期刊文献+
共找到104篇文章
< 1 2 6 >
每页显示 20 50 100
Effect of rock mechanical properties on electromagnetic radiation mechanism of rock fracturing 被引量:2
1
作者 Peng Lin Pengcheng Wei +2 位作者 Cheng Wang Shengzu Kang Xin Wang 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2021年第4期798-810,共13页
The influence of rock mechanical properties on the electromagnetic radiation(EMR)mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of r... The influence of rock mechanical properties on the electromagnetic radiation(EMR)mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of rock fracturing considering the fracture factor,elastic modulus,Poisson’s ratio,radiation distance and crack length is derived based on the Hertz oscillator array assumption.An experimental system,including an electromagnetic shielding module,an EMR signal induction and transmission module,a signal recording module and a loading module,is developed to understand the EMR characteristics of four different rocks.The validity of the EMR theoretical model is verified and the relationships between the rock cracking morphology and the EMR waveform,amplitude and frequency are revealed.It is found that rock mechanical properties have obvious influences on the EMR waveform,amplitude and frequency during rock fracturing.This study provides a better understanding on the EMR mechanism of rock fracturing and can help to improve the accuracy of rock disaster prediction based on EMR. 展开更多
关键词 Electromagnetic radiation(EMR)mechanism Rock mecahnical properties Rock fracturing Cracking morphology EMR waveform
下载PDF
Radiation Spectral Analysis of 3D Dust Molecular Clusters(PAHs)and Peptoids under Ionization and Electric Field in ISM
2
作者 Ruiqing Wu Chunhua Zhu +5 位作者 Guoliang Lü Xiaojiao Zhang Xizhen Lu Jinlong Yu Wujin Chen Mengqiu Long 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第1期70-77,共8页
Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of s... Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field.We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures.By the Vienna Ab-initio Simulation Package code,the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust.When the radius of spherical dust clusters is~[0.009-0.042]μm,the dust radiation spectrum agrees well with the Z=0.02 mMMP stellar spectra,and the PAHs radiation spectrum of NGC 4676 at wavelengths of(0-5]μm and(5-10]μm,respectively.In the ionized state,the N-PAH,C_(10)H_(9)N,2(C_(4)H_(4))^(1+),and peptoids 4(CHON),(C_(8)H_(10)N_(2)O_(5))^(1+)dust clusters at 3.3μm,while the 2(C_(22)H_(21)N_(3)O_(2))^(1+),4(CHON)dust clusters at 5.2μm have obvious peaks.There is a characteristic of part of PAHs and peptoids clusters radiation at the nearinfrared wavelength of 2μm.However,especially after applying an electric field to the dust,the emission spectrum of the dust increases significantly in the radiation wavelength range[3-10]μm.Consequently,the dust clusters of PAHs,PANHs,and peptoids of the radius size~[0.009-0.042]μm are likely to exist in the ISM. 展开更多
关键词 ISM:structure ISM:molecules radiation mechanisms:general (ISM:)dust EXTINCTION
下载PDF
Medical Radiation Exposure and Human Carcinogenesis-Genetic and Epigenetic Mechanisms 被引量:8
3
作者 Yildiz Dincer Zeynep Sezgin 《Biomedical and Environmental Sciences》 SCIE CAS CSCD 2014年第9期718-728,共11页
Ionizing radiation (IR) is a potential carcinogen. Evidence for the carcinogenic effect of IR radiation has been shown after long-term animal investigations and observations on survivors of the atom bombs in Hiroshi... Ionizing radiation (IR) is a potential carcinogen. Evidence for the carcinogenic effect of IR radiation has been shown after long-term animal investigations and observations on survivors of the atom bombs in Hiroshima and Nagasaki. However, IR has been widely used in a controlled manner in the medical imaging for diagnosis and monitoring of various diseases and also in cancer therapy. The collective radiation dose from medical imagings has increased six times in the last two decades, and grow continuously day to day. A large number of evidence has revealed the increased cancer risk in the people who had frequently exposed to x-rays, especially in childhood. It has also been shown that secondary malignancy may develop within the five years in cancer survivors who have received radiotherapv, because of IR-mediated damage to healthy cells. In this article, we review the current knowledge about the role of medical x-ray exposure in cancer development in humans, and recently recognized epigenetic mechanisms in IR-induced carcinogenesis. 展开更多
