J/ApJ/728/9 Quasi-periodic oscillations from XTE J1701-462 (Barret+, 2011)
The drop of the coherence of the lower kilohertz quasi-periodic brightness
variations is also observed in XTE J1701-462.
Barret D., Bachetti M., Miller M.C.
<Astrophys. J., 728, 9 (2011)>
=2011ApJ...728....9B 2011ApJ...728....9B
ADC_Keywords: Binaries, X-ray
Keywords: accretion, accretion disks - stars: individual (XTE J1701-462) -
X-rays: binaries - X-rays: individual (XTE J1701-462) - X-rays: stars
Abstract:
We investigate the quality factor and root mean square (rms) amplitude
of the lower kilohertz quasi-periodic brightness variations (kHz QPOs)
from XTE J1701-462, a unique X-ray source which was observed in both
the so-called Z and atoll states. Correcting for the frequency drift
of the QPO, we show that, as in all sources for which such a
correction can be applied, the quality factor and rms amplitude drops
sharply above a critical frequency. For XTE J1701-462, this frequency
is estimated to be ∼800Hz, where the quality factor reaches a maximum
of ∼200 (e.g., a value consistent with the one observed from more
classical systems, such as 4U 1636-536). Such a drop has been
interpreted as the signature of the innermost stable circular orbit,
and that interpretation is consistent with the observations we report
here. The kHz QPOs in the Z state are much less coherent and lower
amplitude than they are in the atoll state. We argue that the change
of the QPO properties between the two source states is related to the
change of the scale height of the accretion disk; a prediction of the
toy model proposed by Barret et al. As a by-product of our analysis,
we also increased the significance of the upper kHz QPO detected in
the atoll phase up to 4.8σ (single trial significance) and show
that the frequency separation (266.5±13.1Hz) is comparable with the
one measured from simultaneous twin QPOs in the Z phase.
Description:
In this paper, we revisit the RXTE observations reported by Sanna et
al. (2010MNRAS.408..622S 2010MNRAS.408..622S), focusing on the lower kHz QPO and apply the
same analysis procedures (frequency drift correction) as described in
Barret et al. (2006MNRAS.370.1140B 2006MNRAS.370.1140B).
We follow the definition of the Z and atoll states as in Sanna et al.
(2010MNRAS.408..622S 2010MNRAS.408..622S): the separation is estimated around the end of
2007 April. We have retrieved from the HEASARC archive science event
mode and single bit data recorded by the RXTE PCA. We consider data as
segments of continuous observation (an ObsID may contain more than 1
segment). For each segment, we have computed an average Power Density
Spectrum (PDS) with a 1Hz resolution and an integration time of 16s,
using events recorded between 2 and 40keV.
Objects:
--------------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------------
17 00 58.46 -46 11 08.6 XTE J1701-462 = SWIFT J1700.9-4610
--------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 47 1754 QPO frequency data
--------------------------------------------------------------------------------
See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2012)
J/A+A/522/A68 : Variable sources detected by INTEGRAL (Telezhinsky+, 2010)
J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007)
J/A+A/467/585 : Sources detected by ISGRI (Bodaghee+, 2007)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "YYYY/MM/DD" Obs.date Date of PDS segment start (1)
12- 19 A8 "h:m:s" Obs.time Time of PDS segment start (1)
21- 29 I9 s Start Starting date of PDS segment (2)
31- 39 I9 s Stop Stoping date of PDS segment (2)
41- 47 F7.3 Hz Freq QPO frequency estimated for PDS segment
--------------------------------------------------------------------------------
Note (1): Each segment is 16 second long.
Note (2): In elapsed seconds since January 1, 1994.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 31-Aug-2012