The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.Th...The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.展开更多
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 ...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.展开更多
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 （...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.展开更多
We report the observing results of a short time scale monitoring of the 22 GHz water maser emission in GGD25. A rapid water maser outburst with the time scales of 4 d has been detected, and the variations are accompan...We report the observing results of a short time scale monitoring of the 22 GHz water maser emission in GGD25. A rapid water maser outburst with the time scales of 4 d has been detected, and the variations are accompanied by some changes in the line width. The time variations were probably caused by a collision pump which led to changes in the pump input.展开更多
The excitation of H2O masers usually needs very high density gas,hence it can serve as a marker of dense gas in HⅡ region. We selected a sample of H2O maser sources from Plume et al. （four with, and four without det...The excitation of H2O masers usually needs very high density gas,hence it can serve as a marker of dense gas in HⅡ region. We selected a sample of H2O maser sources from Plume et al. （four with, and four without detected CS（J = 7 - 6） emission）, and observed them in ^13CO（J=1-0） and C^18O （J=1-0）. C^18O （J=1-0） emission was detected only in three of the sources with detected CS（J=7-6） emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.展开更多
We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant an...We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds, we tentatively identify the clouds that are respectively interacting with the two SNRs.展开更多
We report on 43 GHz v=1, J=1-0 SiO maser proper motions in the circumstellar envelope of the M-type semi-regular variable star VX Sgr, observed by Very Long Baseline Array （VLBA） at 3 epochs during 1999 April-May. A...We report on 43 GHz v=1, J=1-0 SiO maser proper motions in the circumstellar envelope of the M-type semi-regular variable star VX Sgr, observed by Very Long Baseline Array （VLBA） at 3 epochs during 1999 April-May. Applying the statistical parallax analysis to these proper motions, we estimated a distance of VX Sgr of 1.57±0.27kpc, which is consistent with that based on the proper motions of H20 masers, or on the assumption that VX Sgr belongs to the Sgr OB1 association. At this distance, VX Sgr can be classified as a red supergiant. Comparing the statistical parallax method with those of model fitting and annual parallax, we think that the statistical parallax method may be a good way of estimating SiO maser distances at present.展开更多
We present a model which explains the observed multi-linear spatial structures with different velocity gradients of the 50-61A+ methanol line at 6.7 GHz. We consider this and other hypotheses and conclude that the met...We present a model which explains the observed multi-linear spatial structures with different velocity gradients of the 50-61A+ methanol line at 6.7 GHz. We consider this and other hypotheses and conclude that the methanol maser emission probably comes from some thin rings variously inclined to the line of sight.展开更多
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, ...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<SUP>?1</SUP>, and one from about 11 to 20 km s<SUP>?1</SUP>. 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.展开更多
With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are...With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are reported. 21 sources have been identified as molecular outflow candidates.展开更多
This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources ...This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.展开更多
We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new d...We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new detections. The detection rate of H2O masers in our sample is 9% which is very low. The detection rate of H2O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H2O masers increase as the sources evolve. The detection rate of H2O masers toward BGPS sources without HCO＋ emission is low. The BGPS sources associated with both H2O and CH3OH masers seem to be more compact than those only associated with H2O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H2O maser source G133.715＋01.217, also well known as W3 IRS 5 which has a flux density of 2.9 × 103 Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H2O masers and their angular distance from the true source location, we get the influence radius r = 1/0.8 1og（F0/3rms）. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection.展开更多
Synchro-curvature radiation describes the emission from a relativistic charged particle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation incl...Synchro-curvature radiation describes the emission from a relativistic charged particle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, including the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchrocurvature radiation including drift can generate maser even in vacuum. We discuss the possibilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars.展开更多
We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX...We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX data, and make a sta- tistical study. MSX sources associated with stellar 1612 MHz OH masers are located mainly above the blackbody line; this is caused by the dust absorption of stellar en- velopes, especially in the MSX_A band. The mid-IR sources associated with stellar OH masers are concentrated in a small region in an [A]-[D] vs.[A]-[E] diagram with a small fraction of contamination; this gives us a new criterion to search for new stellar OH masers and distinguish stellar masers from unknown types of OH masers. IR sources associated with 1612 MHz stellar OH masers show an expected result： the average flux of sources with F60 〉 F25 increases with increasing wavelength, while those with F60 〈 F25 vary little with wavelength, because the sources with F60 〈 F25 are much hotter than those with F60 〉 F25.展开更多
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 rota...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.展开更多