关键词 DNAmethylation Medical radiation Exposure and Human Carcinogenesis-Genetic and Epigenetic mechanisms
下载PDF
Differential Proteomics Reveals the Potential Injury Mechanism Induced by Heavy Ion Radiation in Mice Ovaries 被引量:1
4
作者 HE Yu Xuan ZHANG Hong +4 位作者 LI Hong Yan ZHANG Yong JIA Qi Peng LI Zong Shuai ZHAO Xing Xu 《Biomedical and Environmental Sciences》 SCIE CAS CSCD 2017年第4期301-307,共7页
In the present study, we used a proteomics approach based on a two-dimensional electrophoresis (2-DE) reference map to investigate protein expression in the ovarian tissues of pubertal Swiss-Webster mice subjected t... In the present study, we used a proteomics approach based on a two-dimensional electrophoresis (2-DE) reference map to investigate protein expression in the ovarian tissues of pubertal Swiss-Webster mice subjected to carbon ion radiation (CIR). Among the identified proteins, ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) is associated with the cell cycle[1] and that it influences proliferation in ovarian tissues. We analyzed the expression of UCH-L1 and the proliferation marker proliferation cell nuclear antigen (PCNA) following CIR using immunoblotting and immunofluorescence. The proteomics and biochemical results provide insight into the underlying mechanisms of CIR toxicity in ovarian tissues. 展开更多
关键词 Differential Proteomics Reveals the Potential Injury mechanism Induced by Heavy Ion radiation in Mice Ovaries Figure
下载PDF
Evolution of High-energy Electron Distribution in Pulsar Wind Nebulae
5
作者 Yi-Ming Liu Hou-Dun Zeng +2 位作者 Yu-Liang Xin Si-Ming Liu Yi Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第7期198-214,共17页
In this paper,we analyze the spectral energy distributions of 17 powerful(with a spin-down luminosity greater than10~(35)erg s~(-1))young(with an age less than 15,000 yr)pulsar wind nebulae(PWNe)using a simple timein-... In this paper,we analyze the spectral energy distributions of 17 powerful(with a spin-down luminosity greater than10~(35)erg s~(-1))young(with an age less than 15,000 yr)pulsar wind nebulae(PWNe)using a simple timein-dependent one-zone emission model.Our aim is to investigate correlations between model parameters and the ages of the corresponding PWNe,thereby revealing the evolution of high-energy electron distributions within PWNe.Our findings are as follows:(1)The electron distributions in PWNe can be characterized by a double power-law with a super-exponential cutoff.(2)As PWNe evolve,the high-energy end of the electron distribution spectrum becomes harder with the index decreasing from approximately 3.5 to 2.5,while the low-energy end spectrum index remains constant near 1.5.(3)There is no apparent correlation between the break energy or cutoff energy and the age of PWNe.(4)The average magnetic field within PWNe decreases with age,leading to a positive correlation between the energy loss timescale of electrons at the break energy or the high-energy cutoff and the age of the PWN.(5)The total electron energy within PWNe remains constant near 2×10~(48)erg,while the total magnetic energy decreases with age. 展开更多
关键词 radiation mechanisms non-thermal-ISM general-ISM supernova remnants-gamma-rays GENERAL
下载PDF
A Possible X-ray Quasi-periodic Oscillation in the Narrow-line Seyfert 1 Galaxy Mrk 142
6
作者 Xiao-Gu Zhong Jian-Cheng Wang +1 位作者 Yong-Yun Chen Xiao-Ling Yu 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第6期191-200,共10页
A possible quasi-periodic oscillation(QPO) at frequency 7.045 × 10^(-5) Hz is found in the narrow-line Seyfert 1galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11.We find that the QPO signal is s... A possible quasi-periodic oscillation(QPO) at frequency 7.045 × 10^(-5) Hz is found in the narrow-line Seyfert 1galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11.We find that the QPO signal is statistically significantly larger than the 5σ level and highly coherent with quality factor Q > 5 at the 0.3–10 keV band by using the method of the Lomb–Scargle Periodogram,the Weighted Wavelet Z-transform and the REDFIT.We analyze the data in 0.3–0.6 keV,0.6–1 keV,1–3 keV and 3–10 keV energy bands,and find obvious QPO signals at 0.3–0.6 keV and 1–3 keV bands.We then analyze the time-average spectra and time variability at the QPO frequency of 7.045 × 10^(-5) Hz,and use a model to fit them.We find that the QPO signal mainly comes from the X-ray hot corona. 展开更多
