arXiv subjects

Nidhal Guessoum

Publications and source records attributed to Nidhal Guessoum.

17 recordsLinked to original sources

arXiv2026

Can We Find the Emission Mechanism Behind the Extremely Bright GRB 230812B?

GRB 230812B is a bright long-duration GRB with a luminous, long-lived afterglow and an AstroSat/CZTI polarization measurement during the prompt phase, enabling a joint study of its prompt spectral evolution, polarization, and broadband afterglow. Time-resolved spectroscopy of the prompt emission shows that during the rising phase, the low-energy Band-function index exceeds the synchrotron line of death, favoring the presence of an additional thermal component. At later times, from $T_0+2$ s to $T_0+32$ s, the prompt spectra are consistent with predominantly non-thermal emission. Polarization analysis of the prompt emission in the $300$-$600$ keV band yields a marginal lower limit on the polarization fraction of $\Pi \gtrsim 50\%$ at the $1\sigma$ level. The long X-ray monitoring of the afterglow shows no jet break over the observed baseline. Multiwavelength afterglow modeling favors a wide jet with an inferred half-opening angle of $\theta_j = 15^{+6}_{-4}$ degrees observed close to the jet axis with a viewing angle of $\theta_v = 0.9^{+1.8}_{-0.6}$ degrees. The inferred circumburst density is low, $n_0 = 1.2^{+0.3}_{-0.1}\times10^{-4}\,\textrm{cm}^{-3}$, and the isotropic-equivalent kinetic energy of the jet is $E_{{\rm k}, iso} = 4.0^{+1.5}_{-0.8} \times 10^{53}$ erg. Taken together, the prompt spectral evolution favors an early phase with a thermal contribution followed by a later phase dominated by non-thermal emission. The polarization constraint in the late prompt phase is consistent with synchrotron emission, although a higher-significance polarization measurement will be required to robustly constrain the magnetic-field geometry and the relative contribution of photospheric emission.

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arXiv2025

The Effect of Vera C. Rubin Observatory Cadence Selections on Kilonova Detectability

The discovery of the optical/infra-red counterpart (AT2017gfo) to the binary neutron star gravitational-wave detection (GW170817), which was followed by a short gamma-ray burst (GRB170817), marked a groundbreaking moment in multi-messenger astronomy. To date, it remains the only confirmed joint detection of its kind. However, many experiments are actively searching for similar fast-fading electromagnetic counterparts, known as kilonovae. Fortunately, the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) provides excellent prospects for identifying kilonova candidates either from, or independent of, gravitational-wave and gamma-ray burst triggers. Cadence choices for LSST surveys are especially important for maximising the likelihood of kilonovae detections. In this work, we explore the possibility of optimizing Rubin Observatory's ability to detect kilonovae by implementing a fast transient metric shown to be successful with an existing wide field survey, e.g. the Zwicky Transient Facility (ZTF). We study existing LSST cadences, how detection rates are affected by filter selections, the return timescales for visits of the same area in the sky, and other relevant factors. Through our analysis, we have found that employing baseline cadences and utilizing triplet families like presto gap produced the highest likelihood of kilonova detection.

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arXiv2023

Characterizing the Ordinary Broad-lined Type Ic SN 2023pel from the Energetic GRB 230812B

We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 230812B, and its associated supernova (SN) SN 2023pel. The proximity ($z = 0.36$) and high energy ($E_{γ, \rm{iso}} \sim 10^{53}$ erg) make it an important event to study as a probe of the connection between massive star core-collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak $r$-band magnitude of $M_r = -19.46 \pm 0.18$ mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of $M_{\rm{Ni}} = 0.38 \pm 0.01$ $\rm{M_\odot}$, and a peak bolometric luminosity of $L_{\rm{bol}} \sim 1.3 \times 10^{43}$ $\rm{erg}$ $\rm{s^{-1}}$. We confirm SN 2023pel's classification as a broad-lined Type Ic SN with a spectrum taken 15.5 days after its peak in $r$ band, and derive a photospheric expansion velocity of $v_{\rm{ph}} = 11,300 \pm 1,600$ $\rm{km}$ $\rm{s^{-1}}$ at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass $M_{\rm{ej}} = 1.0 \pm 0.6$ $\rm{M_\odot}$ and kinetic energy $E_{\rm{KE}} = 1.3^{+3.3}_{-1.2} \times10^{51}$ $\rm{erg}$. We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and $E_{γ, \rm{iso}}$ for their associated GRBs, across a broad range of 7 orders of magnitude, provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.

