arXiv subjects

M. Saleem

Publications and source records attributed to M. Saleem.

12 recordsLinked to original sources

arXiv2026

Testing the Kerr hypothesis beyond the quadrupole with GW241011

All multipole moments of a Kerr black hole are uniquely determined by its mass and spin. Gravitational wave observations can test this prediction by measuring spin-induced multipole moments imprinted on the inspiral phase of compact binary mergers. In this Letter, we show that the recently reported compact binary coalescence GW241011 enables a simultaneous test of deviations in the spin-induced quadrupole and octupole moments of the binary components from their black hole values. We find no evidence for deviations from the Kerr prediction and place the first constraints on spin-induced octupole moments of the compact binary. This approach complements tests of the Kerr nature of compact binary merger remnants based on quasinormal mode measurements in the ringdown phase.

gr-qc↗

arXiv2022

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 $>1$~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.

astro-ph.HE↗

arXiv2022

Multiparameter tests of general relativity using principal component analysis with next-generation gravitational wave detectors

Principal Component Analysis (PCA) is an efficient tool to optimize the multiparameter tests of general relativity (GR) where one tests for simultaneous deviations in multiple post-Newtonian (PN) phasing coefficients by introducing fractional deformation parameters. We use PCA to construct the `best-measured' linear combinations of the PN deformation parameters from the data. This helps to set stringent limits on deviations from GR and detect possible beyond-GR physics. In this paper, we study the effectiveness of this method with the proposed next-generation gravitational wave detectors, Cosmic Explorer (CE) and Einstein Telescope (ET). Observation of compact binaries with total masses between 20-200 $\mathrm{M}_{\odot}$ in the detector frame and at a luminosity distance of 500 Mpc, CE can measure the three most dominant linear combinations to an accuracy better than 10%, and the most dominant one to better than 0.1%. For specific ranges of masses and linear combinations, constraints from ET are better by a few factors than CE. This improvement is because of the improved low frequency sensitivity of ET compared to CE (between 1-5 Hz). In addition, we explain the sensitivity of the PCA parameters to the different PN deformation parameters and discuss their variation with total mass. We also discuss a criterion for quantifying the number of most dominant linear combinations that capture the information in the signal up to a threshold.

gr-qc↗

arXiv2021

The Science Case for LIGO-India

The global network of gravitational-wave detectors has completed three observing runs with $\sim 50$ detections of merging compact binaries. A third LIGO detector, with comparable astrophysical reach, is to be built in India (LIGO-Aundha) and expected to be operational during the latter part of this decade. Multiple detectors operating at different parts of the globe will provide several pairs of interferometers with longer baselines and an increased network SNR. This will improve the sky localisation of GW events. Multiple detectors simultaneously in operation will also increase the baseline duty factor, thereby, leading to an improvement in the detection rates and, hence, the completeness of surveys. In this paper, we quantify the improvements due to the expansion of the LIGO Global Network (LGN) in the precision with which source properties will be measured. We also present examples of how this expansion will give a boost to tests of fundamental physics.

gr-qc↗

arXiv2020

Imprints of the redshift evolution of double neutron star merger rate on the signal to noise ratio distribution

Proposed third generation gravitational wave (GW) interferometers such as Cosmic Explorer will have the sensitivity to observe double neutron star (DNS) mergers up to a redshift of $\sim 5$ with good signal to noise ratios. We argue that the comoving spatial distribution of DNS mergers leaves a unique imprint on the statistical distribution of signal to noise ratios (SNRs) of the detected DNS mergers. Hence the SNR distribution of DNS mergers will facilitate a novel probe of their redshift evolution independent of the luminosity distance measurements. We consider detections of DNS mergers by the third generation detector Cosmic Explorer and study the SNR distribution for different possible redshift evolution models of DNSs and employ Anderson Darling p-value statistic to demonstrate the distinguishability between these different models. We find that a few hundreds of DNS mergers in the Cosmic Explorer era will allow us to distinguish between different models of redshift evolution.

gr-qc↗

arXiv2020

Prospects of joint detections of neutron star mergers and short-GRBs with Gaussian structured jets

