arXiv subjects

Zeinab Kalantari

Publications and source records attributed to Zeinab Kalantari.

4 recordsLinked to original sources

arXiv2025

Machine Learning Identification of Gravitationally Microlensed Gamma-Ray Bursts

Gravitational microlensing of gamma-ray bursts (GRBs) provides a unique opportunity to probe compact dark matter and small-scale structures in the Universe. However, identifying such microlensed GRBs within large data sets is a significant challenge. In this study, we develop a machine learning (ML) approach to distinguish lensed GRBs from their nonlensed counterparts, using simulated light curves. A comprehensive data set is generated, comprising labeled light curves for both categories. Features are extracted using the Cesium package, capturing critical temporal properties of the light curves. Multiple ML models are trained on the extracted features, with Random Forest achieving the best performance, delivering an accuracy of 86% and an F1 score of 0.86 (0.87) for the nonlensed (lensed) class. This approach successfully demonstrates the potential of ML for identifying gravitational lensing in GRBs, paving the way for future observational applications.

astro-ph.HE↗

arXiv2024

A Study of Cosmological Models Based on Long Gamma-ray Bursts Duration Histogram

The duration of more than one thousand gamma-ray bursts (GRBs) has been measured by Swift satellite. Besides the redshift distribution of GRBs, the burst duration could be another significant property of GRBs that can be analyzed. In this project, First, we find the detection rate of Swift/BAT for a cosmological model with the $ ωCDM$ model, then by performing a Monte-Carlo simulation, we find the "long" GRB duration histogram to compare the cosmological model with the $ ωCDM$ model and the $ΛCDM$ model. The $χ^2$ minimization method is employed to determine the optimal value of $α$ in the dark energy equation of state, $P= c ω(z) ρ$, with $ω(z)=1+αz$ as $α=0.08 ^{+ 0.04}_{-0.02}$. We showed that the $ωCDM$ model is statistically favored over the $ΛCDM$ model. Other studies by measuring the expansion rate of the Universe directly from the SNIa data by Pantheon and DES-SN3YR samples and the combinations of SNIa, CMB, and BAO data confirmed that the value of $α$ in the dark energy equation of state is not zero \citep{Dark_energy_Abbott, 2011Beutler, 2014Anderson, 2015Ross, 2016PlanckCollaboration, Alam2017, Mazumdar2021}.

astro-ph.CO↗

arXiv2022

Fermi-GBM Observation of GRB 090717034: $χ^2$ Test Confirms Evidence of Gravitational Lensing by a Supermassive Black Hole with Million Solar Mass

Gravitational lensing of gamma-ray bursts (GRBs) can provide an opportunity to probe the massive compact objects in the universe at different redshifts. We have discovered two consecutive pulses in the light curve of GRB 090717034, with the same temporal profile and different count rate, separated by a time interval, which is identified as gravitationally lensed candidate in Fermi/GBM GRB catalogue \citep{Kalantari}. Here, we use the $χ^2$ method to investigate the similarity of the temporal profile variability of the two pulses as a gravitationally lensed candidate GRB. We find the magnification factor and the time delay between two pulses to correspond to minimising the $χ^2$ function. Then, we perform a Monte Carlo simulation on a sample of mock lensed GRBs and compare the $χ^2$ of the lensed GRB candidate with the simulation, which confirms this candidate with $1σ$ confidence level. Assuming that GRB 090717034 is lensed by a point-like object, the redshifted lens mass is about $M_L(1+z)=(4.220\pm 6.615) \times 10^6 M_{\odot}$. The lens of this GRB is a candidate for a super-massive black hole along the line of sight to the GRB.

astro-ph.HE↗

arXiv2022

Imprints of Gravitational Millilensing on the Light Curve of GRBs

In this work, we search for signatures of gravitational millilensing in Gamma-ray bursts (GRB) in which the source-lens-observer geometry produces two images that manifest in the GRB light curve as superimposed peaks with identical temporal variability (or echoes), separated by the time delay between the two images. According to the sensitivity of our detection method, we consider millilensing events due to point mass lenses in the range of $10^5 - 10^7 M_{\odot}$ at lens redshift about half that of the GRB, with a time delay in the order of $10$ seconds. Current GRB observatories are capable of resolving and constraining this lensing scenario if the above conditions are met. We investigated the Fermi/GBM GRB archive from the year 2008 to 2020 using the autocorrelation technique and we found one millilensed GRB candidate out of 2137 GRBs searched, which we use to estimate the optical depth of millilensed GRBs by performing a Monte-Carlo simulation to find the efficiency of our detection method. Considering a point-mass model for the gravitational lens, where the lens is a supermassive black hole, we show that the density parameter of black holes ($Ω_{BH}$) with mass $\approx10^6 M_\odot$ is about $0.007 \pm 0.004$. Our result is one order of magnitude larger compared to consist with previous work in a lower mass range ($10^2 - 10^3 M_{\odot}$), which gave a density parameter $Ω_{BH} \approx 5\times 10^{-4}$, and recent work in the mass range of $10^2 - 10^7 M_{\odot}$ that reported $Ω_{BH} \approx 4.6\times 10^{-4}$. The mass fraction of black holes in this mass range to the total mass of the universe would be $f\approx Ω_{BH}/Ω_M=0.027 \pm 0.016$.

astro-ph.CO↗