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arXiv2023

Using Neural Networks to Perform Rapid High-Dimensional Kilonova Parameter Inference

On the 17th of August, 2017 came the simultaneous detections of GW170817, a gravitational wave that originated from the coalescence of two neutron stars, along with the gamma-ray burst GRB170817A, and the kilonova counterpart AT2017gfo. Since then, there has been much excitement surrounding the study of neutron star mergers, both observationally, using a variety of tools, and theoretically, with the development of complex models describing the gravitational-wave and electromagnetic signals. In this work, we improve upon our pipeline to infer kilonova properties from observed light-curves by employing a Neural-Network framework that reduces execution time and handles much larger simulation sets than previously possible. In particular, we use the radiative transfer code POSSIS to construct 5-dimensional kilonova grids where we employ different functional forms for the angular dependence of the dynamical ejecta component. We find that incorporating an angular dependence improves the fit to the AT2017gfo light-curves by up to ~50% when quantified in terms of the weighted Mean Square Error.

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arXiv2021

Data-driven expectations for electromagnetic counterpart searches based on LIGO/Virgo public alerts

Searches for electromagnetic counterparts of gravitational-wave signals have redoubled since the first detection in 2017 of a binary neutron star merger with a gamma-ray burst, optical/infrared kilonova, and panchromatic afterglow. Yet, one LIGO/Virgo observing run later, there has not yet been a second, secure identification of an electromagnetic counterpart. This is not surprising given that the localization uncertainties of events in LIGO and Virgo's third observing run, O3, were much larger than predicted. We explain this by showing that improvements in data analysis that now allow LIGO/Virgo to detect weaker and hence more poorly localized events have increased the overall number of detections, of which well-localized, gold-plated events make up a smaller proportion overall. We present simulations of the next two LIGO/Virgo/KAGRA observing runs, O4 and O5, that are grounded in the statistics of O3 public alerts. To illustrate the significant impact that the updated predictions can have, we study the follow-up strategy for the Zwicky Transient Facility. Realistic and timely forecasting of gravitational-wave localization accuracy is paramount given the large commitments of telescope time and the need to prioritize which events are followed up. We include a data release of our simulated localizations as a public proposal planning resource for astronomers.

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arXiv2021

GRBs luminosity function synthesized from \textit{Swift/BAT}, \textit{Fermi/GBM} and \textit{Konus-Wind} data

We study the luminosity function of long gamma-ray bursts (LGRBs) using the peak flux obtained from three LGRB samples with known redshifts: (a) a sample of 251 LGRBs from the \textit{Swift/BAT} satellite/instrument; (b) a sample of 37 LGRBs from the \textit{Fermi/GBM} telescope; (c) a sample of 152 GRBs from the \textit{Konus-Wind} instrument. For the \textit{Swift/BAT} and \textit{Fermi/GBM} samples, we use data available on the Swift Burst Analyser websites (\url{http://www.swift.ac.uk/burst_analyser}; \citep{Evans:2010}) and (\url{http://swift.gsfc.nasa.gov/archive/grb/table/}) and on the Fermi website (\url{https://heasarc.gsfc.nasa.gov/}\url{W3Browse /fermi /fermigbrst.html}; \citep{{Gruber_2014}, {von_Kienlin_2014}, {Bhat_2016}}) to calculate the luminosity at the peak of the flux by using a cut-off power-law spectrum (CPL). For the \textit{Konus-Wind} sample, we use the Yonetoku correlation relationship \citep{Yonetoku:2010} to determine the isotropic luminosity from the energy at the peak of the flux measured in the source frame \citep{Minaev:2019}. With these three samples (totalling 439 GRBs), we use the Monte Carlo method to synthesize 10,000 "artificial" GRBs similar to each real GRB by considering that each physical quantity observed obeys a normal distribution, where the tabulated value and uncertainty represent the mean and the $3σ$ error. The results obtained for the luminosity function from our data samples are consistent with those published in previous works.

