We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with ...the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below image ergs s super(-1), as probed by the most recent observational results. We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws, and IMFs. We identify models that produce XLFs consistent with the observations both in shape and absolute normalization, suggesting that a primordial galactic field LMXB population can make a significant contribution to the total population of an elliptical galaxy. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF, since the modeled populations are dominated by transient X-ray systems.
We present observations of XRF 050406, the first burst detected by Swift showing a flare in its X-ray light curve. During this flare, which peaks at $t_{\rm peak} \sim 210$ s after the BAT trigger, a ...flux variation of $\delta F / F \sim 6$ in a very short time $\delta t / t_{\rm peak} \ll 1$ was observed. Its measured fluence in the 0.2-10 keV band was ~$1.4 \times 10^{-8}$ erg cm-2, which corresponds to 1-15% of the prompt fluence. We present indications of spectral variations during the flare. We argue that the producing mechanism is late internal shocks, which implies that the central engine is still active at 210 s, though with a reduced power with respect to the prompt emission. The X-ray light curve flattens to a very shallow slope with decay index of ~0.5 after ~4400 s, which also supports continued central engine activity at late times. This burst is classified as an X-ray flash, with a relatively low fluence (~10-7 erg cm-2 in the 15-350 keV band, $E_{\rm iso} \sim 10^{51}$ erg), a soft spectrum (photon index 2.65), no significant flux above ~50 keV and a peak energy $E_{\rm p} < 15$ keV. XRF 050406 is one of the first examples of a well-studied X-ray light curve of an XRF. We show that the main afterglow characteristics are qualitatively similar to those of normal GRBs. In particular, X-ray flares superimposed on a power-law light curve have now been seen in both XRFs and GRBs. This indicates that a similar mechanism may be at work for both kinds of events.
Steviol glycosides (SVglys) are a group of diterpenoids mainly present in the leaves of stevia (Stevia rebaudiana Bertoni). An experiment was conducted to find the functional role of SVglys compounds ...in stevia affected by drought stress. In this study, a liquid blend of SVglys (200 ppm) was sprayed on stevia plants grown in well-watered (90% field capacity) and drought-stress conditions (45% field capacity) and then the morphological traits and metabolites were evaluated. It was observed that leaf losses caused by drought stress were stopped through external application of SVglys and consequently the harvest index of stevia was increased. Metabolite analysis of stevia leaves showed that the total SVglys content was significantly decreased due to drought stress, but was compensated by external application of SVglys. Among the SVglys, Rebaudioside A responded more to external SVglys. A slight promotion in total antioxidant activity of stevia leaves was observed when external SVglys was applied. The glucose availability in stevia leaves was increased by external application of SVglys but only in well-watered plants. According to our findings, it can be concluded that in stevia, SVglys may have a positive function in drought stress tolerance by exerting a protective role under such conditions.
Since its launch in late 2004, the Swift satellite triggered or observed an average of one gamma-ray burst (GRB) every 3 days, for a total of 771 GRBs by 2012 January. Here, we report the development ...of a pipeline that semi-automatic ally performs the data-reduction and data-analysis processes for the three instruments on board Swift (BAT, XRT, UVOT). The pipeline is written in Perl, and it uses only HEAsoft tools and can be used to perform the analysis of a majority of the point-like objects (e.g., GRBs, active galactic nuclei, pulsars) observed by Swift. We run the pipeline on the GRBs, and we present a database containing the screened data, the output products, and the results of our ongoing analysis. Furthermore, we created a catalog summarizing some GRB information, collected either by running the pipeline or from the literature. The Perl script, the database, and the catalog are available for downloading and querying at the HEASARC Web site.
