Search

Measuring the properties of the intergalactic medium (IGM) and sources during the Epoch of Reionization (EoR) is of immense importance. We explore the prospects of probing the IGM and sources through redshifted 21-cm observations of individual ionized bubbles surrounding known luminous sources during the EoR. Accordingly, we simulate HI 21-cm maps, foreground contaminants and system noise which are specific to the uGMRT and SKA1-Low observations. Following the subtraction of the foreground from the total visibility, we employ a visibility-based matched filter technique to optimally combine the desired HI 21-cm signal while minimizing the system noise. Our analysis suggests that these ionized bubbles can be detected with more than $5 \sigma$ significance using approximately $\sim 2000$ and $\sim 3000$ hours of observation time with the uGMRT at redshift $7.1$ and $8.3$ respectively. The SKA1-Low should be able to detect these with more than $8 \sigma$ significance using just $\sim 100$ hrs of observations. Further, we investigate the impact of the foreground subtraction on the detectability and find the signal-to-noise ratio decreases when smaller bandwidth is used. More importantly, we show that the matched filtering method can measure ionized bubble radius and constrain HI-neutral fraction reasonably well, helping deeper insights into source properties and the intergalactic medium., Comment: 26 pages, 14 figures, 1 table

It is believed that the first star-forming galaxies are the main drivers of cosmic reionization. It is usually assumed that there is a one-to-one relationship between the star formation rate (SFR) inside a galaxy and the host halo mass in semi-analytical/numerical modeling of large-scale reionization. However, more accurate simulations and observations suggest that the SFR and ionizing luminosity in galaxies may vary considerably even if the host halo mass is the same. This astrophysical scatter can introduce an additional non-Gaussianity in the HI 21-cm signal, which the power spectrum might not capture adequately. In this work, we have studied the impact of the scatter on the HI 21-cm bispectrum using semi-numerical simulations. Although the fractional change in the HI 21-cm bispectra due to the scatter is found to be more than a factor of $10$ at large scales ($k_1 \lesssim 1\, {\rm Mpc}^{-1}$) for $z=7.4$, it is found to be statistically insignificant. However, at small scales ($k_1\sim2.55$~Mpc$^{-1}$), we have found the impact due to the scatter to be high in magnitude ($|\langle \Delta B \rangle/B_{\text{no-scatter}}| \sim 1$) and statistically significant ($|\langle\Delta B\rangle/\sigma_{\Delta B}| \gtrsim 5$) at neutral fraction, $\overline{x}_{\rm HI}\sim 0.8$ for $z=7.4$. The impact due to scatter is found to be even more prominent ($|\langle \Delta B \rangle/B_{\text{no-scatter}}| \gtrsim 10$) at small scales for $z=10$ and $\overline{x}_{\rm HI}\sim 0.8$, but with reduced statistical significance ($|\langle\Delta B\rangle/\sigma_{\Delta B}| \sim 3$), compared to $z=7.4$ at the same neutral fraction. In the most optimistic scenario, SKA1-Low might be able to detect these signatures of astrophysical scatter, at $\sim 3\sigma$ and $\sim 5\sigma$ detection significance for $\overline{x}_{\rm HI} \sim$ 0.8 and 0.9 respectively, for the equilateral HI 21-cm bispectrum at $z=7.4$., Comment: 26 pages, 12 figures, comments are welcome, accepted in JCAP

In this review article, we briefly outline our current understanding of the physics associated with the HI 21-cm signal from cosmic dawn. We discuss different phases of cosmic dawn as the ambient gas and the background radiations evolve with the redshift. We address the consequences of several possible heating sources and radiation background on the global 21-cm signal. We further review our present perspective of other important aspects of the HI 21-cm signal such as the power spectrum and imaging. Finally, we highlight the future key measurements of the Square Kilometre Array and other ongoing/upcoming experiments that will enlighten our understanding of the early Universe., Comment: 22 pages, 9 figures, Accepted for publication in Journal of Astrophysics and Astronomy(JoAA)