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arXiv2021

Optimizing Serendipitous Detections of Kilonovae: Cadence and Filter Selection

The rise of multi-messenger astronomy has brought with it the need to exploit all available data streams and learn more about the astrophysical objects that fall within its breadth. One possible avenue is the search for serendipitous optical/near-infrared counterparts of gamma-ray bursts (GRBs) and gravitational-wave (GW) signals, known as kilonovae. With surveys such as the Zwicky Transient Facility (ZTF), which observes the sky with a cadence of ~ three days, the existing counterpart locations are likely to be observed; however, due to the significant amount of sky to explore, it is difficult to search for these fast-evolving candidates. Thus, it is beneficial to optimize the survey cadence for realtime kilonova identification and enable further photometric and spectroscopic observations. We explore how the cadence of wide field-of-view surveys like ZTF can be improved to facilitate such identifications. We show that with improved observational choices, e.g., the adoption of three epochs per night on a ~ nightly basis, and the prioritization of redder photometric bands, detection efficiencies improve by about a factor of two relative to the nominal cadence. We also provide realistic hypothetical constraints on the kilonova rate as a form of comparison between strategies, assuming that no kilonovae are detected throughout the long-term execution of the respective observing plan. These results demonstrate how an optimal use of ZTF increases the likelihood of kilonova discovery independent of GWs or GRBs, thereby allowing for a sensitive search with less interruption of its nominal cadence through Target of Opportunity programs.

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arXiv2020

Optical follow-up of the neutron star-black hole mergers S200105ae and S200115j

LIGO and Virgo's third observing run (O3) revealed the first neutron star-black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements creating optical/near-IR "kilonova" (KN) emission. The joint gravitational-wave (GW) and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter, and independently measure the local expansion rate of the universe. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility (ZTF). ZTF observed $\sim$\,48\% of S200105ae and $\sim$\,22\% of S200115j's localization probabilities, with observations sensitive to KNe brighter than $-$17.5\,mag fading at 0.5\,mag/day in g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art KN models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with depths of $\rm m_{\rm AB}\approx 22$ mag, attainable in meter-class, wide field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high BH spins, and large neutron star radii.

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arXiv2020

Implications of the search for optical counterparts during the second part of the Advanced LIGO's and Advanced Virgo's third observing run: lessons learned for future follow-up observations

Joint multi-messenger observations with gravitational waves and electromagnetic data offer new insights into the astrophysical studies of compact objects. The third Advanced LIGO and Advanced Virgo observing run began on April 1, 2019; during the eleven months of observation, there have been 14 compact binary systems candidates for which at least one component is potentially a neutron star. Although intensive follow-up campaigns involving tens of ground and space-based observatories searched for counterparts, no electromagnetic counterpart has been detected. Following on a previous study of the first six months of the campaign, we present in this paper the next five months of the campaign from October 2019 to March 2020. We highlight two neutron star - black hole candidates (S191205ah, S200105ae), two binary neutron star candidates (S191213g and S200213t) and a binary merger with a possible neutron star and a "MassGap" component, S200115j. Assuming that the gravitational-wave candidates are of astrophysical origin and their location was covered by optical telescopes, we derive possible constraints on the matter ejected during the events based on the non-detection of counterparts. We find that the follow-up observations during the second half of the third observing run did not meet the necessary sensitivity to constrain the source properties of the potential gravitational-wave candidate. Consequently, we suggest that different strategies have to be used to allow a better usage of the available telescope time. We examine different choices for follow-up surveys to optimize sky localization coverage vs.\ observational depth to understand the likelihood of counterpart detection.

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arXiv2020

Dynamic Scheduling: Target of Opportunity Observations of Gravitational Wave Events

The simultaneous detection of electromagnetic and gravitational waves from the coalescence of two neutron stars (GW170817 and GRB170817A) has ushered in a new era of "multi-messenger" astronomy, with electromagnetic detections spanning from gamma to radio. This great opportunity for new scientific investigations raises the issue of how the available multi-messenger tools can best be integrated to constitute a powerful method to study the transient universe in particular. To facilitate the classification of possible optical counterparts to gravitational-wave events, it is important to optimize the scheduling of observations and the filtering of transients, both key elements of the follow-up process. In this work, we describe the existing workflow whereby telescope networks such as GRANDMA and GROWTH are currently scheduled; we then present modifications we have developed for the scheduling process specifically, so as to face the relevant challenges that have appeared during the latest observing run of Advanced LIGO and Advanced Virgo. We address issues with scheduling more than one epoch for multiple fields within a skymap, especially for large and disjointed localizations. This is done in two ways: by optimizing the maximum number of fields that can be scheduled, and by splitting up the lobes within the skymap by right ascension to be scheduled individually. In addition, we implement the ability to take previously observed fields into consideration when rescheduling. We show the improvements that these modifications produce in making the search for optical counterparts more efficient, and we point to areas needing further improvement.

