Chin-Ping Hu

The unprecedented optical outburst of the quasar 3C 454.3 : The WEBT campaign of 2004-2005

Context. The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was

A PARAMETERIZATION STUDY OF THE PROPERTIES OF THE X-RAY DIPS IN THE LOW-MASS X-RAY BINARY X1916-053

R=12.0

PRECISE ORBITAL PARAMETERS AND ANOMALOUS PHASE VARIATIONS OF THE ACCRETION-POWERED MILLISECOND PULSAR XTE J1807-294

, which represents the most luminous quasar state thus far observed (

Tracking the Evolution of Quasi-periodic Oscillation in RE J1034+396 Using the Hilbert-Huang Transform

M_B \sim -31.4

DISCOVERY OF X-RAY PULSATION FROM THE GEMINGA-LIKE PULSAR PSR J2021+4026

). Aims. In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Methods. Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. Results. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the brightening of the radio core and show an increasing polarization. An exceptionally bright X-ray state was detected in May 2005, corresponding to the rising mm flux and suggesting an inverse-Compton nature of the hard X-ray spectrum. Conclusions. A further multifrequency monitoring effort is needed to follow the next phases of this unprecedented event.

EXPLORING THE INTRABINARY SHOCK FROM THE REDBACK MILLISECOND PULSAR PSR J2129-0429

The ultracompact low-mass X-ray binary X1916–053, which is composed of a neutron star and a semidegenerate white dwarf, exhibits periodic X-ray dips of variable width and depth. We have developed a new method to parameterize this dipping behavior to systematically study its variations. This can help in further understanding binary and accretion disk behaviors. Observations by the Rossi X-Ray Timing Explorer from 1998 clearly show a 4.87 day periodic variation in the dip width. This is probably due to nodal precession of the accretion disk, although an epoch-folding search finds no significant sidebands in the spectrum. From the negative-superhump model of Larwood et al., the mass ratio can be estimated as q = 0.045. Combining more than 24 years of historical data, we find an orbital period derivative orb/Porb = (1.62 ± 0.34) × 10−7 yr−1 and establish a quadratic ephemeris for the X-ray dips. This period derivative seems inconsistent with the prediction from the standard model of binary orbital evolution proposed by Rappaport et al. On the other hand, Tavanis radiation-driven model can properly account for the period derivative, although the large mass outflow predicted by this model has never been observed in this system. With the best ephemeris, we find that the standard deviation of the primary dips is smaller than that of the secondary dips. This means that the primary dips are more stable than the secondary dips. Thus, we conclude that the primary dips of X1916–053 occur from the bulge where the accretion stream encounters the rim of the disk, rather than the inner disk ring as previously proposed by Frank et al.

A possible 55-d X-ray period of the ultraluminous accreting pulsar M82 X–2

This study reports pulse variation analysis results for the forth discovered accretion-powered millisecond pulsar XTE J1807-294 during its 2003 outburst observed by Rossi X-ray Timing Explorer. The pulsation is significantly detected only in the first ∼90d out of ∼150d observations. The pulse phase variation is too complex to be described as an orbital motion plus a simple polynomial model. The precise orbital parameters with Porb = 40.073601(8) min and ax sini = 4.823(5) lt-ms were obtained after applying the trend removal to the daily observed 150s segments pulse phases folded with a constant spin frequency without Keplerian orbit included. The binary barycenter corrected pulse phases show smooth evolution and clear negative phase shifts coincident with the flares seen on the light curve and the enhancements of fractional pulse amplitude. The non-flare pulse phases for the first ∼60d data are well described as a fourth order polynomial implying that the neutron star was spun-up during the first ∼60d with a rate u � = (1.7 ± 0.3) × 10 −13 Hz/s at the beginning of the outburst. Significant soft phase lags up to ∼500 µs (∼10% cycle) between 2 to 20 keV were detected for the nonflare pulse phases. We conclude that the anomalous phase shifts are unlikely due to the accretion torque but could result from the “hot spot” moving on the surface of neutron star.

Searches for Millisecond Pulsar Candidates among the Unidentified Fermi Objects

RE J1034+396, a narrow-line Seyfert 1 active galactic nucleus (AGN), is the first example of AGNs that exhibited a nearly coherent quasi-periodic oscillation (QPO) for the data collected by XMM-Newton in 2007. The spectral behaviors and timing properties of the QPO have been studied since its discovery. We present an analysis of the QPO in RE J1034+396 based on the Hilbert-Huang transform. Comparing with other time-frequency analysis methods, the Hilbert spectrum reveals the variation of the QPO period in great detail. Furthermore, the empirical mode decomposition provides bandpass-filtered data that can be used in the O – C and correlation analysis. We suggest that it is better to divide the evolution of the QPO in this observation into three epochs according to their different periodicities. In addition to the periodicities, the correlations between the QPO periods and corresponding mean count rates are also different in these three epochs. Further examining the phase lags in these epochs, we found no significant phase lags between the soft and hard X-ray bands, which is also confirmed in the QPO phase-resolved spectral analysis. Finally, we discuss the indications of current models including a spotted accretion disk, diskoseismology, and oscillation of shock according to the observed time-frequency and spectral behaviors.

DISCOVERY OF AN ULTRACOMPACT GAMMA-RAY MILLISECOND PULSAR BINARY CANDIDATE

We report the discovery of an X-ray periodicity of ∼265.3 ms from a deep XMM-Newton observation of the radioquiet γ -ray pulsar, PSR J2021+4026, located at the edge of the supernova remnant G78.2+2.1 (γ -Cygni). The detected frequency is consistent with the γ -ray pulsation determined by the observation of the Fermi Gamma-ray Space Telescope at the same epoch. The X-ray pulse profile resembles the modulation of a hot spot on the surface of the neutron star. The phase-averaged spectral analysis also suggests that the majority of the observed X-rays have thermal origins. This is the third member in the class of radio-quiet pulsars with significant pulsations detected from both X-ray and γ -ray regimes.

TIME-FREQUENCY ANALYSIS OF THE SUPERORBITAL MODULATION OF THE X-RAY BINARY SMC X-1 USING THE HILBERT-HUANG TRANSFORM

We have investigated the intrabinary shock emission from the redback millisecond pulsar PSR J2129-0429 with XMM-Newton and Fermi. Orbital modulation in X-ray and UV can be clearly seen. Its X-ray modulation has a double-peak structure with a dip in between. The observed X-rays are non-thermal dominant which can be modeled by a power-law with a photon index of ~1.2. Intrabinary shock can be the origin of the observed X-rays. The UV light curve is resulted from the ellipsoidal modulation of the companion. Modeling the UV light curve prefers a large viewing angle. The heating effect of the UV light curve is found to be negligible which suggests the high energy radiation beam of PSR J2129-0429 does not direct toward its companion. On the other hand, no significant orbital modulation can be found in gamma-ray which suggests the majority of the gamma-rays come from the pulsar.