The Epoch of Reionization (EoR) remains a poorly understood cosmic era for the most part. Yet, efforts are still going on to probe and understand this epoch. We present a review of the latest developments in the techniques (especially line-intensity mapping) to study the EoR and try to highlight the contribution of the Indian community in this field. Line-emissions like [H I]$_{\rm 21cm}$, Lyman-$\alpha$, [C II]$_{\text{158}\mu\text{m}}$ and their role as tracers in probing the EoR are discussed. While the [H I]$_{\rm 21cm}$ is an excellent probe of the early IGM, the others are mainly targeted to do an unresolved and large-scale survey of the reionizing sources. Techniques to model these signals include simulations and machine learning approaches, along with the challenge to tackle foregrounds or interlopers. We also discuss synergy opportunities among the various tracers that we mention. Synergy addresses different aspects of the problem, which otherwise is difficult or impossible to tackle. They include statistics like cross-power spectrum, cross-bispectrum, and other techniques such as follow-up studies. We present updates on the relevant experiments; these include the upper limits on the [H I]$_{\rm 21cm}$ power spectrum, along with some highlights on high-redshift galaxy surveys. Finally, we highlight what can be improved further within the community: applying machine learning and simulations based on hydrodynamic and radiative-transfer techniques. Next-generation experiments also need to be conceived to address issues currently beyond our reach., Comment: Review article, 24 pages, 6 figures, comments are welcome, accepted in Journal of Astrophysics and Astronomy

It is extremely important to understand the processes through which the thermal state of the inter-galactic medium (IGM) evolved in the early universe in order to study the evolution of HI 21-cm signal during cosmic dawn. Here, we consider the heating of the IGM due to cosmic ray protons generated by the supernovae from both early Pop III and Pop II stars. The low energy cosmic ray protons from Pop III supernovae can escape from minihalos and heat the IGM via collision and ionization of hydrogen. Furthermore, high energy protons generated in Pop II supernovae can escape the hosting halos and heat the IGM via magnetosonic Alfv\'en waves. We show that the heating due to these cosmic ray particles can significantly impact the IGM temperature and hence the global 21-cm signal at $z\sim 14-18$. The depth, location, and duration of the 21-cm absorption profile are highly dependent on the efficiencies of cosmic ray heating. In particular, the EDGES signal can be well fitted by the cosmic ray heating along with the Lyman-$\alpha$ coupling, and the dark matter-baryon interaction that we consider to achieve a `colder IGM background'. Further, we argue that the properties of cosmic rays and the nature of first generation of stars could be constrained by accurately measuring the global 21-cm absorption signal during the cosmic dawn., Comment: 15 pages, 9 figures, accepted for publication in MNRAS

Detecting the line-intensity mapping (LIM) signal from the galaxies of the Epoch of Reionization is an emerging tool to constrain their role in reionization. Ongoing and upcoming experiments target the signal fluctuations across the sky to reveal statistical and astrophysical properties of these galaxies via signal statistics, e.g., the power spectrum. Here, we revisit the [C II]$_{158 \mu \text{m}}$ LIM power spectrum under non-uniform line-luminosity scatter, which has a halo-mass variation of statistical properties. Line-luminosity scatter from a cosmological hydrodynamic and radiative transfer simulation of galaxies at $z=6$ is considered in this study. We test the robustness of different model frameworks that interpret the impact of the line-luminosity scatter on the signal statistics. We use a simple power-law model to fit the scatter and demonstrate that the mean luminosity-halo mass correlation fit cannot preserve the mean intensity of the LIM signal (hence the clustering power spectrum) under non-uniform scatter. In our case, the mean intensity changes by $\sim 48$ per cent compared to the mean correlation fit in contrast to the general case with semi-analytic scatter. However, we find that the prediction for the mean intensity from the most-probable fit can be modelled robustly, considering the generalized and more realistic non-uniform scatter. We also explore the possibility of diminishing luminosity bias under non-uniform scatter, affecting the clustering power spectrum, although this phenomenon might not be statistically significant. Therefore, we should adopt appropriate approaches that can consistently interpret the LIM power spectrum from observations., Comment: 9 pages, 8 figures, comments are welcome, accepted in MNRAS

