2141453
Probing the Cosmic Metallicity Evolution with Gamma-Ray Bursts
The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows to test the assumption that GRBs trace the star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not known yet. In this paper, I investigate the possibility for interpreting the observed discrepancy between the GRB rate history and the star formation rate history by the cosmic metallicity evolution, motivated by the observation that the cosmic metallicity evolves strongly with redshift and GRBs prefer to occur in low metallicity galaxies. Adopting a simple model for the relation between the GRB production and the cosmic metallicity history as proposed by Langer & Norman, and a star formation rate determined by Hopkins & Beacom from current observations, I show that the observed redshift distribution of the Swift GRBs can be reproduced with a fairly good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, the results suggest that GRBs trace both the star formation and the metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution with the study on the redshift distribution of GRBs.
11909154
The X‐ray transient 080109 in NGC 2770: an X‐ray flash associated with a normal core‐collapse supernova
Although it is generally thought that long-duration gamma-ray bursts (LGRBs) are associated with core-collapse supernovae (SNe), so far only four pairs of GRBs and SNe with firmly established connection have been found. All the four GRB-SNe belong to special class of Type Ic – called the broad-lined SNe indicative of a large explosion energy, suggesting that only a small fraction of SNe Ibc have GRBs associated with them. This scheme has been refreshed by the discovery of a bright X-ray transient in NGC 2770 on 2008 January 9, which was followed by a rather normal Type Ib SN 2008D. In this paper, I argue that the transient 080109 is an X-ray flash (XRF, the soft version of a GRB) because of the following evidence. (1) The transient cannot be interpreted as a SN shock breakout event. (2) The GRB X-ray flare interpretation is not supported by the high-energy observation. I then show that XRF 080109 satisfies the well-known relation between the isotropic-equivalent energy and the peak spectral energy for LGRBs, which highly strengthens the XRF interpretation. Finally, I point out that the peak spectral energy of XRF 080109 and the maximum bolometric luminosity of SN 2008D agree with the E γ, peak–LSN,max relationship of Li, strengthening the validity of the relationship. I speculate that events like XRF 080109 may occur at a rate comparable to SNe Ibc, and a soft X-ray telescope devoted to surveying for nearby X-ray flares will be very fruitful in discovering them.
118518653
Constraining fast radio burst progenitors with gravitational lensing
Fast Radio Bursts (FRBs) are new transient radio sources discovered recently. Because of the angular resolution restriction in radio surveys, no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs. In this paper we propose to use radio lensing survey to constrain FRB progenitors. We show that, different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies, since different type progenitors result in different redshift distributions of FRBs. For example, the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars, because double stars and single stars have different evolution timescales. With detailed calculations, we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models. We argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.
10326293
New light on time machines: Against the chronology protection conjecture.
I construct a spacetime with closed timelike curves and without closed causal geodesics. There is a noncompactly generated Cauchy horizon separating the region with closed timelike curves from that without closed causal curves. This spacetime might be stable against the vacuum fluctuation of matter fields. Whether such a spacetime is stable against the vacuum fluctuation of a gravitational field is an open question.
11692409
Electromagnetic energy for a charged Kerr black hole in a uniform magnetic field
With the Komar mass formula we calculate the electromagnetic energy for a charged Kerr black hole in a uniform magnetic field. We find that the total electromagnetic energy takes the minimum when the Kerr black hole possesses a nonzero net charge $Q=2\ensuremath{\xi}{B}_{0}{J}_{H}$ where ${B}_{0}$ is the strength of the magnetic field, ${J}_{H}$ is the angular momentum of the black hole, and $\ensuremath{\xi}$ is a dimensionless parameter determined by the spin of the black hole. However, the Wald state with ${Q=2B}_{0}{J}_{H}$ does not minimize the electromagnetic energy.
39373169
Can the universe create itself
The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a Big Bang explosion, the question of what happened before the Big Bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the Big Bang must have had a beginning also. Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question --- that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs giving no first-cause. This region of CTCs, may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models --- with CTCs --- are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. We show such a Universe can be classically stable and self-consistent if and only if the potentials are retarded, giving a natural explanation of the arrow of time. Some specific scenarios (out of many possible ones) for this type of model are described. For example: an inflationary universe gives rise to baby universes, one of which turns out to be itself. Interestingly, the laws of physics may allow the Universe to be its own mother.
118380628
Binary interactions on the calibrations of star formation rate
Using the Yunnan evolutionary population synthesis (EPS) models with and without binary interactions, we present the luminosity of H alpha recombination line (L-H alpha), the luminosity of [O II]lambda 3727 forbidden line doublet (L-[O II]), the ultraviolet (UV) fluxes at 1500 and 2800 angstrom (L-i,L-UV) and far-infrared flux (L-FIR) for burst, S0, Sa-Sd and Irr galaxies, and present the calibrations of star formation rate (SFR) in terms of these diagnostics. By comparison, we find that binary interactions lower the SFR versus L-H alpha and SFR versus L-[O II] conversion factors by similar to 0.2 dex. The main reason is that binary interactions raise the UV flux (shortwards of the Lyman limit) of the stellar population (SP) in the age range 6.7 < log t/yr < 8.4 and thus more ionizing photons are present in the nebula. Moreover, binary interactions do not significantly vary the calibrations of SFR in terms of L-i,L-UV. This is because binary interactions raise the flux at 1500 angstrom of the SP in the range 8.75 < log t/yr < 9.2 and the maximal difference is about 1 dex. In addition, binary interactions have little effect on the flux at 2800 angstrom. At last, the calibration of SFR from L-FIR is almost unaffected by binary interactions. This is caused by the fact that binary interactions almost do not affect the bolometric magnitudes of SPs. We also discuss the effects of initial mass function (IMF), gas-recycle assumption and EPS models [including GISSEL98 (Galaxy Isochrone Synthesis Spectral Evolution Library), BC03, STARBURST99, POPSTAR and PEGASE models] on these SFR calibrations. Comparing the results obtained by using the Salpeter (hereafter S55) IMF with those by using the Miller & Scalo (hereafterMS79) IMF, we find that the SFR versus L-H alpha and SFR versus L-[O II] conversion factors obtained by using the S55 IMF are greater by 0.4 and 0.2 dex than those by using the MS79 IMF for the Yunnan models with and without binary interactions, respectively. The SFR versus L-i,L-UV and SFR versus L-FIR conversion factors by using the S55 IMF are larger by an amount of 0.2 dex than the corresponding ones by using the MS79 IMF. The inclusion of gas-recycle assumption only lowers these SFR calibrations at faint SFR. Moreover, comparing the results when using different EPS models, we find that the differences in the SFR versus L-H alpha and SFR versus L-[O II] conversion factors reach similar to 0.7 and 0.9 dex, the difference in the SFR versus L-FIR conversion factor reaches 0.4 and 0.8 dex, and the differences in the SFR versus L-i,L-UV conversion factors reach 0.3 and 0.2 dex when using the S55 and non-S55 IMFs (including Chabrier, Kroupa-Aarseth-Hurley, Kroupa-Tout-Gilmore and Miller-Scalo IMFs, partly caused by the difference in the IMF), respectively. At last, we give the conversion coefficients between SFR and these diagnostics for all models.
100860790
A curve-based material recognition method in MeV dual-energy X-ray imaging system
High-energy dual-energy X-ray digital radiography imaging is mainly used in the material recognition of cargo inspection. We introduce the development history and principle of the technology and describe the data process flow of our system. The system corrects original data to get a dual-energy transparence image. Material categories of all points in the image are identified by the classification curve, which is related to the X-ray energy spectrum. For the calibration of classification curve, our strategy involves a basic curve calibration and a real-time correction devoted to enhancing the classification accuracy. Image segmentation and denoising methods are applied to smooth the image. The image contains more information after colorization. Some results show that our methods achieve the desired effect.
116828727
Effects of Binary interactions and metallicity on the calibrations of star formation rate
Using the Yunnan evolutionary population synthesis (EPS) models with and without binary interactions, we present the LHa, L[OII], Li,UV and LFIR for burst, E, S0, Sa-Sd and Irr galaxies at Z =0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02 and 0.03, present the conversion coefficients between star formation rate (SFR) and these diagnostics, and discuss the effects of binary interactions and metallicity on these SFR calibrations. 
The inclusion of binary interactions can lower the SFR versus LHa and SFR versus L[OII] conversion factors (CHa, C[OII]) by 0.1-0.2 dex, C1500 by 0.1 dex and C2800 by 0.2-0.1 dex, but raise CFIR by 0.05 dex. The differences in the CHa, C[OII] and C2800 caused by binary interactions are dependent of metallicity and those in the C1500 and CFIR are independent of metallicity. The higher is the metallicity, the larger are the differences in the CHa and C[OII], however, the smaller is the difference in the C2800 . 
The ratio of the difference in the conversion factor caused by metallicity to the [Fe/H] range, Delta_{case,Z}/Delta_{[Fe/H]}, reaches 0.2 for LHa and L[OII], 0.1 for Li,UV and 0.1-0.2 for LFIR. The dC_{case,Z}/d[Fe/H] is different within different [Fe/H] ranges and reaches the maximum value near the solar metallicity. At last, the Li,UV is not suitable to linear calibration of SFR at low metallicities. 
We also obtain the LHa, L[OII], Li,UV and LFIR for burst, E, S0, Sa-Sd and Irr galaxies by using the EPS models of BC03 (0.0001<Z<0.05), SB99 (0.0004<Z<0.05), PEGASE (0.0001<Z<0.1) and POPSTAR (0.0001<Z<0.05), present the conversion coefficients between SFR and these diagnostics, discuss the effects of the initial mass function and metallicity on these conversion coefficients, and compare the conclusions with those from our models.
125836359
Test of QCD using multijets in neutral current DIS at HERA
54192865
A Comprehensive Study of Gamma-Ray Burst Optical Emission. I. Flares and Early Shallow-decay Component
Well-sampled optical light curves of 146 gamma-ray bursts (GRBs) are compiled from the literature. By empirical fitting, we identify eight possible emission components and summarize the results in a 'synthetic' light curve. Both optical flare and early shallow-decay components are likely related to long-term central engine activities. We focus on their statistical properties in this paper. Twenty-four optical flares are obtained from 19 GRBs. The isotropic R-band energy is smaller than 1% of E{sub {gamma},iso}. The relation between the isotropic luminosities of the flares and gamma rays follows L{sup F}{sub R,iso}{proportional_to}L {sup 1.11{+-}0.27}{sub {gamma},iso}. Later flares tend to be wider and dimmer, i.e., w{sup F} {approx} t{sup F}{sub p}/2 and L{sup F}{sub R,iso}{proportional_to}[t{sup F}{sub p}/(1 + z)]{sup -1.15{+-}0.15}. The detection probability of the optical flares is much smaller than that of X-ray flares. An optical shallow-decay segment is observed in 39 GRBs. The relation between the break time and break luminosity is a power law, with an index of -0.78 {+-} 0.08, similar to that derived from X-ray flares. The X-ray and optical breaks are usually chromatic, but a tentative correlation is found. We suggest that similar to the prompt optical emission that tracks {gamma}-rays, the optical flares are alsomore » related to the erratic behavior of the central engine. The shallow-decay component is likely related to a long-lasting spinning-down central engine or piling up of flare materials onto the blast wave. Mixing of different emission components may be the reason for the diverse chromatic afterglow behaviors.« less