The late jet in gamma-ray bursts and its interactions with a supernova ejecta and a cocoon (2009)
Shen, Rongfeng, Kumar, Pawan, Piran, Tsvi
Late X-ray flares observed in X-ray afterglows of gamma-ray bursts (GRBs) suggest late central engine activities at a few minuets to hours after the burst. A few unambiguously confirmed cases of...
Lorentz Factor Constraint from the very early external shock of the gamma-ray burst ejecta (2009)
While it is generally agreed that the emitting regions in Gamma-Ray Bursts (GRBs) move ultra relativistically towards the observer, different estimates of the initial Lorentz factors, $\Gamma_0$,...
Piran, Tsvi, Shaviv, Nir J., Nakar, Ehud
Recent measurements of the positron/electron ratio in the cosmic ray (CR) flux exhibits an apparent anomaly, whereby this ratio increases between 10 and 100 GeV. In contrast, this ratio should...
Gamma-ray burst light curves in the relativistic turbulence and relativistic subjet models (2009)
Lazar, Ayah, Nakar, Ehud, Piran, Tsvi
Randomly oriented relativistic emitters in a relativistically expanding shell provide an alternative to internal shocks as a mechanism for producing gamma-ray bursts' variable light curves with...
Observational limits on inverse Compton processes in gamma-ray bursts (2009)
Piran, Tsvi, Sari, Re'em, Zou, Yuan-Chuan
Inverse Compton (IC) scattering is one of two viable mechanisms that can produce prompt non-thermal soft gamma-ray emission in gamma-ray bursts. IC requires low-energy seed photons and a population...
Clues from the Prompt Emission of GRB 080319B (2009)
Zou, Yuan-Chuan, Piran, Tsvi, Sari, Re'em
The extremely bright optical flash that accompanied GRB 080319B suggested, at first glance, that the prompt γ-rays in this burst were produced by synchrotron self-Compton (SSC). We analyze here the...
In Situ Probes of the First Galaxies and Reionization: Gamma-ray Bursts (2009)
McQuinn, Matthew, Bloom, Joshua S., Grindlay, Jonathan, Band, David, Barthelmy, S. D., Berger, E., ...
The first structures in the Universe formed at z>7, at higher redshift than all currently known galaxies. Since GRBs are brighter than other cosmological sources at high redshift and exhibit simple...
Bloom, Joshua S., Holz, Daniel E., Hughes, Scott A., Menou, Kristen, Adams, Allan, Anderson, Scott F., ...
It is widely expected that the coming decade will witness the first direct detection of gravitational waves (GWs). The ground-based LIGO and Virgo GW observatories are being upgraded to advanced...
Shaviv, Nir J., Nakar, Ehud, Piran, Tsvi
Recent measurements of the positron/electron ratio in the cosmic ray (CR) flux exhibits an apparent anomaly, whereby this ratio increases with energy between 10 and 100 GeV. In contrast, this ratio...
GRB Light Curves in the Relativistic Turbulence Model (2009)
Lazar, Ayah, Nakar, Ehud, Piran, Tsvi
Randomly oriented relativistic emitters in a relativistically expanding shell provides an alternative to internal shocks as a mechanism for producing GRBs' variable light curves with efficient...
Zou, Yuan-Chuan, Fan, Yi-Zhong, Piran, Tsvi
We calculate the high energy (sub-GeV to TeV) prompt and afterglow emission of GRB 080319B that was distinguished by a naked-eye optical flash and by an unusual strong early X-ray afterglow. There...
We examine what the absorbed spectra of extra-galactic TeV gamma-ray sources, such as blazars, would look like in the presence of Lorentz invariance violation (LIV). Pair-production with the...
Observational Limits on Inverse Compton Processes in GRBs (2008)
Piran, Tsvi, Sari, Re'em, Zou, Yuan-Chuan
Inverse Compton (IC) scattering is one of two viable mechanisms that can produce the prompt gamma-ray emission in Gamma-Ray Bursts. IC requires low energy seed photons and a population of...
Mazzali, Paolo A., Valenti, Stefano, Della Valle, Massimo, Chincarini, Guido, Sauer, Daniel N., Benetti, Stefano, ...
The only supernovae (SNe) to have shown early gamma-ray or X-ray emission thus far are overenergetic, broad-lined Type Ic SNe (Hypernovae - HNe). Recently, SN 2008D shows several novel features: (i)...
High energy gamma-ray emission from Gamma-Ray Bursts -- before GLAST (2008)
Gamma-ray bursts (GRBs) are short and intense emission of soft gamma-rays, which have fascinated astronomers and astrophysicists since their unexpected discovery in 1960s. The X-ray/optical/radio...
Bohdan's Impact on Our Understanding of Gamma-ray Bursts (2008)
Bohdan Paczy'nski was one of the pioneers of the cosmological GRB model. His ideas on how GRBs operate and what are their progenitors have dominated the field of GRBs in the hectic nineties during...
γ-Ray Bursts and Neutron Star Mergers (2008)
fl-ray bursts have baffled theorists ever since their accidental discovery at the sixties. We suggest that these bursts originate in merger of neutron star binaries, taking place at cosmological...
Mazzali, Paolo A., Valenti, Stefano, Della Valle, Massimo, Chincarini, Guido, Sauer, Daniel N., Benetti, Stefano, ...
Central engine afterglow of Gamma-ray Bursts (2007)
Fan, Yi-Zhong, Piran, Tsvi, Wei, Da-Ming
Before 2004, nearly all GRB afterglow data could be understood in the context of the external shocks model. This situation has changed in the past two years, when it became clear that some afterglow...