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arXiv2019

Teamwork Makes the Dream Work: Optimizing Multi-Telescope Observations of Gravitational-Wave Counterparts

The ever-increasing sensitivity of the network of gravitational-wave detectors has resulted in the accelerated rate of detections from compact binary coalescence systems in the third observing run of Advanced LIGO and Advanced Virgo. Not only has the event rate increased, but also the distances to which phenomena can be detected, leading to a rise in the required sky volume coverage to search for counterparts. Additionally, the improvement of the detectors has resulted in the discovery of more compact binary mergers involving neutron stars, revitalizing dedicated follow-up campaigns. While significant effort has been made by the community to optimize single telescope observations, using both synoptic and galaxy-targeting methods, less effort has been paid to coordinated observations in a network. This is becoming crucial, as the advent of gravitational-wave astronomy has garnered interest around the globe, resulting in abundant networks of telescopes available to search for counterparts. In this paper, we extend some of the techniques developed for single telescopes to a telescope network. We describe simple modifications to these algorithms and demonstrate them on existing network examples. These algorithms are implemented in the open-source software \texttt{gwemopt}, used by some follow-up teams, for ease of use by the broader community.

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arXiv2019

Detecting the imprint of a kilonova or supernova \\ in short GRB afterglows

Short gamma-ray bursts result from mergers of two neutron stars or from collapsars, but probably at a smaller rate. In the first case, a kilonova occurs while in the second case a Type Ic supernova is expected. } {Even if future observations of kilonovae in association with gravitational wave events provide better data, detecting a kilonova during an afterglow follow-up would remain useful for exploring the diversity of the kilonova phenomenon. As supernovae produce a weaker gravitational signal, afterglow follow-up will be the only possible method to find one. In this work, we identify the conditions of the burst energy, external density, kilonova mass, supernova luminosity, that are necessary for the detection of a kilonova or supernova in the follow-up of short GRB afterglows.} {We have used a simple kilonova model to obtain the peak luminosities and times as a function of mass, expansion velocity and ejected matter opacity. Afterglow light curves are computed for a uniform medium and a stellar wind, in the kilonova and supernova cases, respectively.} {We represent, using diagrams of the burst kinetic energy vs. density of the external medium, the domains where the kilonova or supernova at maximum is brighter than the afterglow. %\LEt{Please check I have retained your intended meaning -> It's OK

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arXiv2018

Distributions of Pseudo-Redshifts and Durations (Observed and Intrinsic) of Fermi GRBs

Ever since the insightful analysis of the durations of GRBs by [Kouveliotou:93], GRBs have most often been classified into two populations: "short bursts" (shorter than 2.0 seconds) and "long bursts" (longer than 2.0 seconds). However, recent works have suggested the existence of an intermediate population in the bursts observed by the Swift satellite. Moreover, some researchers have questioned the universality of the 2.0-second dividing line between short and long bursts: some bursts may be short but actually result from collapsars, the physical mechanism behind normally long bursts, and some long ones may originate from mergers, the usual progenitors of short GRBs. In this work, we focus on GRBs detected by the Fermi satellite and study the distribution of their durations measured in the observer's reference frame and, for those with known redshifts, in the bursts' reference frames. However, there are relatively few bursts with measured redshifts, and this makes an accurate study difficult. To overcome this problem, we follow [Zhang:2018] and determine a "pseudo-redshift" from the correlation relation between the luminosity $L_p$ and the energy $E_p$, both of which are calculated at the peak of the flux. Interestingly, we find that the uncertainties in the quantities observed and used in the determination of pseudo-redshifts, do affect the precision of the individual results significantly, but they keep the distribution of pseudo-redshifts very similar to that of the actual ones and thus allow us to use pseudo-redshifts for our statistical study. We use the reduced chi-square and the maximization of the log-likelihood to statistically analyze the distribution of Fermi GRB durations. Both methods show that the distribution of the observed and the intrinsic bursts durations are better represented by two groups, rather than three.

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arXiv2016

Determination of Cosmological Parameters from Gamma Ray Burst Characteristics and Afterglow Correlations

