2024/04/26 by Anuj Nandi, Santabrata Das, Nandi, Anuj +9 · 3 citations
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Mechanics and Biomechanics Studies #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.2404.17160
openalex publication_date 2024/04/26 · openalex created_date 2024/04/30 · openalex updated_date 2026/07/28
We report the first detection of evolving Low-Frequency Quasi-periodic Oscillation (LFQPO) frequencies in hard X-rays upto 100 keV with AstroSat/LAXPC during `unusual' outburst phase of Swift J1727.8-1613 in hard-intermediate state (HIMS). The observed LFQPO in 20 - 100 keV has a centroid ν_\rm QPO=1.43 Hz, a coherence factor Q= 7.14 and an amplitude \rm rms_\rm QPO = 10.95% with significance σ= 5.46. Type-C QPOs (1.09-2.6 Hz) are found to evolve monotonically during HIMS of the outburst with clear detection in hard X-rays (80 - 100 keV), where \rm rms_\rm QPO decreases (∼ 12-3%) with energy. Further, ν_\rm QPO is seen to correlate (anti-correlate) with low (high) energy flux in 2-20 keV (15-50 keV). Wide-band (0.7 - 40 keV) energy spectrum of NICER/XTI and AstroSat/LAXPC is satisfactorily described by the `dominant' thermal Comptonization contribution (∼ 88%) in presence of a `weak' signature of disk emissions (kT\rm in ∼ 0.36 keV) indicating the harder spectral distribution. Considering source mass M\rm BH=10M_\odot and distance 1.5 < \rm d~(kpc) < 5, the unabsorbed bolometric luminosity is estimated as ∼ 0.03-0.92%L\rm Edd. Finally, we discuss the implications of our findings in the context of accretion dynamics around black hole X-ray binaries.