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Detection of Additional Periodicities in RXTE ASM Light Curves

ATel #940; Alan M. Levine (MIT MKI) and Robin Corbet (NASA/GSFC and USRA)
on 9 Nov 2006; 15:49 UT
Credential Certification: Alan M. Levine (aml@space.mit.edu)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Pulsar

Referred to by ATel #: 1995

We have detected periodicities in the Rossi X-ray Timing Explorer (RXTE) All-sky Monitor (ASM) X-ray light curves beyond those reported by Wen et al. (2006, ApJS, 163, 372). We analyzed data accumulated over nearly 10 years (1996 March through 2005 November) from some 450 sources. Several weighting and filtering techniques not used by Wen et al. were applied previous to the Fourier analysis in order to reduce noise levels. We have searched for both known and previously unknown periods; the signal strengths required for detection in the two cases are quite different. One periodicity, i.e., that of GRO J1008-57, was found by visual identification of periodically occurring outbursts rather than via the power density spectrum. Our results are listed below.

SourcePeriodComments
X1145-619˜870 salias of 290 s pulse period
X1820-303685.01117 ± 0.0005 s
X1323-6192.94192 ± 0.00004 h
X1636-5363.79315 ± 0.00006 h
X1254-6903.93336 ± 0.00006 h
or 3.93995 ± 0.00006 h
two nearly equally likely values
GX9+94.19344 ± 0.00007 halso see ATEL #839
X1746-3705.16329 ± 0.00016 h
X1957+1159.3175 ± 0.0005 hmarginal detection
GX339-41.7563 ± 0.0003 dnot a strong detection
GRO J1655-402.621 ± 0.007 dnot a strong detection
V4641 Sgr2.8019 ± 0.0002 dnot a strong detection
LMC X-13.9081 ± 0.0015 dsee below
SS43313.075 ± 0.017 dsee below
IGR J18483-031118.55 ± 0.03 dnew periodicity
X1417-6242.12 dperiod from Bildsten et al. 1997
X1845-024242.18 dperiod from Finger et al. 1999
GRO J1008-57248.9 ± 0.5 dsee text below

Periodicities with periods close to those in the above table have been previously reported in all cases except that of IGR J18483-0311.

In an least one power spectrum for GX339-4, the highest power occurs at the frequency corresponding to the 1.7 d period reported by Hynes et al. (2003, ApJL, 583, L95). The magnitude of this power is not so high that the detection is completely secure. However, given the number of frequency bins, and the fact that we do not find high values of power at the frequencies corresponding to the 0.62 d period reported by Callanan et al. (1992, MNRAS, 259,395) or to the 0.7 d period reported by Cowley et al. (2002, ApJ, 123, 1741), we believe that this result confirms the Hynes et al. result.

To our knowledge, this is the first detection of the orbital period of LMC X-1 in X-rays. Hutchings et al. (1983, ApJL, 275, L43) and Hutchings et al. (1987, AJ, 94, 340) reported periods of LMC X-1 based on radial velocities. We find a highly significant peak at a period of 3.9081 ± 0.0015 d that is nearly exactly the first of several possible values given by Hutchings et al. (1983).

Gies et al. (2002, ApJ, 566, 1069) have previously reported the detection in ASM data of the 13.075 d orbital period of SS433.

The orbital periods of X1417-62 and X1845-024 were determined much more accurately via pulse timing analyses by Bildsten et al. (1997, ApJS, 113, 367) and Finger et al. (1999, ApJ, 517, 449), respectively, than in our work.

Previous estimates regarding the period of GRO J1008-57 may be found in Schrader et al. (1999, ApJ, 512, 920) and references therein.