Lorentz-violation-induced arrival delays of cosmological particles (2007)
We point out that previous studies of possible Lorentz-violating effects in astronomical time-of-flight data did not take into account the entire implications of the universe's cosmological...
Towards Understanding Gamma-Ray Bursts (2007)
fl-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the sixties. The BATSE detector on COMPTON-GRO satellite has been detecting GRBs for the last four years at a rate of...
We study analytically the initial value problem for a self-interacting (massive) scalar-field on a Reissner-Nordstrom spacetime. Following the no-hair theorem we examine the dynamical physical...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - II (2007)
We study analytically the initial value problem for a charged massless scalarfield on a Reissner-Nordstrom spacetime. Using the technique of spectral decomposition we extend recent results on this...
We study the nonlinear gravitational collapse of a charged massless scalarfield. We confirm the existence of oscillatory inverse power-law tails along future timelike infinity, future null infinity...
Dipole Anisotropy from an Entropy Gradient (2007)
It is generally accepted that the observed CMBR dipole arises from the motion of the local group relative to the CMBR frame. An alternative interpretation is that the dipole results from an...
Spherical Collapse of a Mass-Less Scalar Field With Semi-Classical Corrections (2007)
We investigate numerically spherically symmetric collapse of a scalar field in the semi-classical approximation. We first verify that our code reproduces the critical phenomena (the Choptuik effect)...
We conjecture (analytically) and demonstrate (numerically) the existence of a fine-structure above the power-law behavior of the mass of black-holes that form in gravitational collapse of spherical...
Critical Behaviour and Universality in Gravitational Collapse of a Charged Scalar Field (2007)
We summarize results from a study of spherically symmetric collapse of a charged (complex) massless scalar-field [1]. We present an analytic argument which conjecture the generalization of the...
A Canonical High Energy Afterglow Emission Light Curve? (2007)
We present self consistent calculations of Synchrotron self Compton (SSC) radiation that takes place within the afterglow blast wave and External inverse Compton (EIC) radiation that takes place when...
High Energy Afterglow from Gamma-ray Bursts (2007)
Fan, Yi-Zhong, Piran, Tsvi, Narayan, Ramesh, Wei, Da-Ming
We calculate the very high energy (sub-GeV to TeV) inverse Compton emission of GRB afterglows. We argue that this emission provides a powerful test of the currently accepted afterglow model. We focus...
Do long-duration GRBs follow star formation? (2007)
We compare the luminosity function and rate inferred from the BATSE long bursts peak flux distribution with those inferred from the Swift peak flux distribution. We find that both the BATSE and the...
GRBs Neutrinos as a Tool to Explore Quantum Gravity induced Lorentz Violation (2006)
Lorentz Invariance Violation (LIV) arises in various quantum-gravity theories. As the typical energy for quantum gravity is the Planck mass, $M_{pl}$, LIV will, most likely, be manifested at very...
Embedding the Reissner-Nordstrom spacetime in Euclidean and Minkowski spaces (2006)
We examine embedding diagrams of hypersurfaces in the Reissner-Nordstrom black hole spacetime. These embedding diagrams serve as useful tools to visualize the geometry of the hypersurfaces and of the...
The Interpretation and Implication of the Afterglow of GRB 060218 (2006)
Fan, Yi-Zhong, Piran, Tsvi, Xu, Dong
The nearby GRB 060216/SN 2006aj was an extremely long, weak and very soft GRB. It was peculiar in many aspects. We show here that the X-ray, ultraviolet/optical and radio afterglow of GRB 060218 have...
Shortly after the discovery of the binary system PSR J0737-3039 we predicted that it has a small proper motion and suggested that this implies that the progenitor mass of the younger pulsar (B) must...
The rate and luminosity function of Short GRBs (2006)
We compare the luminosity function and rate inferred from the BATSE short hard bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE II....
Sub-GeV flashes in $\gamma-$ray burst afterglows as probes of underlying bright UV flares (2006)
Bright optical and X-ray flares have been observed in many Gamma-ray Burst (GRB) afterglows. These flares have been attributed to late activity of the central engine. In most cases the peak energy is...
GRB 051221A and Tests of Lorentz Symmetry (2006)
Martinez, Maria Rodriguez, Piran, Tsvi, Oren, Yonatan
Various approaches to quantum gravity suggest the possibility of violation of Lorentz symmetry at very high energies. In these cases we expect a modification at low energies of the dispersion...
Constraining Lorentz violations with Gamma Ray Bursts (2006)
Martinez, Maria Rodriguez, Piran, Tsvi
Gamma ray bursts are excellent candidates to constrain physical models which break Lorentz symmetry. We consider deformed dispersion relations which break the boost invariance and lead to an...
GRB efficiency and Possible Physical Processes Shaping the Early Afterglow (2006)
The discovery by Swift that a good fraction of Gamma Ray Bursts (GRBs) have a slowly decaying X-ray afterglow phase led to the suggestion that energy injection into the blast wave takes place several...
Implications of the Early X-Ray Afterglow Light Curves of Swift GRBs (2006)
Granot, Jonathan, Konigl, Arieh, Piran, Tsvi
According to current models, gamma-ray bursts (GRBs) are produced when the energy carried by a relativistic outflow is dissipated and converted into radiation. The efficiency of this process,...
The BATSE-Swift luminosity and redshift distributions of short-duration GRBs (2005)
We compare the luminosity function and rate inferred from the BATSE short hard bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE II....
