Open AccessA detailed study of the 5‐Hz quasi‐periodic oscillations in the bright X‐ray transient and black hole candidate GRS 1739–278
Author(s) -
Wijnands Rudy,
Méndez Mariano,
Miller Jon M.,
Homan Jeroen
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04871.x
Subject(s) - physics , overtone , photon , amplitude , astrophysics , oscillation (cell signaling) , photon energy , noise (video) , energy (signal processing) , soft photon , astronomy , spectral line , optics , quantum mechanics , computer science , bremsstrahlung , artificial intelligence , biology , image (mathematics) , genetics
We present a detailed study of the 5‐Hz quasi‐periodic oscillation (QPO) recently discovered in the bright X‐ray transient and black hole candidate (BHC) GRS (Borozdin & Trudolyubov) during a Rossi X‐ray Timing Explorer observation taken on 1996 March 31. In total 6.6 ksec of on‐source data were obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by ∼2.6 ksec. The 5‐Hz QPO was only present during the second data set. The QPO increased in strength from below 2 per cent rms amplitude for photon energies below 4 keV to ∼5 per cent rms amplitude for energies above 10 keV. The soft QPO photons (below 5 keV) lagged the hard ones (above 10 keV) by almost 1.5 rad. Besides the QPO fundamental, its first overtone was detected. The strength of the overtone increased with photon energy (from < 2 per cent rms below 5 keV to ∼8 per cent rms above 10 keV). Although limited statistics did not allow for an accurate determination of the lags of the first overtone, indications are that also for this QPO the soft photons lagged the hard ones. When the 5‐Hz QPO was not detected (i.e., during the first part of the observation), a broad noise component was found for photon energies below 10 keV but it became almost a true QPO (with a Q value of ∼1.9) above that energy, with a frequency of ∼3 Hz. Its hard photons preceded the soft ones in a way reminiscent of the 5‐Hz QPO, strongly suggesting that both features are physically related. We discuss our finding in the framework of low‐frequency QPOs and their properties in BHCs.