arXiv subjects

Arnon Dar

Publications and source records attributed to Arnon Dar.

At least 19 recordsLinked to original sources

arXiv2023

Solution To The Cosmic Rays Puzzle ?

Recent observations provide compelling evidence that the bulk of the high energy cosmic rays (CRs) and gamma-ray bursts (GRBs) are co-produced by highly relativistic jets of plasmoids of stellar matter. These jets are launched by fall back matter on newly born neutron stars and stellar black holes in core collapse of stripped envelope massive stars with or without an associated supernova. The electrons in the plasmoids produce GRB pulses mainly by inverse Compton scattering of photons on their path, while magnetic reflection of the charged particles produces the high energy cosmic rays.

astro-ph.HE↗

arXiv2022

The Maximum Isotropic Equivalent Energy Of Gamma Ray Bursts

The canonball model, which unifies cosmic ray bursts (CRBs) and gamma ray bursts (GRBs), is used to predict the maximum isotropic equivalent gamma ray energy release in a GRB. The predicted maximum is based on the observed knee around 1 TeV in the energy spectrum of Galactic cosmic ray electrons, and on the Amati correlation in GRBs. Both were predicted by the cannonball model of CRBs and GRBs before their empirical discoveries. The predicted maximum agrees well with that concluded from up to date GRB observations.

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arXiv2022

Critical Tests of Leading Gamma Ray Burst Theories II

It has been observationally established that supernovae (SNe) of Type Ic produce long duration gamma ray bursts (GRBs) and that neutron star mergers generate short hard GRBs. SN-Less GRBs presumably originate in a phase transition of a neutron star in a high mass X-ray binary. How these phenomena actually generate GRBs is debated. The fireball and cannonball models of GRBs and their afterglows have been widely confronted with the huge observational data, with their defenders claiming success. The claims, however, may reflect multiple choices and the use of many adjustable parameters, rather than the validity of the models. Only a confrontation of key falsifiable predictions of the models with solid observational data can test their validity. Such critical tests are reviewed in this report.

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arXiv2021

Universal Peaks Ratio In The Spectral Energy Density Of Double Hump Blazars, Gamma Ray Bursts, And Microquasars

The peak frequencies of the two broad humps evident in the spectral energy density of blazars (SED) are time dependent and vary a lot between different blazars. However, their ratio in most blazars, appears to be almost universal and equal to $m_e c^2/4(1+z) ε_p$ to a good approximation, where $m_e$ is the electron mass, $ε_p$ is the peak energy of the cosmic microwave background radiation, and $z$ is the redshift of the blazar. We discuss a possible origin of such a universal ratio in blazars and gamma ray bursts (GRBs). We point out a possible connection between the knee in the energy spectrum of cosmic ray electrons and the maximal peak energies of the two broad humps in the SED of high-energy peaked blazars.

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arXiv2020

Are Fast Radio Bursts Produced By Large Glitches Of Anomalous X-ray Pulsars?

Star quakes and internal phase transitions within anomalous x-ray pulsars (AXPs) and soft $γ$-ray repeaters (SGRs) can produce mini contractions and pulsar glitches. Shocks break out from their surface following such contractions produce thermal x/$γ$-ray bursts. Highly relativistic dipolar $e^+e^-$ bunches launched from the pulsar polar caps emit fast radio bursts (FRBs) of narrowly beamed coherent curvature radiation, visible if they point in the direction of Earth. Although these surface x/$γ$-ray bursts are isotropic and are many orders of magnitude more energetic than the FRBs, they are detectable by the current all sky x-ray and $γ$-ray monitors only from our galaxy and very nearby galaxies.

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arXiv2019

Fast Extragalactic X-ray Transients From Binary Neutron Star Mergers

The observed light curves and other properties of the two extragalactic fast x-ray transients, CDF-S XT1 and CDF-S XT2, which were discovered recently in archival data of the Chandra Deep Field-South (CDF-S) observations, indicate that they belong to two different populations of X-ray transients. XT1 seems to be an x-ray flash (XRF), i.e., a narrowly beamed long duration gamma ray burst viewed from far off-axis while XT2 seems to be a nebular emission powered by a newly born millisecond pulsar in a neutron stars binary merger.