The Origin of the Binary Pulsar J0737-3039 (2005)
It is generally accepted that neutron stars form in core collapse events that are accompanied by a supernovae (types II or Ib or Ic). Typical progenitors are, therefore, larger than $\sim 2.1 \Ms$....
The Evidence of Absence: Galaxy Voids in the Excursion Set Formalism (2005)
Furlanetto, Steven, Piran, Tsvi
We present an analytic model for the sizes of voids in the galaxy distribution. Peebles and others have recently emphasized the possibility that the observed characteristics of voids may point to a...
In Nakar & Piran (2004) we have shown that a large fraction of BATSE bursts cannot satisfy the Amati relation between the isotropic energy - peak energy of GRBs. Our results have been corroborated by...
Neutrino-Dominated Accretion and Supernovae (2005)
Kohri, Kazunori, Narayan, Ramesh, Piran, Tsvi
We suggest that part of the infalling material during the core-collapse of a massive star goes into orbit around the compact core to form a hot, dense, centrifugally-supported accretion disk whose...
The Beaming Factor and Other Open Questions In GRB Jets (2005)
I review several central open questions concerning GRB Jets. 1) I discuss a new estimates of the beaming correction for the rate of GRBs ~ 75 +- 20. 2) I discuss the universal structured jet (USJ)...
Early GRB afterglow from a reverse shock as a tracer of the prompt gamma-ray light curve (2005)
We discuss the optical and radio early afterglow emission of the reverse shock that crosses a baryonic ejecta as it interacts with the external interstellar medium (ISM). We show that the peak of the...
The distances of short-hard GRBs and the SGR connection (2005)
Nakar, Ehud, Gal-Yam, Avishay, Piran, Tsvi, Fox, Derek B.
We present a search for nearby (D
Pure and loaded fireballs in SGR giant flares (2005)
Nakar, Ehud, Piran, Tsvi, Sari, Re'em
On December 27, 2004, a giant flare from SGR 1806$-$20 was detected on earth. Its thermal spectrum and temperature suggest that the flare resulted from an energy release of about $10^{47}$ erg/sec...
Outliers to the Isotropic Energy - Peak Energy Relation in GRBs (2004)
The peak energy - isotropic energy (EpEi) relation is among the most intriguing recent discoveries concerning GRBs. It can have numerous implications on our understanding of the emission mechanism of...
The Origin of the Binary Pulsar J0737-3039B (2004)
Evolutionary scenarios suggest that the progenitor of the new binary pulsar J0737-3039B \cite{ref1,ref2} was a He-star with $M > 2.1-2.3~\Ms$ \cite{ref3,ref4}. We show that this case implies that the...
Gamma Ray Bursts as Probes of Quantum Gravity (2004)
Gamma ray bursts (GRBs) are short and intense pulses of $\gamma$-rays arriving from random directions in the sky. Several years ago Amelino-Camelia et al. pointed out that a comparison of time of...
The Luminosity and Redshift Distributions of Short-Duration GRB (2004)
Using the BATSE peak flux distribution we rederive the short GRBs luminosity function and compare it with the observed redshift distribution of long bursts. We show that both distributions are...
The apparent size of GRB afterglows as a test of the Fireball model (2004)
Oren, Yonatan, Nakar, Ehud, Piran, Tsvi
Taylor et al. (2004) reported recently on the first direct measurement of the apparent size of a GRB afterglow. Here we confront these observations with the predictions of the fireball model. We use...
The Physics of Gamma-Ray Bursts (2004)
Gamma-Ray Bursts (GRBs), short and intense pulses of low energy gamma-rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last...
GRB 990123 revisited: Further Evidence for a Reverse Shock (2004)
Recently we have presented a new theoretical analysis of the reverse shock emission. We use this analysis here to revisit GRB 990123. We find new and compelling evidences that the optical flash and...
Early Afterglow Emission from a Reverse Shock as a Diagnostic Tool for GRB Outflows (2004)
The Gamma-Ray burst (GRB) - afterglow transition is one of the most interesting and least studied GRB phases. During this phase the relativistic ejecta begins interacting with the surrounding matter....
On the Low Progenitor Mass of the Binary Pulsar J0737-3039B (2004)
The observed orbital parameters of the recently discovered binary pulsar J0737-3039 are used to constrain the progenitor system. In particular, the small observed eccentricity and the small inferred...
Some Recent Peculiarities of the Early Afterglow (2003)
Piran, Tsvi, Nakar, Ehud, Granot, Jonathan
We consider some recent developments in GRB/afterglow observations: (i) the appearance of a very hard prompt component in GRB 941017, and (ii) variability in the early afterglow light curves of GRB...
Caged Black Holes: Black Holes in Compactified Spacetimes II - 5d Numerical Implementation (2003)
Sorkin, Evgeny, Kol, Barak, Piran, Tsvi
We describe the first convergent numerical method to determine static black hole solutions (with S^3 horizon) in 5d compactified spacetime. We obtain a family of solutions parametrized by the ratio...
Caged Black Holes: Black Holes in Compactified Spacetimes I -- Theory (2003)
Kol, Barak, Sorkin, Evgeny, Piran, Tsvi
In backgrounds with compact dimensions there may exist several phases of black objects including the black-hole and the black-string. The phase transition between them raises puzzles and touches...
Implications of the $\gamma$-ray Polarization of GRB 021206 (2003)
Nakar, Ehud, Piran, Tsvi, Waxman, Eli
We compare two possible scenarios for the producing of high level of polarization within the prompt emission of a GRB: synchrotron emission from a relativistic jet with a uniform (in space and time)...
