arXiv subjects

Soebur Razzaque

Publications and source records attributed to Soebur Razzaque.

At least 37 records · Page 2Linked to original sources

arXiv2024

Influence of Cosmic Voids on the propagation of TeV Gamma Rays and the Puzzle of GRB 221009A

The recent detection of gamma-ray burst GRB~221009A has attracted attention due to its record brightness and first-ever detection of $\gtrsim 10$ TeV $γ$ rays from a GRB. Despite being the second-nearest GRB ever detected, at a redshift of $z=0.151$, the distance is large enough for severe attenuation of $γ$-ray flux at these energies due to $γγ\to e^\pm$ pair production with the extragalactic background light (EBL). Here, we investigate whether the presence of cosmic voids along the line of sight can significantly impact the detectability of very-high energy (VHE, $>$ 100 GeV) gamma rays from distant sources. Notably, we find that the gamma-gamma opacity for VHE gamma rays can be reduced by approximately 10\% and up to 30\% at around 13 TeV, the highest-energy photon detected from GRB~221009A, for intervening cosmic voids along the line-of-sight with a combined radius of 110 Mpc, typically found from voids catalogs, and 250 Mpc, respectively. This reduction is substantially higher for TeV photons compared to GeV photons, attributable to the broader target photon spectrum that TeV photons interact with. This finding implies that VHE photons are more susceptible to variations in the EBL spectrum, especially in regions dominated by cosmic voids. Our study sheds light on the detection of $\gtrsim 10$ TeV gamma rays from GRB 221009A in particular, and on the detection of extragalactic VHE sources in general.

astro-ph.HE↗

arXiv2024

On non-detection of Gamma-Ray Bursts in three compact binary merger events detected by LIGO

The joint detection of the gravitational wave (GW) event GW170817 and the short-duration gamma-ray burst (SGRB) event GRB 170817A, marked the beginning of GW multi-messenger astronomy and confirmed that binary neutron star mergers are progenitors of at least some SGRBs. An estimated joint detection rate of 0.3 - 1.7 per year between the LIGO-Hanford, LIGO-Livingston and Virgo GW network at design sensitivity, and the Fermi Gamma-ray Burst Monitor was predicted. However, to date, the GW170817/GRB 170817A joint detection has been the only event of its kind so far. Taking into account that SGRBs are narrowly beamed and are emitted perpendicular to the orbital plane of the binary system, we propose that previous mergers involving neutron stars, were orientated such that observation of the emitted SGRB along this narrow jet was not possible. To support this hypothesis we have estimated the inclination of the binary systems for previously detected Binary Neutron Star (BNS) and Black Hole Neutron Star (BHNS) mergers through GW analysis. This analysis was performed using BILBY, a Python based Bayesian inference library, to estimate the inclination of the BNS events GW170817 and GW190425, and the BHNS events GW190917_114630 and GW200115_042309. The results obtained in this study indicate that these binaries may have had inclinations greater than $33^{\circ}$ with respect to the line of sight from Earth, an upper limit on the viewing angle set from observations of GRB 170817A. This then suggests that the observation of the emitted SGRB from these past mergers might not have been possible.

astro-ph.HE↗

arXiv2024

Quantum Spread Complexity in Neutrino Oscillations

Quantum information theory has recently emerged as a flourishing area of research and quantum complexity, one of its powerful measures, is being applied for investigating complex systems in many areas of physics. Its application to practical physical situations, however, is still few and far between. Neutrino flavor oscillation is a widely studied physical phenomena with far reaching consequences in understanding the standard model of particle physics and to search for physics beyond it. Oscillation arises because of mixing between the flavor and mass eigenstates, and their evolution over time. It is an inherent quantum system for which flavor transitions are traditionally studied with probabilistic measures. We have applied quantum complexity formalism as an alternate measure to study neutrino oscillations. In particular, quantum spread complexity revealed additional information on the violation of charge-parity symmetry in the neutrino sector. Our results indicate that complexity favors the maximum violation of charge-parity, hinted recently by experimental data.

