Chang-Yin Huang

A model of the light curves of Gamma-Ray Bursts

Aims. An extreme Kerr black hole (BH) surrounded by a precessing disk is invoked to explain the light curves of gamma-ray bursts (GRBs) based on the coexistence of the Blandford-Znajek (BZ) and the magnetic coupling (MC) processes. Methods. The overall shape of the light curves and the duration of GRBs are interpreted by the evolution of the halfopening angle of the magnetic flux on the BH horizon, and the complex temporal structures are modulated by the precession and nutation of the jet powered by the BZ process. Results. The time profile of the emission exhibits a fast rise and a slow decay due to the effect of the evolution of the half-opening angle. The light curves of several GRBs are well fitted by this model with only six free parameters.

Quasi-periodic variations in x-ray emission and long-term radio observations: Evidence for a two-component jet in Sw J1644+57

The continued observations of Sw J1644+57 in X-ray and radio bands accumulated a rich data set to study the relativistic jet launched in this tidal disruption event. The X-ray light curve of Sw J1644+57 from 5-30 days presents two kinds of quasi=periodic variations: a 200 s quasi=periodic oscillation (QPO) and a 2.7 day quasi=periodic variation. The latter has been interpreted by a precessing jet launched near the Bardeen-Petterson radius of a warped disk. Here we suggest that the similar to 200 s QPO could be associated with a second, narrower jet sweeping the observer line-of-sight periodically, which is launched from a spinning black hole in the misaligned direction with respect to the black holes angular momentum. In addition, we show that this two-component jet model can interpret the radio light curve of the event, especially the re-brightening feature starting similar to 100 days after the trigger. From the data we infer that inner jet may have a Lorentz factor of Gamma(j) similar to 5.5 and a kinetic energy of E-k,E-iso similar to 3.0 x 10(52) erg, while the outer jet may have a Lorentz factor of Gamma(j) similar to 2.5 and a kinetic energy of E-k,E-iso similar to 3.0 x 10(53) erg.

Modelling the ‘outliers’ track of the radio–X-ray correlation in X-ray binaries based on a disc–corona model

ABSTRACT The universal radio–X-ray correlation (F R ∝ F bX , b ∼ 0.5−0.7) has been found for a sampleof black-hole X-ray binaries (BHBs) in their low/hard states, which can roughly be explainedby the coupled model of jet and radiatively inefficient advec tion dominated accretion flow.However, more and more ‘outliers’ were found in last few years, which evidently deviatefrom the universal radio–X-ray correlation and usually show a much steeper correlation withan index of ∼ 1.4. Based on simple physical assumptions, the radiatively effi cient accretionflows are speculated to exist in these ‘outliers’. In this wor k, we test this issue by modellingthe ‘outliers’ track based on the radiatively efficient disc -corona model and the hybrid jetmodel. We find that our model predicts a steeper radio–X-ray c orrelation with slopes &1.2for the typical viscosity parameter of α ∼ 0.05− 0.2. In particular, the slope is ∼ 1.4for thecase of α ∼ 0.1, which is consistent with the observational results of H1743−322 very well.Our results suggest that the ‘outliers’ track may be regulated by the disc-corona model.Key words: accretion, accretion discs — black hole physics — magnetic fi elds — X-rays:binaries

CORRELATION BETWEEN 3:2 QPO PAIRS AND JETS IN BLACK HOLE X-RAY BINARIES

We argue, following our earlier works (the CEBZMC model), that the phenomenon of twin-peak high-frequency quasi-periodic oscillations (QPOs) observed in black hole X-ray binaries is caused by magnetic coupling (MC) between the accretion disk and the black hole (BH). Due to MC, two bright spots occur at separate radial locations rin and rout at the disk surface, energized by a kind of Blandford-Znajek mechanism (BZ). We assume, following the Kluzniak-Abramowicz QPO resonance model, that the Keplerian frequencies at these two locations are in the 3?:?2 ratio. With this assumption, we estimate the BH spins in several sources, including GRO J1655-40, GRS 1915+105, XTE J1550-564, H1743-322, and Sgr A*. We give an interpretation of the jet line in the hardness-intensity plane, discussing the parameter space consisting of the BH spin and the power-law index for the variation of the large-scale magnetic field in the disk. Furthermore, we propose a new scenario for the spectral state transitions in BH X-ray binaries based on fluctuations in the densities of the accreting plasma from a companion star.

