J/AJ/146/60 X-ray variability in 4U 1735-44 (Lei+, 2013)
Evolution of the cross-correlation and time lag of 4U 1735-44 along the
branches.
Lei Y.-J., Zhang H.-T., Zhang C.-M., Qu J.-L., Yuan H.-L., Dong Y.-Q.,
Zhao Y.-H., Wang D.-H., Yin H.-X., Zhang Y.-X., Song L.-M.
<Astron. J., 146, 60 (2013)>
=2013AJ....146...60L 2013AJ....146...60L
ADC_Keywords: Binaries, X-ray
Keywords: accretion, accretion disks - binaries: close -
stars: individual: 4U 1735-44 - X-rays: binaries
Abstract:
We analyze the cross-correlation function between the soft and hard
X-rays of atoll source 4U 1735-44 with RXTE data, and find
anti-correlated soft and hard time lags of about a hecto-second. In
the island state, the observations do not show any obvious
correlations, and most observations of the banana branch show a
positive correlation. However, anti-correlations are detected in the
upper banana branch. These results are different from those of
Z-sources (Cyg X-2, GX 5-1), where anti-correlations are detected in
the horizontal branch and upper normal branch. In this case, the lag
timescales of both this atoll and Z-sources are found to be similar,
at a magnitude of several tens to hundreds of seconds. As a
comparison, it is noted that anti-correlated lags lasting thousands of
seconds have been reported from several black hole candidates in their
intermediate states. In addition, for an observation containing four
segments that show positive or anti-correlation, we analyze the
spectral evolution with the hybrid model. In the observation, the
anti-correlation is detected at the highest flux. The fitting results
show that the Comptonized component is not the lowest at the highest
flux, which suggests that the anti-correlation corresponds to the
transition between the soft and hard states. Finally, we compare the
corresponding results of atoll source 4U 1735-44 with those observed
in Z-sources and black hole candidates, and the possible origins of
the anti-correlated time lags are discussed.
Description:
We analyze all pointed observations of the Proportional Counter Array
(PCA) on board the RXTE satellite. The PCA consists of five
non-imaging, coaligned Xe multiwire proportional counter units (PCUs).
In this work, except for the Power Density Spectrum (PDS), the data
are adopted only from PCU2, which is the best calibrated unit and has
the longest observational duration. Only data segments longer than
2000s are used to analyze the cross-correlation function.
Objects:
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RA (ICRS) DE Designation(s) (Period)
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17 38 58.3 -44 27 00 4U 1735-44 = 1ES 1735-44.4 (P = 4.654hr)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 248 Log of all observations (>2000s) showing a positive
or ambiguous correlation hard/soft X-ray emission
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See also:
V/106 : Catalogue of X-ray binaries (Liu+ 2001)
J/ApJ/685/436 : X-ray variability in 4U 1636-53 (Altamirano+, 2008)
J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- C Positive (P) or ambiguous (A) correlation
3- 16 A14 --- ObsID XRTE observation identification
17 A1 --- --- [_]
18 A1 --- m_ObsID [abcde ] We label the segments (>2000s) of the
light curves as a, b, and so on
20- 30 A11 "Y:M:D" Date Date of observation
32- 34 A3 --- Reg Region (I-IV) in color-color diagram (CCD) (1)
36- 41 F6.1 s lag ? Time delay between the soft and hard X-rays
43- 47 F5.1 s e_lag ? Uncertainty in lag
49- 52 F4.2 --- CC [0.09/0.63]? Cross-correlation coefficient
54- 57 F4.2 --- e_CC ? Uncertainty in CC
59- 63 F5.3 --- HR1 [3.865/4.788] Soft color (3.5-6)/(2-3.5) (2)
65- 69 F5.3 --- HR2 [0.48/5.33] Hard color (9.7-16)/(6-9.7) (2)
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Note (1): The four regions correspond to the average values of the hardness
ratios (see Fig.2 in the paper). The data in regions I, II, III, and IV
are mainly related to Island State (IS), the Lower Left Banana (LLB), the
Lower Banana (LB), and the Upper Banana (UB).
Note (2): We have defined the soft and the hard colors as the count-rate ratios
3.5-6.0keV/2.0-3.5keV and 9.7-16keV/6.0-9.7keV. The ratio of soft color to
hard color gives the hardness ratio.
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History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 03-Jul-2014