hep-ph↗

arXiv2024

Deep Neural Networks for Estimation of Gamma-Ray Burst Redshifts

While the available set of Gamma-ray Burst (GRB) data with known redshift is currently limited, a much larger set of GRB data without redshift is available from different instruments. This data includes well-measured prompt gamma-ray flux and spectral information. We estimate the redshift of a selection of these GRBs detected by Fermi-GBM and Konus-Wind using Machine Learning techniques that are based on spectral parameters. We find that Deep Neural Networks with Random Forest models employing non-linear relations among input parameters can reasonably reproduce the pseudo-redshift distribution of GRBs, mimicking the distribution of GRBs with spectroscopic redshift. Furthermore, we find that the pseudo-redshift samples of GRBs satisfy (i) Amati relation between the peak photon energy of the time-averaged energy spectrum in the cosmological rest frame of the GRB ${E}_{\rm i, p}$ and the isotropic-equivalent radiated energy ${E}_{\rm iso}$ during the prompt phase; and (ii) Yonetoku relation between ${E}_{\rm i, p}$ and isotropic-equivalent luminosity ${L}_{\rm iso}$, both measured during the peak flux interval.

astro-ph.HE↗

arXiv2023

Very high-energy gamma rays from GRB 180720B and GRB 190829A with external Compton emission

Gamma-ray bursts (GRBs) comprise of short, bright, energetic flashes of emission from extragalactic sources followed by a longer afterglow phase of decreased brightness. Recent discoveries of very-high-energy (VHE, $\gtrsim 100$ GeV) afterglow emission from GRB 180720B and GRB 190829A by H.E.S.S. have raised questions regarding the emission mechanism responsible. We interpret these observed late-time emission to be the result of inverse Compton emission of ultra-relativistic electrons in the GRB blastwave in an external radiation field, i.e., external Compton (EC), considering both the wind and interstellar medium scenarios. We present predictions of multiwavelength light curves and energy spectra, ranging from optical to VHE, and include the synchrotron and synchrotron self-Compton (SSC) radiation mechanisms as well. We corrected the EC and SSC model for the $γ$-ray attenuation by absorption of photons through their interaction with the extragalactic background light (EBL). We compared our results to multiwavelength data and found that EC gives a satisfactory fit for a given set of fixed model parameters for GRB 180720B, whereas SSC result in a better fit for GRB 190829A. For both GRBs a wind environment is preferred over constant density inter-stellar medium, and the Cosmic Microwave Background as the external radiation field. However, with more data and an effective optimisation tool we can find a more robust fit of the model, implying better constraints on the GRB environment and the particle energy requirements for the emission observed at late times. This has consequences for future observations of GRBs at these extreme energies.

astro-ph.HE↗

arXiv2023

Gamma rays from a reverse shock with turbulent magnetic fields in GRB 180720B

Gamma-ray bursts (GRBs) are the most electromagnetically luminous cosmic explosions. They are powered by collimated streams of plasma (jets) ejected by a newborn stellar-mass black hole or neutron star at relativistic velocities (near the speed of light). Their short-lived (typically tens of seconds) prompt $γ$-ray emission from within the ejecta is followed by long-lived multi-wavelength afterglow emission from the ultra-relativistic forward shock. This shock is driven into the circumburst medium by the GRB ejecta that are in turn decelerated by a mildly-relativistic reverse shock. Forward shock emission was recently detected up to teraelectronvolt-energy $γ$-rays, and such very-high-energy emission was also predicted from the reverse shock. Here we report the detection of optical and gigaelectronvolt-energy $γ$-ray emission from GRB 180720B during the first few hundred seconds, which is explained by synchrotron and inverse-Compton emission from the reverse shock propagating into the ejecta, implying a low-magnetization ejecta. Our optical measurements show a clear transition from the reverse shock to the forward shock driven into the circumburst medium, accompanied by a 90-degree change in the mean polarization angle and fluctuations in the polarization degree and angle. This indicates turbulence with large-scale toroidal and radially-stretched magnetic field structures in the reverse and forward shocks, respectively, which tightly couple to the physics of relativistic shocks and GRB jets -- launching, composition, dissipation and particle acceleration.