Implications of Spacetime Quantization for the Bahcall-Waxman Neutrino Bound (2003)
Amelino-Camelia, Giovanni, Arzano, Michele, NG, Y. Jack, Piran, Tsvi, Van Dam, Hendrik
There is growing interest in quantum-spacetime models in which small departures from Lorentz symmetry are governed by the Planck scale. In particular, several studies have considered the possibility...
On the Collapse of Charged Scalar Fields (2003)
We explore numerically the evolution of a collapsing spherical shell of charged, massless scalar field. We obtain an external \RN space-time, and an inner space-time that is bounded by a singularity...
The Variable Light Curve of GRB 030329: The Case for Refreshed Shocks (2003)
Granot, Jonathan, Nakar, Ehud, Piran, Tsvi
GRB 030329 is unique in many aspects. It has a very low redshift for a GRB, $z=0.1685$, and is therefore very bright and easy to monitor, making it the most well studied afterglow to date. It shows a...
Modeling Fluctuations in the GRB-Afterglow Light Curves (2003)
The fluctuations observed in the light curves of some GRB-afterglows (such as GRB 021004) provide a useful tool to probe the circum-burst density profile and to probe the variations in the energy of...
The Jet Angular Profile and the Afterglow Light Curves (2003)
Granot, Jonathan, Kumar, Pawan, Piran, Tsvi
We investigate how the angular structure of GRB jets effects the afterglow light curves at different viewing angles, $\theta_{v}$, from the jet symmetry axis. A numerical hydrodynamical modeling for...
Initial Data for Black Holes and Black Strings in 5d (2002)
We explore time-symmetric hypersurfaces containing apparent horizons of black objects in a 5d spacetime with one coordinate compactified on a circle. We find a phase transition within the family of...
Variability in GRB Afterglows and GRB 021004 (2002)
Nakar, Ehud, Piran, Tsvi, Granot, Jonathan
We present general analytic expressions for GRB afterglow light curves arising from a variable external density profile and/or a variable energy in the blast wave. The former could arise from a...
On-Axis Orphan Afterglows (2002)
In many GRB inner engine models the highly relativistic GRB jets are engulfed by slower moving matter. This could result in different beaming for the prompt $\gamma$-ray emission and for the lower...
Gamma-Ray Bursts - a Primer For Relativists (2002)
Gamma-Ray Bursts (GRBs) - short bursts of 100-1MeV photons arriving from random directions in the sky are probably the most relativistic objects discovered so far. Still, somehow they did not attract...
The Detectability of Orphan Afterglows (2002)
Nakar, Ehud, Piran, Tsvi, Granot, Jonathan
The realization that GRBs release a constant amount of energy implies that the post jet-break afterglow evolution would be largely universal. For a given redshift all afterglows should be detected up...
The realization that GRBs are narrowly beamed implied that the actual rate of GRBs is much larger than the observed one. There are 500 unobserved GRBs for each observed one. The lack of a clear...
How to Construct a GRB Engine? (2002)
According to the fireball model GRBs are produced when a relativistic flow is dissipated by shocks. The questions how does a GRB's "inner engine" accelerates and collimated the relativistic flow is...
The Energy of Gamma-Ray Bursts (2001)
The energy of a Gamma-Ray Burst is one of the most interesting factors that can help determining the origin of these mysterious explosions. After the discovery that GRBs are cosmological it was...
The Energy Distribution of Long Duration GRBS (2001)
Piran, Tsvi, Kumar, Pawan, Panaitescu, Alin, Piro, Luigi
The energy release in gamma-ray bursts is one of the most interesting clues on the nature of their "inner engines". We show here that the total energy release in GRBs varies by less than one order of...
Theory of GRB Afterglow (2001)
The most interesting current open question in the theory of GRB afterglow is the propagation of jetted afterglows during the sideway expansion phase. Recent numerical simulations show hydrodynamic...
Gamma-Ray Bursts - When Theory Meets Observations (2001)
Gamma-Ray Bursts (GRBs) are the brightest objects observed. They are also the most relativistic objects known so far. GRBs occur when an ultrarelativisitic ejecta is slowed down by internal shocks...
Formation and Evaporation of Charged Black Holes (2001)
We investigate the dynamical formation and evaporation of a spherically symmetric charged black hole. We study the self-consistent one loop order semiclassical back-reaction problem. To this end the...
Accretion Models of Gamma-Ray Bursts (2001)
Narayan, Ramesh, Piran, Tsvi, Kumar, Pawan
Many models of gamma-ray bursts (GRBs) involve accretion onto a compact object, usually a black hole, at a mass accretion rate of order a fraction of a solar mass per second. If the accretion disk is...
Energetics of Gamma Ray Bursts (2001)
Jimenez, Raul, Band, David, Piran, Tsvi
We determine the distribution of total energy emitted by gamma-ray bursts for bursts with fluences and distance information. Our core sample consists of eight bursts with BATSE spectra and...
Time Scales in Long GRBs (2001)
We analyze a sample of bright long bursts and find that the pulses duration have a lognormal distribution while the intervals between pulses have an excess of long intervals (relative to lognormal...
Temporal properties of short GRBs (2001)
We analyze a sample of bright short bursts from the BATSE 4B-catalog and find that many short bursts are highly variable ($\delta t_{min}/T\ll 1$, where $\delta t_{min}$ is the shortest pulse...
Light Curves from an Expanding Relativistic Jet (2001)
Granot, Jonathan, Miller, Mark, Piran, Tsvi, Suen, Wai-Mo, Hughes, Philip A.
