OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系

利用66个OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系,得到log L(OH)=1.71log L(IR)-17.67,即L(OH)α[L(IR)]1。71.这个结果介于Baan所得到的L(OH)α[L(IR)]2和Kandalian所得到的L(OH)α[L(IR)]1.38的结果之间.由于统计时所取的样本数最多,因此结果更能反映实际情况.进一步,可把这66个OH megamaser分为两类;第一类为L(OH)<102L(?)的小光度OH megamaser,小光度OH megamaser包含了14个OH megamaser;第二类为L(OH)≥102L的大光度OH megamaser,大光度OH megamaser包含了52个OHmegamaser.研究结果表明,小光度OH megamaser的光度和它们的宿主星系的红外光度之间相关关系为L(OH)α[L(IR)]1.43,与Kandalia所得到的结果相接近.大光度OH megamaser的光度和它们的宿主星系的红外光度之间的相关关系为L(OH)α[L(IR)]2,与Baan所得到的结果相一致.

Simplified nonlinear theory of the dielectric loaded rectangular Cerenkov maser

To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser, a simplified nonlinear theory is proposed, in which the variations of wave amplitude and wave phase are determined by two coupled first-order differential equations. Through combining with the relativistic equation of motion and adopting the forward wave assumption, the evolutions of the forward wave power, the power growth rate, the axial wave number, the accumulated phase offset, and the information of the particle movement can be obtained in a single-pass calculation. For an illustrative example, this method is used to study the influences of the beam current, the gap distance between the beam and the dielectric surface, and the momentum spread on the forward wave. The variations of the saturated power and the saturation length with the working frequency for the beams with different momentum spreads have also been studied. The result shows that the beam wave interaction is very sensitive to the electron beam state. To further verify this simplified theory, a comparison with the result produced from a rigorous method is also provided, we find that the evolution curves of the forward wave power predicted by the two methods exhibit excellent agreement. In practical applications, the developed theory can be used for the design and analysis of the rectangular Cerenkov maser.

Analysis of single frequency modulation for passive hydrogen maser

Based on the theory of the passive hydrogen maser, along with the technology of frequency modulation and modulation transfer spectroscopy, the theoretical expression of the single frequency modulation for the passive hydrogen maser and the function of the cavity and H line error signals separation are derived, which are basically coincident with the experiment. The absorption and dispersion spectrum curves with different resonance widths show that the cavity and hydrogen transition serve as discriminators, and the two error signals can be separated. Through the calculations of the two error signals in the passive hydrogen maser, it analyzes the traditional method of the two error signals separation, and then describes a new improved method for the passive hydrogen servo loops consisting in the use of a single modulation frequency and frequency discrimination. A null interaction of the two error signals for the new selection of the phase setting is deduced theoretically and validated by the simulation. The preliminary experimental result confirms the feasibility of this new approach, which can reduce the influence from the cavity frequency variety on the crystal oscillator and contribute significantly to the long term performance of the passive hydrogen maser.

Infrared Characteristics of Associated Sources of Water Masers

We present an analysis of the infrared properties of 1417 water masers collected from the literature published by December 2004. The associated infrared sources of the water masers were identified with IRAS and MSX （Midcourse Space Experiment） catalogues. There are 1252 water masers associated with IRAS sources within 11, which include 700 interstellar and 552 stellar sources. For 382 sources, the IRAS counterpart identification and the maser classification are new. We found the colors of the interstellar maser sources are much redder than those of the stellar ones at IRAS wavelength bands; 99% of the interstellar maser sources are above black body line, while 95% of the stellar masers are below. The distribution difference of the two kinds of masers shown in the color-color diagram is due to their different optical depths and temperature distributions of dust regions. There are 743 water masers with MSX counterparts, of which 552 are interstellar masers and 191 are stellar masers. MSX colors of the associated sources of water masers are here analyzed for the first time. The color differences among the MSX bands are small and the interstellar masers are redder than the stellar masers. There is a correlation between the intensity of the stellar water maser emission and that of the 12μm and 25μm emissions, while there is no correlation between the water maser emission and the 8μm emission. The infrared intensity increases with increasing wavelength for the interstellar masers, while it is the opposite for stellar masers. These results may provide clues for the pumping of water maser and for the properties of the two kinds of maser emission regions.

Transmission Probability of an Ultracold Three-Level Atom Through a Micromaser Cavity

The transmission probability of an ultracold cascade three-level atom through a micromaser cavity is calculated and analyzed. It is shown that the micromaser cavity can be used as a velocity selector for ultracold three-level atoms, and the velocity selectivity is better for three-level atoms than for two-level atoms.