astro-ph.HE↗

arXiv2023

Lepto-hadronic interpretation of 2021 RS Ophiuchi nova outburst

Very high energy (VHE; 100 GeV $<$ E $\leq$ 100 TeV) and high energy (HE; 100 MeV $<$ E $\leq$ 100 GeV) gamma-rays were observed from the symbiotic recurrent nova RS Ophiuchi (RS Oph) during its outburst in August 2021, by various observatories such as High Energy Stereoscopic System (H.E.S.S.), Major Atmospheric Gamma Imaging Cherenkov (MAGIC), and {\it Fermi}-Large Area Telescope (LAT). The models explored so far tend to favor a hadronic scenario of particle acceleration over an alternative leptonic scenario. This paper explores a time-dependent lepto-hadronic scenario to explain the emission from the RS Oph source region. We have used simultaneous low frequency radio data observed by various observatories, along with the data provided by H.E.S.S., MAGIC, and \textit{Fermi}-LAT, to explain the multi-wavelength (MWL) spectral energy distributions (SEDs) corresponding to 4 days after the outburst. Our results show that a lepto-hadronic interpretation of the source not only explains the observed HE-VHE gamma-ray data but the corresponding model synchrotron component is also consistent with the first 4 days of low radio frequency data, indicating the presence of non-thermal radio emission at the initial stage of nova outburst. We have also calculated the expected neutrino flux from the source region and discussed the possibility of detecting neutrinos.

astro-ph.HE↗

arXiv2023

Possible Evidence for Lorentz Invariance Violation in Gamma-ray Burst 221009A

The preliminary detections of the gamma-ray burst 221009A up to 18 TeV by LHAASO and up to 251 TeV by Carpet 2 have been reported through Astronomer's Telegrams and Gamma-ray Coordination Network circulars. Since this burst is at redshift $z=0.1505$, these photons may at first seem to have a low probability to avoid pair production off of background radiation fields and survive to reach detectors on Earth. By extrapolating the reported $0.1-1.0$\ GeV LAT spectrum from this burst to higher energies and using this to limit the intrinsic spectrum of the burst, we show that the survival of the 18 TeV photon detected by LHAASO is not unlikely with many recent extragalactic background light models, although the detection of a 251 TeV event is still very unlikely. This can be resolved if Lorentz invariance is violated at an energy scale $E_{\rm QG}< 49 E_{\rm Planck}$\ in the linear ($n=1$) case, and $E_{\rm QG}< 10^{-6}E_{\rm Planck}$\ in the quadratic ($n=2$) case (95\% confidence limits), where $E_{\rm Planck}$ is the Planck energy. This could potentially be the first evidence for subluminal Lorentz invariance violation.

astro-ph.HE↗

arXiv2023

Study of maximum electron energy of sub-PeV pulsar wind nebulae by multiwavelength modelling

Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the discovery of 12 ultrahigh-energy (UHE; $\mathrm{\varepsilon} \ge 100$ TeV) gamma-ray sources located in the Galactic plane. A few of these UHE gamma-ray emitting regions are in spatial coincidence with pulsar wind nebulae (PWNe). We consider a sample of five sources; two of them are LHAASO sources (LHAASO J1908+0621 and LHAASO J2226+6057) and the remaining three are GeV-TeV gamma-ray emitters. In addition, X-rays, radio observations, or upper limits are also available for these objects. We study multiwavelength radiation from these sources by considering a PWN origin, where the emission is powered by the spin-down luminosity of the associated pulsars. In this leptonic emission model, the electron population is calculated at different times under the radiative (synchrotron and inverse-Compton) and adiabatic cooling. We also include the onset of the reverberation phase for the PWN, by assuming radially symmetric expansion. However, in this work, we find that multiwavelength emission can be interpreted before the onset of this phase. The maximum energy of the electrons based on the spectral fit is found to be above 0.1 PeV and close to 1 PeV. For LHAASO J2226+6057, using its observations in radio to UHE gamma-rays, we find that UHE gamma-rays can be interpreted using electrons with maximum energy of 1 PeV. We estimate the upper limits on the minimum Lorentz factor of the electrons and it also infers the minimum value of the pair-multiplicity of charged pairs.

astro-ph.HE↗

arXiv2023

Ultrahigh-energy cosmic-ray signature in GRB 221009A

The brightest long gamma-ray burst detected so far by the Swift-BAT and Fermi-GBM telescopes, GRB~221009A, provides an unprecedented opportunity for understanding the high-energy processes in extreme transient phenomena. We find that the conventional leptonic models, synchrotron and synchrotron-self-Compton, for the afterglow emission from this source have difficulties explaining the observation of $\gtrsim 10$ TeV $γ$ rays, by the LHAASO detector, and extending up to 18 TeV energies. We model $γ$-ray spectrum estimated in the energy range 0.1-1 GeV by the Fermi-LAT detector. The flux predicted by our leptonic models is severely attenuated at $> 1$ TeV due to $γγ$ pair production with extragalactic background light, and hence an additional component is required at $\gtrsim 10$ TeV. Ultrahigh-energy cosmic rays can be accelerated in the GRB blastwave, and their propagation induces an electromagnetic cascade in the extragalactic medium. The line of sight component of this flux can explain the emission at $\gtrsim 10$ TeV detected by LHAASO, requiring a fraction of the GRB blastwave energy in ultrahigh-energy cosmic rays. This could be an indication of ultrahigh-energy cosmic-ray acceleration in GRBs.

astro-ph.HE↗

arXiv2022

The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept

The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions and accelerators. The main science themes include: supermassive black holes and their connections to neutrinos and cosmic rays; binary neutron star mergers and the relativistic jets they produce; cosmic ray particle acceleration sources including Galactic supernovae; and continuous monitoring of other astrophysical events and sources over the full sky in this important energy range. AMEGO-X will probe the medium energy gamma-ray band using a single instrument with sensitivity up to an order of magnitude greater than previous telescopes in the energy range 100 keV to 1 GeV that can be only realized in space. During its three-year baseline mission, AMEGO-X will observe nearly the entire sky every two orbits, building up a sensitive all-sky map of gamma-ray sources and emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of Opportunity.

astro-ph.IM↗

arXiv2022

Implications of multiwavelength spectrum on cosmic-ray acceleration in blazar TXS 0506+056

MAGIC collaboration has recently analyzed data from a long-term multiwavelength campaign of the $γ$-ray blazar TXS 0506+056. In December 2018, it was flaring in the very-high-energy (VHE; $E>100$ GeV) $γ$-ray band, but no simultaneous neutrino event was detected. We model the observed spectral energy distribution (SED), using a one-zone leptohadronic emission. We estimate the neutrino flux through the restriction from observed X-ray flux on the secondary radiation due to hadronic cascade, initiated by protons with energy $E_p \lesssim 0.1$ EeV. We assume ultrahigh-energy cosmic rays (UHECRs; $E\gtrsim0.1$ EeV), with the same slope and normalization as the low-energy spectrum, are accelerated in the jet but escape efficiently. We propagate the UHE protons in a random, turbulent extragalactic magnetic field (EGMF). The leptonic emission from the jet dominates the GeV range, whereas the cascade emission from CR interactions in the jet contributes substantially to the X-ray and VHE range. The line-of-sight cosmogenic $γ$ rays from UHECRs produce a hardening in the VHE spectrum. Our model prediction for neutrinos from the jet is consistent with the 7.5-year flux limit by IceCube and shows no variability during the MAGIC campaign. Therefore, we infer that the correlation between GeV-TeV $γ$-rays and neutrino flare is minimal. The luminosity in CRs limits the cosmogenic $γ$-ray flux, which, in turn, bounds the RMS value of the EGMF to $\gtrsim 10^{-5}$ nG. The cosmogenic neutrino flux is lower than the IceCube-Gen2 detection potential for 10 yrs of observation. VHE $γ$-ray variability should arise from increased activity inside the jet; thus, detecting steady flux at multi-TeV energies may indicate UHECR acceleration. Upcoming $γ$-ray imaging telescopes such as the CTA will be able to constrain the cosmogenic $γ$-ray component in the SED of TXS 0506+056.

