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Multimission Observations of GS 1354-64 during the 2025-2026 Outburst: First Results
Dipak Debnath, Hsiang-Kuang Chang, Subham Srimani +1
The Galactic transient black hole GS 1354-64 recently showed a new outburst, which has been continuously monitored by {\it MAXI}, {\it NuSTAR} and {\it Insight-HXMT} missions. The…
Bridging X-ray Polarization with Timing & Spectroscopic Parameters of a galactic black hole: Swift J1727.8-1613
Arka Chatterjee, Sujoy K. Nath, Kaushik Chatterjee +5
We report the discovery of a correlated energy-dependent time lag and degree of polarization for Swift J1727.8-1613 during its 2023 outburst. The energy-dependent time lag is measu…
Evolution of Time-Lags of Swift J1727.8-1613 during the Rising Phase of Its Discovery Outburst
Sujoy Kumar Nath, Dipak Debnath, Hsiang-Kuang Chang
We investigate the accretion dynamics of the black hole X-ray binary Swift J1727.8-1613 during its discovery outburst that lasted for months. Insight-HXMT moni…
Observational Relationship between Spectral Properties of Gamma-ray and X-ray Emissions from Pulsars
Ashwin Aravindaraj, Hsiang-Kuang Chang
Correlations between gamma-ray and X-ray spectral properties of pulsars are investigated in order to provide observational hints on physics involved in pulsars' high-energy emissio…
Multi-wavelength properties of changing-state active galactic nuclei: I. the evolution of soft excess and X-ray continuum
Arghajit Jana, Claudio Ricci, Alessia Tortosa +11
Changing-state active galactic nuclei (CSAGNs) exhibit rapid variability, with mass accretion rates that can change by several orders of magnitude in a few years. This provides us…
Investigating the Anti-Correlation between Photon Index and Flux of the Crab using RXTE and NuSTAR
Debjit Chatterjee, Hsiang-Kuang Chang, Dipak Debnath +2
We present a systematic study of the recently reported anti-correlation between X-ray flux and photon index () in the Crab Nebula, using archival RXTE/PCA (3 - 50 keV), RXTE/HEX…
Evolution of QPO During Discovery Outburst of MAXI J1834-021: Estimation of Intrinsic Parameters from Spectro-Temporal Study
Dipak Debnath, Hsiang-Kuang Chang
The Galactic transient black hole candidate (BHC) MAXI~J1834-021 was detected for the first time by MAXI/GSC on February 05, 2023 and it was active for next ~months. A mon…
Distinct Fe-K Line Complexes in MAXI J1744-294 Revealed by XRISM High-Resolution Spectroscopy
Kaushik Chatterjee, Santanu Mondal, Biswaraj Palit +7
The newly discovered Galactic transient MAXI J1744-294 went into its first X-ray outburst in 2025. We study the spectral properties of this source in the 2-10 keV energy band durin…
Detection of X-ray Polarization in the Hard State of IGR J17091-3624: Spectro-Polarimetric Study with IXPE and NuSTAR Data
Dipak Debnath, Subham Srimani, Hsiang-Kuang Chang
The class-transition Galactic X-ray binary IGR~J17091--3624 was simultaneously monitored by the \textit{IXPE} and \textit{NuSTAR} satellites. We present a detailed spectro-polarime…
Accretion Flow Properties of MAXI J1834-021 during Its Multi-peaked Outburst in 2023
Dipak Debnath, Hsiang-Kuang Chang
The Galactic transient black hole candidate MAXI J1834-021 exhibited `faint' outburst activity for approximately months following its discovery on February 5, 2023. We study t…
Accretion Flow Properties of Swift J1727.8-1613 and Estimation of the BH Mass
Dipak Debnath, Hsiang-Kuang Chang, Sujoy Kumar Nath +1
The rising phase of the 2023-24 outburst of the recently discovered bright transient black hole candidate Swift J1727.8-1613 was monitored by {\it Insight}-HXMT. We study the evolu…
NGC 7314: X-ray Study of the Evolving Accretion Properties
Debjit Chatterjee, Arghajit Jana, A. Mangalam +1
We present a comprehensive analysis of the timing and spectral properties of NGC 7314, a Seyfert 1.9 galaxy, using X-ray observations from {\it XMM-Newton}, {\it NuSTAR}, and {\it…
Detection of QPO Soft Lag during Outburst of Swift J1727.8-1613: Estimation of Instrinsic Parameters from Spectral Study
Dipak Debnath, Sujoy Kumar Nath, Debjit Chatterjee +2
The recently discovered bright transient black hole candidate Swift J1727.8-1613 is studied in a broad energy range ( keV) using combined NICER and NuSTAR data on 29 August…
Anti-correlation between Flux and Photon Index of Hard X-ray Emission from The Crab
Koothodil Abhijith Augustine, Hsiang-Kuang Chang
Using \textit{Swift} Burst Alert Telescope (BAT) event-mode data during Gamma Ray Burst (GRB) occurrences, we conducted spectral analysis for the Crab system. From 38 good observat…
Accretion properties of soft X-ray transient XTE J1856+053 during its 2023 Outburst
Debjit Chatterjee, Arghajit Jana, Hsiang-Kuang Chang
Soft X-ray transients are a subclass of the low mass X-ray binaries that occasionally show a sudden rise in their soft X-ray luminosity; otherwise, they remain in an extremely fain…
Spectral Properties of GX~339--4 in the Intermediate State Using AstroSat Observation
Arghajit Jana, Debjit Chatterjee, Hsiang-Kuang Chang +2
We present the results obtained from the spectral studies of black hole X-ray binary GX~339--4 using \astrosat~ observations during its 2021 outburst. \astrosat~ observed the sourc…
MAXI J0637-430: A Possible Candidate for Bulk Motion Comptonization?
Kaushik Chatterjee, Dipak Debnath, Sujoy Kumar Nath +1
The transient Galactic black hole candidate MAXI J0637-430 went through an outburst in 2019--20 for the very first time. This outburst was active for almost 6 months from November…
AstroSat Observation of Non-Resonant Type-C QPOs in MAXI J1535-571
D. Chatterjee, D. Debnath, A. Jana +8
Galactic transient black hole candidate (BHC) MAXI J1535-571 was discovered on 2017 September 02 simultaneously by {\it MAXI}/GSC and {\it Swift}/BAT instruments. It has also been…