J/ApJ/902/146 Swift/BAT and RXTE/ASM obs. of Hercules X-1 (Leahy+, 2020)
Swift/BAT and RXTE/ASM observations of the 35 day X-ray cycle of Hercules X-1.
Leahy D., Wang Y.
<Astrophys. J., 902, 146 (2020)>
=2020ApJ...902..146L 2020ApJ...902..146L
ADC_Keywords: Binaries, X-ray; X-ray sources
Keywords: Hz Herculis x-ray binary stars ; X-ray photometry ;
Neutron stars
Abstract:
Swift/BAT and RXTE/ASM observations have monitored the X-ray binary
system Her X-1 for approximately 14.5yr each, and both were monitoring
Her X-1 for a period of ∼5.5yr. Here we study the 35d cycle using
these observations. Using a cross-correlation method we find the times
of peaks of the 35 day cycles for ∼150 cycles observed by Swift/BAT
and ∼150 cycles observed by RXTE/ASM. These cycles include
∼60 observed with both instruments. The noise level of the RXTE/ASM
measurements is larger than that of Swift/BAT, resulting in larger
uncertainty in peak times. The distribution of 35d cycle lengths can
be fit with a Gaussian with mean 34.79d and σ of 1.1d. The
distribution of orbital phases of 35 day cycle peaks is well fit by a
uniform distribution, with 76% of the cycles, plus a Gaussian
distribution peaked at orbital phase ∼0.5, with 24% of the cycles. We
construct the long-term average 35 day lightcurve in the 15-50keV band
from Swift/BAT, and in the 2-12keV band from RXTE/ASM. The high-energy
band shows more variability in the short high state and the low-energy
band shows more variability in the main high state. This is consistent
with a precessing accretion disk model as the cause of the 35d cycle.
Description:
The Swift Burst Alert Telescope (BAT) is used to monitor X-ray sources
on a regular basis and to create long-term lightcurves for these
sources. For Hercules X-1, we downloaded the data for the energy range
of 15-50keV, covering 14yr of observation with 71165 points from
February 2005 to November 2019.
The Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor (ASM) monitored
the sky in the 2-12keV energy band. The RXTE/ASM lightcurves for
Her X-1 were obtained from the Massachusetts Institute of Technology
(MIT) online archives. The data cover the time period from 1996
January to 2011 December, with a total number of 95782 points.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
16 57 49.81 +35 20 32.5 Hercules X-1 = X Her X-1
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 33 154 Swift/BAT cycles
table2.dat 33 160 RXTE/ASM cycles
table4.dat 24 59 ASM & BAT comparison for overlap period
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/swift : Swift Master Catalog (HEASARC, 2004-)
B/xmm : XMM-Newton Observation Log (XMM-Newton Science Operation Center, 2012)
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2017)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
V/106 : Catalogue of X-ray binaries (Liu+ 2001)
J/AZh/79/1087 : UBV photometry of X-ray binary HZ Her (Sheffer+, 2002)
J/A+A/467/785 : SuperWASP/ROSAT periodic variable stars (Norton+, 2007)
J/A+A/522/A68 : Variable sources detected by INTEGRAL (Telezhinsky+, 2010)
J/ApJS/187/149 : StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)
J/AJ/141/129 : Chandra Transmission Grating Data Cat. (Huenemoerder+, 2011)
J/A+A/548/A79 : INTEGRAL-OMC optically var. sources (Alfonso-Garzon+, 2012)
J/ApJS/209/14 : The Swift/BAT hard X-ray transient monitor (Krimm+, 2013)
J/A+A/550/A110 : Her X-1 pulse profiles (Staubert+, 2013)
J/BaltA/24/395 : X-ray and radio sources in binaries (Malkov+, 2015)
J/other/NewA/47.81 : Distances of X-ray binaries (Islam+, 2016)
J/ApJS/223/15 : 8yr INTEGRAL/IBIS soft gamma-ray source obs. (Bird+, 2016)
J/A+A/625/A122 : CIELO-RGS, soft X-ray ionized emission lines cat. (Mao+, 2019)
J/A+A/645/A18 : SVOM-ECLAIRs known X-ray sources catalogue (Dagoneau+, 2021)
http://xte.mit.edu/asmlc/ASM.html : RXTE ASM Light Curves home page
http://swift.gsfc.nasa.gov/results/transients/ : Swift/BAT Hard X-ray Transient
Monitor home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- NumB [0/151] Cycle number
5- 15 F11.5 d MJD [53437.82/58692] Modified Julian Date
of the main high state (MH) peak time (G1)
17- 22 F6.3 d Length [31.2/39.5] Cycle length (G1)
24- 31 F8.5 --- Phase [-1/0.998] MH peak orbital phase (G1)(G2)
33 I1 --- Label [0/2]? Label of cycle (G3)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- NumA [2/162] Cycle number (1)
5- 15 F11.5 d MJD [50146.5/55705.5] Modified Julian Date
of the main high state (MH) peak time (G1)
17- 22 F6.3 d Length [-1/38.7] Cycle length (G1)
24- 31 F8.5 --- Phase [-1/0.99] MH peak orbital phase (G2)
33 I1 --- Label [0/1]? Label of cycle (G3)
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Note (1): Numbering of cycle starts from 2 in order to better compare with
Table 1 of Leahy & Igna (2010ApJ...521..328L 2010ApJ...521..328L). For the same reason
cycle #50 is skipped. We use 17 cycles, each 35.744days long, during
the anomalous low state from MJD51223 to MJD51831, while
Leahy & Igna (2010ApJ...521..328L 2010ApJ...521..328L) have 14 cycles of 33.4-day lengths
from MJD51222 to MJD51757. The cycles would have lengths of 33.759days
if there are 18 cycles during this ALS time period.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- NumA [97/162] Cycle number for ASM
5- 6 I2 --- NumB [0/65] Cycle number for BAT
8- 15 F8.5 d dt [-1.27/1.6] MH peak time difference; ASM-BAT
17- 24 F8.5 --- dphi [-1.11/1.92] MH peak orbital phase difference;
ASM-BAT
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Global notes:
Note (G1): Cycles with orbital phases marked "-1.00000" are not identified
by the cross-correlation algorithm. Their MJD time and cycle lengths
are calculated from the MJD time of cycles right before and after.
Note (G2): Orbital phase ≥0.0 and <1.0. A "-1.00000" means the cycle has
calculated peak times and cycle lengths.
Note (G3): Label of cycle as follows:
0 = cycles detected by algorithm;
1 = weak cycles (relative low CC peak value and added manually)
for detected orbital phase;
1 = calculated peak times (cycle lengths averaged with previous and
later peak times) for orbital phase assigned "-1.00000";
2 = a range of time due to missing data in between (cycle number
duplicated for the cycle and the one before it to show range of cycle
lengths).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 22-Apr-2022