astro-ph.HE↗

arXiv2022

The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope -- Data Release 3

An incremental version of the fourth catalog of active galactic nuclei (AGNs) detected by the Fermi-Large Area Telescope is presented. This version (4LAC-DR3) derives from the third data release of the 4FGL catalog based on 12 years of E>50 MeV gamma-ray data, where the spectral parameters, spectral energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates and four radio galaxies. We describe the properties of the new sample and outline changes affecting the previously published one. We also introduce two new parameters in this release, namely the peak energy of the SED high-energy component and the corresponding flux. These parameters allow an assessment of the Compton dominance, the ratio of the Inverse-Compton to the synchrotron peak luminosities, without relying on X-ray data.

astro-ph.HE↗

arXiv2022

Non-unitary neutrino mixing in the NO$ν$A near detector data

The $ν_μ\to ν_e$ oscillation probability over short baseline ($\lesssim 1$~km) would be negligible in case the mixing matrix for three active neutrinos is unitary. However, in case of non-unitary mixing of three neutrinos, this probability would be non-negligible due to the so-called "zero distance" effect. Hence, the near detector of the accelerator experiments such as NO$ν$A can provide strong constraints on the parameters of the non-unitary mixing with very large statistics. By analyzing the NO$ν$A near detector data we find that the non-unitary mixing does not improve fits to the $ν_e$ or $ν_μ$ events over the standard unitary mixing. This leads to constraints on the non-unitary parameters: $α_{00}>0.911$, $|α_{10}|<0.020$ and $α_{11}>0.952$ at 90\% C.L. A combined analysis with the near and far detector data does not change these constraints significantly.

hep-ph↗

arXiv2022

A review of the tension between the T2K and NO$ν$A appearance data and hints to new physics

In this article, we review the status of the tension between the long-baseline accelerator neutrino experiments T2K and NO$ν$A. The tension arises mostly due to the mismatch in the appearance data of the two experiments. We explain how this tension arises based on $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ oscillation probabilities. We define the reference point of vacuum oscillation, maximal $θ_{23}$ and $δ_{CP}=0$ and compute the $ν_e/\barν_e$ appearance events for each experiment. We then study the effects of deviating the unknown parameters from the reference point and the compatibility of any given set of values of unknown parameters with the data from T2K and NO$ν$A. T2K observes a large excess in the $ν_e$ appearance event sample compared to the expected $ν_e$ events at the reference point, whereas \nova observes a moderate excess. The large excess in T2K dictates that $δ_{CP}$ be anchored at $-90^\circ$ and that $θ_{23}>π/4$ with a preference for normal hierarchy. The moderate excess at NO$ν$A leads to two degenerate solutions: A) NH, $0<δ_{CP}<180^\circ$, and $θ_{23}>π/4$; B) IH, $-180^\circ<δ_{CP}<0$, and $θ_{23}>π/4$. This is the main cause of the tension between the two experiments. We have reviewed the status of three beyond standard model (BSM) physics scenarios, (a) non-unitary mixing, (b) Lorentz invariance violation and (c) non-standard neutrino interactions, to resolve the tension.

