26 papers
X-ray Variability of Mrk 421 in 2025 January: A Ten-Day XPoSat XSPECT Campaign with Contemporaneous NICER Coverage
Sikandar Akbar, Zahir Shah, Zahoor Malik +3
We present an X-ray study of the high-synchrotron-peaked blazar Mrk 421 using ten days of XPoSat/XSPECT observations (2025 January 20-29; 202 ks) and contemporaneous NICER data. Th…
Short-timescale X-ray variability of the blazar 1ES 1959+650 observed with AstroSat/SXT
Sikandar Akbar, Zahir Shah
We analyse the AstroSat Soft X-ray Telescope (SXT) observation of the high-synchrotron-peaked blazar 1ES 1959+650 taken on 2023 September 2, which covers 362 ks with about 95 ks of…
Probing the High-Energy Emission of the VHE-emitting Changing-Look Blazar B2 1420+32
Anjum Peer, Zahir Shah, Sikandar Akbar +2
We present a multi-wavelength temporal and spectral study of the changing-look blazar B2~1420+32 using \emph{Fermi}-LAT, \emph{Swift}-XRT, and \emph{Swift}-UVOT data from MJD~58818…
Exploring the Transitional Parameter Space of Blazars using Gamma-ray and X-ray Population Diagnostics
Zahoor Malik, Sikandar Akbar, Zahir Shah +1
We investigate the -ray and X-ray population properties of changing-look blazars (CLBs) using sources from the Fourth \textit{Fermi} LAT Source Catalog Data Release 4 (4FGL-DR4)…
Advance warning of -ray blazar flares from \textit{Fermi}-LAT light curves: a strictly causal machine-learning backtest
Zahir Shah, Sikandar Akbar
Long-term \textit{Fermi}-LAT monitoring makes it possible to ask whether a blazar light curve shows signs of an upcoming flare before the flare becomes obvious in the -ray emiss…
Indication of gamma-Ray Quasi-periodicity in GB6 J1037+5711 from Multi-technique Timing Analysis
Zahoor Malik, Sikandar Akbar, Zahir Shah +1
We report the indication of a long-term quasi-periodic oscillation (QPO) in the -ray emission of the BL Lac object 4FGL J1037.7+5711 (GB6 J1037+5711) using more than 17 years of…
Characterizing Short-Timescale Optical Variability in Non-blazar Active Galactic Nucleus PKS~052136 Using TESS
Sikandar Akbar, Zahir Shah
We present a systematic analysis of high-cadence optical light curves of the non-blazar AGN PKS~052136 obtained with \textit{TESS} across three sectors: Sectors~5 and~6 (Cycle~1…
A Possible Short-Timescale Optical Quasi-Periodic Oscillation in PKS\,080507 from High-Cadence TESS Observations
Sikandar Akbar, Zahir Shah, Athar A. Dar +1
We present a timing analysis of the high-cadence optical light curve of the high-redshift flat-spectrum radio quasar PKS\,080507 obtained during \textit{TESS} Sector~34 (MJD~=~5…
Broadband Variability Analysis of FSRQ PKS\,0402-362 with Indications of Quasi-Periodic Modulation
Zeeshan Nazir, Sikandar Akbar, Zahir Shah +2
We present a comprehensive temporal and spectral study of the flat-spectrum radio quasar PKS~0402362 using \textit{Fermi}-LAT/Swift-XRT/UVOT observations spanning from MJD 54686…
Spectral State Switching in Mrk 421: Results from the AstroSat LAXPC/SXT Observations
Sikandar Akbar, Zahir Shah, Ranjeev Misra +1
We carried a detailed time and flux resolved X-ray spectral analysis of the high-synchrotron-peaked blazar Mrk\,421 using simultaneous LAXPC20 and SXT observations. The 100\,s binn…
Multiwavelength spectral and temporal analysis of VHE Blazar 1ES 1959+650: Tracing emission mechanisms across flux states
Peer Anjum, Athar A. Dar, Zahir Shah +2
The high-synchrotron-peaked BL Lac object 1ES\,1959+650 exhibited pronounced activity between MJD~60310 -- 60603, including a very high energy (VHE) detection reported by LHAASO. T…
Indication for Dual Periodic Signatures in PKS 0805-07 from Multi-technique Time Series Analysis
Sikandar Akbar, Zahir Shah, Ranjeev Misra +2
We report the identification of two statistically significant quasi-periodic oscillations in the weekly binned -ray light curve of the flat-spectrum radio quasar PKS 080507,…
Comprehensive Variability Analysis of Blazars Using Fermi Light Curves Across Multiple Timescales
Zahir Shah, Athar A. Dar, Sikandar Akbar +8
In this study, we conducted a systematic analysis of long-term Fermi-LAT γ-ray data for a sample of blazars, including FSRQs, BL\,Lacs, and BCUs, to investigate their -ray varia…
Statistical Insights into Flux and Photon Index Distributions of VHE FSRQs from Fermi-LAT Observations
Zahoor Malik, Sikandar Akbar, Zahir Shah +8
This study examines the flux and photon index distributions of 11 Very High Energy (VHE) Flat Spectrum Radio Quasars (FSRQs) using over 16 years of Fermi-LAT -ray data. The dist…
Study of Multi-Wavelength Variability, Emission Mechanism and Quasi-Periodic Oscillation for Transition Blazar S5 1803+784
Javaid Tantry, Ajay Sharma, Zahir Shah +2
This work present the results of a multi-epoch observational study of the blazar S5\,1803+784, carried out from 2019 to 2023. The analysis is based on simultaneous data obtained fr…
Signature of hadronic emission in gamma-ray spectrum of B2 1308+326
Athar A. Dar, Zahir shah, Sunder Sahayanathan +3
The Flat Spectrum Radio Quasar (FSRQ) B2\,1308+326 was in its highest -ray flaring state during 60260-60310\,MJD. During this period, the source was detected in very high energy…
Probing Spectral Evolution and Intrinsic Variability of Mkn\,421: A Multi-Epoch AstroSat Study of X-ray Spectra
Sikandar Akbar, Zahir Shah, Ranjeev Misra +2
Our study presents a time-resolved X-ray spectral analysis of Mkn 421, using AstroSat observations taken during different epochs between 2016 and 2019. The variability of the sourc…
Probing Broadband Spectral Energy Distribution and Variability of Mrk\,501 in the low flux state
Javaid Tantry, Zahir Shah, Ranjeev Misra +2
We conducted a multi-wavelength analysis of the blazar Mrk\,501, utilizing observations from \emph{Astro}Sat (SXT, LAXPC), \emph{Swift-UVOT}, and \emph{Fermi-LAT} during the period…
Insights into the Long-Term Flaring Events of Blazar PKS 0805-07: A Multi-Wavelength Analysis over the 2009-2023 Period
Sikandar A. Dar, Zahir Shah, Ranjeev Misra +1
We conducted a comprehensive temporal and spectral study of the FSRQ PKS 0805-07 by using the broadband observations from the Fermi-LAT and Swift-XRT/UVOT instruments over the peri…
Broadband spectral and temporal study of Ton 599 during the brightest January 2023 flare
Aaqib Manzoor, Zahir Shah, Sunder Sahayanathan +2
In this work, we provide a detailed analysis of the broadband temporal and spectral properties of the blazar Ton\,599 by using the observations from \emph{Fermi}-LAT and \emph{Swif…
Can FSRQ 3C 345 be a Very High Energy Blazar Candidate?
Athar A. Dar, Sunder Sahayanathan, Zahir Shah +1
The recent detection of very high energy (VHE) emissions from flat spectrum radio quasars (FSRQs) at high redshifts has revealed that the universe is more transparent to VHE -ra…
Multi-wavelength variability and broadband SED modeling of BL Lac during a bright flaring period MJD 59000-59943
Zahir Shah
We carried a detailed temporal and spectral study of the BL\,Lac by using the long-term \emph{Fermi}-LAT and \emph{Swift}-XRT/UVOT observations, during the period MJD\,59000-59943.…
Understanding the Broadband Emission Process of 3C 279 through Longterm Spectral Analysis
Aminabi Thekkoth, S. Sahayanathan, Zahir Shah +2
The long term broadband spectral study of Flat Spectrum Radio Quasars during different flux states has the potential to infer the emission mechanisms and the cause of spectral vari…
Understanding the Very High Energy γ-ray excess in nearby blazars using leptonic model
Aaqib Manzoor, Sunder Sahayanathan, Zahir Shah +3
The availability of simultaneous X-ray and Very High Energy (VHE) observations of blazars helps to identify the plausible radiative contributors to the VHE emission. Under leptonic…