GW170817 was the first ever joint detection of gravitational waves (GW) from a binary neutron star (BNS) merger with the detections of short $γ$-ray burst (SGRB) counterparts. Analysis of the multi-band afterglow observations of over more than a year revealed that the outflow from the merger end-product was consistent with structured relativistic jet models with the core of the jet narrowly collimated to half opening angles $\sim5$ deg. In this work, assuming all the BNS mergers produce Gaussian structured jets with properties as inferred for GW170817, we explore the prospects of joint detections of BNS mergers and prompt $γ-$ray emission, expected during the current and upcoming upgrades of LIGO-Virgo-KAGRA detectors. We discuss three specific observational aspects: 1) the distribution of detected binary inclination angles 2) the distance reach and 3) the detection rates. Unlike GW-only detections, the joint detections are greatly restricted at large inclination angles, due to the structure of the jets. We find that at lower inclination angles (say below 20 deg), the distance reach as well as the detection rates of the joint detections are limited by GW detectability while at larger inclinations (say above 20 deg), they are limited by the $γ$-ray detectability.

astro-ph.HE↗

arXiv2020

On the energetics of a possible relativistic jet associated with the binary neutron star merger candidate S190425z

Advanced LIGO and Virgo detectors reported the first binary neutron star merger candidate in the third observing run, S190425z, on 25th April 2019. A weak $γ$-ray excess was reported nearly coincidentally by the INTEGRAL satellite which accidentally covered the entire localization region of AdvLIGO/VIRGO. Electromagnetic follow-up in longer wavelengths has not lead to the detection of any associated counterparts. Here we combine the available information from gravitational-wave measurements and upper limits of fluence from \textit{INTEGRAL} to show that the observations are completely consistent with a relativistic Gaussian structured jet and a typical short duration Gamma-Ray Burst (GRB) being produced in the merger. We obtain posterior bounds on the on-axis isotropic equivalent energy of the associated GRB under different prior distributions. This study demonstrates that even limited GW and EM information could be combined to produce valuable insights about outflows from mergers. Future follow-ups may help constrain the jet structure further, especially if there is an orphan afterglow detection associated with the candidate.

astro-ph.HE↗

arXiv2019

Constraints on the binary black hole nature of GW151226 and GW170608 from the measurement of spin-induced quadrupole moments

According to the "no-hair" conjecture, a Kerr black hole (BH) is completely described by its mass and spin. In particular, the spin-induced quadrupole moment of a Kerr BH with mass $m$ and dimensionless spin $χ$ can be written as $Q=-κ\,m^3χ^2$, where $κ_{\rm BH}=1$. Thus by measuring the spin-induced quadrupole parameter $κ$, we can test the binary black hole nature of compact binaries and distinguish them from binaries comprised of other exotic compact objects, as proposed in [N. V. Krishnendu et al., PRL 119, 091101 (2017)]. Here, we present a Bayesian framework to carry out this test where we measure the symmetric combination of individual spin-induced quadrupole moment parameters fixing the anti-symmetric combination to be zero. The analysis is restricted to the inspiral part of the signal as the spin-induced deformations are not modeled in the post-inspiral regime. We perform detailed simulations to investigate the applicability of this method for compact binaries of different masses and spins and also explore various degeneracies in the parameter space which can affect this test. We then apply this method to the gravitational wave events, GW151226 and GW170608 detected during the first and second observing runs of Advanced LIGO and Advanced Virgo detectors. We find the two events to be consistent with binary black hole mergers in general relativity. By combining information from several more of such events in future, this method can be used to set constraints on the black hole nature of the population of compact binaries that are detected by the Advanced LIGO and Advanced Virgo detectors.

gr-qc↗

arXiv2018

Exploring Short-GRB afterglow parameter space for observations in coincidence with gravitational waves