We present a statistical analysis of a sky survey of interstellar H<SUB>2</SUB>O and OH masers. These masers can be classified into three categories: isolated H<SUB>2</SUB>O masers, isolated OH...We present a statistical analysis of a sky survey of interstellar H<SUB>2</SUB>O and OH masers. These masers can be classified into three categories: isolated H<SUB>2</SUB>O masers, isolated OH masers, and simple OH/H<SUB>2</SUB>O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain ~ 10<SUP>5</SUP> yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.展开更多
We present results of 13CO（1-0）,C18O（1-0）,and HCO＋（1-0） map observations and N2H＋（1-0） single point observations directed towards a sample of nine low-luminosity 6.7-GHz masers.N2H ＋ line emission has been ...We present results of 13CO（1-0）,C18O（1-0）,and HCO＋（1-0） map observations and N2H＋（1-0） single point observations directed towards a sample of nine low-luminosity 6.7-GHz masers.N2H ＋ line emission has been detected from six out of nine sources,C18O line emission has been detected from eight out of nine sources,and HCO ＋ and 13CO emission has been detected in all sources.In particular,a ＂blue profile＂ of the HCO ＋ spectrum,a signature of inflow,is found towards one source.From integrated intensity emission maps,we identified 17 cores in the sample.Among them,nine cores are closely associated with low-luminosity methanol masers.For these cores,we derive the column densities,core sizes,masses and molecular abundances.Comparison of our results with similar molecular line surveys towards the southern sky methanol masers indicates that linewidths of our sample,including only the low-luminosity masers,are smaller than the sample that includes both lowand high-luminosity masers.For the maser associated cores,their gas masses have the same order of magnitude as their virial masses,indicating that these cores are gravitationally bound systems.In addition,we have found from our observations that the low-luminosity methanol masers tend to coexist with H2O masers and outflows rather than with OH masers.展开更多
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 sour...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.展开更多
1 Introduction Since the first OH maser source was detected in 1965, the astronomical masers have been used as powerful probes for the study of the early activities of stars and evolutions of stats. Among all the pres...1 Introduction Since the first OH maser source was detected in 1965, the astronomical masers have been used as powerful probes for the study of the early activities of stars and evolutions of stats. Among all the presently known maser sources, as it has a wide distribution and intense emission, and intimately associates with the early and late stages of stellar evolution, the OH maser has drawn a lot of attention and展开更多
It is recognized that the interstellar methanol-107GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pu...It is recognized that the interstellar methanol-107GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pumping mechanism - methanol masers without population inversion. It can explain the formation of 107GHz methanol masers, with the 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.展开更多
基金sponsored by the MOST (Grant No.2017YFA0402701)the NSFC (Grant Nos.11873019, 11673066 and 11503033)+4 种基金the CAS (Grant No.QYZDJ-SSW-SLH047)the Youth Innovation Promotion Association of CASsupported by the Key Laboratory for Radio Astronomy, CASthe Open Project Program of the Key Laboratory of FAST, NAOC, CASFunding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement
文摘The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in astrophysics.In this review we firstly summarize various methods with different tracers used to solve this puzzle.The astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky Way.Based upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented detail.Meanwhile, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km s-1.We found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.
基金the National Natural Science Foundation of China
文摘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.
基金Supported by the National Natural Science Foundation of China.
文摘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.
基金The observations weresupported by the United Open Radio Astronomy Laboratory of the Chinese Academy of Sciences.
文摘We report the observing results of a short time scale monitoring of the 22 GHz water maser emission in GGD25. A rapid water maser outburst with the time scales of 4 d has been detected, and the variations are accompanied by some changes in the line width. The time variations were probably caused by a collision pump which led to changes in the pump input.
基金Supported by the National Natural Science Foundation of China.
文摘The excitation of H2O masers usually needs very high density gas,hence it can serve as a marker of dense gas in HⅡ region. We selected a sample of H2O maser sources from Plume et al. （four with, and four without detected CS（J = 7 - 6） emission）, and observed them in ^13CO（J=1-0） and C^18O （J=1-0）. C^18O （J=1-0） emission was detected only in three of the sources with detected CS（J=7-6） emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.
基金Supported by the National Natural Science Foundation of China.
文摘We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds, we tentatively identify the clouds that are respectively interacting with the two SNRs.
基金the National Natural Science Foundation of China.
文摘We report on 43 GHz v=1, J=1-0 SiO maser proper motions in the circumstellar envelope of the M-type semi-regular variable star VX Sgr, observed by Very Long Baseline Array （VLBA） at 3 epochs during 1999 April-May. Applying the statistical parallax analysis to these proper motions, we estimated a distance of VX Sgr of 1.57±0.27kpc, which is consistent with that based on the proper motions of H20 masers, or on the assumption that VX Sgr belongs to the Sgr OB1 association. At this distance, VX Sgr can be classified as a red supergiant. Comparing the statistical parallax method with those of model fitting and annual parallax, we think that the statistical parallax method may be a good way of estimating SiO maser distances at present.
基金the National Natural Science Foundation of China,under Grant No 19973017.
文摘We present a model which explains the observed multi-linear spatial structures with different velocity gradients of the 50-61A+ methanol line at 6.7 GHz. We consider this and other hypotheses and conclude that the methanol maser emission probably comes from some thin rings variously inclined to the line of sight.
基金Supported by the National Natural Science Foundation of China.