We perform fully relativistic hydrodynamic simulations of the deceleration and lateral expansion of a relativistic jet as it expands into an ambient medium. The hydrodynamic calculations use a 2D...
Gravitational Radiation from Gamma-Ray Bursts (2001)
Gamma Ray Bursts (GRBs) are the most relativistic objects known so far, involving, on one hand an ultra-relativistic motion with a Lorentz factor $\Gamma > 100$ and on the other hand an accreting...
Remnants from Gamma-Ray Bursts (2000)
We model the intermediate time evolution of a "jetted" gamma-ray burst by two blobs of matter colliding with the interstellar medium. We follow the hydrodynamical evolution of this system numerically...
Cosmic Censorship: The Role of Quantum Gravity (2000)
The cosmic censorship hypothesis introduced by Penrose thirty years ago is still one of the most important open questions in {\it classical} general relativity. In this essay we put forward the idea...
Deducing the Source of Ultrahigh Energy Cosmic Rays (2000)
Farrar, Glennys R., Piran, Tsvi
The apparent lack of suitable astrophysical sources for cosmic rays with E > 10^{19.7} eV (UHECRs) is the "GZK Paradox". We argue that whatever mechanism produces them must also account for events...
Neutron Stars with a Stable, Light Supersymmetric Baryon (2000)
Balberg, Shmuel, Farrar, Glennys R., Piran, Tsvi
If a light gluino exists, the lightest gluino-containing baryon, the \OSO, is a possible candidate for self-interacting dark matter. In this scenario, the simplest explanation for the observed ratio...
Effects of Pair Creation on Charged Gravitational Collapse (2000)
We investigate the effects of pair creation on the internal geometry of a black hole, which forms during the gravitational collapse of a charged massless scalar field. Classically, strong central...
A Model of Void Formation (2000)
Friedmann, Yasmin, Piran, Tsvi
We introduce a simple model for the formation of voids. In this model the underdensity of galaxies in voids is the product of two factors. The first arises from a gravitational expansion of the...
The synchrotron spectrum of fast cooling electrons revisited (2000)
Granot, Jonathan, Piran, Tsvi, Sari, Re'em
We discuss the spectrum arising from synchrotron emission by fast cooling electrons when fresh electrons are continually accelerated by a strong blast wave into a power law distribution of energies....
Amelino-Camelia, Giovanni, Piran, Tsvi
One of the most puzzling current experimental physics paradoxes is the arrival on Earth of Ultra High Energy Cosmic Rays with energies above the GZK threshold. The recent observation of 20TeV photons...
COBE- and Cluster-Normalized CDM Simulations (2000)
Piran, Tsvi, El-Ad, Hagai, Martel, Hugo, Lecar, Myron
We introduce a set of four new publicly available N-body simulations, the most recent additions to the Texas P^3M Database. Our models probe the less studied parameter space region of moderate volume...
Cosmic rays and TeV photons as probes of quantum properties of space-time (2000)
Amelino-Camelia, Giovanni, Piran, Tsvi
It has been recently observed that small violations of Lorentz invariance, of a type which may arise in quantum gravity, could explain both the observations of cosmic rays above the GZK cutoff and...
The Synchrotron Spectrum of Fast Cooling Electrons Revisited (2000)
Granot, Jonathan, Piran, Tsvi, Sari, Re'em
We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power law distribution of...
Granot, Jonathan, Miller, Mark, Piran, Tsvi, Suen, Wai-Mo
We describe fully relativistic three dimensional calculations of the slowing down and spreading of a relativistic jet by an external medium like the ISM. We calculate the synchrotron spectra and...
Energetics and Luminosity Function of Gamma-ray Bursts (1999)
Gamma-ray bursts are believed to be some catastrophic event in which material is ejected at a relativistic velocity, and internal collisions within this ejecta produce the observed $\gamma$-ray...
A case devoid of bias: ORS voids vs. IRAS voids (1999)
We present a comparison between the voids in two nearly all sky redshift surveys: the ORS and the IRAS 1.2 Jy. While the galaxies in these surveys are selected differently and their populations are...
Gamma-ray Bursts - A Puzzle Being Resolved (1999)
For a few seconds a gamma-ray burst (GRB) becomes the brightest object in the Universe, over-shining the rest of the Universe combined! Clearly this reflects extreme conditions that are fascinating...
GZK Violation - a Tempest in a (Magnetic) Teapot? (1999)
Farrar, Glennys R., Piran, Tsvi
The apparent lack of suitable astrophysical sources for the observed highest energy cosmic rays (UHECRs) within $\approx 20$ Mpc is the "GZK Paradox". We constrain representative models of the...
Some Observational Consequences of GRB Shock Models (1999)
In the internal shock scenario for GRBs we expect some fraction of the energy of the burst to be carried by slow moving shells that were ejected at late times. These slow shells collide with faster...
Sari, Re'em, Piran, Tsvi, Halpern, Jules
In several GRBs afterglows, rapid temporal decay is observed which is inconsistent with spherical (isotropic) blast-wave models. In particular, GRB 980519 had the most rapidly fading of the...
The Inner Structure of Black Holes (1999)
We study the gravitational collapse of a self-gravitating charged scalar-field. Starting with a regular spacetime, we follow the evolution through the formation of an apparent horizon, a Cauchy...
GRB990123, The Optical Flash and The Fireball Model (1999)
We compare the ongoing observations of the remarkable burst GRB990123, the mother of all bursts, with the predictions of the afterglow theory. We show that the observations agree with the recent...
Predictions for The Very Early Afterglow and The Optical Flash (1999)
According to the internal-external shocks model for $\gamma $-ray bursts (GRBs), the GRB is produced by internal shocks within a relativistic flow while the afterglow is produced by external shocks...
