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The Epoch of Reionization (EoR) is a crucial link to grasp the complete evolutionary history of the universe. Several attempts with a variety of observables have been utilized in the past to understand the thermal and ionization evolution of the Intergalactic Medium during EoR. In this study, we explore the simultaneous prospects of two important observables which are expected to be available in the near future, i.e. Dispersion Measure (DM) of high redshift FRBs and large scale 21 cm power spectra. For this purpose, we use an earlier developed explicitly photon conserving semi numerical model, $\texttt{SCRIPT}$ including realistic recombination and radiative feedback effect. We check that DM evolution of 100 mock FRBs at high redshifts ($7.0\le z\le15.0$) is sufficient to recover the underlying reionization model, while 1000 FRB mocks at redshift range can constrain the reionization timeline within the percentage level uncertainties at 68\% confidence limit. Further, we study the effect of including large scale 21~cm power spectra (using only a single bin, $k\sim0.14~h/\mathrm{cMpc}$) at three redshifts along with FRB DM distribution. The joint exploration using these two observables can significantly improve the constraints on the various parameters ($\lesssim 8\%$ uncertainties for reionization interval and midpoint at 95\% confidence) alleviating the degeneracies and can narrow down the thermal history of the universe by discarding some of the extreme heating models., Comment: Accepted for publication in A&A

Efficient exploration of parameter spaces is crucial to extract physical information about the Epoch of Reionization from various observational probes. To this end, we propose a fast technique based on Gaussian Process Regression (GPR) training applied to a semi-numerical photon-conserving reionization model, SCRIPT. Our approach takes advantage of the numerical convergence properties of SCRIPT and constructs a training set based on low-cost, coarse-resolution simulations. A likelihood emulator is then trained using this set to produce results in approximately two orders of magnitude less computational time than a full MCMC run, while still generating reasonable 68% and 95% confidence contours. Furthermore, we conduct a forecasting study using simulated data to demonstrate the applicability of this technique. This method is particularly useful when full MCMC analysis is not feasible due to expensive likelihood computations., Comment: Accepted for publication in MNRAS

One of the most promising probes to constrain the reionization history of the universe is the power spectrum of neutral hydrogen 21 cm emission fluctuations. The corresponding analyses require computationally efficient modelling of reionization, usually achieved through semi-numerical simulations. We investigate the capability of one such semi-numerical code, SCRIPT, to constrain the reionization parameters. Our study involves creating a mock data set corresponding to the upcoming SKA-Low, followed by a Bayesian inference method to constrain the model parameters. In particular, we explore in detail whether the inferred parameters are unbiased with respect to the inputs used for the mock, and also if the inferences are insensitive to the resolution of the simulation. We find that the model is successful on both fronts. We also develop a simple template model of reionization which can mimic the complex physical processes like inhomogeneous recombinations and radiative feedback and show that it can recover the global reionization history reliably with moderate computational cost. However, such simple models are not suitable for constraining the properties of the ionizing sources. Our results are relevant for constraining reionization using high-quality data expected in future telescopes., Comment: Accepted for publication in MNRAS

Given that the reionization history of cosmic hydrogen is yet to be stringently constrained, it is worth checking the prospects of doing so using physically motivated models and available observational data. For this purpose, we use an extended version of the explicitly photon-conserving semi-numerical model of reionization, $\texttt{SCRIPT}$, which also includes thermal evolution of the intergalactic medium (IGM). The model incorporates the effects of inhomogeneous recombination and radiative feedback self-consistently and is characterized by five free parameters (two for the redshift-dependent ionization efficiency, two for the ionizing escape fraction, and another for reionization temperature increment). We constrain these free parameters by simultaneously matching with various observational probes, e.g., estimates of the ionized hydrogen fraction, the CMB scattering optical depth and the galaxy UV luminosity function. In addition, we include the low-density IGM temperature measurements obtained from Lyman-$\alpha$ absorption spectra at $z \sim 5.5$, a probe not commonly used for Bayesian analysis of reionization parameters. We find that the interplay of the various data sets, particularly inclusion of the temperature data, leads to tightening of the parameter constraints. Our default models prefer a late end of reionization (at $z \lesssim 6$), in agreement with other recent studies. We can also derive constraints on the duration of reionization, $\Delta z=1.81^{+0.51}_{-0.67}$ and the midpoint of reionization, $z_{\mathrm{mid}}=7.0^{+0.30}_{-0.40}$. The constraints can be further tightened by including other available and upcoming data sets., Comment: Accepted for publication in MNRAS

The ionization and thermal state of the intergalactic medium (IGM) during the epoch of reionization has been of interest in recent times because of their close connection to the first stars. We present in this paper a semi-numerical code which computes the large-scale temperature and ionized hydrogen fields in a cosmologically representative volume accounting for the patchiness in these quantities arising from reionization. The code is an extension to a previously developed version for studying the growth of ionized regions, namely, Semi Numerical Code for ReionIzation with PhoTon Conservation (SCRIPT). The main additions in the present version are the inhomogeneous recombinations which are essential for temperature calculations. This extended version of SCRIPT also implements physical consequences of photoheating during reionization, e.g., radiative feedback. These enhancements allow us to predict observables which were not viable with the earlier version. These include the faint-end of the ultra-violet luminosity function of galaxies (which can get affected by the radiative feedback) and the temperature-density relation of the low-density IGM at $z\sim 6$. We study the effect of varying the free parameters and prescriptions of our model on a variety of observables. The conclusion of our analysis is that it should be possible to put constraints on the evolution of thermal and ionization state of the IGM using available observations accounting for all possible variations in the free parameters. A detailed exploration of the parameter space will be taken up in the future., Comment: Accepted for publication in MNRAS

We report the lowest frequency measurements of gamma-ray burst (GRB) 171205A with the upgraded Giant Metrewave Radio Telescope (uGMRT) covering a frequency range from 250--1450 MHz and a period of $4-937$ days. It is the first GRB afterglow detected at 250--500 MHz frequency range and the second brightest GRB detected with the uGMRT. Even though the GRB is observed for nearly 1000 days, there is no evidence of transition to non-relativistic regime. We also analyse the archival ${\it Chandra}$ X-ray data on day $\sim 70$ and day $\sim 200$. We also find no evidence of a jet break from the analysis of combined data. We fit synchrotron afterglow emission arising from a relativistic, isotropic, self-similar deceleration as well as from a shock-breakout of wide-angle cocoon. Our data also allow us to discern the nature and the density of the circumburst medium. We find that the density profile deviates from a standard constant density medium and suggests that the GRB exploded in a stratified wind like medium. Our analysis shows that the lowest frequency measurements covering the absorbed part of the light curves are critical to unravel the GRB environment. Our data combined with other published measurements indicate that the radio afterglow has contribution from two components: a weak, possibly slightly off-axis jet and a surrounding wider cocoon, consistent with the results of Izzo et al. (2019). The cocoon emission likely dominates at early epochs, whereas the jet starts to dominate at later epochs, resulting in flatter radio lightcurves., Comment: Accepted for publication in ApJ

Scenario bouncing can give the cosmology singularity problem a possible way out. Finding a solution for the universe's bouncing model requires proper estimation of the state equation. We present two such state equations that give us the solution for a bounce. One such case is the exotic radiation, where we assumed that exotic radiation dominated the universe during the bounce occurrence. We also considered another case where quintom matter scenario existed previously, and the newly proposed exotic radiation scenario coexisted. In these two cases, we have shown that all the necessary conditions for the bounce are fulfilled. Such new ways certainly increase support and flexibility for the bouncing universe model., Comment: 10 pages, 2 figures