Effects of Magnetic Fields on Neutrino-dominated Accretion Model for Gamma-ray Bursts

Many models of gamma-ray bursts suggest a common central engine: a black hole of several solar masses accreting matter from a disk at an accretion rate from 0.01 to 10 M⊙ s−1, the inner region of the disk is cooled by neutrino emission and large amounts of its binding energy are liberated, which could trigger the fireball. We improve the neutrino-dominated accreting flows by including the effects of magnetic fields. We find that more than half of the liberated energy can be extracted directly by the large-scale magnetic fields in the disk, and it turns out that the temperature of the disk is a bit lower than the neutrino-dominated accreting flows without magnetic field. Therefore, the outflows are magnetically-dominated rather than neutrino dominated. In our model, the neutrino mechanism can fuel some GRBs (not the brightest ones), but cannot fuel X-ray flares. The magnetic processes (both BZ and electromagnetic luminosity from a disk) are viable mechanisms for most of GRBs and their following X-ray flares.

A resonance model with magnetic connection for 3:2 HFQPO pairs in black hole binaries

We apply epicyclic resonances to the magnetic connection (MC) of a black hole (BH) with a relativistic accretion disc, interpreting the high frequ ency quasi-periodic oscillations (HFQPOs) with 3:2 pairs observed in three BH X-ray binaries. It turns out that the 3:2 HFQPO pairs are associated with the steep power-law states, and the severe damping can be overcome by transferring energy and angular momentum from a spinning BH to the inner disc in the MC process.

A magnetic reconnection model for quasi-periodic oscillations in black hole systems

The quasi-periodic oscillations (QPOs) in black hole (BH) systems with different scales are interpreted based on the magnetic reconnection of large-scale magnetic fields generated by toroidal electric currents flowing in the inner region of the accretion disk, where the current density is assumed to be proportional to the mass density of the accreting plasma. The magnetic connection (MC) is taken into account in resolving dynamic equations describing the accretion disk, in which the MC between the inner and outer disk regions, between the plunging region and the disk, and between the BH horizon and the disk are involved. It turns out that a single QPO frequency associated with several BH systems with different scales can be fitted by invoking the magnetic reconnection due to the MC between the inner and outer regions of the disk, including the BH binaries XTE J1859+226, XTE J1650 i 500 and GRS 1915+105 and the massive BHs in NGC 5408 X-1 and RE J1034+396. In addition, the X-ray spectra corresponding to the QPOs for these sources are fitted based on the typical disk-corona model.

A model of low-frequency quasi-periodic oscillations in black hole X-ray binaries

A model of low-frequency quasi-periodic oscillations (LFQPOs) of black hole X-ray binaries (BHXBs) is proposed based on the perturbed magnetohydrodynamic equations of an accretion disk. It turns out that the LFQPO frequencies of some BHXBs can be fitted by the frequencies of the toroidal Alfven wave oscillation corresponding to the maximal radiation flux. In addition, the positive correlation of the LFQPO frequencies with the radiation flux from an accretion disk is well interpreted.

A model for 3:2 HFQPO pairs in black hole binaries based on cosmic battery

A model for 3:2 high-frequency quasi-periodic oscillations (HFQPOs) with 3:2 pairs observed in four black hole X-ray binaries (BHXBs) is proposed by invoking the epicyclic resonances with the magnetic connection (MC) between a spinning black hole (BH) with a relativistic accretion disc. It turns out that the MC can be worked out due to Poynting-Robertson cosmic battery (PRCB), and the 3:2 HFQPO pairs associated with the steep power-law states can be fitted in this model. Furthermore, the severe damping problem in the epicyclic resonance model can be overcome by transferring energy from the BH to the inner disc via the MC process for emitting X-rays with sufficient amplitude and coherence to produce the HFQPOs. In addition, we discuss the important role of the magnetic field in state transition of BHXBs.

A disk-corona model for the low/hard state of black hole X-ray binaries ∗

A disk-corona model for fitting the low/hard (LH) state of the associated steady jet in black hole X-ray binaries (BHXBs) is proposed based on the large-scale magnetic field configuration that arises from the coexistence of the Blandford-Znajek (BZ) and Blandford-Payne (BP) processes, where the magnetic field configuration for the BP process is determined by the requirement of energy conversion from Poynting energy flux into kinetic energy flux in the jet. It is found that corona current is crucial to guarantee the consistency of the jet launching from the accretion disk. The relative importance of the BZ and BP processes in powering jets from black hole accretion disks is discussed, and the LH state of several BHXBs is fitted based on our model. In addition, we suggest that magnetic field configuration can be regarded as the second parameter for governing the state transition of BHXBs.