文摘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<SUP>?1</SUP>, and one from about 11 to 20 km s<SUP>?1</SUP>. 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.
文摘With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are reported. 21 sources have been identified as molecular outflow candidates.
文摘This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.
基金funded by the National Natural Science Foundation of China under grant 11373062supported by the National Basic Research Program of China (973 program,2012CB821802)+1 种基金the National Natural Science Foundation of China under grant Nos.11433008,11303081 and 10873025the Program of the Light in China’s Western Region (LCRW) under grant Nos.RCPY201202 and XBBS-2014-24
文摘We performed an H20 maser survey towards 274 Bolocam Galactic Plane Survey （BGPS） sources with 85° 〈 1 〈 193° using the Nanshan 25 m radio telescope. We detected 25 H2O masers, and five of them are new detections. The detection rate of H2O masers in our sample is 9% which is very low. The detection rate of H2O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H2O masers increase as the sources evolve. The detection rate of H2O masers toward BGPS sources without HCO＋ emission is low. The BGPS sources associated with both H2O and CH3OH masers seem to be more compact than those only associated with H2O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H2O maser source G133.715＋01.217, also well known as W3 IRS 5 which has a flux density of 2.9 × 103 Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H2O masers and their angular distance from the true source location, we get the influence radius r = 1/0.8 1og（F0/3rms）. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection.
基金Supported by the National Natural Science Foundation of China.
文摘Synchro-curvature radiation describes the emission from a relativistic charged particle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, including the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchrocurvature radiation including drift can generate maser even in vacuum. We discuss the possibilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10778703 and10873025) the Program of the Light in China’s Western Region (LCWR) (Nos. RCPY200605 and RCPY200706)
文摘We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX data, and make a sta- tistical study. MSX sources associated with stellar 1612 MHz OH masers are located mainly above the blackbody line; this is caused by the dust absorption of stellar en- velopes, especially in the MSX_A band. The mid-IR sources associated with stellar OH masers are concentrated in a small region in an [A]-[D] vs.[A]-[E] diagram with a small fraction of contamination; this gives us a new criterion to search for new stellar OH masers and distinguish stellar masers from unknown types of OH masers. IR sources associated with 1612 MHz stellar OH masers show an expected result： the average flux of sources with F60 〉 F25 increases with increasing wavelength, while those with F60 〈 F25 vary little with wavelength, because the sources with F60 〈 F25 are much hotter than those with F60 〉 F25.
文摘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.
基金the National Natural Science Foundation of China.
文摘We present a statistical analysis of a sky survey of interstellar H<SUB>2</SUB>O and OH masers. These masers can be classified into three categories: isolated H<SUB>2</SUB>O masers, isolated OH masers, and simple OH/H<SUB>2</SUB>O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain ~ 10<SUP>5</SUP> yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.
基金supported by National Natural Science Foundation of China (Grant Nos.11073054,10733030,10703010 and 10621303)the National Basic Research Program of China (2007CB815403)supported in part by the Key Laboratory for Radio Astronomy,CAS
文摘We present results of 13CO（1-0）,C18O（1-0）,and HCO＋（1-0） map observations and N2H＋（1-0） single point observations directed towards a sample of nine low-luminosity 6.7-GHz masers.N2H ＋ line emission has been detected from six out of nine sources,C18O line emission has been detected from eight out of nine sources,and HCO ＋ and 13CO emission has been detected in all sources.In particular,a ＂blue profile＂ of the HCO ＋ spectrum,a signature of inflow,is found towards one source.From integrated intensity emission maps,we identified 17 cores in the sample.Among them,nine cores are closely associated with low-luminosity methanol masers.For these cores,we derive the column densities,core sizes,masses and molecular abundances.Comparison of our results with similar molecular line surveys towards the southern sky methanol masers indicates that linewidths of our sample,including only the low-luminosity masers,are smaller than the sample that includes both lowand high-luminosity masers.For the maser associated cores,their gas masses have the same order of magnitude as their virial masses,indicating that these cores are gravitationally bound systems.In addition,we have found from our observations that the low-luminosity methanol masers tend to coexist with H2O masers and outflows rather than with OH masers.
基金supported by the National Natural Science Foundation of China (Grant No. 10633010)the Guangdong provincial Natural Science Foundation (8451009101001047)
文摘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.
基金Project supported by the Radio Astronomy Combining Laboratory, Academia Sinica
文摘1 Introduction Since the first OH maser source was detected in 1965, the astronomical masers have been used as powerful probes for the study of the early activities of stars and evolutions of stats. Among all the presently known maser sources, as it has a wide distribution and intense emission, and intimately associates with the early and late stages of stellar evolution, the OH maser has drawn a lot of attention and
基金NationalNatural Science Foundation of China (Nos. l9873003 and 20073005).
文摘It is recognized that the interstellar methanol-107GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pumping mechanism - methanol masers without population inversion. It can explain the formation of 107GHz methanol masers, with the 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.
