Hyper Velocity Stars and the Restricted Parabolic 3-body Problem (2009)
Sari, Re'em, Kobayashi, Shiho, Rossi, Elena M.
Motivated by detections of hypervelocity stars that may originate from the Galactic Center, we revist the problem of a binary disruption by a passage near a much more massive point mass. The six...
Discrete Self-Similarity in Ultra-Relativistic Type-II Strong Explosions (2009)
A solution to the ultra-relativistic strong explosion problem with a non-power law density gradient is delineated. We consider a blast wave expanding into a density profile falling off as a steep...
Discrete self-similarity in ultrarelativistic type-II strong explosions (2009)
A solution to the ultrarelativistic strong explosion problem with a nonpower law density gradient is delineated. We consider a blast wave expanding into a density profile falling off as a steep...
Klein–Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum (2009)
Nakar, Ehud, Ando, Shin'ichiro, Sari, Re'em
We present analytic approximations to the optically thin synchrotron and synchrotron self-Compton (SSC) spectra when Klein-Nishina (KN) effects are important and pair production and external...
The Creation of Haumea's Collisional Family (2009)
Schlichting, Hilke E., Sari, Re'em
Recently, the first collisional family was discovered in the Kuiper Belt. The parent body of this family, Haumea, is one of the largest objects in the Kuiper Belt and is orbited by two satellites. It...
Discrete Self-Similarity in Type-II Strong Explosions (2009)
We present new solutions to the strong explosion problem in a non-power law density profile. The unperturbed self-similar solutions discovered by Waxman & Shvarts describe strong Newtonian shocks...
The Creation of Haumea's Collisional Family (2009)
Schlichting, Hilke E., Sari, Re'em
Recently, the first collisional family was discovered in the Kuiper belt. The parent body of this family, Haumea, is one of the largest objects in the Kuiper belt and is orbited by two satellites. It...
Discrete self-similarity in type-II strong explosions (2009)
We present new solutions to the strong explosion problem in a nonpower law density profile. The unperturbed self-similar solutions discovered by Waxman and Shvarts describe strong Newtonian shocks...
Collins, Benjamin F., Sari, Re'em
We present a systematic examination of the changes in semimajor axis of a protoplanet as it interacts with other protoplanets in the presence of eccentricity dissipation. For parameters relevant to...
Klein-Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum (2009)
Nakar, Ehud, Ando, Shin'ichiro, Sari, Re'em
We present analytic approximations to the optically thin synchrotron and synchrotron self-Compton (SSC) spectra when Klein-Nishina (KN) effects are important and pair production and external...
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...
Tidal Evolution of Rubble Piles (2009)
Many small bodies in the solar system are believed to be rubble piles, a collection of smaller elements separated by voids.We propose a model for the structure of a self-gravitating rubble pile....
Dekel, Avishai, Sari, Re'em, Ceverino, Daniel
We present a simple theoretical framework for massive galaxies at high redshift, where most of the assembly and star formation occurred. The evolution is governed by the interplay between fueling by...
GeV emission from prompt and afterglow phases of gamma-ray bursts (2008)
Ando, Shin'ichiro, Nakar, Ehud, Sari, Re'em
We investigate the GeV emission from gamma-ray bursts (GRBs) using the results from the Energetic Gamma Ray Experimental Telescope (EGRET) and in view of the Gamma-Ray Large Area Space Telescope...
GeV emission from prompt and afterglow phases of gamma-ray bursts (2008)
Ando, Shin'ichiro, Nakar, Ehud, Sari, Re'em
We investigate the GeV emission from gamma-ray bursts (GRBs) using the results from the Energetic Gamma Ray Experimental Telescope (EGRET) and in view of the Gamma-Ray Large Area Space Telescope...
Lévy Flights of Binary Orbits due to Impulsive Encounters (2008)
Collins, Benjamin F., Sari, Re'em
We examine the evolution of an almost-circular Keplerian orbit interacting with unbound perturbers. We calculate the change in eccentricity and angular momentum that results from a single encounter,...
The ratio of retrograde to prograde orbits: a test for Kuiper Belt binary formation theories (2008)
Schlichting, Hilke E., Sari, Re'em
With the discovery of Kuiper Belt binaries that have wide separations and roughly equal masses, new theories were proposed to explain their formation. Two formation scenarios were suggested by...
Levy Flights of Binary Orbits due to Impulsive Encounters (2008)
Collins, Benjamin F., Sari, Re'em
We examine the evolution of an almost circular Keplerian orbit interacting with unbound perturbers. We calculate the change in eccentricity and angular momentum that results from a single encounter,...
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)...
GeV Emission from Prompt and Afterglow Phases of Gamma-Ray Bursts (2008)
Ando, Shin'ichiro, Nakar, Ehud, Sari, Re'em
We investigate the GeV emission from gamma-ray bursts (GRBs), using the results from the Energetic Gamma Ray Experimental Telescope (EGRET), and in view of the Gamma-ray Large Area Space Telescope...
