Phase Lag and Coherence Function of X-ray emission from Black Hole Candidate XTE J1550-564

We report the results from measuring the phase lag and coherence function of X-ray emission from black hole candidate (BHC) XTE J1550-564. These X-ray temporal properties have been recognized to be increasingly important in providing important diagnostics of the dynamics of accretion flows around black holes. For XTE J1550-564, we found significant hard lag --- the X-ray variability in high energy bands {\em lags} behind that in low energy bands --- associated both with broad-band variability and quasi-periodic oscillation (QPO). However, the situation is more complicated for the QPO: while hard lag was measured for the first harmonic of the signal, the fundamental component showed significant {\em soft} lag. Such behavior is remarkably similar to what was observed of microquasar GRS 1915+105. The phase lag evolved during the initial rising phase of the 1998 outburst. The magnitude of both the soft and hard lags of the QPO increases with X-ray flux, while the Fourier spectrum of the broad-band lag varies significantly in shape. The coherence function is relatively high and roughly constant at low frequencies, and begins to drop almost right after the first harmonic of the QPO. It is near unity at the beginning and decreases rapidly during the rising phase. Also observed is that the more widely separated the two energy bands are the less the coherence function between the two. It is interesting that the coherence function increases significantly at the frequencies of the QPO and its harmonics. We discuss the implications of the results on the models proposed for BHCs.Comment: To appear in ApJ Letter

Could higher standards of living discourage tax evasion?

How often does law get made in China, and what kinds of law? We construct a dataset on subnational lawmaking to address these questions. The dataset builds on a basic insight: Chinese politicians choose among three types of instruments to implement policy—statutes, regulations, and informal policy directives (IPDs). IPDs are easier to promulgate than statutes and regulations, and the fact that they lack the force of law rarely impedes enforcement. Why then do politicians make law at all? Several findings shed light on this puzzle. First, the choice between formal lawmaking and IPDs depends on the policy subject. Second, provinces and cities have distinct policy specializations. Specialization may lead one level of government to invest in lawmaking in the subject, or lead the other level of government to refrain from doing so. Third, politician tenure has little impact on lawmaking. Fourth, while population is a relevant predictor of lawmaking, other factors that might seem to represent the “demand for law” bear unexpected correlations with the quantity of law

When Do Chinese Subnational Governments Make Law?

How often does law get made in China, and what kinds of law? We construct a dataset on subnational lawmaking to address these questions. The dataset builds on a basic insight: Chinese politicians choose among three types of instruments to implement policy—statutes, regulations, and informal policy directives (IPDs). IPDs are easier to promulgate than statutes and regulations, and the fact that they lack the force of law rarely impedes enforcement. Why then do politicians make law at all? Several findings shed light on this puzzle. First, the choice between formal lawmaking and IPDs depends on the policy subject. Second, provinces and cities have distinct policy specializations. Specialization may lead one level of government to invest in lawmaking in the subject, or lead the other level of government to refrain from doing so. Third, politician tenure has little impact on lawmaking. Fourth, while population is a relevant predictor of lawmaking, other factors that might seem to represent the “demand for law” bear unexpected correlations with the quantity of law

Decentralizing Legislation in China’s Law on Legislation Amendment

We present a novel account of China’s recent move to decentralize legislation through amending the Law on Legislation (LL). Conventional wisdom pervading both Chinese political discourse and social scientific scholarship on China portrays law as incompatible with experimentation and as only suitable for codifying policies adopted after experimentation. Moreover, the value of legislatures is viewed as lying in their independence from the executive branch. We highlight rationales offered by the Chinese Communist Party for the LL amendment that repudiate these assumptions: the Party proclaimed the intention to promote lawmaking as a central instrument of policy experimentation; moreover, the Party’s intervention in legislative processes may rescue legislatures from their irrelevance. We trace this new position regarding the role of lawmaking through the amended LL’s legislative history and initial implementation. We further show how this new official ideology clashed with the views of legislative officials, for whom “constraining government” has become a central preoccupation—both as a consequence of, and reinforcing, legislation’s political irrelevance. We argue that, to understand the political calculus underlying Xi’s approach to law, one does well to acknowledge the coherence and appeal of initiatives such as the LL amendment

Strong Aperiodic X-ray Variability and Quasi-Periodic Oscillation in X-ray Nova XTE J1550-564

We report the discovery of strong aperiodic X-ray variability and quasi-periodic oscillation (QPO) in the X-ray light curves of a new X-ray Nova, XTE J1550-564, and the evolution of the observed temporal properties during the rise of the recent X-ray outburst. The power spectral analysis of the first observation reveals strong aperiodic X-ray variability of the source (~28%), as well as the presence of a QPO at ~82 mHz with fractional rms amplitude ~14% over the 2-60 keV energy range. Also apparent is the first harmonic of the QPO with the amplitude ~9%. As the X-ray flux increases, the source tends to become less variable, and the QPO frequency increases rapidly, from 82 mHz to 4 Hz, over the flux (2-50 keV) range of 1.73-5.75 x 10^{-8} ergs cm^{-2} s^{-1}. The amplitude of the fundamental component of the QPO varies little, while that of the harmonic follows a decreasing trend. The fundamental component strengthens toward high energies, while its harmonic weakens. Initially, the power spectrum is roughly flat at low frequencies and turns into a power law at high frequencies, with the QPO harmonic sitting roughly at the break. In later observations, however, the high-frequency portion of the continuum can actually be better described by a broken power law (as opposed to a simple power law). This effect becomes more apparent at higher energies. The overall amplitude of the continuum shows a similar energy dependence to that of the fundamental component of the QPO. Strong rapid X-ray variability, as well as hard energy spectrum, makes XTE J1550-564 a good black hole candidate. We compare its temporal properties with those of other black hole candidates.Comment: 12 pages, including 5 figures. To appear in ApJ Letters, vol. 512 (1999