arXiv subjects

M. T. Mirtorabi

Publications and source records attributed to M. T. Mirtorabi.

10 recordsLinked to original sources

arXiv2026

GRB 220101A: a most energetic $10^{54}$ erg long GRB triggered by two supernovae 3.5 seconds apart

GRB 220101A is a long GRB, with a total energy exceeding $10^{54}$ erg with a redshift $z = 4.61$ and one of the largest ever high-quality multi-wavelength observational coverage, from a large number of space-based and ground-based telescopes. We interpret this source in a doubly Binary driven peta nova (BdP-N) model. The progenitor is composed of a massive CO core of $\sim 10\,M_\odot$, highly magnetized with $B \sim 10^{6}$ G, associated to a neutron star (NS) and a white dwarf (WD) with orbital periods from minutes to hours. The large GRB luminosity is explained by a sequence of 7 episodes: episode 1 is triggered by a new kind of pair supernova (HB) which originates from the collapse of the strongly magnetized CO core. Accretion of the HB supernova ejecta (the ejecta) onto the white dwarf companion triggers after 3.5 sec the episode 2: the second supernova emitting neutrinos and creating a new neutron star ($ν$NS). The ejecta, interacting with the magnetosphere of the binary NS companion originate the episode 3: the Ultra relativistic Prompt Emission (UPE) emission by far the most energetic episode of this GRB, with the formation of a powerful jet normal to the plane of the GRB. Following the UPE energy loss, the accretion of the ejecta on the NS companion leads to the episode 4: the formation of a black hole (BH) of $2.3 \ M_\odot$ leading to the observed GeV afterglow emission. Further accretion of the ejecta spin up the $ν$NS to a period of $1.3$ ms which gives origin to the episode 5: the birth of a pulsar. The interaction of this milli-second pulsar with the remnants lead to the Episode 6: the synchrotron emission observed in the X-ray, optical and radio, The episode 7 is a 56.7 ms pulsar, as observed $10^{10}$ s after the first burst in the crab nebula.

astro-ph.HE↗

arXiv2026

Evidence for Two SNe Type Triggering GRB 220101A: a Pair SN and a Rotating Magnetized Core Collapse SN

The traditional interpretation of gamma ray bursts (GRBs) as originating from a single black hole has been extended by the Binary Driven Hypernova (BdHN) model, in which a GRB arises from a binary system composed of a carbon oxygen (CO) core and a neutron star (NS) companion. This framework successfully reproduces the six canonical emission episodes observed in GRBs. Recent observations of energetic events, such as GRB 220101 and GRB 240825, suggest a more powerful variant involving a rapidly rotating, strongly magnetized CO core in a binary system with an NS. In this scenario, the collapse and possible fission of the CO core lead to the formation of a highly magnetized, rapidly rotating newborn neutron star. A pair instability supernova (pair SN) is triggered when rotation and magnetic effects drive the core to instability, influencing its collapse dynamics. This process results in a millisecond neutron star that later evolves into a pulsar. Concurrently, accretion of supernova ejecta onto the NS companion can induce its collapse into a black hole, powering high energy emission. This framework introduces two distinct classes of supernovae: (i) pair instability supernovae leaving no compact remnant, and (ii) magnetized, rotating core collapses producing pulsars. The model further incorporates the role of magnetic field amplification and magnetohydrodynamic processes, including the generation of overcritical fields and electron positron pair production. This represents a significant departure from earlier non rotating models and aligns with modern pair SN scenarios. BdHNe are characterized by seven physical episodes; notably, in pair SN cases, the final episode is not powered by radioactive nickel decay but by pulsar formation. These modifications are described within a leading order analytical framework.

astro-ph.HE↗

arXiv2024

FNet II: Spectral Classification of Quasars, Galaxies, Stars, and broad absorption line (BAL) Quasars

In this work, we enhance the FNet, a 1-dimensional convolutional neural network (CNN) with a residual neural network (ResNet) architecture, to perform spectral classification of quasars, galaxies, stars, and broad absorption line (BAL)-quasars in the SDSS-IV catalog from DR17 of eBOSS. Leveraging its convolutional layers and the ResNet structure with different kernel sizes, FNet autonomously identifies various patterns within the entire sample of spectra. Since FNet does not require the intermediate step of identifying specific lines, a simple modification enabled our current network to classify all SDSS spectra. This modification involves changing the final output layer from a single value (redshift) to multiple values (probabilities of all classes), and accordingly adjusting the loss function from mean squared error (MSE) to cross-entropy. FNet achieves a completeness of 99.00\% $\pm$ 0.20 for galaxies, 98.50\% $\pm$ 0.30 for quasars, 99.00\% $\pm$ 0.18 for BAL-quasars, and 98.80\% $\pm$ 0.20 for stars. These results are comparable to those obtained using QuasarNET, a standard CNN employed in the SDSS routine, comprises convolutional layers without the ResNet structure with equal kernel sizes, and is utilized for redshift measurement and classification by identifying seven emission lines. QuasarNET, in order to overcome the problem of finding a CIV emission line with broad absorption which is slightly more challenging than that of detecting emission lines requires to add BAL CIV line to the list of lines that the network learns to identify. However, this procedure is not necessary in FNet as it learns the features through a self-learning procedure.