Short duration Gamma Ray Bursts(SGRB) and their afterglows are among the most promising electro-magnetic (EM) counterparts of Neutron Star (NS) mergers. The afterglow emission is broadband, visible across the entire electro-magnetic window from $γ$-ray to radio frequencies. The flux evolution in these frequencies is sensitive to the multi-dimensional afterglow physical parameter space. Observations of gravitational wave (GW) from BNS mergers in spatial and temporal coincidence with SGRB and associated afterglows can provide valuable constraints on afterglow physics. We run simulations of GW-detected BNS events and assuming all of them are associated with a GRB jet which also produces an afterglow, investigate how detections or non-detections in X-ray, optical and radio frequencies can be influenced by the parameter space. We narrow-down the regions of afterglow parameter space for a uniform top-hat jet model which would result in different detection scenarios. We list inferences which can be drawn on the physics of GRB afterglows from multi-messenger astronomy with coincident GW-EM observations.

astro-ph.HE↗

arXiv2018

Rates of Short-GRB afterglows in association with Binary Neutron Star mergers

Assuming all binary Neutron Star mergers produce Short Gamma Ray Bursts (SGRBs), we combine the merger rates of binary Neutron Stars (BNS) from population synthesis studies, the sensitivities of advanced Gravitational Wave (GW) interferometer networks, and of the electromagnetic (EM) facilities in various wave bands, to compute the detection rate of associated afterglows in these bands. Using the inclination angle measured from GWs as a proxy for the viewing angle and assuming a uniform distribution of jet opening angle between 3 to 30 degrees, we generate light curves of the counterparts using the open access afterglow hydrodynamics package BoxFit for X-ray, Optical and Radio bands. For different EM detectors we obtain the fraction of EM counterparts detectable in these three bands by imposing appropriate detection thresholds. In association with BNS mergers detected by five (three) detector network of advanced GW interferometers, assuming a BNS merger rate of $0.6-774{\rm Gpc}^{-3}{\rm yr}^{-1}$~\citep{dominik2012double}, we find the afterglow detection rates (per year) to be $0.04-53$ ($0.02-27$), $0.03-36$ ($0.01-19$) and $0.04-47$ ($0.02-25$) in the X-ray, optical and radio bands respectively. Our rates represent maximum possible detections for the given BNS rate since we ignore effects of cadence and field of view in EM follow up observations.

astro-ph.HE↗

arXiv2018

The Hiperwall Visualization Platform for Big Data Research

In the era of Big Data, with the increasing use of large-scale data-driven applications, the visualization of very large high-resolution images and extracting useful information (searching for specific targets or rare signal events) from these images can pose challenges to the current video-wall display technologies. At Bellarmine University, we have set up an Advanced Visualization and Computational Lab (AVCL) using a state-of-the-art next generation video-wall technology, called Hiperwall (Highly Interactive Parallelized Display Wall). The 16 feet wide by 4.5 feet high Hiperwall visualization system consists of eight display tiles that are arranged in a 4x2 tile format and has an effective resolution of 16.5 Megapixels. Using Hiperwall, we can perform interactive visual data analytics of large images by conducting comparative views of multiple large images in Astronomy and multiple data events in experimental High Energy Physics (HEP). Users can display a single large image across all the display tiles, or view many different images simultaneously on multiple display tiles. Hiperwall enables simultaneous visualization of multiple high resolution images and its contents on the entire display wall without loss of clarity. Hiperwall's middleware also allows researchers in geographically diverse locations to collaborate on large scientific experiments. In this paper we will provide a description of a new generation of display wall setup at Bellarmine University that is based on the Hiperwall technology, which is a robust visualization system for Big Data research.

cs.HC↗

arXiv2011

Measurement of the Top Pair Production Cross section at ATLAS

We present the measurement of the production cross section for top quark pair ($t\bar{t}$) in pp collisions at $\sqrt{s}$ = 7 TeV using the data recorded with the ATLAS detector at the Large Hadron Collider (LHC). Events are selected in single lepton (electron or muon) and dilepton ($ee$, $μμ$, $eμ$) topologies with multi-jets, and large missing transverse energy (MET). The combined result from these measurements is $σ_{t\bar{t}}$ = $176 \pm 5 \mathrm{(stat.)} ^{+13}_{-10}\mathrm{(syst.)} \pm 7 \mathrm{(lumi.)} \mathrm{pb}$, which is in good agreement with the Standard Model prediction.

hep-ex↗