astro-ph.HE↗

arXiv2019

On The Missing Counterparts Of LIGO-Virgo Binary Merger Events

Despite world-wide ground, underground, and space based observations in search of anticipated electromagnetic and perhaps neutrino counterparts to the 29 compact binary merger events, which have been detected by the upgraded LIGO-Virgo gravitational wave detectors in the first half year of their observation period O3, no such counterparts were found. Although such a situation could be due to a poor localization of nearby merger events and/or a complex background of short extragalactic transients, it could be intrinsic. We show that, indeed, it is expected in the cannonball model of gamma ray bursts and their afterglows.

astro-ph.HE↗

arXiv2019

Fast Extragalactic X-ray Transients From Gamma Ray Bursts Viewed Far Off Axis

The observed lightcurves and estimated sky rate of fast extragalactic x-ray transients (XRTs) discovered in archival Chandra data indicate that they belong to two distinct XRT populations. The first population of relatively short duration pulses, which typically last less than few minutes seems to be pulses of x-ray flashes (XRFs), which are nearby long duration gamma ray bursts viewed from far off axis. The second population of much longer pulses, which typically last hours, seems to be the early time afterglows of short gamma ray bursts (SGRBs) which are beamed away from Earth, as was shown in a previous paper.

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arXiv2019

Universal Afterglow Of Supernova-Less Gamma Ray Bursts

The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born pulsar.

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arXiv2019

Critical Tests Of Leading Gamma Ray Burst Theories

Although it has been established observationally beyond doubt that broad-line stripped envelope supernovae (SNe) of type Ic produce long duration gamma ray bursts (GRBs), that neutron star mergers produce short hard GRBs (SHBs), and that phase transition of neutron stars in high mass X-ray binaries (HMXBs) may produce SN-Less GRBs, their production mechanism is still debated. The two leading theoretical models of GRBs and their afterglows, the fireball model and the cannonball model, have been widely confronted with the mounting observational data on GRBs and SHBs during the last two decades. Both have claimed success in reproducing the observational data, despite their complexity and diversity. This claimed success, however, may reflect multiple choices and the use of many free adjustable parameters, rather than the true validity of the models. Only confrontation of the key falsifiable predictions of the models with solid observational data can test their validity. Such critical tests are summarized in this report. Conclusions left to the reader.

astro-ph.HE↗

arXiv2018

The Smoking Guns Of Neutron Stars Mergers

The short hard gamma ray burst (SHB) 170817A that followed GW170817A, the first neutron stars merger (NSM) detected in gravitational waves (GWs), has shown beyond doubt that NSMs produce beamed SHBs. Its low luminosity and other properties that differ from those of ordinary SHBs were predicted by the cannonball model of gamma ray bursts. Low luminosity (LL) SHBs are mainly ordinary SHBs viewed far off-axis. They are produced mainly by nearby NSMs. Because of beaming, most of the NSMs, including those within the current horizon of Ligo-Virgo, produce SHBs most of which are invisible from Earth. But, their pulsar wind nebula powered by the spin down of the remnant neutron star produces an early-time isotropic afterglow with a universal temporal shape. This smoking gun of NSMs is detectable independent of whether the SHB was visible, or was invisible from Earth because of being beamed away.

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arXiv2018

The superluminal motion of the jet launched in GW170817, the Hubble constant, and critical tests of gamma ray bursts theory

The direction of the axis of the orbital motion of the merging binary neutron stars in the GW170817 event coincided with that of the apparent superluminal jet, which produced the short hard gamma ray burst (SHB) 170817A, if the local value of the Hubble constant is that provided by standard candle Type Ia supernovae, H_0=73.24 +/- 1.74 km/s Mpc. This value differs by 3 sigma from the cosmic value H_0=67.74 +/- 0.46 km/s Mpc obtained from the cosmic microwave background radiation by Planck assuming the standard Lambda-CDM cosmology. The measured superluminal motion of the jet also allows critical tests of the assumed production mechanism of SHBs in general and of SHB170817A in particular.

