Correlations in Horizontal Branch Oscillations and Break Components in Xte J1701-462 and Gx 17+2

Abstract

We studied the horizontal branch oscillations (HBO) and the band-limited components observed in the power spectra of the transient neutron star low-mass X-ray binary XTE J1701-462 and the persistent "Sco-like" Z source GX 17+2.These two components were studied based on the state-resolved spectra. We found that the frequencies of XTE J1701-462 lie on the known correlations (WK and PBK), showing consistency with other types of X-ray binaries (black holes, atoll sources and millisecond X-ray pulsars). However, GX 17+2 is shifted from the WK correlation like other typical Z sources. We suggest that the WK/PBK main track forms a boundary which separates persistent sources from transient sources. The characteristic frequencies of break and HBO are independent of accretion rate in both sources, although it depends on spectral models. We also report the energy dependence of the HBO and break frequencies in XTE J1701-462 and how the temporal properties change with spectral state in XTE J1701-462 and GX 17+2. We studied the correlation between rms at the break and the HBO frequency. We suggest that HBO and break components for both sources probably arise from a similar physical mechanism: Comptonization emission from the corona. These two components could be caused by same kind of oscillation in a corona who with uneven density, and they could be generated from different areas of corona. We further suggest that different proportions of the Comptonization component in the total flux cause the different distribution between GX 17+2 and XTE J1701-462 in the rms break -rms HBO diagram. 1989; van der Klis 2006; van der Klis 1995; Homan et al. 2001; Belloni et al. 2004; Homan & Belloni 2005; Belloni et al. 2005). Based on X-ray spectra properties and rapid variability behaviors, bright NS-LMXBs are commonly classified into two sub-types, the Z sources and the atoll sources (Hasinger & van der Klis 1989). The Z sources have luminosity approaching the Eddington limit (∼ 0.1 − 1L Edd or more), while the atoll sources show luminosity of ∼ 0.01 − 0.5L Edd . The Color-Diagram (CD) and Hardness Intensity Diagram (HID) of a typical Z source include three branches, the horizontal branch (HB), the normal branch (NB), and the flare branch (FB). Depending on further details about the shape and orientation of these branches, the Z sources were further classified into the "Cyg-like" Z sources and the "Sco-like" Z sources. Three distinct types of LFQPOs were observed in the Fourier power density spectra of Z sources: horizontal branch oscillation (HBO) with centroid frequency ∼ 9.5 − 60 Hz, normal branch oscillation (NBO) with centriod frequency ∼ 6 − 20 Hz, and flare branch oscillation (FBO) with centroid frequency ∼ 20 Hz. Atoll sources also show ∼ 20 − 60 Hz LFQPOs.

X-ray spectral and timing evolution of MAXI J1727–203 with NICER

“…Some NS show a similar behaviour (e.g. XTE J1701-462; Bu et al 2015). The rms spectra of broad-band noise components of NS increase with energy in some cases (Bu et al 2015;Bult 2017, studying XTE J1701-462 and MAXI J0911-655, respectively), as MAXI J1727-203 did during most of the outburst.…”

“…XTE J1701-462; Bu et al 2015). The rms spectra of broad-band noise components of NS increase with energy in some cases (Bu et al 2015;Bult 2017, studying XTE J1701-462 and MAXI J0911-655, respectively), as MAXI J1727-203 did during most of the outburst. Unfortunately, neither of those works present the evolution of the rms spectra during a whole outburst, so at the moment we cannot compare the evolution of these sources and that of MAXI J1727-203.…”

Timing analysis of the black hole candidate EXO 1846-031 with Insight-HXMT monitoring

“…For the possible QPO components, we fit the poisson-extracted PDS using a model consisting of several Lorentzians accounting for the possible broad band noise (BBN), the possible QPO fundamental and (sub) harmonics. Since we use the rms normalization in PDS, the fractional rms of QPO is given by (Bu et al 2015):…”

INSIGHT-HXMT Observations of the New Black Hole Candidate MAXI J1535−571: Timing Analysis

“…We consider the background contribution to the fractional rms calculation. The formula is rms = √ P * (S + B)/S (Bu et al 2015), where S and B stand for source and background count rates respectively, and P is the power normalized according to Miyamoto (Miyamoto et al 1991). In the region where LE and ME or ME and HE overlap, there is a good agreement between the two detectors.…”