检索结果-南通市图书馆

SKA-era localized fast radio bursts as a precise cosmological probe

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2023年第12期66卷 255-255页

作者： zi-gao dai Deep Space Exploration Laboratory Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China

Despite unclear physical origins,fast radio bursts(FRBs)with known redshifts measured from precisely localized host galaxies have been widely proposed as a cosmological probe(see ref.[1]for a recent review).This is realized by the Macquart relation[2],which makes a connection between the intergalactic medium(IGM)dispersion measure(DM)and redshift.

关键词： bursts galaxies galactic

Implication from GRB 221009A:Can TeV emission come from the GRB prompt phase?

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2023年第8期66卷 139-149页

作者： Kai Wang Zhi-Peng Ma Ruo-Yu Liu Yuan-Chuan Zou Zhuo Li zi-gao dai Department of Astronomy School of PhysicsHuazhong University of Science and TechnologyWuhan 430074China School of Astronomy and Space Science Nanjing UniversityNanjing 210023China Key Laboratoryof Modern Astronomy and Astrophysics Ministry of EducationNanjing UniversityNanjing 20023China Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy University of Science and Technology of ChinaHefei 230026China

Recently,the B.O.A.T.(“brightest of all time”)gamma-ray burst,dubbed GRB 221009A,was detected by various ***,the GRB presented very-high-energy(VHE,energy above 0.1 Te V)gamma-ray emission with energy extending above 10 Te V,as reported by the Large High Altitude Air Shower Observatory(LHAASO).We here demonstrate that the VHE and especially>10 Te V emission may originate from the internal hadronic dissipation of the GRB,without the need of invoking any exotic processes as suggested by some previous *** possible prompt origin of LHAASO photons may imply the first detection of the GRB prompt phase in the VHE *** also discuss the constraints on the properties of the GRB ejecta from multiwavelength and multi-messenger observations,which favors a magnetically dominated GRB *** suggested Poynting-flux-dominated GRB ejecta in this work supports the Blandford&Znajek(BZ)mechanism as the possible central engine model of GRB,as well as the possible strong magnetic dissipation and acceleration.

关键词： cosmological neutrinos neutrino astronomy high energy astrophysics gamma-ray bursts cosmic rays

GRB jet beaming angle statistics

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2010年第2期10卷 142-150页

作者： Yah gao zi-gao dai Department of Astronomy Nanjing University Nanjing 210093 China

Existing theory and models suggest that a Type I （merger） GRB should have a larger jet beaming angle than a Type II （collapsar） GRB, but so far no statistical evidence is available to support this suggestion. In this paper, we obtain a sample of 37 beaming angles and calculate the probability that this is true. A correction is also devised to account for the scarcity of Type I GRBs in our sample. The probability is calculated to be 83% without the correction and 71% with it.

关键词： gamma rays: bursts -- ISM: jets and outflows -- methods: statistical

Estimate of an environmental magnetic field of fast radio bursts

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2016年第3期16卷 11-16页

作者： Wei-Li Lin zi-gao dai School of Astronomy and Space Science Nanjing University Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education

Fast radio bursts （FRBs） are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown dis- tances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method. Starting withdispersion measures and rotation measures （RMs）, we try to obtain the parallel magnetic field component ^-B ││ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifls are now unavailable, we demonstrate the dependence of ^-B ││ on these two separate quantities. This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB.

关键词： radio continuum: general -- pulsars: general -- galaxies: magnetic fields -- Galaxy: structure

Multiband fitting to three long GRBs with Fermi/LAT data:structured ejecta sweeping up a density-jump medium

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2011年第9期11卷 1046-1066页

作者： Si-Yi Feng zi-gao dai Department of Astronomy Nanjing University Nanjing 210093 China Key Laboratory of Modern Astronomy and Astrophysics （Nanjing University） Ministry of Education Nanjing 210093 China

We present broadband （radio, optical, X-ray and GeV） fits to the afterglow light curves and spectra of three long-duration gamma-ray bursts （GRBs 080916C, 090902B, and 090926A） detected by the Gamma-Ray Burst Monitor and Large Area Telescope （LAT） instruments on the Fermi satellite. Using the observed broadband data, we study the origin of the high energy emission, and suggest that the early-time GeV emission and the late-time radio, optical, and X-ray afterglows can be under- stood as being due to synchrotron emission from an external forward shock caused by structured ejecta propagating in a wind bubble jumping to a homogeneous density medium. If the ceasing time for a majority of the energy injection is assumed to be close to the deceleration time of the forward shock, the structured ejecta with con- tinuous energy injection towards the forward shock can well explain the early rising feature of the GeV mission from these bursts, and the density-jump medium can ac- count for some particular plateaus or flares in the late afterglows. From our fits, we find that, on one hand, the external shock origin of the GeV photons will make the optical depth not have a significant contribution to the early LAT rising part, which will loosen the strong constraint of lower limits of the Lorentz factor. On the other hand, these Fermi-LAT events preferentially occur in a low-density circumburst environment, in which case the Klein-Nishina cutoff will significantly suppress the Self- Synchrotron Compton radiation. Such an environment might result from superbubbles or low-metallicity progenitor stars （which have a low mass-loss rate at late times of stellar evolution） of type Ib/c supernovae.