关键词 X-rays:galaxies galaxies:Seyfert ACCRETION accretion disks radiation mechanisms:general
下载PDF
Characteristics of Emission Non-nulling Pulsars Through Simulation
7
作者 Rai Yuen 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第4期91-102,共12页
We investigate the population and several properties of radio pulsars whose emission does not null(non-nulling)through simulation of a large pulsar sample.Emission from a pulsar is identified as non-nulling if(i)the e... We investigate the population and several properties of radio pulsars whose emission does not null(non-nulling)through simulation of a large pulsar sample.Emission from a pulsar is identified as non-nulling if(i)the emission does not cease across the whole pulse profile,and(ii)the emission is detectable.For(i),we adopt a model for switching in the plasma charge density,and emission persists if the charge density is non-zero.For(ii),we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight.We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 42°.5,and almost half the samples maintain a duty cycle between 0.05 and 0.2.Furthermore,the pulsar population is not fixed but dependent on the obliquity angle,with the population peaking at 20°.In addition,three evolutionary phases are identified in the pulsar population as the obliquity angle evolves,with the majority of samples having an obliquity angle between 20°and 65°.Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime. 展开更多
关键词 radiation mechanisms:non THERMAL stars:neutron (stars:)pulsars:general
下载PDF
Temporal and Spectral Characteristics of Persistent Emission and Special Bursts of Magnetar SGR J1935+2154 Based on Insight-HXMT
8
作者 Xue-Feng Lu Li-Ming Song +7 位作者 Ming-Yu Ge Shuang-Nan Zhang Jin-Lu Qu Ce Cai Cong-Zhan Liu Cheng-Kui Li Yu-Cong Fu Ying-Chen Xu 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第6期225-233,共9页
In October 2022,the magnetar SGR J1935+2154 entered the active outburst state.During the episode,the InsightHXMT satellite carried out a long observation that lasted for 20 days.More than 300 bursts were detected,and ... In October 2022,the magnetar SGR J1935+2154 entered the active outburst state.During the episode,the InsightHXMT satellite carried out a long observation that lasted for 20 days.More than 300 bursts were detected,and a certain amount of persistent radiation signals were also accumulated.This paper mainly introduces the results of persistent radiation profile folding and period search based on Insight-HXMT data.At the same time,the burst phase distribution characteristics,spectral lag results of burst,the spectral characteristics of zero-lag bursts and the time-resolved spectral evolution characteristics of high-flux bursts are reported.We found that there is no significant delay feature during different energy bands for the bursts of SGR J1935+2154.The observed zero-lag burst does not have a unique spectrum.The time-resolved spectrum of the individual burst has consistent spectral types and spectral parameters at different time periods of the burst.We also find that the burst number phase distribution and the burst photon phase distribution have the same tendency to concentrate in specific regions of the persistent emission profile. 展开更多
关键词 radiation mechanisms:general dense matter magnetic fields
下载PDF
Optical Transient Source AT2021lfa:A Possible“Dirty Fireball”
9
作者 Xue-Mei Ye Da-Ming Wei +1 位作者 Yi-Ming Zhu Zhi-Ping Jin 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第4期124-133,共10页
AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 UTC.Follow-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XR... AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 UTC.Follow-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XRT and VLA instruments.AT2021lfa is classified as an“orphan afterglow”candidate due to its rapid flux decline and its reddened color(g-r=0.17±0.14 mag).For an optical transient source without promp gamma-ray detection,one key point is to determine its burst time.Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3,at 22:09:50 UTC.Using afterglowpy,we model the multi-band afterglow of AT2021lfa and find that the standard model canno reproduce the late radio observations well.Considering that the microphysical parameters ε_(e),ε_(B)(the energy fraction given to electrons and magnetic field),andξN(the fraction of accelerated electrons)may vary with time we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ε_(e),ε^(B),and ξ_(N) and find in this case the multi-wavelength observations can be reproduced well.The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow,which yields a value of about 18 suggesting that AT2021lfa should be classified as a“dirty fireball.”From the upper limit for the prompt emission energy of AT2021lfa,we obtain that the radiation efficiency is less than 0.02%,which is much smaller than that of ordinary gamma-ray bursts(GRBs).It is also interesting that the fitted values of jet angle and viewing angle are very large,θ_(c)~0.66 rad,θ_(v)~0.53 rad,which may lead to the low Lorentz factor and radiation efficiency.When compared with GRB afterglow samples,it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples.Additionally,the luminosity of AT2021lfa falls within the range of observations for GRB samples;however,approximately 1 day after the burst,its luminosity exceeds that of the majority of GRB samples. 展开更多
关键词 gamma-rays:ISM methods:numerical radiation mechanisms:non-thermal
下载PDF
The Optical Variability Properties of TeV Blazars
10
作者 Zi-An Su Wen-Xin Yang +4 位作者 Xiang-Tao Zeng Le-Jian Ou Ze-Lin Li Jiang-He Yang Jun-Hui Fan 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第9期66-75,共10页
Variability is one of the typical observational properties of blazars and the spectral changes are usually associated with variability,although this kind of association is unclear yet.In this work,we used data from th... Variability is one of the typical observational properties of blazars and the spectral changes are usually associated with variability,although this kind of association is unclear yet.In this work,we used data from the Steward Observatory blazar monitoring program to investigate the optical variability properties including the short-term timescale,the brightness-dependent spectral property,the correlation between the the brightness variation and the polarization,and then estimate the Doppler factors based on the obtained short timescale to study the polarization property for a sample of 20 TeV blazars.Our analyses arrive at the following results:(1)The largest variation amplitude in R-band,ΔR_(M),covers a range from ΔR_(M)=0.29 mag(1ES 2344+514)to ΔR_(M)=4.66 mag(3C 279).(2)Intra-day variability was found from five sources with timescales from 0.14 day for S50716+714 to 0.98 day for PKS 2155-304.Sixteen sources show spectra that are bluer when they become brighter,suggesting a common bluer-when-brighter property.(3)The plot of the polarization versus estimated Doppler factor is consistent with the Doppler factor dependent formula of polarization.(4)The largest polarization is correlated with the largest optical variation,suggesting that the high polarization and high amplitude variation are both the indicator of beaming effect. 展开更多
关键词 galaxies:active galaxies:jets radiation mechanisms:non-thermal
下载PDF
On the Energy Budget of Starquake-induced Repeating Fast Radio Bursts
11
作者 Wei-Yang Wang Chen Zhang +7 位作者 Enping Zhou Xiaohui Liu Jiarui Niu Zixuan Zhou He Gao Jifeng Liu Renxin Xu Bing Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第10期180-188,共9页
With a growing sample of fast radio bursts(FRBs),we investigate the energy budget of different power sources within the framework of magnetar starquake triggering mechanism.During a starquake,the energy can be release... With a growing sample of fast radio bursts(FRBs),we investigate the energy budget of different power sources within the framework of magnetar starquake triggering mechanism.During a starquake,the energy can be released in any form through strain,magnetic,rotational,and gravitational energies.The strain energy can be converted from three other kinds of energy during starquakes.The following findings are revealed:(1)The crust can store free magnetic energy of~10^(46)erg by existing toroidal fields,sustaining 10^(6)bursts with frequent starquakes occurring due to crustal instability.(2)The strain energy develops as a rigid object spins down,which can be released during a global starquake accompanied by a glitch.However,it takes a long time to accumulate enough strain energy via spindown.(3)The rotational energy of a magnetar with P■0.1 s can match the energy and luminosity budget of FRBs.(4)The budget of the total gravitational energy is high,but the mechanism and efficiency of converting this energy to radiation deserve further exploration. 展开更多