The HI 21-cm optical depth ($\tau_b$) can be considerably large as the kinetic and spin temperature of the inter-galactic medium (IGM) is expected to be very low during cosmic dawn. It will be particularly higher at regions with HI over-density. We revisit the validity of the widely used linearized equation for estimating the HI 21-cm differential brightness temperature ($T_b$) which assumes $\tau_b << 1$ and approximates $[1-\exp({-\tau_b})]$ as $\tau_b$. We consider two scenarios, one without any additional cooling mechanism or radio background (referred as the standard scenario) and the other (referred as the excess-cooling} scenario) assumes the EDGES-like absorption profile and an excess cooling mechanism. We find that given a measured global absorption signal, consistent with the standard (excess-cooling) scenario, the linearized equation overestimates the spin temperature by $\sim 5\%(10\%)$. Further, using numerical simulations, we study the impact that the large optical depth has on various signal statistics. We observe that the variance, skewness and kurtosis, calculated at simulation resolution ($\sim 0.5 h^{-1} \, {\rm Mpc}$), are over-predicted up to $\sim 30\%$, $30\%$ and $15\%$ respectively for the standard and up to $\sim 90\%$, $50\%$ and $50\%$ respectively for the excess-cooling scenario. Moreover, we find that the probability distribution function of $T_b$ is squeezed and becomes more Gaussian in shape if no approximation is made. The spherically averaged HI power spectrum is overpredicted by up to $\sim 25 \%$ and $80\%$ at all scales for the standard and excess-cooling scenarios respectively., Comment: 9 pages, 6 figures. Accepted for publication in the MNRAS

CII line intensity mapping (LIM) is a potential technique to probe the early galaxies from the Epoch of Reionization (EoR). Several experiments e.g. CONCERTO, TIME, CCAT-p are underway to map the CII LIM signal fluctuations from the EoR, enabling us to estimate the CII power-spectrum and CII$\times$21-cm cross-power spectrum. Observed LIM signal will have its time evolution embedded in it along the Line of Sight (LoS) due to the finite travel time of the signal from its origin to the observer. We have investigated this so-called light-cone effect on the observed statistics of our semi-numerically simulated CII signal from the EoR. Using a suit of simulated CII and neutral hydrogen 21-cm maps and corresponding light-cone boxes, we have shown that the light-cone effect can impact the CII power spectrum by more than 15% at large scales ($k\sim 0.1\, \text{Mpc}^{-1}$, at $z=6.8$). We have also observed that the impact of light-cone effect on the CII power spectrum drops with decreasing redshift within the redshift range considered here ($7.2 \lesssim z \lesssim 6$). The CII$\times$21-cm cross-power spectrum is also affected by light-cone, and in our models where reionization ends before $z=6$, we find that the maximum impact on cross-power can reach up to 20%. At $z=6.4$, we find comparatively pronounced variation in the light-cone effect with reionization history on the cross power. Faster reionization histories have a more drastic light-cone effect on cross-power. We conclude that we need to incorporate the light-cone in order to properly model the signal, constrain the EoR-related astrophysical parameters and reionization history using the CII$\times$21-cm cross-power spectrum., Comment: 10 pages, 6 figures, comments are welcome, Accepted in MNRAS

Weakly Interacting Massive Particles (WIMPs) are considered to be one of the favoured dark matter candidates. Searching for any detectable signal due to the annihilation and decay of WIMPs over the entire electromagnetic spectrum has become a matter of interest for the last few decades. WIMP annihilation to Standard Model particles gives rise to a possibility of detection of this signal at low radio frequencies via synchrotron radiation. Dwarf Spheroidal Galaxies (dSphs) are expected to contain a huge amount of dark matter which makes them promising targets to search for such large scale diffuse radio emission. In this work, we present a stacking analysis of 23 dSph galaxies observed at low frequency (147.5MHz) as part of the TIFR-GMRT Sky Survey (TGSS). The non-detection of any signal from these stacking exercises put very tight constraints on the dark matter parameters. The best limit comes from the novel method of stacking after scaling the radio images of the individual dSph galaxy fields after scaling them by the respective half-light radius. The constraint on the thermally averaged cross-section is below the thermal relic cross-section value over a range of WIMP mass for reasonable choices of relevant astrophysical parameters. Such analysis using future deeper observation of individual targets as well as stacking can potentially reveal more about the WIMP dark matter properties., Comment: 7 pages, 7 figures. Accepted for publication in MNRAS. The definitive version will be available at https://academic.oup.com/mnras

