13 research outputs found
Fresnel zone plate telescopes for X-ray imaging II: numerical simulations with parallel and diverging beams
We present the results of simulations of shadows cast by a zone plate
telescope which may have one to four pairs of zone plates. From the shadows we
reconstruct the images under various circumstances. We discuss physical basis
of the resolution of the telescope and demonstrate this by our simulations. We
allow the source to be at a finite distance (diverging beam) as well as at an
infinite distance (parallel beam) and show that the resolution is worsened when
the source is nearby. By reconstructing the zone plates in a way that both the
zone plates subtend the same solid angles at the source, we obtain back high
resolution even for sources at a finite distance. We present simulated results
for the observation of the galactic center and show that the sources of varying
intensities may be reconstructed with accuracy. Results of these simulations
would be of immense use in interpreting the X-ray images from recently launched
CORONAS-PHOTON satellite.Comment: 17 pages, 36 figures, Published in Experimental Astronom
Fresnel zone plates for Achromatic Imaging Survey of X-ray sources
A telescope with Fresnel Zone Plates has been contemplated to be an excellent
imaging mask in X-rays and gamma-rays for quite some time. With a proper choice
of zone plate material, spacing and an appropriate readout system it is
possible to achieve any theoretical angular resolution. We provide the results
of numerical simulations of how a large number of X-ray sources could be imaged
at a high resolution. We believe that such an imager would be an excellent tool
for a future survey mission for X-ray and gamma-ray sources which we propose.Comment: 4 Pages, 5 Figures, Proceeding of the 2nd Kolkata Conference on
"Observational Evidence for the Black Holes in the Universe", Published in
AIP, 200
Daksha: On Alert for High Energy Transients
We present Daksha, a proposed high energy transients mission for the study of
electromagnetic counterparts of gravitational wave sources, and gamma ray
bursts. Daksha will comprise of two satellites in low earth equatorial orbits,
on opposite sides of earth. Each satellite will carry three types of detectors
to cover the entire sky in an energy range from 1 keV to >1 MeV. Any transients
detected on-board will be announced publicly within minutes of discovery. All
photon data will be downloaded in ground station passes to obtain source
positions, spectra, and light curves. In addition, Daksha will address a wide
range of science cases including monitoring X-ray pulsars, studies of
magnetars, solar flares, searches for fast radio burst counterparts, routine
monitoring of bright persistent high energy sources, terrestrial gamma-ray
flashes, and probing primordial black hole abundances through lensing. In this
paper, we discuss the technical capabilities of Daksha, while the detailed
science case is discussed in a separate paper.Comment: 9 pages, 3 figures, 1 table. Additional information about the mission
is available at https://www.dakshasat.in
Science with the Daksha High Energy Transients Mission
We present the science case for the proposed Daksha high energy transients
mission. Daksha will comprise of two satellites covering the entire sky from
1~keV to ~MeV. The primary objectives of the mission are to discover and
characterize electromagnetic counterparts to gravitational wave source; and to
study Gamma Ray Bursts (GRBs). Daksha is a versatile all-sky monitor that can
address a wide variety of science cases. With its broadband spectral response,
high sensitivity, and continuous all-sky coverage, it will discover fainter and
rarer sources than any other existing or proposed mission. Daksha can make key
strides in GRB research with polarization studies, prompt soft spectroscopy,
and fine time-resolved spectral studies. Daksha will provide continuous
monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy
counterparts to Fast Radio Bursts. Using Earth occultation to measure source
fluxes, the two satellites together will obtain daily flux measurements of
bright hard X-ray sources including active galactic nuclei, X-ray binaries, and
slow transients like Novae. Correlation studies between the two satellites can
be used to probe primordial black holes through lensing. Daksha will have a set
of detectors continuously pointing towards the Sun, providing excellent hard
X-ray monitoring data. Closer to home, the high sensitivity and time resolution
of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray
Flashes.Comment: 19 pages, 7 figures. Submitted to ApJ. More details about the mission
at https://www.dakshasat.in
The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI
International audienceThe Cadmium Zinc Telluride Imager (CZTI) on AstroSat is a hard X-ray coded-aperture mask instrument with a primary field-of-view of (FWHM). The instrument collimators become increasingly transparent at energies above 100 keV, making CZTI sensitive to radiation from the entire sky. While this has enabled CZTI to detect a large number of off-axis transient sources, calculating the source flux or spectrum requires knowledge of the direction and energy dependent attenuation of the radiation incident upon the detector. Here, we present a GEANT4-based mass model of CZTI and AstroSat that can be used to simulate the satellite response to the incident radiation, and to calculate an effective âresponse fileâ for converting the source counts into fluxes and spectra. We provide details of the geometry and interaction physics, and validate the model by comparing the simulations of imaging and flux studies with observations. Spectroscopic validation of the mass model is discussed in a companion paper, Chattopadhyay et al. (J. Astrophys. Astr., vol. 42 (2021) https://doi.org/10.1007/s12036-021-09718-2)