771 research outputs found
A broken "-intensity" relation caused by the evolving photosphere emission and the nature of the extraordinarily bright GRB~230307A
GRB~230307A is one of the brightest gamma-ray bursts detected so far. With
the excellent observation of GRB~230307A by Fermi-GBM, we can reveal the
details of the prompt emission evolution. As found in high-time-resolution
spectral analysis, the early low-energy spectral indices () of this
burst exceed the limit of synchrotron radiation (), and gradually
decreases with the energy flux (). A tight
correlation anyhow holds within the whole duration of the burst, where is the spectral peak energy. Such evolution pattern of and with intensity is called ``double tracking". For the relation,
we find a log Bayes factor 210 in favor of a smoothly broken power-law
function over a linear function in log-linear space. We call this particular
relation as broken ``-intensity", and interpret it as the
evolution of the ratio of thermal and non-thermal components, which is also the
evolution of the photosphere. We also show that GRB 230307A with a duration of
, if indeed at a redshift of , is likely a neutron star
merger event (i.e., it is intrinsically ``short"). Intriguingly, different from
GRB 060614 and GRB 211211A, this long event is not composed of a hard spike
followed by a soft tail, suggesting that the properties of the prompt emission
light curves are not a good tracer of the astrophysical origins of the bursts.
The other possibility of would point toward very peculiar nature of
both GRB 230307A and its late time thermal-like emission.Comment: 14 pages, 6 figures, 1 table. We have excluded the GBM instrument
pile-up time interval in the data analysis and also discussed the nature of
this even
The Tall Fescue Turf Grass Class I Chitinase Gene \u3cem\u3eFaChit1\u3c/em\u3e Is Activated by Fungal Elicitors, Dehydration, Ethylene, and Mechanical Wounding
The cDNA, genomic DNA, and promoter sequence of FaChit1, a class I chitinase gene from Festuca arundinacea, were isolated and characterized in the present work. The deduced amino acid sequence of FaChit1 contains the chitin binding, catalytic, and proline and glycine-rich domains characteristic for most class I chitinases, but no C-terminal extension region. FaChit1 is induced effectively by fungal elicitors, dehydration, and ethylene, but only slightly by mechanical wounding. To identify potential stress-related cis-acting elements, 5′ sequences 935, 651, and 233 bp upstream of the FaChit1 start codon were fused to the GUS reporter gene and analyzed in transgenic tobacco. The results indicated that the 935 bp fragment closely mirrored endogenous gene expression and that the 651 bp fragment was sufficient to direct reporter the gene expression in response to fungal elicitors, ethylene, dehydration, or mechanical wounding due to both known and presently uncharacterized cis-acting elements
Understanding the chemical evolution of blue Edge-on Low Surface Brightness Galaxies
We present a sample of 330 blue edge-on low surface brightness galaxies
(ELSBGs). To understand the chemical evolution of LSBGs, we derived the
gas-phase abundance and the [/Fe] ratio. Compared with star-forming
galaxies, ELSBGs show a flatter trend in the mass-metallicity ()
relation, suggesting that the oxygen abundance enhancement is inefficient. We
focus on 77 ELSBGs with HI data and found the closed-box model can not explain
their gas fraction and metallicity relation, implying that infall and/or
outflow is needed. We derived the [/Fe] ratio of normal ELSBG (
10M) and massive ELSBG ( 10M) using single
stellar population grids from MILES stellar library. The mean [/Fe]
ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We
discussed that the long time-scale of star-formation, and/or metal-rich gas
outflow event caused by SNe Ia winds are likely responsible for the
-enhancement of massive ELSBGs.Comment: 9 pages, 9 figures, Accepted for publication in Ap
- …