Measurement of fluctuations in diffuse HI 21 cm background radiation from the post-reionization epoch (z < 6) is a promising avenue to probe the large-scale structure of the Universe and understand the evolution of galaxies. We observe the European Large-Area ISO Survey-North 1 (ELAIS-N1) field at 300-500 MHz using the upgraded Giant Meterwave Radio Telescope (uGMRT) and employ the 'foreground avoidance' technique to estimate the HI 21 cm power spectrum in the redshift range z = 1.96-3.58. Given the possible systematics that may remain in the data, we find the most stringent upper limits on the spherically averaged 21 cm power spectra at k~1.0 Mpc$^{-1}$ are (58.87 mK)$^2$, (61.49 mK)$^2$, (60.89 mK)$^2$, (105.85 mK)$^2$ at z = 1.96,2.19,2.62 and 3.58, respectively. We use this to constrain the product of neutral HI mass density (Omega_HI) and HI bias (b_HI) to the underlying dark matter density field, [Omega_HI*b_HI], as 0.09,0.11,0.12,0.24 at z=1.96,2.19,2.62,3.58, respectively. To the best of our knowledge these are the first limits on the HI 21 cm power spectra at the redshift range z = 1.96 - 3.58 and would play a significant role to constrain the models of galaxy formation and evolution., Comment: Accepted for publication in the Astrophysical Journal Letters (APJL)

The EDGES experiment has observed an excess trough ($-500^{+200}_{-500}$ mK) in the brightness temperature $T_{21}$ of the 21cm absorption line of neutral Hydrogen atom (HI) from the era of cosmic dawn ($z \simeq 17.2$). We consider possible interaction of Dark Matter and Dark Energy fluid along with the cooling off of the baryon matter by its collision with Dark Matter to explain the observed excess trough of $T_{21}$. We make use of three different Dark Matter-Dark Energy (DM-DE) interaction models to taste the viability of those models in explaining the EDGES results. The evolution of Hubble parameter is modified by DM-DE interactions and this is also addressed in this work. This in turn influences the optical depth of HI 21cm as well as the baryon temperature and thus effects the $T_{21}$ brightness temperature. In addition we also find that the DM-DE interaction enables us to explore Dark Matter with varied mass regimes and their viabilities in terms of satisfying the EDGES result., Comment: 19 pages, 10 figures

In the present study, structural changes due to gradual doping of Sr in BaTiO3 were investigated by both x-ray and neutron powder diffraction techniques. Ba1-xSrxTiO3 (x=0.0, 0.5 and 1.0) samples were synthesized by PVA evaporation method and purity was confirmed by x-ray diffraction experiment. After that, neutron diffraction experiments were carried out and diffraction data were analyzed by Rietveld least-square data refinement method using the computer program RIETAN-2000 and FullProf to determine various crystallographic structural parameters. The cation and anion position coordinates were also determined from the data refinement method which confirmed that Ba and Sr atoms possess tetrahedral A site and Ti atoms possess octahedral B site for all three samples BaTiO3, Ba0.5Sr0.5TiO3, and SrTiO3, respectively. Moreover, the lattice parameter values indicate, Ba1-xSrxTiO3 structure undergoes a phase transition from tetragonal to cubic somewhere before x=0.5. The concurrences between observed and calculated profiles were excellent and well consistent with the previously reported values. Furthermore, MEM based analysis was done for charge density measurement.

We study prospects of constraining the primordial magnetic field (PMF) and its evolution during the dark ages and cosmic dawn in light of EDGES 21-cm signal. Our analysis has been carried out on a `colder IGM' background which is one of the promising avenues to interpret the EDGES signal. We consider the dark matter-baryon interactions for the excess cooling. We find that the colder IGM suppresses both the residual free electron fraction and the coupling coefficient between the ionised and neutral components. The Compton heating also gets affected in colder IGM background. Consequently, the IGM heating rate due to the PMF enhances compared to the standard scenario. Thus, a significant fraction of the magnetic energy, for $B_0 \lesssim 0.5 \, {\rm nG}$, gets transferred to the IGM and the magnetic field decays at a much faster rate compared to the simple $(1+z)^2$ scaling during the dark ages and cosmic dawn. This low PMF is an unlikely candidate for explaining the rise of the EDGES absorption signal at lower redshift. We also see that the PMF and DM-baryon interaction together introduces a plateau-like feature in the redshift evolution of the IGM temperature. We find that the upper limit on the PMF depends on the underlying DM-baryon interaction. Higher PMF can be allowed when the interaction cross-section is higher and/or the DM particle mass is lower. Our study shows that the PMF with $B_0$ up to $\sim 0.4 \, {\rm nG}$, which is ruled out in the standard model, can be allowed if DM-baryon interaction with suitable cross-section and DM mass is considered., Comment: 9 pages, 4 figures, accepted for publication in MNRAS