We use the correlation relation between the energy emitted by the GRBs in their prompt phases and the X-ray afterglow fluxes, in an effort to constrain cosmological parameters and aiming to construct a Hubble diagram at high redshifts, i.e. beyond those found with Type Ia supernovae. We use a sample of 126 \textit{Swift} GRBs, that we have selected among more than 800 long bursts observed until April 2015. The selection is based on a few observational constraints: GRB flux higher than 0.4 $photons/cm^2/s$ in the band 15-150 keV, spectrum fitted with simple power law, redshift accurately known and given, and X-ray afterglow observed and flux measured. The statistical method of maximum likelihood is then used to determine the best cosmological parameters ($Ω_M$, $Ω_Λ$) that give the best correlation for two relations: a) the Amati relation (between intrinsic spectral peak energy $E_{p,i}$ and the equivalent isotropic energy), b) the Dainotti relation, namely between the X-ray afterglow luminosity $L_X$ and the break time $T_a$, which is observed in the X-ray flux FX. Although the number of GRBs with high redshifts is rather small, and despite the notable dispersion found in the data, the results we have obtained are quite encouraging and promising. The results obtained using the Amati relation are close to those obtained using the Type Ia supernovae, and they appear to indicate a universe dominated by dark energy. However, those obtained with the correlation between the break time and the X-ray afterglow luminosity is consistent with the findings of the WMAP study of the cosmic microwave background radiation, and they seem to indicate a de Sitter-Einstein universe dominated by matter.

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arXiv2016

Statistical Study of Observed and Intrinsic Durations among BATSE and Swift/BAT GRBs

Studies of \textit{BATSE} bursts \citep{kouveliotou:93} have resulted in the widespread adoption of a two-group categorization: long bursts (those with durations $\geq 2$ seconds) and short bursts (those with durations $\leq 2$ seconds). This categorization, one must recall, used the observed $T_{90}$ time durations for bursts (during which 90\% of a burst's fluence is measured). In this work, we have explored two ideas: 1) a statistical search for a possible third, intermediate category of bursts (between the "short" and the "long" ones) among 2041 \textit{BATSE} GRBs and 757 \textit{Swift/BAT} ones, 2) a study of bursts' intrinsic durations, where durations in the bursts' reference frames (instead of the observed durations) are considered, for this, 248 \textit{Swift/BAT} bursts that have redshift measurements were statistically analyzed for the same categorization goal. We first use a Monte Carlo method to determine the proper binning of each GRB, considering that bursts come with different uncertainties on their durations. Then, using the method of minimization of chi-square $χ^2$, we search for the best fit of the normalized frequency distributions $\frac{1}{N_0}\frac{dN}{d\ln{T}}$ of durations, this allows us to compare fits with two groups ("short" and "long") with fits with three groups ("short", "long", and "intermediate"). Our results indicate that the distributions of observed durations are better fitted by three groups than two groups for \textit{Swift/BAT} data, interestingly, the "intermediate" group appears rather clearly for both observed and intrinsic durations. For BATSE data, the statistical test does not prefer three groups over two. We discuss the results, their possible underlying causes, and reasonable interpretations.

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arXiv2016

Revisiting the Amati and Yonetoku Correlations with Swift GRBs

We use a sample of \textit{Swift} gamma-ray bursts (GRBs) to analyze the Amati and Yonetoku correlations. The first relation is between $E_{p,i}$, the intrinsic peak energy of the prompt GRB emission, and $E_{iso}$, the equivalent isotropic energy. The second relation is between $E_{p,i}$ and $L_{iso}$, the isotropic peak luminosity. We select a sample of 71 \textit{Swift} GRBs that have a measured redshift and whose observed $E^{obs}_p$ is within the interval of energy 15-150 keV with a relative uncertainty of less than 70\%. We seek to find correlation relations for long-duration GRBs (LGRBs) with a peak photon flux $P_{ph}\geq 2.6~ \mathrm{ph/cm^{2}/s}$. Uncertainties (error bars) on the values of the calculated energy flux \textit{P}, the energy $E_{iso}$, and the peak isotropic luminosity $L_{iso}$ are estimated using a Monte Carlo approach. We find 27 \textit{Swift} LGRBs that satisfy all our constraints. Results of our analyses of the sample of 71 GRBs and the selected subsample (27 GRBs) are in good agreement with published results. The plots of the two relations for all bursts show a large dispersion around the best straight lines in the sample of 71 LGRBs but not so much in the subsample of 27 GRBs.

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arXiv1998

Lithium Production in Companions of Accreting X-Ray Binaries by Neutron Spallation of C,N,O Elements

We examine the processes which could lead to the observed enhancement of Li and possibly other light elements (Be, B) in the companions of a number of X-ray novae. We conclude that one of the most promising mechanisms is the spallation of CNO elements on the surface of the companion induced by the neutron flux produced in the hot accretion flow onto the compact object. Direct production of the observed Li and its deposition onto the dwarf companion seem less likely, mainly because of the possibility of its destruction in the production region itself and difficulties in its deposition associated with the configuration of the companion's magnetic field. We discuss other potential observables of the above scenario.

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