hep-ph↗

arXiv2022

Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events

Blazars constitute the vast majority of extragalactic $γ$-ray sources. They can also contribute a sizable fraction of the diffuse astrophysical neutrinos detected by IceCube. In the past few years, the real-time alert system of IceCube has led to multiwavelength follow-up of very high-energy neutrino events of plausible astrophysical origin. Spatial and temporal coincidences of these neutrino events with the high-activity state of $γ$-ray blazars can provide a unique opportunity to decipher cosmic-ray interactions in the relativistic jets. Assuming that blazars accelerate cosmic rays up to ultrahigh energies ($E>10^{17}$ eV), we calculate the "guaranteed" contribution to the line-of-sight cosmogenic $γ$-ray and neutrino fluxes from four blazars associated with IceCube neutrino events. Detection of these fluxes by upcoming $γ$-ray imaging telescopes like CTA and/or by planned neutrino detectors like IceCube-Gen2 may lead to the first direct signature(s) of ultrahigh-energy cosmic-ray (UHECR) sources. We find that detection of the cosmogenic neutrino fluxes from the blazars TXS~0506+056, PKS~1502+106 and GB6~J1040+0617 would require UHECR luminosity $\gtrsim 10$ times the inferred neutrino luminosity from the associated IceCube events. Blazars TXS~0506+056, 3HSP~J095507.9+355101 and GB6~J1040+0617 can be detected by CTA if the UHECR luminosity is $\gtrsim 10$ times the neutrino luminosity inferred from the associated IceCube events. Given their relatively low redshifts and hence total energetics, TXS~0506+056 and 3HSP~J095507.9+355101 should be the prime targets for upcoming large neutrino and $γ$-ray telescopes.

astro-ph.HE↗

arXiv2021

Searching for non-unitary neutrino oscillations in the present T2K and NO$ν$A data

The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy isosinglets, the effective $3\times 3$ mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and \nova data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NO$ν$A data slightly (at $\sim 1\, σ$ C.L.) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the \nova best-fit point in the $\sin^2θ_{23}-δ_{CP}$ plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NO$ν$A and T2K 2019 data prefers the non-unitary mixing at $1\, σ$ C.L.. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NO$ν$A and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at $1\, σ$ C.L. The combined analysis preferes non-unitarity at $2\, σ$ C.L. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.

hep-ph↗

arXiv2021

Modelling synchrotron and synchrotron self-Compton emission of gamma-ray burst afterglows from radio to very-high energies

Synchrotron radiation from a decelerating blastwave is a widely accepted model of radio to X-ray afterglow emission from gamma-ray bursts (GRBs). GeV gamma-ray emission detected by the Fermi Large Area Telescope (LAT) and the duration of which extends beyond the prompt gamma-ray emission phase, is also compatible with broad features of afterglow emission. We revisit the synchrotron self-Compton (SSC) emission model from a decelerating blastwave to fit multiwavelength data from three bright GRBs, namely GRB~190114C, GRB~130427A and GRB~090510. We constrain the afterglow model parameters using the simultaneous fit of the spectral energy distributions at different times and light curves at different frequencies for these bursts. We find that a constant density interstellar medium is favored for the short GRB~090510, while a wind-type environment is favored for the long GRB~130427A and GRB~190114C. The sub-TeV component in GRB~190114C detected by MAGIC is the SSC emission in our modelling. Furthermore we find that the SSC emission in the Thomson regime is adequate to fit the spectra and light curves of GRB~190114C. For the other two GRBs, lacking sub-TeV detection, the SSC emissions are also modeled in the Thomson regime. For the model parameters we have used, the $γγ$ attenuation in the blastwave is negligible in the sub-TeV range compared to the redshift-dependent $γγ$ attenuation in the extragalactic background light.

astro-ph.HE↗