The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest that the kinetic temperature of the inter-galactic medium (IGM) might be significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of DM-baryonic interaction model which is widely used to explain the depth of the EDGES 21-cm signal. We find that, in general, the hydrogen ionisation fraction gets suppressed during the dark ages and cosmic dawn and the suppression gradually increases at lower redshifts until X-ray heating turns on. However, accurate estimation of the ionisation fraction requires knowledge of the entire thermal history of the IGM, from the epoch of thermal decoupling of hydrogen gas and the CMBR to the cosmic dawn. It is possible that two separate scenarios which predict very similar HI differential temperature during the cosmic dawn and are consistent with the EDGES 21-cm signal might have very different IGM temperature during the dark ages. The evolutions of the ionisation fraction in these two scenarios are quite different. This prohibits us to accurately calculate the ionisation fraction during the cosmic dawn using the EDGES 21-cm signal alone. We find that the changes in the ionisation fraction w.r.t the standard scenario at redshift $z \sim 17 $ could be anything between $\sim 0 \%$ to $\sim 36 \%$. This uncertainty may be reduced if measurements of HI 21-cm differential temperature at multiple redshifts are simultaneously used., Comment: 10 pages, 8 figures. The revised version now includes X-ray heating. Revised version accepted for publication in Phys. Rev. D

The light-cone (LC) effect causes the mean as well as the statistical properties of the redshifted 21-cm signal $T_{\rm b}(\hat{\bf n},\nu)$ to change with frequency $\nu$ (or cosmic time). Consequently, the statistical homogeneity (ergodicity) of the signal along the line of sight (LoS) direction is broken. This is a severe problem particularly during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction ($\bar{x}_{\rm HI}$) changes rapidly as the universe evolves. This will also pose complications for large bandwidth observations. These effects imply that the 3D power spectrum $P(k)$ fails to quantify the entire second-order statistics of the signal as it assumes the signal to be ergodic and periodic along the LoS. As a proper alternative to $P(k)$, we use the multi-frequency angular power spectrum (MAPS) ${\mathcal C}_{\ell}(\nu_1,\nu_2)$ which does not assume the signal to be ergodic and periodic along the LoS. Here, we study the prospects for measuring the EoR 21-cm MAPS using future observations with the upcoming SKA-Low. Ignoring any contribution from the foregrounds, we find that the EoR 21-cm MAPS can be measured at a confidence level $\ge 5\sigma$ at angular scales $\ell \sim 1300$ for total observation time $t_{\rm obs} \ge 128\,{\rm hrs}$ across $\sim 44\,{\rm MHz}$ observational bandwidth. We also quantitatively address the effects of foregrounds on MAPS detectability forecast by avoiding signal contained within the foreground wedge in $(k_\perp, k_\parallel)$ plane. These results are very relevant for the upcoming large bandwidth EoR experiments as previous predictions were all restricted to individually analyzing the signal over small frequency (or equivalently redshift) intervals., Comment: Published in Monthly Notices of the Royal Astronomical Society (MNRAS). Available at https://doi.org/10.1093/mnras/staa1026

Understanding the low-frequency radio sky in depth is necessary to subtract foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the Cosmic Dawn, Epoch of Reionization (EoR) and post-reionization era. In this second paper of the series, we present the upgraded Giant Metrewave Radio Telescope (uGMRT) observation of the ELAIS N1 field made at 300-500 MHz. The image covers an area of $\sim 1.8$ $\mathrm{deg}^{2}$ and has a central background rms noise of $\sim$ 15 $\mu \mathrm{Jy}$ $\mathrm{beam}^{-1}$. We present a radio source catalog containing 2528 sources (with flux densities > 100 $\mu$Jy) and normalized source counts derived from that. The detailed comparison of detected sources with previous radio observations is shown. We discuss flux scale accuracy, positional offsets, spectral index distribution and correction factors in source counts. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study (SKADS) simulation. It shows a flattening below $\sim$1 mJy which corresponds to rise in population of star forming galaxies and radio-quiet AGN. For the first time, we estimated the spectral characteristics of the angular power spectrum or Multi-Frequency Angular Power Spectrum (MFAPS) of diffuse Galactic synchrotron emission (DGSE) over the wide frequency bandwidth of $300-500$~MHz from radio interferometric observations. This work demonstrates the improved capabilities of the uGMRT., Comment: There are 14 figures. Accepted for publication in MNRAS. The link of the first paper of this series - arXiv:1906.01655