Extragalactic H_2O Megamaser Sources:Central Black Holes,Nuclear X-ray and Maser Emissions

Extragalactic H2O megamasers are typically found within the innermost few parsecs of active galaxy nuclei （AGN） and the maser emission is considered to be excited most likely by the X-ray irradiation of the AGN. We investigate a comprehensive sample of extragalactic H2O masers in a sample of 38 maser host AGN to check potential correlations of the megamaser emission with parameters of the AGN, such as X-ray luminosity and black hole （BH） masses. We find a relation between the maser luminosities and BH masses LH2O∝MBH^3.6±0.4 which supports basically the theoretical prediction. The relation between the maser emission and X-ray emission is also confirmed.

Two-Photon Micromaser with Initial Atomic Coherence

We investigate the quantum dynamics of a two-photon micromaser pumped by atoms injected in the superposition state of the upper and intermediate levels. We simulate a master equation governing the system by the Monte Carlo wavefunction approach and analyse the steady-state behaviour as a function of the atomic transit time. The atomic coherence can effectively enhance the intensity and sub-Poissonian of the cavity field as compared with the atomic mixture. It is also discovered that the phase of the cavity field can be shifted by adjusting the detuning between the atom and field. This result shows that it is possible to manipulate the phase of the cavity field by detuning, due to atomic coherence.

The potential of FAST in detecting celestial hydroxyl masers and related science topics

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will make contributions to studies of Galactic and extragalactic masers. This telescope, with construction finished and now undergoing commissioning, has an innovative design that leads to the highest sensitivity of any single dish radio telescope in the world. FAST's potential for OH megamaser research is discussed, including the sky density of masers detectable in surveys. The scientific impact expected from FAST maser studies is also discussed.

Linear theory of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam

A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed.Based on this model,the hybrid-mode dispersion equation is derived with the Borgnis potential function by using the field-matching method.Its approximate solution is obtained under the assumption of a dilute electron beam.By using the Ansoft high frequency structural simulator（HFSS） code,the electromagnetic field distribution in the interaction structure is given.Through numerical calculations,the effects of beam thickness,beam and dielectric-layer gap distance,beam voltage,and current density on the resonant growth rate are analysed in detail.

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.

Technology and test results of space adaptability of passive hydrogen maser

Based on the operating principle and the electric property design of the passive hydrogen maser, the technology and test results of its space adaptability are carried out under the special launch conditions and space environment. The various perturbations affecting the output frequency of such a standard used for the navigation satellite system are specified, such as magnetic field change, vibration, thermal vacuum and radiation. Through the adaptability technology in the aspects above, the security and reliability of the space passive hydrogen maser sufficiently fulfill the requirements of space operation. At present, the space passive hydrogen maser is working normally on board, indicating that the space adaptability satisfies the design requirement.

A search for massive young stellar objects with 98 CH_3OH maser sources

Using the 13.7 m telescope of the Purple Mountain Observatory （PMO）, a survey of the 3 = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin. In the survey, except for 43 sources showing complex or multiple-peak profiles, almost all the ^13CO line profiles of the other 55 sources have large line widths of 4.5km s^-1 on average and are usually asymmetric. Fifty corresponding Infrared Astronomical Satellite （IRAS） sources of these 55 sources have Lbdl larger than 10^3 L⊙, which can be identified as possible high-mass young stellar sources. Statistics show that the ^13CO line widths correlate with the bolometric luminosity of the associated IRAS sources. Here, we also report the mapping results of two sources; IRAS 06117＋1350 and IRAS 07299-1651. Two cores were found in IRAS 06117＋1350 and one core was detected in IRAS 07299-1651. The northwest core in IRAS 06117＋1350 and the core in IRAS 07299-1651 can be identified as precursors of UC HII regions or high-mass protostellar objects （HMPOs）. The southeast core of IRAS 06117＋1350 has no infrared counterpart, seeming to be at a younger stage than the pre-UC HII phase.

Linear analysis of a three-dimensional rectangular Cerenkov maser with a sheet electron beam

A linear theory of a rectangular Cerenkov maser （RCM） with a sheet electron beam is developed by using the field- match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hybrid-mode dispersion equation and its analytical solution are derived for the RCM. Through numerical calculations, the effects of the beam-grating gap, beam thickness, current density, beam voltage and waveguide width on the linear growth rate axe analysed. Moreover, the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared. The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction, which is more rational for practical applications.

Research on frequency-temperature compensated sapphire-SrTiO_3 loaded cavity for hydrogen maser

To obtain frequency-temperature compensation in a sapphire loaded cavity for hydrogen maser, a dielectric named SrTiO3 is employed whose temperature coefficient of permittivity is opposite to that of sapphire. Based on theoretical analysis and computer simulation, a TE011 mode of a sapphire loaded cavity associated with two small rings of SrTiO3 with different thickness is solved, and the useful parameters that influence the temperature coefficient of cavity are calculated. Finally an experiment is brought forward and its results are very close to the computing results. When the thickness of SiTiO3 dielectric is 7 mm and the diameter is 17 mm in configuration b, the temperature coefficient of cavity is decreased from -58.8 kHz/K to -8.2 kHz/K and the quality factor is 40248.