Analytical solutions for expanding fireballs (2008)
Many models of gamma-ray bursts (GRBs) as well as of soft gamma repeaters (SGRs) involve a fireball — an optically thick concentration of radiation energy with a high ratio of energy density to...
The Ratio of Retrograde to Prograde Orbits: A Test for Kuiper Belt Binary Formation Theories (2008)
Schlichting, Hilke E., Sari, Re'em
With the discovery of Kuiper Belt binaries that have wide separations and roughly equal masses new theories were proposed to explain their formation. Two formation scenarios were suggested by...
The flow resulting from a strong ultrarelativistic shock moving through a stellar envelope with a polytrope-like density profile has been studied analytically and numerically at early times while the...
Formation of Kuiper Belt binaries (2008)
Schlichting, Hilke E., Sari, Re'em
The discovery that a substantial fraction of Kuiper Belt objects (KBOs) exists in binaries with wide separations and roughly equal masses has motivated a variety of new theories explaining their...
Mazzali, Paolo A., Valenti, Stefano, Della Valle, Massimo, Chincarini, Guido, Sauer, Daniel N., Benetti, Stefano, ...
Tidal Evolution of Rubble Piles (2007)
Many small bodies in the solar system are believed to be rubble piles, a collection of smaller elements separated by voids. We propose a model for the structure of a self-gravitating rubble pile....
Centred approach to the period of anharmonic oscillators (2007)
We present a simple method for obtaining a concise series expression for the period of one-dimensional classical oscillators. The series converges well for typical potentials and is of a form that is...
Formation of Kuiper Belt Binaries (2007)
Schlichting, Hilke E., Sari, Re'em
The discovery that a substantial fraction of Kuiper Belt objects (KBOs) exists in binaries with wide separations and roughly equal masses, has motivated a variety of new theories explaining their...
Collins, Benjamin F., Sari, Re'em
We present a systematic examination of the changes in semi-major axis caused by the mutual interactions of a group of massive bodies orbiting a central star in the presence of eccentricity...
The Self-Similarity of Shear-dominated Viscous Stirring (2007)
Collins, Benjamin F., Schlichting, Hilke E., Sari, Re'em
We examine the growth of eccentricities of a population of particles with nearly circular orbits around a central massive body. Successive encounters between pairs of particles increase the...
The effect of Semi-Collisional Accretion on Planetary Spins (2006)
Schlichting, Hilke E., Sari, Re'em
Planetesimal accretion during planet formation is usually treated as collisionless. Such accretion from a uniform and dynamically cold disk predicts protoplanets with slow retrograde rotation....
The Self-Similarity of Shear-Dominated Viscous Stirring (2006)
Collins, Benjamin F., Schlichting, Hilke E., Sari, Re'em
We examine the growth of eccentricities of a population of particles with initially circular orbits around a central massive body. Successive encounters between pairs of particles increase the...
Gamma Ray Bursts and Their Afterglows (2006)
Gamma-Ray Bursts are extreme astrophysical events, which emit the bulk of their energy as photons in the 0.1 – 1.0 MeV range, and whose durations span milliseconds to tens of minutes. They are...
We compare different examples of spherical accretion onto a gravitating mass. Limiting cases include the accretion of a collisionally dominated fluid and the accretion of collisionless particles. We...
Protoplanet Dynamics in a Shear-Dominated Disk (2006)
Collins, Benjamin F., Sari, Re'em
The velocity dispersion, or eccentricity distribution, of protoplanets interacting with planetesimals is set by a balance between dynamical friction and viscous stirring. We calculate analytically...
We compare different examples of spherical accretion onto a gravitating mass. Limiting cases include the accretion of a collisionally dominated fluid and the accretion of collisionless particles. We...
We derive self-similar solutions for ultrarelativistic shock waves propagating into cold material of power law density profile in radius rho[proportional]r^–k. We treat both implosions and...
We derive self similar solutions for ultra-relativistic shock waves propagating into cold material of powerlaw density profile in radius rho ~ r^-k. We treat both implosions and explosions in three...
Self-similar solutions for relativistic shocks emerging from stars with polytropic envelopes (2005)
We consider a strong ultrarelativistic shock moving through a star whose envelope has a polytrope-like density profile. When the shock is close to the star's outer boundary, its behavior follows the...
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...
Planet Formation by Coagulation: A Focus on Uranus and Neptune (2004)
Goldreich, Peter, Lithwick, Yoram, Sari, Re'em
Planets form in the circumstellar disks of young stars. We review the basic physical processes by which solid bodies accrete each other and alter each others' random velocities, and we provide...
Final Stages of Planet Formation (2004)
Goldreich, Peter, Lithwick, Yoram, Sari, Re'em
We address three questions regarding solar system planets. What determined their number? Why are their orbits nearly circular and coplanar? How long did they take to form? Runaway accretion in a disk...