We consider the minimal k-grouping problem: given a graph G=(V,E) and a constant k, partition G into subgraphs of diameter no greater than k, such that the union of any two subgraphs has diameter greater than k. We give a silent self-stabilizing asynchronous distributed algorithm for this problem in the composite atomicity model of computation, assuming the network has unique process identifiers. Our algorithm works under the weakly-fair daemon. The time complexity (i.e., the number of rounds to reach a legitimate configuration) of our algorithm is O(nD/k) where n is the number of processes in the network and \diam is the diameter of the network. The space complexity of each process is O((n +n_{false})log n) where n_{false} is the number of false identifiers, i.e., identifiers that do not match the identifier of any process, but which are stored in the local memory of at least one process at the initial configuration. Our algorithm guarantees that the number of groups is at most $2n/k+1$ after convergence. We also give a novel composition technique to concatenate a silent algorithm repeatedly, which we call loop composition., Comment: This is a revised version of the conference paper [6], which appears in the proceedings of the 18th International Conference on Distributed Computing and Networking (ICDCN), ACM, 2017. This revised version slightly generalize Theorem 1

We present results on the last topic we collaborate with our late friend, Professor Ajoy Kumar Datta (1958-2019). In this work, we shed new light on a self-stabilizing wave algorithm proposed by Colette Johnen in 1997. This algorithm constructs a BFS spanning tree in any connected rooted network. Nowadays, it is still the best existing self-stabilizing BFS spanning tree construction in terms of memory requirement, {\em i.e.}, it only requires $\Theta(1)$ bits per edge. However, it has been proven assuming a weakly fair daemon. Moreover, its stabilization time was unknown. Here, we study the slightly modified version of this algorithm, still keeping the same memory requirement. We prove the self-stabilization of this variant under the distributed unfair daemon and show a stabilization time in $O(D.n^2)$ rounds, where $D$ is the network diameter and $n$ the number of processes.

In this first paper of the series, we present initial results of newly upgraded Giant Meterwave Radio Telescope (uGMRT) observation of European Large-Area ISO Survey-North 1 (ELAIS-N1) at 325 MHz with 32 MHz bandwidth. Precise measurement of fluctuations in Galactic and extragalactic foreground emission as a function of frequency as well as angular scale is necessary for detecting redshifted 21-cm signal of neutral hydrogen from Cosmic Dawn, Epoch of Reionization (EoR) and post-reionization epoch. Here, for the first time we have statistically quantified the Galactic and extragalactic foreground sources in the ELAIS-N1 field in the form of angular power spectrum using the newly developed Tapered Gridded Estimator (TGE). We have calibrated the data with and without direction-dependent calibration techniques. We have demonstrated the effectiveness of TGE against the direction dependent effects by using higher tapering of field of view (FoV). We have found that diffuse Galactic synchrotron emission (DGSE) dominates the sky, after point source subtraction, across the angular multipole range $ 1115 \leqslant \mathcal{\ell} \leqslant 5083 $ and $ 1565 \leqslant \mathcal{\ell} \leqslant 4754 $ for direction-dependent and -independent calibrated visibilities respectively. The statistical fluctuations in DGSE has been quantified as a power law of the form $\mathcal{C}_{\mathcal{\ell}}= A \mathcal{\ell}^{-\beta} $. The best fitted values of (A, $\beta$) are ($ 62 \pm 6$ $mK^{2}$, $2.55 \pm 0.3 $) and ($ 48 \pm 4$ $mK^{2}$, $2.28 \pm 0.4 $ ) for the two different calibration approaches. For both the cases, the power law index is consistent with the previous measurements of DGSE in other parts of sky., Comment: 13 pages, 5figures, 4 tables; accepted for publication in MNRAS

The Square Kilometer Array is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z>6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centered on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z=7-10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at redshifts z=10 or below. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z~10, due to the very small number of line-of-sight interlopers expected at similar redshifts., Comment: 18 pages, 7 figures, v.2: Accepted for publications in MNRAS

This white paper highlights the crucial and urgent synergies required between WFIRST, Subaru Hyper Suprime-Cam or other >25m-class telescopes galaxy observations and SKA 21cm measurements to constrain the nature of reionization (ionization history and topology) and its sources., Comment: 6 pages, 3 figures