astro-ph.HE↗

arXiv2018

Cannonball model diagnosis of the short gamma ray burst 170817A

The rich and complex data obtained from multi-wavelength observations of SHB170817A, the short hard gamma ray burst (SHB) associated with GW170817 --the first neutron stars merger event detected in gravitational waves (GWs)-- are analyzed in the framework of the cannonball model of SHBs. In this model a highly relativistic jet is launched by fall back matter on the nascent neutron star (or black hole) into a surrounding glory (light from the surrounding wind nebula of the binary neutron stars) which was present already before the merger. The SHB was produced by inverse Compton scattering of glory photons by the jet, which was viewed far off-axis. The fading glory, which produced the initial UVOIR afterglow, was powered by a neutron star remnant. It was overtaken by a late time X-ray, UVOIR and radio afterglow produced by synchrotron radiation from the decelerating jet in the interstellar medium of the host galaxy. If the radio afterglow of SHB170817A was indeed produced by the jet, it should display a superluminal motion relative to the SHB location, still detectable in VLA and VLBI radio observations.

astro-ph.HE↗

arXiv2018

Origin Of The Far Off-Axis GRB171205A

We show that observed properties of the low luminosity GRB171205A and its afterglow, like those of most other low-luminosity (LL) gamma ray bursts (GRBs) associate with a supernova (SN), indicate that it is an ordinary SN-GRB, which was produced by inverse Compton scattering of glory light by a highly relativistic narrowly collimated jet ejected in a supernova explosion and viewed from a far off-axis angle. As such, VLA/VLBI follow-up radio observations of a superluminal displacement of its bright radio afterglow from its parent supernova, will be able to test clearly whether it is an ordinary SN-GRB viewed from far off-axis or it belongs to a distinct class of GRBs, which are different from ordinary GRBs, and cannot be explained by standard fireball models of GRBs as ordinary GRBs

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arXiv2017

The Smoking Guns Of Short Hard Gamma Ray Bursts

The X-ray afterglow of short hard bursts (SHBs) of gamma rays provides compelling evidence that SHBs are produced by highly relativistic jets launched in the birth of rotationally powered millisecond pulsars in merger of neutron stars and/or in mass accretion on neutron stars in low mass X-ray binaries. Gravitational wave detection of relatively nearby neutron star mergers by Ligo-Virgo, followed by far off-axis short GRBs or orphan afterglows of beamed away SHBs with an MSP-like light curve will verify beyond doubt the neutron star merger origin of SHBs.

astro-ph.HE↗

arXiv2017

On The Origin of Supernova-Less Long Gamma Ray Bursts

The fraction of long duration gamma ray bursts (GRBs) without an associated bright supernovae (SNe) at small redshifts $(z<0.15)$ is comparable to that of GRBs associated with SNe. We show, that their X-ray afterglow and the X-ray afterglow of most of the nearby $(z<1)$ GRBs without a confirmed association with SNe, are well reproduced by the launch of highly relativistic jets in the SN-less birth of millisecond pulsars in neutron star mergers or through phase transition of neutron stars to quark stars following mass accretion in compact binaries. Such a large fraction of GRBs with pulsar-like afterglow that extends to very large redshifts $(z>4)$, however, favors phase transition of neutron stars to quark stars in high mass X-ray binaries (HMXBs), rather than merger of neutron stars, as the origin of SN-less GRBs.

astro-ph.HE↗

arXiv2016

Hyperluminal Signatures in the Afterglows of Gamma-Ray Bursts 980425 and 030329

The late-time high-resolution X-ray and radio observations of GRB980425/SN1998bw, the closest known gamma ray burst (GRB) associated with a supernova (SN) explosion, may have actually resolved the hyperluminal source that produced the GRB and its afterglow. Its hyperluminal speed ~350c is consistent with that expected in the cannonball (CB) model of GRBs. The observed superluminal expansion of the late-time radio image of GRB030329/SN2003dh, the GRB with the brightest and longest followed up radio afterglow to date, is also consistent with that expected in the CB model of GRBs and extrapolates to an apparent early-time hyperluminal expansion.

astro-ph.HE↗

arXiv2016

Critical Test Of Gamma Ray Burst Theories

Very long and precise follow-up measurements of the X-ray afterglow of very intense gamma ray bursts (GRBs) allow a critical test of GRB theories. Here we show that the single power-law decay with time of the X-ray afterglow of GRB 130427A, the record long and most accurately measured X-ray afterglow of an intense GRB by the Swift, Chandra and XMM Newton space observatories, and of all other known intense GRBs, is that predicted by the cannonball (CB) model of GRBs from their measured spectral index, while it disagrees with that predicted by the widely accepted fireball (FB) models of GRBs.

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