3,655 research outputs found
On the origin of the various types of radio emission in GRS 1915+105
We investigate the association between the radio ``plateau'' states and the
large superluminal flares in GRS 1915+105 and propose a qualitative scenario to
explain this association. We identify several candidate superluminal flare
events from available monitoring data on this source and analyze the
contemporaneous RXTE pointed observations. We detect a strong correlation
between the average X-ray flux during the ``plateau'' state and the total
energy emitted in radio during the subsequent radio flare. We find that the
sequence of events is similar for all large radio flares with a fast rise and
exponential decay morphology. Based on these results, we propose a qualitative
scenario in which the separating ejecta during the superluminal flares are
observed due to the interaction of the matter blob ejected during the X-ray
soft dips, with the steady jet already established during the ``plateau''
state. This picture can explain all types of radio emission observed from this
source in terms of its X-ray emission characteristics.Comment: Corrected typo in the author names, contents unchanged, accepted in
Ap
Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06
In this paper we report on the Markarian 501 results obtained during our TeV
-ray observations from March 11 to May 12, 2005 and February 28 to May
7, 2006 for 112.5 hours with the TACTIC -ray telescope. During 2005
observations for 45.7 hours, the source was found to be in a low state and we
have placed an upper limit of 4.62 10 photons cm
s at 3 level on the integrated TeV -ray flux above 1 TeV
from the source direction. However, during the 2006 observations for 66.8h,
detailed data analysis revealed the presence of a TeV -ray signal from
the source with a statistical significance of 7.5 above
1 TeV. The time averaged differential energy spectrum of the
source in the energy range 1-11 TeV is found to match well with the power law
function of the form () with and .Comment: 16 pages and 8 Figures Accepted for publication in the Journal of
Physics
Reconstructing Single Field Inflationary Actions From CMBR Data
This paper describes a general program for deriving the action of single
field inflation models with nonstandard kinetic energy terms using CMBR power
spectrum data. This method assumes that an action depends on a set of
undetermined functions, each of which is a function of either the inflaton wave
function or its time derivative. The scalar, tensor and non-gaussianity of the
curvature perturbation spectrum are used to derive a set of reconstruction
equations whose solution set can specify up to three of the undetermined
functions. The method is then used to find the undetermined functions in
various types of actions assuming power law type scalar and tensor spectra. In
actions that contain only two unknown functions, the third reconstruction
equation implies a consistency relation between the non-gaussianty, sound speed
and slow roll parameters. In particular we focus on reconstructing a
generalized DBI action with an unknown potential and warp factor. We find that
for realistic scalar and tensor spectra, the reconstructed warp factor and
potential are very similar to the theoretically derived result. Furthermore,
physical consistency of the reconstructed warp factor and potential imposes
strict constraints on the scalar and tensor spectral indices.Comment: 33 pages, 3 figures: v3 - References adde
Instruments of RT-2 Experiment onboard CORONAS-PHOTON and their test and evaluation III: Coded Aperture Mask and Fresnel Zone Plates in RT-2/CZT Payload
Imaging in hard X-rays of any astrophysical source with high angular
resolution is a challenging job. Shadow-casting technique is one of the most
viable options for imaging in hard X-rays. We have used two different types of
shadow-casters, namely, Coded Aperture Mask (CAM) and Fresnel Zone Plate (FZP)
pair and two types of pixellated solid-state detectors, namely, CZT and CMOS in
RT-2/CZT payload, the hard X-ray imaging instrument onboard the CORONAS-PHOTON
satellite. In this paper, we present the results of simulations with different
combinations of coders (CAM & FZP) and detectors that are employed in the
RT-2/CZT payload. We discuss the possibility of detecting transient Solar
flares with good angular resolution for various combinations. Simulated results
are compared with laboratory experiments to verify the consistency of the
designed configuration.Comment: 27 pages, 16 figures, Accepted for publication in Experimental
Astronomy (in press
Generation of Bianchi type V cosmological models with varying -term
Bianchi type V perfect fluid cosmological models are investigated with
cosmological term varying with time. Using a generation technique
(Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are
solvable for any arbitrary cosmic scale function. Solutions for particular
forms of cosmic scale functions are also obtained. The cosmological constant is
found to be decreasing function of time, which is supported by results from
recent type Ia supernovae observations. Some physical aspects of the models are
also discussed.Comment: 16 pages, 3 figures, submitted to CJ
An “Axiom Cajanus SNP Array” based high density genetic map and QTL mapping for high-selfing flower and seed quality traits in pigeonpea
Background
Pigeonpea has considerable extent of insect-aided natural out-crossing that impedes genetic purity of seeds. Pre-anthesis cleistogamy in pigeonpea promotes self-pollination which helps in maintaining genetic purity. The cleistogamous flowers are linked with shriveled seeds, an undesirable trait from variety adoption point of view, and breeding using genomics tools can help in overcoming this constraint. Therefore, in order to identify genomic regions governing these target traits, one recombinant inbred line (RIL) population was developed using contrasting parents (ICPL 99010 and ICP 5529) for flower shape and shriveled seeds. The RILs were phenotyped for two years and genotyped using the Axiom Cajanus SNP Array.