We introduce a new type of binary magnonic crystal, where Ni$_{80}$Fe$_{20}$ nanodots of two different sizes are diagonally connected forming a unit and those units are arranged in a square lattice. The magnetization dynamics of the sample is measured by using time-resolved magneto-optical Kerr effect microscope with varying magnitude and in-plane orientation ($\phi$) of the bias magnetic field. Interestingly, at $\phi=0^{\circ}$, the spin-wave mode profiles show frequency selective spatial localization of spin-wave power within the array. With the variation of $\phi$ in the range $0^{\circ}<\phi\leq 45^{\circ}$, we observe band narrowing due to localized to extended spin-wave mode conversion. Upon further increase of $\phi$, the spin-wave modes slowly lose the extended nature and become fully localized again at 90$^{\circ}$. We have extensively demonstrated the role of magnetostatic stray field distribution on the rotational symmetries obtained for the spin-wave modes. From micromagnetic simulations, we find that the dipole-exchange coupling between the nano-dots leads to remarkable modifications of the spin-wave mode profiles when compared with arrays of individual small and large dots. Numerically, we also show that the physical connection between the nano-dots provides more control points over the spin-wave propagation in the lattice at different orientations of bias magnetic field. This new type of binary magnonic crystal may find potential applications in magnonic devices such as spin-wave waveguide, filter, coupler, and other on-chip microwave communication devices., Comment: 14 pages, 7 figures, 4 pages of supplemental materials

We report spin-wave excitations in annular antidot lattice fabricated from 15 nm-thin Ni80Fe20 flm. The nanodots of 170 nm diameters are embedded in the 350 nm (diameter) antidot lattice to form the annular antidot lattice, which is arranged in a square lattice with edge-to-edge separation of 120 nm. A strong anisotropy in the spin-wave modes are observed with the change in orientation angle ({\phi}) of the in-plane bias magnetic field by using Time-resolved Magneto-optic Kerr microscope. A fattened fourfold rotational symmetry, mode hopping and mode conversion leading to mode quenching for three prominent spin-wave modes are observed in this lattice with the variation of the bias field orientation. Micromagnetic simulations enable us to successfully reproduce the measured evolution of frequencies with the orientation of bias magnetic field, as well as to identify the spatial profles of the modes. The magnetostatic field analysis, suggest the existence of magnetostatic coupling between the dot and antidot in annular antidot sample. Further local excitations of some selective spin-wave modes using numerical simulations showed the anisotropic spin-wave propagation through the lattice., Comment: 9 pages, 7 figures, 8 pages of supplementary material

The light-cone (LC) effect imprints the cosmological evolution of the redshifted 21-cm signal $T_{\rm b} ({\hat{\bf{n}}}, \nu)$ along the frequency axis which is the line of sight (LoS) direction of an observer. The effect is particularly pronounced during the Epoch of Reionization (EoR) when the mean hydrogen neutral fraction ${\bar{x}_{\rm HI}}(\nu)$ falls rapidly as the universe evolves. The multi-frequency angular power spectrum (MAPS) ${{\mathcal C}_{\ell}}(\nu_1,\nu_2)$ quantifies the entire second-order statistics of $T_{\rm b} ({\hat{\bf{n}}}, \nu)$ considering both the systematic variation along $\nu$ due to the cosmological evolution and also the statistically homogeneous and isotropic fluctuations along all the three spatial directions encoded in ${\hat{\bf{n}}}$ and $\nu$. Here we propose a simple model where the systematic frequency $(\nu_1,\nu_2)$ dependence of ${{\mathcal C}_{\ell}}(\nu_1,\nu_2)$ arises entirely due to the evolution of ${\bar{x}_{\rm HI}}(\nu)$. This provides a new method to observationally determine the reionization history. Considering a LC simulation of the EoR 21-cm signal, we use the diagonal elements $\nu_1=\nu_2$ of ${{\mathcal C}_{\ell}}(\nu_1,\nu_2)$ to validate our model. We demonstrate that it is possible to recover the reionization history across the entire observational bandwidth provided we have the value ${\bar{x}_{\rm HI}}$ at a single frequency as an external input., Comment: Published in Monthly Notices of the Royal Astronomical Society (MNRAS) Letters. Available at https://doi.org/10.1093/mnrasl/sly226