关键词： gamma-rays: bursts -- gamma-rays: theory

Constraining Dark Energy and Cosmological Transition Redshift with Type Ia Supernovae

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 561-571页

作者： Fa-Yin Wang zi-gao dai Department of Astronomy Nanjing University Nanjing 210093

The property of dark energy and the physical reason for the acceleration of the present universe are two of the most difficult problems in modern cosmology. The dark energy contributes about two-thirds of the critical density of the present universe from the observations of type-Ia supernovae （SNe Ia） and anisotropy of cosmic microwave background （CMB）. The SN Ia observations also suggest that the universe expanded from a deceleration to an acceleration phase at some redshift, implying the existence of a nearly uniform component of dark energy with negative pressure. We use the ＂Gold＂ sample containing 157 SNe Ia and two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore the properties of dark energy and the transition redshift. For a fiat universe with the cosmological constant, we measure ΩM=0.28-0.05^＋0.04 which is consistent with Riess et al. The transition redshift is zT=0.60-0.08^＋0.04. We also discuss several dark energy models that define w（z） of the parameterized equation of state of dark energy including one parameter and two parameters （w（z） being the ratio of the pressure to energy density）. Our calculations show that the accurately calculated transition redshift varies from zT =0.29-0.06^＋0.07 to zT =0.60-0.08^＋0.06 across these models. We also calculate the minimum redshift zc at which the current observations need the universe to accelerate.

关键词： cosmology observations -- distance scale -- supernovae general

Testing Lorentz violation using propagating UHECRs

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2009年第4期9卷 409-421页

作者： Cong-Xin Qiu zi-gao dai Department of Astronomy Nanjing University Nanjing 210093 China

Lorentz invariant violation （LIV） test is important for studying modem physics. All the known astrophysical constraints either have a very small examinable parameter space or are only suitable for some special theoretical models. Here, we suggest that it is possible to directly detect the time-delay of ultra-high-energy cosmic-rays （UHECRs）. We discuss some difficulties in our method, including the intergalactic magnetic fields. It seems that none of them are crucial, hence this method could give a larger examinable parameter space and a stronger constraint on LIV.

关键词： cosmic rays-gamma rays bursts-ISM magnetic fields-relativity

Time delay and extended halo for constraints on the intergalactic magnetic field

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2015年第12期15卷 2173-2186页

作者： Yuan-Pei Yang zi-gao dai School of Astronomy and Space Science Nanjing University Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education

Primary gamma rays emitted from extragalactic very-high-energy （VHE） sources, such as blazars, will generate cascade radiation in intergalactic space with a scale of -- 100 Mpc, for z - 0.1 and Eγ -1 TeV. These cascades proceed through electron-positron pair production and inverse Compton （IC） scattering in the cosmic background radiation fields, mainly cosmic microwave background （CMB） radiation and extragalactic background light in the voids of the universe. The existence of an intergalactic magnetic field （IGMF） would deflect paths of electron-positron pairs that scatter CMB photons, causing some observable effects, such as time delay, an ex- tended halo, and a spectral change. Here we reanalyze the diffusion of an electron jet deflected by IGMF and propose a unified semi-analytical model. By using publicly available data from the Fermi/LAT detector and contemporaneous TeV observations, we find that the cascade photon flux is not significantly affected by the IGMF strength for non-variable blazars when the IGMF is weaker than ,-~ 10-16 G. This result is clearly different from previous works that analyzed the extended halo and time de- lay separately for non-variable blazars and flaring blazars. By applying our model to two extreme blazars （1ES 0229＋200 and 1ES 1218＋304）, we obtain the IGMF lower limit of order ≥10-13 --10-14 G in the non-variable case, which is a stronger constraint on the IGMF strength than previous works （≥10-16 ,-- 10-18 G）, and ≥10-18 -- 10-19 G in the case of flaring blazars. Furthermore, we study the light curves and extended halo of the cascade photons by considering the effects of the IGME

关键词： gamma rays: general -- galaxies: magnetic field -- galaxies: individual(1ES 0229+200 1ES 1218+304)

Tail Emission from a Ring-like Jet: Its Application to Shallow Decays of Early Afterglows and GRB 050709

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 551-554页

作者： Yuan-Chuan Zou zi-gao dai Department of Astronomy Nanjing University Nanjing 210093

Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the precessing magnetic axis. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with a temporal index of - 1/2 if the Lorentz factor of the ejecta is not very high, which is consistent with the shallow decay phase of some early X-ray afterglow detected by Swift. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation for the re-brightening and sharp decay of the X-ray afterglow＇of GRB 050709.

关键词： gamma rays bursts - X-rays general