8 research outputs found
Quantum SI: The New System of Units
This article gives an overview of the new SI and a few details as to how its
setting up was achieved. Those interested in the story of how the kilogram was
fixed by tying it to the Planck constant can go straight to section five.
Otherwise, apart from the introduction given as section one which also presents
excerpts from the relevant official documents on key aspects of the new system,
section two gives a brief timeline of the history of the decimal metric system,
section three gives a few details of the procedural steps -- from the setting
up of a standard of measurement to its percolation to the public, taking the
time standard as an example and, section four attempts to give a flavour of the
actual process of the setting up of a standard.Comment: 16 pages, 5 figures, written for Resonance - Journal of Science
Education, published by the Indian Academy of Science
Discovery of a 0.02 Hz QPO feature in the Transient X-ray Pulsar KS 1947+300
We report the discovery of Quasi Periodic Oscillations (QPO) at 0.02 Hz in a
transient high mass X-ray binary pulsar KS 1947+300 using {\em RXTE}-PCA. The
QPOs were detected during May-June 2001, at the end of a long outburst. This is
the 9th transient accretion powered high magnetic field X-ray pulsar in which
QPOs have been detected and the QPO frequency of this source is lowest in this
class of sources. The unusual feature of this source is that though the
outburst lasted for more than 100 days, the QPOs were detected only during the
last few days of the outburst when the X-ray intensity had decayed to 1.6% of
the peak intensity. The rms value of the QPO is large, with a
slight positive correlation with energy. The detection of QPOs and strong
pulsations at a low luminosity level suggests that the magnetic field strength
of the neutron star is not as high as was predicted earlier on the basis of a
correlation between the spin-up torque and the X-ray luminosity.Comment: Accepted in MNRA
RXTE-PCA observations of 1A 1118--61: timing and spectral studies during an outburst
We report detailed timing and spectral analysis of RXTE-PCA data obtained
from observations during the outburst of a transient X-ray pulsar 1A 1118--61
in January 2009. The pulse profile showed significant evolution during the
outburst and also significant energy dependence - a double peaked profile upto
10 keV and a single peak at higher energy. We have also detected quasi-periodic
oscillations (QPO) at 0.07--0.09 Hz. The rms value of the QPO is 5.2% and it
shows a significant energy dependence with highest rms of 7% at 9 keV. The QPO
frequency changed from 0.09 Hz to 0.07 Hz within 10 days. The magnetic field
strength calculated using the QPO frequency and the X-ray luminosity is in
agreement with the magnetic field strength measured from the energy of the
cyclotron absorption feature detected in this source. The 3-30 keV energy
spectrum over the 2009 outburst of 1A 1118--61 can be well fitted with a
partial covering power-law model with a high energy cutoff and an iron
fluorescence line emission. The pulse phase resolved spectral analysis shows
that the partial covering and high energy cutoff model parameters have
significant changes with the pulse phase.Comment: Accepted for publication in MNRA
Square Kilometre Array—India Consortium: Education and Public Outreach
International audienceThis paper presents a report on the activities and the proposed action plan of the Education and Public Outreach Working Group (EPO WG) of Square Kilometre Array–India Consortium (SKAIC). Details of a set of flagship programs as well as supporting activities are presented, in consonance with the scale of India’s involvement in Square Kilometre Array Observatory (SKAO), as well as the educational and science literacy contexts in the country. Ongoing independent EPO activities by some of the member institutions are also included
UVIT view of NGC 5291: Ongoing star formation in tidal dwarf galaxies at 0.35 kpc resolution
International audienceNGC 5291, an early-type galaxy surrounded by a giant H I ring, is believed to be formed from collision with another galaxy. Several star forming complexes and tidal dwarf galaxies are distributed along the collisional ring which are sites of star formation in environments where extreme dynamical effects are involved. Dynamical effects can affect the star formation properties and the spatial distribution of star forming complexes along the tidal features. To study and quantify the star formation activity in the main body and in the ring structure of the NGC 5291 system, we use high spatial resolution FUV and NUV imaging observations from the Ultraviolet Imaging Telescope onboard AstroSat. A total of 57 star-forming knots are identified to be part of this interacting system out of which 12 are new detections (star forming complexes that lie inside the H I contour) compared to the previous measurements from lower resolution UV imaging. We estimate the attenuation in UV for each of the resolved star-forming knots using the UV spectral slope β, derived from the FUV - NUV colour. Using the extinction corrected UV fluxes, we derive the star formation rate of the resolved star forming complexes. The extinction corrected total star formation rate of this system is estimated as 1.75 ± 0.04 M⊙ yr-1. The comparison with dwarf galaxy populations (BCD, Sm and dIm galaxies) in the nearby Universe shows that many of the knots in the NGC 5291 system have SFR values comparable to the SFR of BCD galaxies