カテゴリー: X-ray binary

Component separation of rapid variations in black hole X-ray binaries

Omama, T., Uemura, M., Ikeda, S. and Morii, M., “Extracting common signal components from the X-ray and optical light curves of GX 339−4: New view for anti-correlation”, PASJ, 73, 716, 2021

Simultaneous X-ray and optical observations of black hole X-ray binaries have shown that the light curves contain multiple correlated and anti-correlated variation components when the objects are in the hard state. In the case of the black hole X-ray binary GX 339-4, the cross correlation function (CCF) of the light curves suggests a positive correlation with an optical lag of 0.15 s and anti-correlations with an optical lag of 1 s and X-ray lag of 4 s. This indicates that the two light curves have some common signal components with different delays. In this study we extracted and reconstructed those signal components from the data for GX 339-4. The results confirmed that correlation and anti-correlation with the optical lag are two common components. However, we found that the reconstructed light curve for the anti-correlated component indicates a positively correlated variation with an X-ray lag of ~+1 s. In addition, the CCF for this signal component shows anti-correlations not only with the optical lag, but also with the X-ray lag, which is consistent with the CCF for the data. Therefore, our results suggest that the combination of the two positively correlated components, that is, the X-ray preceding signal with the 0.15 s optical lag and the optical preceding signal with the 1 s X-ray lag, can make the observed CCF without anti-correlated signals. The optical preceding signal may be caused by synchrotron emission in a magnetically dominated accretion flow or in a jet, while further study is required to understand the mechanism of the X-ray time lag.

Optical Observation of the 2003 Outburst of a Black Hole X-Ray Binary, V4641 Sagittarii

M. Uemura, T. Kato, R. Ishioka, A. Imada, D. Nogami, et al., “Optical Observation of the 2003 Outburst of a Black Hole X-Ray Binary, V4641 Sagittarii,” PASJ, vol. 56, pp. 823-829, 2004.

We report on the results of our optical photometric observations of a black hole X-ray binary, V4641 Sgr during an outburst in 2003 August. During the outburst, we detected several properties having noteworthy similarities to those observed during an outburst in 2002 May; the outburst lasted about 6 days, during which it exhibited flares and rapid fluctuations, having timescales of 102-4s. In complicated profiles of light curves, we identified several recurring patterns, which were also observed during the 2002 outburst. First, the object frequently experienced sudden temporary fadings, which we call “dips”, appearing just after the states characterized by strong short-term fluctuations. Second, we detected optical flashes, which are characterized by a brightening by ˜ 0.5 mag within ˜ 50 s. Based on the similarity of the outbursts in 2002 and 2003, we conclude that they have the same nature. This is the first time that repetitive outburst phenomena have been confirmed in V4641 Sgr. The object probably has an outburst interval that can be as small as 1-2 years.

uem04v4641

Optical Variations of XTE J1859+226 during the 1999 Outburst

M. Uemura, T. Kato, E. Pavlenko, S. Shugarov, M. Mitskevich, et al., “Optical Variations of XTE J1859+226 during the 1999 Outburst,” PASJ, vol. 56, p. 147, 2004.

We report on our optical photometric observations of a black hole X-ray transient, XTE J1859 + 226 (= V406 Vul). We detected an optical reflare associated with an X-ray reflare about 50d after the outburst maximum. The X-ray delay of the reflare was shorter than 2.3d. We detected coherent modulations having a period of 0.38385 ± 0.00073 d. The modulation appeared within 7d after the outburst maximum. We propose two obvious interpretations for the nature of the modulations, that is, superhumps or orbital-period variations caused by an irradiated secondary star or an outer disk. The asymmetric profile of the modulations suggests the superhump scenario. The early appearance of superhumps indicates that the tidal dissipation had already grown before the reflare. The growing tidal dissipation is hence less likely to induce the reflare. In conjunction with the short X-ray delay of the reflare, the reflare may be triggered by the X-ray irradiation onto an outer cold disk. The appearance of humps may be earlier than the eccentricity growth time expected from the tidal instability model. It may imply a mass ratio larger than what could be inferred from the reported orbital period.

uem03j1859

1 2