astro-ph.GA↗

arXiv2024

Ten Supernova-rise in Binary Driven Gamma-ray Bursts

The observation of a gamma-ray burst (GRB) associated with a supernova (SN) coincides remarkably with the energy output from a binary system comprising a very massive carbon-oxygen (CO) core and an associated binary neutron star (NS) by the Binary-Driven Hypernova (BdHN) model. The dragging effect in the late evolution of such systems leads to co-rotation, with binary periods on the order of minutes, resulting in a very fast rotating core and a binary NS companion at a distance of $\sim 10^5$ km. Such a fast-rotating CO core, stripped of its hydrogen and helium, undergoes gravitational collapse and, within a fraction of seconds, leads to a supernova (SN) and a newly born, fast-spinning neutron star ($ν$NS), we name the emergence of the SN and the $ν$NS as the SN-rise and $ν$NS-rise. Typically, the SN energies range from $10^{51}$ to $10^{53}$ erg. We address this issue by examining 10 cases of Type-I BdHNe, the most energetic ones, in which SN accretion onto the companion NS leads to the formation of a black hole (BH). In all ten cases, the energetics of the SN events are estimated, ranging between $0.18$ and $12 \times 10^{52}$ erg. Additionally, in all 8 sources at redshift $z$ closer than $4.61$, a clear thermal blackbody component has been identified, with temperatures between $6.2$ and $39.99$ keV, as a possible signature of pair-driven SN. The triggering of the X-ray afterglow induced by the $ν$NS-rise are identified in three cases at high redshift where early X-ray observations are achievable, benefits from the interplay of cosmological effects.

astro-ph.HE↗

arXiv2024

Probing electromagnetic-gravitational wave emission coincidence in type I binary-driven hypernova family of long GRBs at very-high redshift

The repointing time of the XRT instrument on the Neil Gehrels Swift Observatory satellite has posed challenges in observing and studying the early X-ray emissions within $\approx40$ s after a gamma-ray burst (GRB) trigger. To address this issue, we adopt a novel approach that capitalizes on the cosmological time dilation in GRBs with redshifts ranging from $3$ to $9$. Applying this strategy to Swift/XRT data, we investigate the earliest X-ray emissions of $368$ GRBs from the Swift catalog, including short and long GRBs. We compare the time delay between the GRB trigger and the initial Swift/XRT observation, measured in the GRB observer frame (OTD) and the cosmological rest-frame (RTD). This technique is here used in the analysis of GRB 090423 at $z=8.233$ (RTD $\sim8.2$ s), GRB 090429B at $z\approx9.4$ (RTD $\sim10.1$ s), and GRB 220101A at $z=4.61$ (RTD $\sim14.4$ s). The cosmological time dilation enables us to observe the very early X-ray afterglow emission in these three GRBs. We thus validate the observation of the collapse of the carbon-oxygen (CO) core and the coeval newborn neutron star ($ν$NS) formation triggering the GRB event in the binary-driven hypernova (BdHN) scenario. We also evidence the $ν$NS spin-up due to supernova ejecta fallback and its subsequent slowing down due to the X-optical-radio synchrotron afterglow emission. A brief gravitational wave signal may separate the two stages due to a fast-spinning $ν$NS triaxial-to-axisymmetric transition. We also analyze the long GRB redshift distribution for the different BdHN types and infer that BdHNe II and III may originate the NS binary progenitors of short GRBs.

astro-ph.HE↗

arXiv2022

Deep Learning in Searching the Spectroscopic Redshift of Quasars

Studying the cosmological sources at their cosmological rest-frames is crucial to track the cosmic history and properties of compact objects. In view of the increasing data volume of existing and upcoming telescopes/detectors, we here construct a 1--dimensional convolutional neural network (CNN) with a residual neural network (ResNet) structure to estimate the redshift of quasars in Sloan Digital Sky Survey IV (SDSS-IV) catalog from DR16 quasar-only (DR16Q) of eBOSS on a broad range of signal-to-noise ratios, named \code{FNet}. Owing to its $24$ convolutional layers and the ResNet structure with different kernel sizes of $500$, $200$ and $15$, FNet is able to discover the "\textit{local}" and "\textit{global}" patterns in the whole sample of spectra by a self-learning procedure. It reaches the accuracy of 97.0$\%$ for the velocity difference for redshift, $|Δν|< 6000~ \rm km/s$ and 98.0$\%$ for $|Δν|< 12000~ \rm km/s$. While \code{QuasarNET}, which is a standard CNN adopted in the SDSS routine and is constructed by 4 convolutional layers (no ResNet structure), with kernel sizes of $10$, to measure the redshift via identifying seven emission lines (\textit{local} patterns), fails in estimating redshift of $\sim 1.3\%$ of visually inspected quasars in DR16Q catalog, and it gives 97.8$\%$ for $|Δν|< 6000~ \rm km/s$ and 97.9$\%$ for $|Δν|< 12000~ \rm km/s$. Hence, FNet provides similar accuracy to \code{QuasarNET}, but it is applicable for a wider range of SDSS spectra, especially for those missing the clear emission lines exploited by \code{QuasarNET}. These properties of \code{FNet}, together with the fast predictive power of machine learning, allow \code{FNet} to be a more accurate alternative for the pipeline redshift estimator and can make it practical in the upcoming catalogs to reduce the number of spectra to visually inspect.