关键词 stars:magnetars stars:neutron radiation mechanisms:non-thermal
下载PDF
Vibration and Acoustic Radiation from Orthogonally Stiffened Infinite Circular Cylindrical Shells in Water 被引量:5
12
作者 陈军明 黄玉盈 曾革委 《China Ocean Engineering》 SCIE EI 2002年第4期437-452,共16页
Based on the motion differential equations of vibration and acoustic coupling system for thin elastic shells with ribs, by means of the Fourier integral transformation and the Fourier inverse transformation, as well a... Based on the motion differential equations of vibration and acoustic coupling system for thin elastic shells with ribs, by means of the Fourier integral transformation and the Fourier inverse transformation, as well as the stationary phase method, an analytic solution, which has satisfying computational effectiveness and precision, is derived for the solution to the vibration and acoustic radiation from a submerged stiffened infinite circular cylinder with both ring and axial ribs. It is easy to analyze the effect of stiffening supports in the acoustic radiation field by use of the formulas obtained by the presented method and corresponding numerical computation. It is shown that the axial-stiffeners can improve the mechanical and acoustical characteristics. Moreover, the present method can be used to study the acoustic radiation mechanism of the type of structure. 展开更多
关键词 coupling system stiffened cylindrical shell vibration and acoustic radiation analytic solution acoustic radiation mechanism
下载PDF
Polarization in cyclotron radiation in strong magnetic fields 被引量:1
13
作者 Luidmila Semionova Denis Leahy Jorge Paez 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2010年第10期1023-1040,共18页
We revisit the problem of radiative transitions of electrons in the presence of a strong magnetic field. We derive fully relativistic cyclotron transition rates for an arbitrary magnetic field, for any orientation of ... We revisit the problem of radiative transitions of electrons in the presence of a strong magnetic field. We derive fully relativistic cyclotron transition rates for an arbitrary magnetic field, for any orientation of electron spin and for any polarization of the emitted radiation. Also, we obtain the transition rates for any value of the initial electron's parallel momentum. For very strong magnetic fields, transitions to the ground state predominate. Transition rates summed over the electron's spin orientation and for unpolarized radiation are also obtained, which confirm previous results by Latal. Transition widths are calculated for different electron spin orientations and different polarizations of radiation. We obtain general expressions for transition rates that reduce to the results for the non-relativistic case and for unpolarized radiation. Additionally we get, for the non-relativistic approximation, the transition rates for any polarization of radiation. As an application, the first five emission lines are evaluated and compared to the X-ray emitting neutron star V0332+53, which has multiple observable cyclotron lines, taking into account gravitational redshift. The most probable polarization is ε(2). 展开更多
关键词 STARS neutron -- radiation mechanisms non-thermal -- stars magneticfields -- polarization
下载PDF
VIBRATION AND ACOUSTIC RADIATION FROM SUBMERGED STIFFENED SPHERICAL SHELL WITH DECK-TYPE INTERNAL PLATE 被引量:1
14
作者 ChenJnnming HuangYuying 《Acta Mechanica Solida Sinica》 SCIE EI 2003年第3期210-219,共10页
Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface,in which Dirac-δ functions are employed to ... Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface,in which Dirac-δ functions are employed to introduce the moments and forces applied by the attachment on the surface of shell,by means of expanding field quantities as Legendre series,a semi-analytic solution is derived for the vibration and acoustic radiation from a submerged stiffened spherical shell with a deck-type internal plate,which has a satisfactory computational effectiveness and precision for an arbitrary frequency range.It is easy to analyze the effect of the internal plate on the acoustic radiation field by using the formulas obtained by the method proposed.It is concluded that the internal plate can significantly change the mechanical and acoustic characteristics of shell,and give the coupling system a very rich resonance frequency spectrum.Moreover,the method can be used to study the acoustic radiation mechanism in similar structures as the one studied here. 展开更多