Shaping the Kuiper belt size spectrum by shattering large but strengthless bodies (2004)
The observed size distribution of Kuiper belt objects (KBOs)--small icy and rocky solar system bodies orbiting beyond Neptune--is well described by a power law at large KBO sizes. However, recent...
Planet - Disk Symbiosis (2003)
Planets form in disks around young stars. Interactions with these disks cause them to migrate and thus affect their final orbital periods. We suggest that the connection between planets and disks may...
Jets in GRBs: Tests and Predictions for the Structured Jet Model (2003)
Perna, Rosalba, Sari, Re'em, Frail, Dale
The two leading interpretations of achromatic breaks that are observed in the light curves of GRBs afterglow are (i) the manifestation of the edge of a jet, which has a roughly uniform energy profile...
A generalization of the Lagrangian points: studies of resonance for highly eccentric orbits (2003)
We develop a framework based on energy kicks for the evolution of high-eccentricity long-period orbits with Jacobi constant close to 3 in the restricted circular planar three-body problem where the...
Evolution of the polarization of the optical afterglow of the y-ray burst GRB030329 (2003)
Greiner, Jochen, Klose, Sylvio, Reinsch, Klaus, Schmid, Hans Martin, Sari, Re'em, Hartmann, Dieter H., ...
Formation of Kuiper Belt Binaries (2002)
Goldreich, Peter, Lithwick, Yoram, Sari, Re'em
It appears that at least several percent of large Kuiper belt objects are members of wide binaries. Physical collisions are too infrequent to account for their formation. Collisionless gravitational...
Eccentricity Evolution for Planets in Gaseous Disks (2002)
We investigate the hypothesis that interactions between a giant planet and the disk from which it forms promote eccentricity growth. These interactions are concentrated at discrete Lindblad and...
The Shape of Spectral Breaks in GRB Afterglows (2001)
Gamma-Ray Burst (GRB) afterglows are well described by synchrotron emission from relativistic blast waves expanding into an external medium. The blast wave is believed to amplify the magnetic field...
Physical Constraints From Broadband Afterglow Fits:GRB000926 as an Example (2001)
Yost, Sarah A., Sari, Re'em, Harrison, Fiona A., Berger, Edo, Diercks, Alan, Galama, Titus, ...
We develop a model to fit the broadband afterglows of GRBs from the intrinsic parameters of the fireball's synchrotron emission, and apply it to a few well-studied events, with the goal of...
The prompt energy release of gamma-ray bursts using a cosmological k-correction (2001)
Bloom, Joshua S., Frail, Dale A., Sari, Re'em
The fluences of gamma-ray bursts (GRBs) are measured with a variety of instruments in different detector energy ranges. A detailed comparison of the implied energy releases of the GRB sample...
Ultra Efficient Internal Shocks (2000)
Gamma-ray bursts are believed to originate from internal shocks which arise in an irregular relativistic wind. The process has been thought to be inefficient, converting only a few percent of the...
Lower Limits on Lorentz Factors in Gamma Ray Bursts (2000)
As is well-known, the requirement that gamma ray bursts (GRB's) be optically thin to high energy photons yields a lower limit on the Lorentz factor (\gamma) of the expansion. In this paper, we...
Optical flashes and radio flares in GRB afterglows: Numerical study (2000)
We numerically study the evolution of an adiabatic relativistic fireball interacting with an ambient uniform medium, both in the initial energy transfer stage and in its late evolution. It is shown...
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....
We consider the effects of inverse Compton scattering of synchrotron photons from relativistic electrons in GRB afterglows. We compute the spectrum of the inverse Compton emission and find that it...
Impulsive and Varying Injection in GRB Afterglows (2000)
The standard model of Gamma-Ray Bursts afterglows is based on synchrotron radiation from a blast wave produced when the relativistic ejecta encounters the surrounding medium. We reanalyze the...
Beaming and Jets in GRBs (2000)
The origin of GRBs have been a mystery for almost 30 years. The afterglow observed in the last few years enabled redshift determination for a handful of bursts, and the cosmological origin is now...
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...
Optical Flashes and Radio Flares in GRBs afterglow: Numerical Study (1999)
The strong optical flash observed by ROTSE, as well as the radio flare associated with GRB 990123 can be attributed to the emission of the fireball ejecta, initially heated by the reverse shock. We...
Linear Polarization and Proper Motion in The Afterglow of Beamed GRBs (1999)
We investigate the polarization and proper motion expected in a beamed Gamma-Ray Burst's ejecta. We find that even if the magnetic field has well defined orientation relative to the direction of...
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...
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...
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...
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...
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 Observed Size and Shape of GRB Afterglow (1997)
The detection of delayed emission in X-ray, optical and radio wave length, ``afterglow'', following a gamma-ray burst can be described by the emission of a relativistic shell decelerating upon...
Hydrodynamics of GRB After-Glow (1997)
The detection of delayed emission at X-ray optical and radio wavelengths, ``after-glow'', suggests that the relativistic shell which emitted the initial GRB due to internal shocks decelerates on...
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...
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...
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...
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...
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...
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...