The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation fields （abbreviated as npe^± gas） with or without external neutrino flux are investigated, and a general chemical potential equilibrium equation μn = μp ＋ Cμe is obtained to describe the steady equilibrium at high temperatures （T 〉 10^9 K）. An analytic fitting formula of coefficient C is presented for the sake of simplicity, when neutrinos and antineutrinos are transparent. It is a simple method to estimate the electron fraction for the steady equilibrium npe^± gas that adopts the corresponding equilibrium condition. As an example, we apply this method to the GRB accretion disk and confirm that the composition in the inner region is approximately in equilibrium when the accretion rate is low. For the case with external neutrino flux, we calculate the initial electron fraction of neutrino-driven wind from the proto-neutron star model M15-l1-r1. The results show that the improved equilibrium condition makes the electron fraction decrease significantly more than the case μn = μp ＋ μe when the time is less than 5s post bounce, which may be useful for r-process nucleosynthesis models.
Development of the Super High Angular Resolution Principle （SHARP） for coded-mask X-ray imaging is presented. We prove that SHARP can be considered as a generalized coded mask imaging method with a coding pattern comprised of diffraction-interference fringes in the mask pattern. The angular resolution of SHARP can be improved by detecting the fringes more precisely than the mask＇s element size, i.e. by using a detector with a pixel size smaller than the mask＇s element size. The proposed mission SHARP-X for solar X-ray observations is also briefly discussed.
GRB 090423 is the new high-z record holder of Gamma-ray bursts(GRBs) with z-8.2.We present a detailed analysis of both the spectral and temporal features of GRB 090423 observed with Swift/BAT and Fermi/GBM.We find that the T90 observed with BAT in the 15-150 keV band is 13.2 s,corresponding to-1.4 s at z=8.2.It once again gives rise to the issue of whether the progenitors of high-z GRBs are massive stars or mergers since the discovery of GRB 080913 at z=6.7.In comparison with the T90 distribution in the burst frame of the current redshift-known GRB sample,we find that it is marginally grouped into the long group(Type II GRBs).The spectrum observed with both BAT and GBM is well fitted by a power-law with exponential cutoff,which yields an Ep=(50.4±7.0) keV.The event satisfies the Amati-relation well for Type II GRBs within their 3σ uncertainty range.Our results indicate that this event would be produced by the death of a massive star.Based on the Amati-relation,we derive its distance modulus,which follows the Hubble diagram of the concordance cosmology model at a redshift of-8.2.
LIN Lin1,LIANG EnWei2 & ZHANG ShuangNan3 1 Department of Physics and Center for Astrophysics,Tsinghua University,Beijing 100084,China
We have analyzed International Gamma-Ray Astrophysics Laboratory(INTEGRAL) data corresponding to observations of the high mass X-ray binary(HMXB) V0332+53 during its huge outburst which occurred in 2004-2005,and found that there is a quasi periodic signal with ultra low frequency of roughly 4-5×10-5 Hz in the observation.This feature is revealed through a series of consistent analyses of imagings and fittings of the energy spectrum for each science window(SCW),and shows up in the corresponding light curves.The analysis of the power spectrum also provides a hint of a power peak located around 4×10-5 Hz,after subtracting off the linear trend of the light curve,and shows the consistency with the previous analyses.A similar feature shows up in our analysis of the light curve of Crab in hexagonal dithering mode.Therefore,an instrumental effect on the flux modulation might exist in the INTEGRAL data product of different levels:imaging,spectral fitting and light curve analysis,at least for the observational mode of hexagonal dithering.Such an effect is,to our knowledge,not yet available in the current literature.
CHEN YuPeng,ZHANG Shu,WANG JianMin,LI TiPei & QU JinLu Laboratory for Particle Astrophysics,Institute of High Energy Physics,Beijing 100049,China
We present the X-ray variability properties of the X-ray and TeV bright blazar Mrk 421 with a-60 ks long XMM-Newton observation performed on November 9-10,2005.The source experienced a pronounced flare,of which the inter-band time lags were determined with a very high confidence level.The soft(0.6-0.8 keV) X-ray variations lagged the hard(4-10 keV) ones by 1.09+0.11-0.12 ks,and the soft lag increases with increasing difference in the photon energy.The energy-dependent soft lags can be well fitted with the difference of the energy-dependent cooling timescales of the relativistic electron distribution responsible for the observed X-ray emission,which constrains the magnetic field strength and Doppler factor of the emitting region to be Bδ 1/3-1.78 Gauss.