The Single Particle Theory of Backward-Wave Amplifications Based on Electron Cyclotron Maser with a Rectilinear Beam

The theory of slow backward-wave amplifications is developed based on electron cyclotron maser （ECM） mechanism employing an initially rectilinear beam, A nonlinear evolution equation is derived to describe the electron energy. Numerical calculations show that the saturated interaction efficiency in this system may exceed 20~, and the saturated interaction length spans 3-6 centimeters. The distinctive interaction mechanism is promising for the design of compact backward microwave amplification devices, Numerical studies are also presented for the slow-wave ECM efficiency with inclusion of Gaussian beam electron velocity spread. It is shown that the velocity spread reduces the interaction e^ciency.

XMM-Newton observations of H_2O maser galaxy NGC 7479

The XMM-Newton observations of H2O megamaser galaxy NGC 7479 are presented. Its smoothed X-ray image clearly shows spiral morphology, which matches well with its optical asymmetric spiral structure. One prominent source can be found at the tip of its northern spiral arm, which is much brighter than its nuclear X-ray source （about a 50% higher count rate）. For the nuclear source （a circular region with a radius of 20 ″）, the spectra show soft excess below 2 keV and a strong iron Kα emission line. The best fitting model includes a partially absorbed model for the hard continuum and one thermal plasma model for the soft scatter component. Both the high column density （NH - 6.88 × 10^23 cm^-2） and strong fluorescent iron line （with an equivalent width of - 1.5 keV） support the existence of one heavily obscured AGN. For the bright prominent source, its radial profile is consistent with that of a single point-like source. Its spectra are extracted from the circular region around its peak, with a radius of 20″ and 6″ respectively and both spectra show models for the ultra-luminous X-ray source no significant difference. Four alternative （ULXs） can reproduce the spectra well： an absorbed power law, thermal bremsstrahlung, multicolor blackbody disk plus another blackbody or power law. Further observations （e.g., the tremendous improvement in the spatial resolution of the Chandra X-ray observations） and studies are desirable for probing the nature of this prominent source. In addition, we also estimate the mass of its central engine to be 1.18 × 10^7 M⊙ and maser disk parameters： the disk radius of -0.7 pc and the dimensionless accretion rate （L2-10kev/LEdd） of 1.2 × 10^-4.

Statistical Properties of 6.7 GHz Methanol Maser Sources

We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25-12] ≤ 1.30 and 1.30 ≤ [60-12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s?1, and one from about 11 to 20 km s?1. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.

CHARACTERISTICS OF CYCLOTRON AUTORESONANCE MASER WITH A LARGE-ORBIT ELECTRON RING IN A PARTIALLY DIELECTRIC-LOADED WAVEGUIDE

The cyclotron autoresonace masers with a large-orbit electron ring in a dielectric-loaded waveguide have been analyzed.The stability properties are investigated self-consistentlyon the basis of the linearized Vlasov-Maxwell equations.The numerical results show that thedielectric liner can greatly reduce the energy of the electron beam,and a novel effective radiationdevice with low electron beam energy in the millimeter and submillimeter wave region have beenproposed.

PLASMA-FILLED DIELECTRIC CHERENKOV MASER WITH A LONGITUDINAL MAGNETIC FIELD

The use of a background plasma in a dielectric Cherenkov maser can effectively increase the efficiency and the microwave output power of the device. Here, the effect of the longitudinal uniform magnetic field on the wave-beam interaction of the plasma-filled dielectric Cherenkov maser is examined by solving the beam-plasma, dielectric lined waveguide dispersion equation. And the effects of the longitudinal magnetic field, plasma density and dielectric parameters on the linear spatial growth rate and the energy ratio are presented.

First MERLIN Observations of Line Emission from the OH Megamaser toward IRAS 10173+0828

Many galaxies are thought to contain massive black holes, with masses in excess of ten million solar masses, at their centres and warped circumnuclear toruses. The best evidence comes from observing gas or masers rotating rapidly within a circumnuclear torus surrounding a central body. Here we report on the first MERLIN observations of line emission from the OH megamaser toward IRAS 10173+0828. The position of peak flux contours of the OH megamaser is consistent with that of the continuum in IRAS 10173+0828. This means that the OH megamaser is a diffuse unsaturated maser which could amplify the diffuse 18 cm continuum emission with an amplification factor of order unity.