J. H. You

Does the Iron Kα Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?

When thermal relativistic electrons with isotropic distribution of velocities move in a gas region or impinge upon the surface of a cloud that consists of a dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic emission lines, which is known as the Cerenkov line-like radiation. This newly recognized emission mechanism may find wide applications in high-energy astrophysics. In this paper we tentatively adopt this new line emission mechanism to discuss the origin of the iron Kα feature of active galactic nuclei (AGNs). The motivation of this research is to attempt a solution to a problem encountered by the disk fluorescence line model, i.e., the lack of temporal response of the observed iron Kα line flux to the changes of the X-ray continuum flux. If the Cerenkov line emission is indeed responsible significantly for the iron Kα feature, the conventional scenario around the central supermassive black holes of AGNs would need to be modified to accommodate more energetic, more violent, and much denser environments than previously thought.

Corrected formula system for Cerenkov linelike radiation in optical wave band

When thermal relativistic electrons with isotropic distribution of velocities move through a dense gas region or impinge on the surface of a cloud of dense gas, the Cerenkov effect will produce peculiar atomic or ionic emission lines, which we call the Cerenkov linelike radiation. Besides the iron K lines in active galactic nuclei (AGNs) and in the afterglow of gamma-ray bursts (GRBs), explored in our previous papers, contribution of the Cerenkov linelike radiation to other observed lines may also be significant. In order to extend the application of the new line emission mechanism to the optical region, in this paper we present a corrected formula system, suitable for describing the optical Cerenkov line radiation. We point out that the Cerenkov line mechanism is unable to produce the optical high-ionization lines, e.g., C IV , O III, and N V, because the plasma oscillation in the highly ionized plasma suppresses the Cerenkov radiation significantly. However, for the hydrogen lines and other low-ionization lines, e.g., Mg II and O I, produced in the low-ionized plasma, the Cerenkov line mechanism has to be taken into account.

Does the Prompt γ-Ray Emission of Gamma-Ray Bursts Arise from Resonant Inverse Compton Scattering?

We argue that the dominant radiation mechanism responsible for the early prompt γ-ray emission of gamma-ray bursts could be the resonant inverse Compton scattering of relativistic electrons in an intense magnetic field. By using this mechanism, some problems in the field of gamma-ray bursts could be clarified, e.g., the origin of the Amati relation, the formation of the observed broken power-law spectra, and the related deadline problem, among others. Our model also predicts that the emitted γ-rays could be highly polarized.

Significant Contribution of the Cerenkov Line-like Radiation to the Broad Emission Lines of Quasars

The Cerenkov line-like radiation in a dense gas (N H > 1013 cm–3) is potentially important in the exploration of the optical broad emission lines of quasars and Seyfert 1 galaxies. With this quasi-line emission mechanism, some long standing puzzles in the study of quasars could be resolved. In this paper, we calculate the power of the Cerenkov line-like radiation in dense gas and compare with the powers of other radiation mechanisms by a fast electron to confirm its importance. From the observed gamma-ray luminosity of 3Cxa0279, we show that the total number of fast electrons is sufficiently high to allow effective operation of the quasi-line emission. We present a model calculation for the luminosity of the Cerenkov Lyα line of 3Cxa0279, which is high enough to compare with observations. We therefore conclude that the broad line of quasars may be a blend of the Cerenkov emission line with the real line produced by the bound-bound transition. A new approach to the absorption of the Cerenkov line is presented with the method of escape probability, which markedly simplifies the computation in the optically thick case. The revised set of formulae for the Cerenkov line-like radiation is more convenient in applications.

The Cerenkov iron Kα line in Active Galactic Nuclei - calculation in the optically thin case

In this paper we continue the research on the Cerenkov origin of the iron Kα line in AGNs. We claim again that the newly recognized line emission mechanism, Cerenkov line-like radiation, could be significantly responsible for the observed iron K-lines of AGNs. We give a new model calculation of the luminosity of the iron Kα line in the optically thin condition, which is an important extension of our previous calculation in the optically thick case. The new calculation is also comparable to the typical observed luminosity of iron Kα line, thus confirming the effectiveness of the new mechanism. Besides, we analyze a possible negative influence of the hydrogen-dominated plasma upon the efficiency of Cerenkov line-like radiation in detail, which was ignored in our previous paper (You et al. 2003). We conclude that such a negative effect of the plasma oscillation is unimportant and can be neglected.

Does the prompt γ‐ray emission of GRB arise from RICS?

We argue that the dominant radiation mechanism responsible for the early prompt γ‐rayemission of gamma‐ray bursts could be the resonant inverse Compton scattering(RICS) of relativistic electrons in an intense magnetic field. By using this mechanism, some problems in the GRB study could be clarified, e.g., the origin of the Amati relation, the formation of the observed broken power law spectra, and the related “deadline problem,” the solution of the “compactness problem,” etc.. Our model also predicts that the emitted γ‐rayscould be highly polarized.

Thermal Iron K and Alpha: Line Emission from the X-Ray Binary GX 339-4

Abstract The accretion rate of the black hole candidate X-ray binary GX 339-4 in the ‘off’ state is low, and an advection dominated accretion flow (ADAF) is present. Hydrogen-like and helium-like iron Kα emission lines at 6.7 and 6.95 keV from hot plasma of ADAF can be produced by recombination-cascade processes with moderately high intensities, which are markedly distinguished from the fluorescent iron Kα line at ∼6.4 keV. We show that the observational features of GX 339-4 can be explained by the ADAF model, if the iron abundance is more than 10 times the solar value, though the reason for such a high abundance is still unclear. We suggest that the increase of the accretion rate makes GX 339-4 change from off, low, intermediate, to high and very high states, and the line center of iron Kα will therefore shift from ∼6.83 to ∼6.4 keV, i.e. to the fluorescent disc-line, since the disappearance of the ADAF due to its high accretion rate.

Soft X-ray and magnetic field of late-type stars

Abstract We used four coronal models to fit ROSAT data of a sample of late-type stars. The merits and demerits of each was discussed. We found a good correlation between the cornoal temperature so derived and the magnetic field strength. This indicates magnetic heating of the corona and provides a possible, indirect means of estimating the photospheric magnetic field.

Temperature evolution of the envelope of SN 1987A

Abstract We present a theoretical derivation of the H α line luminosity of the expanding envelope of SN 1987A from the theory of hydrogen recombination lines. A remarkable deviation of our calculated H α light curve from the observed light curve was found when a constant temperature was assumed. From the deviation we easily derive the temperature evolution. The temperature actually rises after day 500 and this may be explained as follows: as the shell expands, the electron and ion densities rapidly fall, greatly reducing the recombination cooling rate, while heating continues.

Effect of free electron scattering on the emission line profiles of SN 1987 A

Abstract Observations of SN 1987A showed many of its emission lines (especially those of heavy elements) to have the following features: asymmetric line profile, redshift and large FWHM. If these heavy element lines come from the vicinity of the core region and pass through the outer expanding hydrogen envelope, then these features can be satisfactorily explained by Thomson scattering of photons by free electrons in the envelope. An approximate method of calculating such line profiles is used in this paper. Our results show a good agreement with the observed profile of Ar II of SN 1987A. In the course of fitting the observed profile some physical parameters of the expanding shell are derived.