We calculate the expected spectrum and light curves of the early afterglow. For short GRBs the peak of the afterglow will be delayed, typically, by a few dozens of seconds after the burst. The x-ray...
Images, Light Curves and Spectra of GRB Afterglow (1999)
Granot, Jonathan, Piran, Tsvi, Sari, Re'em
We calculate the light curve and spectra near the peak and the self absorption break, for an adiabatic blast wave described by the Blandford-McKee solution, considering the emission from the whole...
Gamma-Ray Bursts and the Fireball Model (1998)
Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the late sixties. The BATSE detector on the COMPTON-GRO satellite has been detecting one burst per day for the...
Radiative Efficiencies of Continuously Powered Blast Waves (1998)
We use general arguments to show that a continuously powered radiative blast wave can behave self similarly if the energy injection and radiation mechanisms are self similar. In that case, the...
Synchrotron Self Absorption in GRB Afterglow (1998)
Granot, Jonathan, Piran, Tsvi, Sari, Re'em
GRB afterglow is reasonably described by synchrotron emission from relativistic blast waves at cosmological distances. We perform detailed calculations taking into account the effect of synchrotron...
Gamma-Ray Bursts - The Second Revolution (1998)
Gamma-ray bursts GRBs are among the most mysterious astronomical phenomenon ever discovered. Unlike most astronomical discoveries which were explained within weeks or months after their initial...
Images and Spectra From the Interior of a Relativistic Fireball (1998)
Granot, Jonathan, Piran, Tsvi, Sari, Re'em
The detection of an afterglow, following a gamma-ray burst (GRB), can be described reasonably well by synchrotron emission from a relativistic spherical expanding blast wave, driven by an expanding...
Fluid dynamics of partially radiative blast waves (1998)
Cohen, Ehud, Piran, Tsvi, Sari, Re'em
We derive a self similar solution for the propagation of an extreme relativistic (or Newtonian) radiative spherical blast wave into a surrounding cold medium. The solution is obtained under the...
Hydrodynamics of a Relativistic Fireball: the Complete Evolution (1998)
Kobayashi, Shiho, Piran, Tsvi, Sari, Re'em
We study numerically the evolution of an adiabatic relativistic fireball expanding into a cold uniform medium. We follow the stages of initial free expansion and acceleration, coasting and then...
Mass-Inflation in Dynamical Gravitational Collapse of a Charged Scalar-Field (1998)
We study the inner-structure of a charged black-hole which is formed from the gravitational collapse of a self-gravitating charged scalar-field. Starting with a regular spacetime, we follow the...
Large Scale Fluctuations in the X-Ray Background (1998)
Treyer, Marie, Scharf, Caleb, Lahav, Ofer, Jahoda, Keith, Boldt, Elihu, Piran, Tsvi
We present an attempt to measure the large angular scale fluctuations in the X-Ray Background (XRB) from the HEAO1-A2 data, expressed in terms of spherical harmonics. We model the harmonic...
We study analytically the initial value problem for a self-interacting (massive) scalar-field on a Reissner-Nordstr\"om spacetime. Following the no-hair theorem we examine the dynamical physical...
We study the nonlinear gravitational collapse of a charged massless scalar-field. We confirm the existence of oscillatory inverse power-law tails along future timelike infinity, future null infinity...
Gamma-Ray Bursts and Related Phenomena (1998)
Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the sixties. The BATSE detector on the COMPTON-GRO satellite has been detecting one burst per day for the last six...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - II (1998)
We study analytically the initial value problem for a charged massless scalar-field on a Reissner-Nordstr\"om spacetime. Using the technique of spectral decomposition we extend recent results on this...
Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - I (1997)
We study analytically the asymptotic evolution of charged fields around a Reissner-Nordstr\"om black-hole. Following the no-hair theorem we focus attention on the dynamical mechanism by which the...
Spectra and Light Curves of Gamma-Ray Burst Afterglows (1997)
Sari, Re'em, Piran, Tsvi, Narayan, Ramesh
The recently discovered GRB afterglow is believed to be described reasonably well by synchrotron emission from a slowing down relativistic shell that collides with an external medium. To compare...
The Hardness Distribution of Gamma-Ray Bursts (1997)
Cohen, Ehud, Piran, Tsvi, Narayan, Ramesh
It is often stated that gamma-ray bursts (GRBs) have typical energies of several hundreds $\keV$, where the typical energy may be characterized by the hardness H, the photon energy corresponding to...
On Gravitational Repulsion (1997)
The concepts of negative gravitational mass and gravitational repulsion are alien to general relativity. Still, we show here that small negative fluctuations - small dimples in the primordial density...
The Implications of Direct Red-Shift Measurement of $\gamma$-ray Bursts (1997)
The recent discoveries of X-ray and optical counterparts for GRBs, and a possible discovery of a host galaxy, implies that a direct measurement of the red-shift of some GRBs host galaxies is eminent....
Can internal shocks produce the variability in GRBs? (1997)
Kobayashi, Shiho, Piran, Tsvi, Sari, Re'em
We discuss the possibility that gamma-ray bursts result from internal shocks in an ultra-relativistic matter. Using a simple model we calculate the temporal structure and we estimate the efficiency...
Spherical Collapse of a Mass-Less Scalar Field With Semi-Classical Corrections (1997)
We investigate numerically spherically symmetric collapse of a scalar field in the semi-classical approximation. We first verify that our code reproduces the critical phenomena (the Choptuik effect)...
