121881392
Extended chiral Hartree-Fock model for nuclear matter
We study the properties of nuclear matter with extended chiral Hartree‐Fock model. The two‐particle‐two‐hole (2p‐2h) states are introduced in the nucleon ground wave function to take the tensor components of pion into account. We also consider the form factor effect of pion to regularize its high momentum behavior. We find that the pion contribution from 2p‐2h states plays a very important role in the saturation mechanism of nuclear matter. Furthermore, the saturation properties are also influenced by the cut‐off moment of form factor.
121460689
Relativistic Hartree-Fock model with bare nucleon-nucleon interaction for neutron-rich matter
Abstract We study neutron-rich matter in the relativistic Hartree–Fock model (RHF) with the bare nucleon–nucleon interaction. As an important ingredient, we take into account the short range correlation in terms of the unitary correlation operator method (UCOM). We calculate the equations of state (EOS) of neutron-rich matter with Bonn potential. Our results on neutron-rich matter compare very nicely with those in the Relativistic Brueckner–Hartree–Fock (RBHF) theory. On the other hand, when we apply the RHF model with the UCOM on symmetric nuclear matter, the EOS is largely different from the RBHF result particularly in the low density region. This is because the other important ingredient as the tensor interaction plays important role in symmetric nuclear matter. We also discuss the proton and neutron Dirac masses in neutron-rich matter and find that the proton Dirac mass is larger than the neutron mass in agreement with the RBHF theory using projection techniques.
15020605
The type Ia supernova 1997br in ESO 576-G40
The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35 ± 0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measuring the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epochs. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.
119402342
ROSAC: Studying the clustering properties of X-ray selected AGNs
We present the first ROSAC results of an AGN clustering analysis. This study comprises a sample of 200 AGNs, 75% of which being at low redshifts z<0.5, in the Ursa Major constellation. The spatial 2-point-correlation function (SCF) as well as the minimal spanning tree (MST) technique were applied. Some evidence for clustering is found in the SCF, although with low significance. Using the MST technique, we could find two AGN groups. This result is preliminary and the exact significance will be tested with careful simulations.
118614193
Reexamination of reaction rates for a key stellar reaction of $^{14}$O($\alpha$,p)$^{17}$F
The reaction rates of the key stellar reaction of O(α,p)F have been reexamined. The previous conclusion, the 6.15-MeV state (Jπ=1−) dominating this reaction rate, has been overthrown by a careful reanalysis of the previous experimental data [J. Gómez del Campo et al., Phys. Rev. Lett. 86, 43 (2001)]. According to the present R-matrix analysis, the previous 1− assignment for the 6.15MeV state is definitely wrong. Most probably, the 6.286-MeV state is the 1− state and the 6.15-MeV state is a 3− one, and hence the resonance at Ex=6.286 MeV (J π=1−) dominates the reaction rates in the temperature region of astrophysical interests. The newly calculated reaction rates for the O(α,p)F reaction are quite different from the previous ones, for instance, it’s only about 1/6 of the previous value around 0.4 GK, while it’s about 2.4 times larger than the previous value around 2 GK. The astrophysical implications have been discussed based on the present conclusions.
119772144
Microscopic study of the ground state properties of light nuclei
Ground state properties of light isotopes from helium to oxygen, such as binding energies, spin parities, rms radii, and halo phenomena are studied systematically by the Skyrme Hartree-Fock model with fit E{sub {sigma} } as the effective interaction. Since the particle number of the studied system is rather small, pairing interactions between identical nucleons are treated with the particle number conservation method. The results of the calculation show that most of the ground state properties can be well described. Some unsuccessful points of the calculation are pointed out. {copyright} {ital 1997} {ital The American Physical Society}
11077788
A GRB Follow-up System at the Xinglong Observatory and Detection of the High-Redshift GRB 060927 ⋆
A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN) alerts. Both telescopes slew relatively fast, being able to point to a new target field within ~1 min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006 the system responded to 15 GRBs and detected seven early afterglows. In 2007 six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z = 5.5) are shown, which started as early as 91 s after the GRB trigger. The afterglow was detected in the combined image of the first 19×20 s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON).