Reexamination of inflation in noncommutative space-time after Planck results

An inflationary model in the framework of noncommutative space-time may generate a nontrivial running of the scalar spectral index, but usually induces a large tensor-to-scalar ratio simultaneously. With the latest observational data from the Planck mission, we reexamine the inflationary scenarios in a noncommutative space-time. We find that either the running of the spectral index is tiny compared with the recent observational result, or the tensor-to-scalar ratio is too large to allow a sufficient number of $e$-folds. As examples, we show that the chaotic and power-law inflation models with the noncommutative effects are not favored by the current Planck data.Comment: 8 pages, 4 figures; version published in Physical Review

Cosmology-Independent Distance Moduli of 42 Gamma-Ray Bursts between Redshift of 1.44 and 6.60

This report is an update and extension of our paper accepted for publication in ApJ (arXiv:0802.4262). Since objects at the same redshift should have the same luminosity distance and the distance moduli of type Ia supernovae (SNe Ia) obtained directly from observations are completely cosmology independent, we obtain the distance modulus of a gamma-ray burst (GRB) at a given redshift by interpolating or iterating from the Hubble diagram of SNe Ia. Then we calibrate five GRB relations without assuming a particular cosmological model, from different regression methods, and construct the GRB Hubble diagram to constrain cosmological parameters. Based upon these relations we list the cosmology-independent distance moduli of 42 GRBs between redshift of 1.44 and 6.60, with the 1-$\sigma$ uncertainties of 1-3%.Comment: 6 pages, 2 figures, 3 tables. To appear in the proceedings of "2008 Nanjing GRB conference", Nanjing, 23-27 June 200

Intranight optical variability of radio-quiet BL Lacertae objects

Aims: Intranight variation (or microvariation) is a common phenomenon of radio-loud BL Lac objects. However, it is not clear whether the recently found radio-quiet BL Lac objects have the same properties. The occurrence rate of intranight variation is helpful in distinguishing the mechanism of the continuum of radio-quiet BL Lac objects. Methods: We conducted a photometric monitoring of 8 radio-quiet BL Lac objects by the Xinglong 2.16m and Lijiang 2.4m telescopes. The differential light curves are calculated between each target and two comparison stars. To quantify the variation, the significance of variation is examined by a scaled $F$-test. Results: No significant variation is found in the 11 sessions of light curves of 8 radio-quiet BL Lac objects (one galactic source is excluded). The lack of microvariation in radio-quiet BL Lac objects is consistent with the detection rate of microvariation in normal radio-quiet AGNs, but much lower than for radio-loud AGNs. This result indicates that the continua of the radio-quiet BL Lac objects are not dominated by jets that will induce frequent microvariations.Comment: Accepted for publication in Astronomy and Astrophysics; 7 pages, 1 figure, 3 table

Functional studies of the ‘GAFTGA’ motif of Escherichia coli Phage Shock Protein F

In the archetypal bacterial transcription, the multi-subunit core RNA polymerase (RNAP) is specifically bound to the promoter through the sigma factor (σ), forming a closed complex where DNA remains double-stranded. The promoter DNA is initially spontaneously melted by the σ factor within the core enzyme and subsequently loaded into the active channel of the holoenzyme. However, a major alternative transcription paradigm that depends on the sigma factor σ54 also exists in bacteria and controls pathogenicity, biofilm formation, bioluminescence, nitrogen fixation and stress responses. σ54 forms inhibitory interactions with DNA in the closed complex, which can only be alleviated by ATP hydrolysis-driven remodelling catalysed by bacterial enhancer binding proteins (bEBPs). In this regard, σ54- dependent transcription can be viewed analogous to the eukaryotic RNA Pol II system. This study was initiated to advance the understanding of: (i) how the ATP hydrolysis energy is relayed from the ATPase catalytic site to the closed complex for remodelling, (ii) the hexameric interface organisation of bEBPs for ATP hydrolysis, and (iii) the role of core RNAP in σ54-dependent transcription. A newly devised cross-linking technique combined with the DNA footprinting methods provided new insights of the organisation of each transcription component. The data gathered from this study updated the current working model for ATPdependent transcription. In addition, the cross-linking method proved to be an excellent tool to study protein-protein and nucleo-protein interactions

Parameter constraints in a near-equipartition model with multi-frequency \emph{NuSTAR}, \emph{Swift} and \emph{Fermi-LAT} data from 3C 279

Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs of \emph{Swift} and \emph{NuSTAR} observations, are analyzed using a near-equipartition model. We apply a one-zone leptonic model with a three-parameter log-parabola electron energy distribution (EED) to fit the \emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and \emph{Fermi}-LAT $\gamma$-ray data. The Markov Chain Monte Carlo (MCMC) technique is used to search the high-dimensional parameter space and evaluate the uncertainties on model parameters. We show that the two spectra can be successfully fit in near-equipartition conditions, defined by the ratio of the energy density of relativistic electrons to magnetic field $\zeta_{\rm e}$ being close to unity. In both spectra, the observed X-rays are dominated by synchrotron-self Compton photons, and the observed $\gamma$ rays are dominated by Compton scattering of external infrared photons from a surrounding dusty torus. Model parameters are well constrained. From the low state to the high state, both the curvature of the log-parabola width parameter and the synchrotron peak frequency significantly increase. The derived magnetic fields in the two states are nearly identical ($\sim1$\ G), but the Doppler factor in the high state is larger than that in the low state ($\sim$28 versus $\sim$18). We derive that the gamma-ray emission site takes place outside the broad-line region, at $\gtrsim$ 0.1 pc from the black hole, but within the dusty torus. Implications for 3C 279 as a source of high-energy cosmic-rays are discussed.Comment: accepted by MNRA