Voids in the Large-Scale Structure (1997)
Voids are the most prominent feature of the LSS of the universe. Still, they have been generally ignored in quantitative analysis of it, essentially due to the lack of an objective tool to identify...
Implication of Temporal Structure in GRB (1997)
The highly variable temporal structure observed in most GRBs provides us with unexpected clues. We show that variable GRBs cannot be produced by external shocks models and consequently cannot be...
Variability in GRBs - A Clue (1997)
We show that external shocks cannot produce a variable GRB, unless they are produced by an extremely narrow jets (angular opening of < ~10^{-4}) or if only a small fraction of the shell emits the...
The X-Ray Background as a Probe of Density Fluctuations at High Redshift (1996)
Lahav, Ofer, Piran, Tsvi, Treyer, Marie A.
The X-Ray Background (XRB) probes structure on scales intermediate between those explored by local galaxy redshift surveys and by the COBE Microwave Background measurements. We predict the large...
Cosmological GRBs: Internal vs. External Shocks (1996)
Internal (IS) or external (ES) shocks in relativistic expanding shells are currently the best known mechanism for producing GRBs. We calculate the hydrodynamic conditions and the cooling processes in...
A catalogue of the voids in the IRAS 1.2-Jy survey (1996)
El-Ad, Hagai, Piran, Tsvi, Da Costa, Luiz Nicolaci
Using the VOID FINDER algorithm we have compiled a catalogue of voids in the IRAS 1.2-Jy sample. The positions of the voids correspond well to underdense regions seen in the IRAS smoothed density...
Spherical Harmonic Expansion of Gamma Ray Burst Distributions: Probing Large Scale Structure? (1996)
We have laid down the formalism and techniques necessary for computing the multipole components in a spherical harmonic expansion for bursting sources given any specific power spectrum of density...
Relativity at Action or Gamma-Ray Bursts (1996)
Gamma ray Bursts (GRBs) - short bursts of few hundred keV $\gamma$-rays - have fascinated astronomers since their accidental discovery in the sixties. GRBs were ignored by most relativists who did...
Critical Behaviour and Universality in Gravitational Collapse of a Charged Scalar Field (1996)
We summarize results from a study of spherically symmetric collapse of a {\it charged} (complex) massless scalar-field \cite{Hod}. We present an analytic argument which conjecture the generalization...
Fine-Structure of Choptuik's Mass-Scaling Relation (1996)
We conjecture (analytically) and demonstrate (numerically) the existence of a fine-structure above the power-law behavior of the mass of black-holes that form in gravitational collapse of spherical...
New Evidence for The Cosmological Origin of Gamma-Ray Bursts (1996)
We find that Gamma-ray bursts (GRBs) at the 3B catalog are correlated (at 95\% confidence level) with Abell clusters. This is the first known correlation of GRBs with any other astronomical...
Cooling Time Scales and Temporal Structure of Gamma-Ray Bursts (1996)
Sari, Re'em, Narayan, Ramesh, Piran, Tsvi
A leading mechanism for producing cosmological gamma-ray bursts (GRBs) is via ultra-relativistic particles in an expanding fireball. The kinetic energy of the particles is converted into thermal...
Waxman, Eli, Fisher, Karl B., Piran, Tsvi
We analyze the anisotropy signature expected if the high energy (above $10^{19}$eV) cosmic ray (CR) sources are extra-Galactic and trace the distribution of luminous matter on large scales. We...
Are There MeV Gamma-Ray Bursts? (1995)
It is often stated that gamma-ray bursts (GRBs) have typical energies of several hundred keV. Is this a real feature of GRBs or is it due to an observational bias? We consider the possibility that...
Hydrodynamic Time Scales and Temporal Structure in GRBs (1995)
We calculate the hydrodynamic time scales for a spherical ultra-relativistic shell that is decelerated by the ISM and discuss the possible relations between these time scales and the observed...
A Simultaneous Spectral Invariant Analysis of the GRB Count Distribution and Time Dilation (1995)
The analysis of the BATSE's count distribution within cosmological models suffers from observational uncertainties due to the variability of the bursts' spectra: when BATSE observes bursts from...
Automated Detection of Voids in Redshift Surveys (1995)
El-Ad, Hagai, Piran, Tsvi, Da Costa, Luiz Nicolaci
We present a new void search algorithm for automated detection of voids in three-dimensional redshift surveys. Based on a model in which the main features of the LSS of the Universe are voids and...
Hydrodynamic Time Scales and Temporal Structure of GRBs (1995)
We calculate the hydrodynamic time scales for a spherical ultra-relativistic shell that is decelerated by the ISM and discuss the possible relations between these time scales and the observed...
Towards Understanding Gamma-Ray Bursts (1995)
$\gamma$-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the sixties. The BATSE detector on COMPTON-GRO satellite has been detecting GRBs for the last four years at a...
Dipole Anisotropy from an Entropy Gradient (1995)
It is generally accepted that the observed CMBR dipole arises from the motion of the local group relative to the CMBR frame. An alternative interpretation is that the dipole results from an...
Void Sizes and CMBR Fluctuations (1995)
Following Blumenthal \etl \cite{blu} and Piran \etl \cite{Pi} I discuss a simple model for the gravitational formation of voids. This model enables us to estimate the primordial perturbation required...
The Distribution Of Cosmological $\gamma$-ray Bursts (1995)
We compare the burst distribution of the new (2B) BATSE catalogue to a cosmological distribution. The observed distribution agrees well with a cosmological one, however, it is insensitive to...
Gamma-Raybursts And Binary Neutron Star Mergers (1995)
. Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1916+13, end their life in a catastrophic merge event (denoted here NS 2 M). The merger releases ß 5 \Delta 10 53...
Gamma-Ray Bursts and Binary Neutron Star Mergers (1994)
Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1916+13, end their life in a catastrophic merge event (denoted here NS$^2$M). The merger releases $\approx 5 \cdot...
Stability of Fireballs and $\gamma$-Ray Bursts (1994)
Fireballs are an essential part of any cosmological $\gamma$-ray burst. We drive here a stability criterion for fireballs and show that fireballs are Rayleigh-Taylor unstable in any region in which...
New Evidence for the Cosmological Origin of Gama-Ray Bursts (1994)
Cohen, Ehud, Kolatt, Tsafrir, Piran, Tsvi
We compare the burst distribution of the new (2B) BATSE catalogue to a cosmological distribution. We find that the distribution is insensitive to cosmological parameters such as Omega and Lambda and...
$\gamma$-Ray Bursts and Neutron Star Mergers (1994)
$\gamma$-ray bursts have baffled theorists ever since their accidental discovery at the sixties. We suggest that these bursts originate in merger of neutron star binaries, taking place at...
The Internal Geometry of an Evaporating Black Hole (1994)
Parentani, Renaud, Piran, Tsvi
We present a semi-classical model for the formation and evaporation of a four dimensional black hole. We solve the equations numerically and obtain solutions describing the entire the space-time...
Quantum propagator for a nonrelativistic particle in the vicinity of a time machine (1994)
Goldwirth, Dalia S., Perry, Malcolm J., Piran, Tsvi, Thorne, Kip S.
We study the propagator of a nonrelativistic, noninteracting particle in any nonrelativistic "time-machine" spacetime of the following type: an external, chronal spacetime in which two spatial...
Fireballs and Gamma-Ray Bursts (1994)
The sudden release of copious $\g$-ray photons into a compact region creates an opaque photon--lepton fireball due to the prolific production of electron--positron pairs. The photons that we observe...
Stability of Fireballs and γ-Ray Bursts (1994)
Fireballs are an essential part of any cosmological fl-ray burst. We drive here a stability criterion for fireballs and show that fireballs are Rayleigh-Taylor unstable in any region in which the...
The Internal Geometry of an Evaporating Black Hole (1994)
Black Hole, Renaud Parentani, Tsvi Piran
We present a semi-classical model for the formation and evaporation of a four dimensional black hole. We solve the equations numerically and obtain solutions describing the entire the space-time...
The Quantum Propagator for a Nonrelativistic Particle in the Vicinity of a Time Machine (1993)
Goldwirth, Dalia S., Perry, Malcolm J., Piran, Tsvi, Thorne, Kip S.
We study the propagator of a non-relativistic, non-interacting particle in any non-relativistic ``time-machine'' spacetime of the type shown in Fig.~1: an external, flat spacetime in which two...
Do Gamma-Ray Burst Sources Repeat (1993)
Following the discovery by Quashnock and Lamb (1993) of an apparent excess of $\gamma$-ray burst pairs with small angular separations, we reanalyze the angular distribution of the bursts in the BATSE...
Gravitational Waves and $\gamma$-Ray Bursts (1993)
Kochanek, Christopher S., Piran, Tsvi
Coalescing binaries in distant galaxies are one of the most promising sources of gravitational waves detectable by the LIGO project.$^{[1-5]}$ They are also a copious source of neutrinos,$^{[1]}$...
Numerical Analysis of Black Hole Evaporation (1993)
Piran, Tsvi, Strominger, Andrew
Black hole formation/evaporation in two-dimensional dilaton gravity can be described, in the limit where the number $N$ of matter fields becomes large, by a set of second-order partial differential...
On the Bimodal Distribution of Gamma-Ray Bursts (1993)
Mao, Shude, Narayan, Ramesh, Piran, Tsvi
Kouveliotou et al. (1993) recently confirmed that gamma-ray bursts are bimodal in duration. In this paper we compute the statistical properties of the short ($\le 2$~s) and long ($>2$~s) bursts using...
Hydrodynamics of Relativistic Fireballs (1993)
Piran, Tsvi, Shemi, Amotz, Narayan, Ramesh
We examine analytically and numerically the evolution of a relativistic fireball. We show that, after an early rearrangement phase, most of the matter and energy in the fireball is concentrated...
Gamma-Ray Bursts and Neutron Star Mergers - Possibly the Strongest Explosions in the Universe (1992)
$\gamma$-ray bursts have baffled theorists ever since their accidental discovery at the sixties. We suggest that these bursts originate in merger of neutron star binaries, taking place at...
Fireballs in the Galactic Halo and $\gamma$-Ray Bursts (1992)
If gamma ray burst sources are in the galactic halo they inevitably involve a creation of an opaque pair plasma fireball, just like in cosmological sources. We find that the typical physical...
The Loss of Unitarity in the Vicinity of a Time Machine (1992)
Goldwirth, Dalia S., Perry, Malcolm J., Piran, Tsvi
We construct the propagator of a non-relativistic non-interacting particle in a flat spacetime in which two regions have been identified. This corresponds to the simplest "time machine". We show that...
Gamma-Ray Bursts as the Death Throes of Massive Binary Stars (1992)
Narayan, Ramesh, Paczyński, Bohdan, Piran, Tsvi
It is proposed that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Bursts with complex profiles and...
7th Jerusalem Winter School for Theoretical Physics (1991)
Coleman, Sidney Richard, Hartle, James B, Piran, Tsvi, Weinberg, Steven