关键词 spherical shell deck-type internal plate vibration and acoustic radiation semianalytic solution acoustic radiation mechanism
下载PDF
Vibration and Acoustic Radiation from Submerged Spherical Double-Shell 被引量:1
15
作者 陈军明 黄玉盈 陈应波 《海洋工程:英文版》 2003年第3期341-354,共14页
Based on the motion differential equations of vibration and acoustic coupling system for a thin elastic spherical double-shell with several elastic plates attached to the shells, in which Dirac-δ functions are employ... Based on the motion differential equations of vibration and acoustic coupling system for a thin elastic spherical double-shell with several elastic plates attached to the shells, in which Dirac-δ functions are employed to introduce the forces and moments applied by the attachments, and by means of expanding field quantities as the Legendre series, a semi-analytic solution is derived for the solution to the vibration and acoustic radiation from a submerged spherical double-shell. This solution has a satisfying computational effectiveness and precision for arbitrary frequency range excitation. It is concluded that the internal plates attached to shells can change significantly the mechanical and acoustical characteristics of shells, and make the coupling system have a very rich resonance frequency spectrum. Moreover, the present method can be used to study the acoustic radiation mechanism of the type of structure. 展开更多
关键词 spherical double-shell vibration and acoustic radiation semi-analytic solution acoustic radiation mechanism
下载PDF
The Synchrotron-self-Compton Radiation Accompanying Shallow Decaying X-Ray Afterglow:the Case of GRB 940217 被引量:1
16
作者 Da-Ming Wei Yi-Zhong Fan 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2007年第4期509-515,共7页
High energy emission (〉 tens MeV) of Gamma-Ray Bursts (GRBs) provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has... High energy emission (〉 tens MeV) of Gamma-Ray Bursts (GRBs) provides an important clue on the physical processes occurring in GRBs that may be correlated with the GRB early afterglow. A shallow decline phase has been well identified in about half of Swift Gamma-ray Burst x-ray afterglows. The widely considered interpretation inv.olves a significant energy injection and possibly time-evolving shock parameter(s). We calculate the synchrotron-self-Compton (SSC) radiation of such an external forward shock and show that it could explain the well-known long term high energy (i.e., tens MeV to GeV) afterglow of GRB 940217. We propose that cooperation of Swift and GLAST will help to reveal the nature of GRBs. 展开更多
关键词 gamma-rays: bursts - ISM: jets and outflows - radiation mechanisms: non-thermal
下载PDF
Fermi/LAT observations of lobe-dominant radio galaxy 3C 207 and possible radiation region of γ-rays
17
作者 Sheng-Chu Guo Hai-Ming Zhang +1 位作者 Jin Zhang En-Wei Liang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2018年第6期93-98,共6页
3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter wit... 3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data acquired during the past 9 years. Different from the radio and optical emission from the core, it is found that theγ-ray emission is steady without detection of flux variation at over a 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical and X-ray data of knot-A,the closest knot from the core at 1.4′′, and compile its spectral energy distribution(SED). Although the single-zone synchrotron+SSC+IC/CMB model that assumes knot-A is at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates from the equipartition condition by 3 orders of magnitude. Assuming that knot-A is moving relativistically, its SED from radio to γ-ray bands would be represented well with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition. These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with radio data. 展开更多
关键词 galaxies: active galaxies: jets radiation mechanisms: non-thermal galaxies: individual(3C 207)
下载PDF
Gamma-ray bursts with extended emission:classifications, energy correlations and radiation properties
18
作者 Xiao-Lu Zhang Chuan-Tao Zhang +4 位作者 Xu-Juan Li Fu-Fang Su Xiao-Fei Dong Heon-Young Chang Zhi-Bin Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2020年第12期287-298,共12页