Results
Out of the 56,512 unique sequence variations on the array, the mapping population showed 8634 single nucleotide polymorphism (SNPs) segregating across the genome. These data facilitated generation of a high density genetic map covering 6818 SNPs in 974 cM with an average inter-marker distance of 0.1 cM, which is the lowest amongst all pigeonpea genetic maps reported. Quantitative trait loci (QTL) analysis using this genetic map and phenotyping data identified 5 QTLs associated with cleistogamous flower, 3 QTLs for shriveled seed and 1 QTL for seed size. The phenotypic variance explained by these QTLs ranged from 9.1 to 50.6%. A consistent QTL “qCl3.2” was identified for cleistogamous flower on CcLG03 covering a span of 42 kb in the pigeonpea genome. Epistatic QTLs were also identified for cleistogamous flower and shriveled seed traits.
Conclusion
Identified QTLs and genomic interactions for cleistogamous flower, shriveled seed and seed size will help in incorporating the required floral architecture in pigeonpea varieties/lines. Besides, it will also be useful in understanding the molecular mechanisms, and map-based gene cloning for the target traits
Observations with the High Altitude GAmma-Ray (HAGAR) telescope array in the Indian Himalayas
The High Altitude GAmma-Ray (HAGAR) array is a wavefront sampling array of 7 telescopes, set-up at Hanle, at 4270 m amsl, in the Ladakh region of the Himalayas (Northern India). It constitutes the first phase of the HImalayan Gamma-Ray Observatory (HIGRO) project. HAGAR is the first array of atmospheric Cherenkov telescopes established at a so high altitude, and was designed to reach a relatively low threshold (currently around 200 GeV) with quite a low mirror area (31 m2). Regular source observations are running since September 2008. Estimation of the sensitivity of the experiment is undergoing using several hours of data from the direction of Crab nebula, the standard candle source of TeV gamma-ray astronomy, and from dark regions. Data were acquired using the On-source/Off-source tracking mode, and by comparing these sky regions the strength of the gamma-ray signal could be estimated. Gamma-ray events arrive close to telescope axis direction while the cosmic-ray background events arrive from the whole field of view. We discuss our analysis procedures for the estimate of arrival direction, estimate of gamma ray flux from Crab nebula, and the sensitivity of the HAGAR system, in this paper
Upper critical field, lower critical field and critical current density of FeTe0.60Se0.40 single crystal
The transport and magnetic studies are performed on high quality
FeTe0.60Se0.40 single crystals to determine the upper critical fields (Hc2),
lower critical field (Hc1) and the Critical current density (Jc). The value of
upper critical field Hc2 are very large, whereas the activation energy as
determined from the slope of the Arrhenius plots are was found to be lower than
that in the FeAs122 superconductor. The lower critical field was determined in
ab direction and c direction of the crystal, and was found to have a anisotropy
of 'gamma'{=(Hc1//c) / (Hc1//b)} ~ 4. The magnetic isotherms measured up to 12
Tesla shows the presence of fishtail behavior. The critical current densities
at 1.8K of the single crystal was found to almost same in both ab and c
direction as 1X105 Amp/cm2 in low field regime.Comment: 9 pages, 6 figure
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