Observations of redshifted 21-cm signal from neutral hydrogen (HI) appear to be the most promising probe of the cosmic dark ages. The signal carries information about the thermal state along with density distribution of the intergalactic medium (IGM). The cosmic microwave background radiation (CMBR), through its interaction with charged particles, plays a major role in determining the kinetic and spin temperature of HI gas in the IGM during dark ages. A Spatially fluctuating ionization fraction, which is caused by inhomogeneous recombinations, causes heat transfer from the CMBR to the IGM gas inhomogeneous. We revisit the impact of this inhomogeneous heat transfer on spatial fluctuations in the observed HI 21-cm signal over a large redshift range during dark ages. Our study shows that the effect negatively impacts fluctuations in the HI spin temperature and results in an enhanced HI 21-cm power spectrum. We find that the effect is particularly important during the transition of the gas kinetic temperature being coupled to the CMBR to fully decoupled from it, i.e., in the redshift range $30 \lesssim z \lesssim 300$. It is found that, on the average the HI power spectrum, $P_{T_b}(k, z)$ is enhanced by $\sim 4\%$, $\sim10 \%$ , $\sim 20\%$, and $\sim 30 \%$ at redshifts $60$, $90$, $140$, and $200$ respectively at $k=0.1 \, {\rm Mpc}^{-1}$. The effect becomes even more significant at lower values of $k_{\parallel}^2/k^2$ due to the reduced dominance of the peculiar velocity. It is observed that the power spectrum is enhanced by $\sim 49\%$ and $\sim 93\%$ at redshifts $140$ and $200$ respectively at $k=0.1 \, {\rm Mpc}^{-1}$ for $k_{\parallel}^2/k^2=0$. This enhancement has a weak $k$-mode dependence., Comment: 6 pages, 4 figures, accepted in PRD

In this paper, we focus on the implementation of distributed programs in using a key-value store where the state of the nodes is stored in a replicated and partitioned data store to improve performance and reliability. Applications of such algorithms occur in weather monitoring, social media, etc. We argue that these applications should be designed to be stabilizing so that they recover from an arbitrary state to a legitimate state. Specifically, if we use a stabilizing algorithm then we can work with more efficient implementations that provide eventual consistency rather than sequential consistency where the data store behaves as if there is just one copy of the data. We find that, although the use of eventual consistency results in consistency violation faults (cvf) where some node executes its action incorrectly because it relies on an older version of the data, the overall performance of the resulting protocol is better. We use experimental analysis to evaluate the expected improvement. We also identify other variations of stabilization that can provide additional guarantees in the presence of eventual consistency.Finally, we note that if the underlying algorithm is not stabilizing, even a single \cvf may cause the algorithm to fail completely thereby making it impossible to benefit from this approach., Comment: submission to ICDCN 2018

Strong light-matter interactions in layered transition metal dichalcogenides (TMDs) open up vivid possibilities for novel exciton-based devices. The optical properties of TMDs are dominated mostly by the tightly bound excitons and more complex quasiparticles, the biexcitons. Instead of physically exfoliated monolayers, the solvent-mediated chemical exfoliation of these 2D crystals is a cost-effective, large-scale production method suitable for real device applications. We explore the ultrafast excitonic processes in WS$_{2}$ dispersion using broadband femtosecond pump-probe spectroscopy at room temperature. We detect the biexcitons experimentally and calculate their binding energies, in excellent agreement with earlier theoretical predictions. Using many-body physics, we show that the excitons act like Weiner-Mott excitons and explain the origin of excitons via first-principles calculations. Our detailed time-resolved investigation provides ultrafast radiative and non-radiative lifetimes of excitons and biexcitons in WS$_{2}$. Indeed, our results demonstrate the potential for excitonic quasiparticle-controlled TMDs-based devices operating at room temperature., Comment: 9 pages, 7 figures

Three-dimensional radiative transfer simulations of the epoch of reionization can produce realistic results, but are computationally expensive. On the other hand, simulations relying on one-dimensional radiative transfer solutions are faster but limited in accuracy due to their more approximate nature. Here, we compare the performance of the reionization simulation codes grizzly and C2-ray which use 1D and 3D radiative transfer schemes respectively. The comparison is performed using the same cosmological density fields, halo catalogues and source properties. We find that the ionization maps, as well as the 21-cm signal maps from these two simulations are very similar even for complex scenarios which include thermal feedback on low mass halos. The comparison between the schemes in terms of the statistical quantities such as the power spectrum of the brightness temperature fluctuation agree with each other within 10% error throughout the entire reionization history. grizzly seems to perform slightly better than the semi-numerical approaches considered in Majumdar et al. (2014) which are based on the excursion set principle. We argue that grizzly can be efficiently used for exploring parameter space, establishing observations strategies and estimating parameters from 21-cm observations., Comment: 16 pages, Submitted to MNRAS