Thanks to more and more gamma-ray bursts with measured redshift and extended emission detected by the recent space telescopes,it is urgent and possible to check whether those previous energy correlations still satisfy... Thanks to more and more gamma-ray bursts with measured redshift and extended emission detected by the recent space telescopes,it is urgent and possible to check whether those previous energy correlations still satisfy the particular sample involving only the bursts accompanied by tail radiations.Using 20 long and 22 short bursts with extended emission,we find that the popular γ-ray energy correlations of the intrinsic peak energy versus the isotropic energy(Amati relation) and the intrinsic peak energy versus the peak luminosity(Yonetoku relation) do exist in both short and long bursts.However,it is much better if these gamma-ray bursts with extended emissions are reclassified into two subgroups of E-Ⅰ and E-Ⅱ that make the above energy correlations more tight.As proposed by Zhang et al.,the energy correlations can be utilized to distinguish these kinds of gamma-ray bursts in the plane of bolometric fluence versus peak energy as well.Interestingly,the peculiar short GRB 170817 A belongs to the E-Ⅰ group in the fluence versus peak energy plane,but it is an outlier of both the Amati and Yonetoku relations even though the off-axis effect has been corrected.Furthermore,we compare the radiation features between the extended emissions and the prompt gamma-rays in order to search for their possible connections.Taking into account all these factors,we conclude that gamma-ray bursts with extended emission are still required to model with dichotomic groups,namely E-Ⅰ and E-Ⅱ classes,which hint that they might have different origins. 展开更多
关键词 gamma-ray burst:general method:statistics radiation mechanisms:non-thermal
下载PDF
New Features of the Pulsar B0950+08 Radiation at the Frequency of 111 MHz
19
作者 V.M.Malofeev I.F.Malov +1 位作者 O.I.Malov D.A.Teplykh 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2022年第3期88-99,共12页
Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019(450 days).A strong vari... Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019(450 days).A strong variability in emission of this pulsar has been detected with changes in signal to noise ratios hundreds of times.Part of the long-time flux density variability can be explained by refractive scintillations in the interstellar medium.The existence of radiation between the interpulse(IP)and main pulse(MP)was confirmed.It was more powerful than at high frequencies.We detected the unusual IP and precursor(Pr)radiation on 2017 August 1.On the basis of 65 strong IPs we found the correlations between energies of IP and Pr and between the phase of IP and the distance Pr–IP.It is shown that the observed peculiarities of this pulsar can be explained in the frame of the aligned rotator model.We estimated distances of radiation levels from the center of the neutron star.The calculated value of the initial period of 0.2 s means that not all pulsars are born with millisecond periods.The large age of the pulsar(6.8 million years)and the small angle between its magnetic moment and the rotation axis(less than 20°)confirm the suggestion related to pulsar evolution with respect to alignment. 展开更多
关键词 (stars:)pulsars:individual(PST B0950+08) radiation mechanisms:general (stars:)pulsars:general
下载PDF
Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma
20
作者 BinLuo Shuang-NanZhang 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2004年第3期275-278,共4页
In normal one-temperature plasma the motion of ions is usually neglected whencalculating the Bremsstrahlung radiation of the plasma. We calculate the Bremsstrahlung radiationof a two-temperature plasma by taking into ... In normal one-temperature plasma the motion of ions is usually neglected whencalculating the Bremsstrahlung radiation of the plasma. We calculate the Bremsstrahlung radiationof a two-temperature plasma by taking into account of the motion of ions. Our results show that thetotal radiation power is always lower if the motion of ions is considered. We also apply thetwo-temperature Bremsstrahlung radiation mechanism for an analytical Advection-Dominated AccretionFlow (ADAF) model; we find the two-temperature correction to the total Bremsstrahlung radiation forADAF is negligible. 展开更多
关键词 PLASMAS radiation mechanisms: thermal
下载PDF
上一页 1 2 6 下一页 到第
使用帮助 返回顶部