We report on two new XMM–Newton observations of the anomalous X-ray pulsar (AXP) 4U 0142+614 performed in 2004 March and July, collecting the most accurate spectrum for this source. Furthermore, we ...analyse two short archival observations performed in 2002 February and 2003 January in order to study the long-term behaviour of this AXP. 4U 0142+614 appears to be relatively steady in flux between 2002 and 2004, and the phase-averaged spectrum does not show any significant variability between the four epochs. We derive the deepest upper limits to date on the presence of lines in 4U 0142+614 spectrum as a function of energy: equivalent width in the 1–3 keV energy range <4 and <8 eV for narrow and broad lines, respectively. A remarkable energy dependence in both the pulse profile and the pulsed fraction is detected, and consequently pulse–phase spectroscopy shows spectral variability as a function of phase. By making use of XMM–Newton and INTEGRAL data, we successfully model the 1–250 keV spectrum of 4U 0142+614 with three models, namely the canonical absorbed blackbody plus two power laws, a resonant cyclotron scattering model plus one power-law and two log-parabolic functions.
The pineal hormone melatonin plays an important role in the
neuroendocrine control of reproductive physiology, but its effects on
hypothalamic GnRH neurons are not yet known. We have found that GT1–7
...GnRH-secreting neurons express membrane-bound G protein-coupled
melatonin receptors, mt1 (Mel-1a) and MT2 (Mel-1b) as well as the
orphan nuclear receptors RORα and RZRβ. Melatonin (1
nm) significantly downregulates GnRH mRNA levels in a 24-h
cyclical manner, an effect that is specifically inhibited by the
melatonin receptor antagonist luzindole (10 μm).
Repression of GnRH gene expression by melatonin appears to occur at the
transcriptional level and can be mapped to the GnRH neuron-specific
enhancer located within the 5′ regulatory region of the GnRH gene.
Using transient transfection of GT1–7 cells, downregulation of GnRH
gene expression by melatonin was further localized to five specific
regions within the GnRH enhancer including −1827/−1819,−
1780/−1772, −1746/−1738, −1736/−1728, and −1697/−1689.
Interestingly, the region located at −1736/−1728 includes sequences
that correspond to two direct repeats of hexameric consensus binding
sites for members of the ROR/RZR orphan nuclear receptor family. To
begin to dissect the mechanisms involved in the 24-h cyclical
regulation of GnRH transcription, we have found that melatonin (10
nm) induces rapid internalization of membrane-bound mt1
receptors through a β-arrestin 1-mediated mechanism. These results
provide the first evidence that melatonin may mediate its
neuroendocrine control on reproductive physiology through direct
actions on the GnRH neurons of the hypothalamus, both at the level of
GnRH gene expression and through the regulation of G protein-coupled
melatonin receptors.
We present a systematic study of the steep decay emission from gamma-ray bursts (GRBs) observed by the Swift X-Ray Telescope (XRT). In contrast to the analysis described in recent literature, we ...produce composite Burst Alert Telescope (BAT) and XRT light curves by extrapolating the XRT data (2-10 keV) into the BAT energy range (15-25 keV) rather than extrapolating the BAT data into the XRT energy band (0.3-10 keV). Based on the fits to the composite light curves, we have confirmed the existence of an exponential decay component which smoothly connects the BAT prompt data to the XRT steep decay for several GRBs. We also find that the XRT steep decay for some of the bursts can be well fit by a combination of a power law with an exponential decay model. We discuss this exponential component within the framework of both the internal and the external shock model.
We present the properties of the discrete X-ray sources detected in our monitoring program of the globular cluster (GC) rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate ...pointings, resulting in a co-added exposure of 458 ks. From this deep observation, 236 sources have been detected within the region overlapped by all observations, 180 of which lie within the D 25 ellipse of the galaxy. These 236 sources range in L X from 3.5 X 1036 erg s-1 (with 3s upper limit <=1 X 1037 erg s-1) to ~2 X 1040 erg s-1, including the central nuclear source which has been classified as a LINER. From optical data, 39 X-ray sources have been determined to be coincident with a GC, these sources tend to have high X-ray luminosity, with 10 of these sources exhibiting L X > 1 X 1038 erg s-1. From X-ray source photometry, it has been determined that the majority of the 236 point sources that have well-constrained colors have values that are consistent with typical low-mass X-ray binary spectra, with 29 of these sources expected to be background objects from the log N-log S relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Three of these sources have been identified as transient candidates, with a further three possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy.
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