astro-ph.HE↗

arXiv2019

Red Giant evolution in Modified Gravity

In this paper, we study the chameleon profile in inhomogeneous density distributions and find that the fifth force in thin shell near the surface is weaker from what expected in homogeneous density distributions. Also, we check the validity of quasi-static approximation for the chameleon scalar field in the astrophysical time scales. We have investigated the rolling down behaviour of the scalar field on its effective potential inside a one solar mass red giant star by using MESA code. We have found that the scalar field is fast enough to follow the minimum of the potential. This adiabatic behaviour reduces the fifth force and extends the screened regions to lower densities where the field has smaller mass and was expected to be unscreened. As a consequence, the star evolution is similar to what expected from standard general relativity. In addition, considering the stability of star, an approximate constraint on the coupling constant $β$ is found.

gr-qc↗

arXiv2018

Linear Polarization Features in the Quiet-Sun Photosphere: Structure and Dynamics

We present detailed characteristics of linear polarization features (LPFs) in the quiet-Sun photosphere from high resolution observations obtained with Sunrise/IMaX. We explore differently treated data with various noise levels in linear polarization signals, from which structure and dynamics of the LPFs are studied. Physical properties of the detected LPFs are also obtained from the results of Stokes inversions. The number of LPFs, as well as their sizes and polarization signals, are found to be strongly dependent on the noise level, and on the spatial resolution. While the linear polarization with signal-to-noise ratio $\geq4.5$ covers about 26% of the entire area in the least noisy data in our study (with a noise level of $1.7\times10^{-4}$ in the unit of Stokes $I$ continuum), the detected (spatially resolved) LPFs cover about 10% of the area at any given time, with an occurrence rate on the order of $8\times10^{-3}$ s$^{-1}$ arcsec$^{-2}$. The LPFs were found to be short lived (in the range of $30-300$ s), relatively small structures (radii of $\approx0.1-1.5$ arcsec), highly inclined, posing hG fields, and move with an average horizontal speed of 1.2 km s$^{-1}$. The LPFs were observed (almost) equally on both upflow and downflow regions, with intensity contrast always larger than that of the the average quiet-Sun.

astro-ph.SR↗

arXiv2018

The Delta Scuti star 38 Eri from the ground and from space

We present and discuss the pulsational characteristics of the Delta Scuti star 38 Eri from photometric data obtained at two widely spaced epochs, partly from the ground (1998) and partly from space (MOST, 2011). We found 18 frequencies resolving the discrepancy among the previously published frequencies. Some of the frequencies appeared with different relative amplitudes at two epochs, however, we carried out investigation for amplitude variability for only the MOST data. Amplitude variability was found for one of three frequencies that satisfy the necessary frequency criteria for linear-combination or resonant-mode coupling. Checking the criteria of beating and resonant-mode coupling we excluded them as possible reason for amplitude variability. The two recently developed methods of rotational-splitting and sequence-search were applied to find regular spacings based only on frequencies. Doublets or incomplete multiplets with l=1, 2 and 3 were found in the rotational splitting search. In the sequence search method we identified four sequences. The averaged spacing, probably a combination of the large separation and the rotational frequency, is 1.724+/-0.092 d-1. Using the spacing and the scaling relation $\barρ= [0.0394, 0.0554]$ gcm$^{-3}$ was derived. The shift of the sequences proved to be the integer multiple of the rotational splitting spacing. Using the precise MOST frequencies and multi-colour photometry in a hybrid way, we identified four modes with l=1, two modes with l=2, two modes with l=3, and two modes as l=0 radial modes.

astro-ph.SR↗

arXiv2015

An Updated Wing TiO Sensitive Index for Classification of M-Type Stars

By careful searching of synthetic and observed spectra in a sample of cool giant and supergiant stars, we have updated the continuum band-passes of near-infrared Wing three filter system. This photometric system measures the strength of Titanium Oxide (TiO) absorption in Near-Infrared (NIR) at 719 nm. We show that new reference continuum band-passes are essentially free from molecular absorptions and the updated TiO-index defines the temperature variation in a sample of cool giants with less scatter. A TiO-index vs. effective temperature calibration is derived based on new continuum band-passes.

astro-ph.SR↗