ZHANG YouHong1,HOU ZhengTian2,SHAO Li3 & ZHANG Peng1 1 Department of Physics and Tsinghua Center for Astrophysics(THCA),Tsinghua University,Beijing 100084,China
For a sample of 33 narrow-line Seyfert 1 galaxies(NLS1s)(z<0.1) from the Sloan Digital Sky Survey,we investigate their morphologies.We find that 24 NLS1s show clear bar structure and 9 NLS1s show no bar structure.The bar frequency in this NLS1s sample is about 70%.We do not find any difference in the location of NLS1s with or without bars on the MBH-σ* diagram.
BIAN WeiHao & HUANG Li Department of Physics and Institute of Theoretical Physics,Nanjing Normal University,Nanjing 210097,China
A sample consisting of 211 narrow line Seyfert 1 galaxies (NLS1s) with high quality spectra from the Sloan Digital Sky Survey (SDSS) is selected to explore where broad line regions are in these objects. We find that the Hβ profile can be fitted well by three (narrow, intermediate and broad) Gaussian components, and the FWHM ratios of the broad to the intermediate components hold a constant of 3.0 roughly for the entire sample. If the broad components originate from the region scaled by the well-determined Hβ reverberation mapping relation, we find that the intermediate components originate from the inner edge of the torus, which is scaled by dust K-band reverberation. We find that the IC and the BC are strongly linked dynamically, but the relation of their covering factors is much more relaxed, implying that both regions are clumpy.
MAO WeiMing 1,2,3 , HU Chen 2 , WANG JianMin 2 , BIAN WeiHao 4 , ZHANG Shu 2 & ZHAO Gang 1 1 Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
The rms-flux relations for some observations of GRS 1915+105 are studied.The rms-flux relations of the light curves in only one state,state C or state A,can be described by the simple non-linear model provided Zhang;we thus interpret that such a linear relation reflects the relative importance of magnetic instability for X-ray emission in the corona of the system,compared to the thermal viscous instability for the X-ray emission in the accretion disk.The rms-flux relations for state B are very scattered,possibly because of the dominance of thermal viscous instability for the X-ray emission in the accretion disk.The complex rms-flux relations for the observations of transitions between two or three states are caused by the combination of the different rms-flux relations of these states.The underlying physical processes are the combination of magnetic topology in the corona and thermal viscous instability in the accretion disk.
HAN Dong1,ZHANG ShuangNan2 & SONG LiMing2 1 Department of Engineering Physics & Center for Astrophysics,Tsinghua University,Beijing 100084,China
For a sample of 411 type II QSOs with redshifts less then 0.3,we use the Balmer decrements to do the reddening correction of the [O III] luminosities and then derive the intrinsic [O III] luminosity function.We find that the host reddening correction of the [O III] 5007 luminosity for type II QSOs cannot be neglected.The median Balmer decrement of Hα/Hβ=4.0 corresponds to an extinction of 0.94 mag for the [O III] 5007 line,which is consistent with the result derived from the median Hβ/Hγ.Comparing the intrinsic luminosity function of type II QSOs with that of type I QSOs,we find that the upper limit of the type II QSO's fraction in the total QSOs is 80% for type II QSOs with z < 0.3 and 8.6≤log(L[O III]/L)≤9.4.
BIAN WeiHao & ZHANG ShiYan Department of Physics,Nanjing Normal University,Nanjing 210097,China
We re-examine the ten Reverberation Mapping(RM) sources with public data based on the two-component model of the Broad Line Region(BLR).In fitting their broad Hβ Mlines,six of them only need one Gaussian component,one of them has a double-peak profile,one has an irregular profile,and only two of them need two components,i.e.,a Very Broad Gaussian Component(VBGC) and an Inter-Mediate Gaussian Component(IMGC).The Gaussian components are assumed to come from two distinct regions in the two-component model;they are the Very Broad Line Region(VBLR) and the Inter-Mediate Line region(IMLR).The two sources with a two-component profile are Mrk 509 and NGC 4051.The time lags of the two components of both sources satisfy tIMLR/tVBLR=V 2VBLR/V 2IMLR,where tIMLR and tVBLR are the lags of the two components while VIMLR and VVBLR represent the mean gas velocities of the two regions,supporting the two-component model of the BLR of Active Galactic Nuclei(AGNs).The fact that most of these ten sources only have the VBGC confirms the assumption that RM mainly measures the radius of the VBLR;consequently,the radius obtained from the R-L relationship mainly represents the radius of VBLR.Moreover,NGC 4051,with a lag of about 5 days in the one component model,is an outlier on the R-L relationship as shown in Kaspi et al.(2005);however this problem disappears in our two-component model with lags of about 2 and 6 days for the VBGC and IMGC,respectively.
ZHU Ling1 & ZHANG ShuangNan2 1 Department of Physics and Tsinghua Center for Astrophysics,Tsinghua University,Beijing 100084,China
