Guillochon, James, Dan, Marius, Ramirez-Ruiz, Enrico, Rosswog, Stephan
We present three-dimensional simulations on a new mechanism for the detonation of a sub-Chandrasekhar CO white dwarf in a dynamically unstable system where the secondary is either a pure He white...
Typing Supernova Remnants Using X-ray Line Emission Morphologies (2009)
Lopez, Laura A., Ramirez-Ruiz, Enrico, Badenes, Carles, Huppenkothen, Daniela, Jeltema, Tesla E., Pooley, David A.
We present a new observational method to type the explosions of young supernova remnants (SNRs). By measuring the morphology of the Chandra X-ray line emission in seventeen Galactic and Large...
Naiman, J. P., Ramirez-Ruiz, Enrico, Lin, Douglas N. C.
Here we show that the overabundance of ultra-luminous, compact X-ray sources (ULXs) associated with moderately young clusters in interacting galaxies such as the Antennae and Cartwheel can be given...
Zemp, Marcel, Ramirez-Ruiz, Enrico, Diemand, Jürg
Merging compact binaries are the one source of gravitational radiation so far identified. Because short-period systems which will merge in less than a Hubble time have already been observed as binary...
Lee, William H., Ramirez-Ruiz, Enrico, Van De Ven, Glenn
A new mechanism is proposed by which short gamma-ray burst (SGRB) production can be achieved. In this new paradigm, it is supposed that the compact objects contained within a globular cluster (GC)...
Gamma Ray Bursts - Maybe not so old after all (2009)
Ramirez-Ruiz, Enrico, Lee, William
The discovery of a short-lived gamma-ray burst at a surprisingly early epoch in the history of the Universe shows how much is still unknown about the evolution of the parent systems of such bursts.
Kocevski, Daniel, Thone, Christina C, Ramirez-Ruiz, Enrico, Bloom, Joshua S., Granot, Jonathan, Butler, Nathaniel R., ...
We present results of an extensive observing campaign of the short duration, hard spectrum gamma-ray burst (GRB) 070724A, aimed at detecting the radioactively-powered emission that might follow from...
Lee, William H., Ramirez-Ruiz, Enrico, Lopez-Camara, Diego
We consider the long term evolution of debris following the tidal disruption of compact stars in the context of short gamma ray bursts (SGRBs). The initial encounter impulsively creates a hot, dense,...
Short Gamma Ray Bursts and their Afterglow Signatures in Dense Stellar Systems (2009)
Parsons, Rion K., Ramirez-Ruiz, Enrico, Lee, William H.
The hypothesis that short GRBs arise from the coalescence of binary compact stars has recently gained support. With this comes the expectation that the afterglow should bear the characteristic...
GRB 080503: implications of a naked short gamma-ray burst dominated by extended emission (2009)
Perley, D. A., Metzger, B. D., Granot, J., Butler, N. R., Sakamoto, T., Ramirez-Ruiz, Enrico, ...
We report on observations of GRB 080503, a short gamma-ray burst (GRB) with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough...
GRB 080503: implications of a naked short gamma-ray burst dominated by extended emission (2009)
Perley, D. A., Metzger, B. D., Granot, J., Butler, N. R., Sakamoto, T., Ramirez-Ruiz, Enrico, ...
We report on observations of GRB 080503, a short gamma-ray burst (GRB) with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough...
On the release of binding energy and accretion power in core collapse-like environments (2008)
Socrates, Aristotle, Ramirez-Ruiz, Enrico
All accretion models of gamma-ray bursts share a common assumption: accretion power and gravitational binding energy is released and then dissipated locally, with the mass of its origin. This is...
Three-Dimensional Simulations of Tidally Disrupted Solar-Type Stars (2008)
Guillochon, James, Ramirez-Ruiz, Enrico, Rosswog, Stephan, Kasen, Daniel
We describe a fully three-dimensional simulation of a 1 Msun solar-type star approaching a 10^6 Msun black hole on a parabolic orbit with a pericenter distance well within the tidal radius. While...
Lopez, Laura A., Ramirez-Ruiz, Enrico, Pooley, David A., Jeltema, Tesla E.
We introduce methods to quantify the X-ray morphologies of supernova remnants observed with the Chandra X-ray Telescope. These include a power-ratio technique to measure morphological asymmetries,...
The star ingesting luminosity of intermediate mass black holes in globular clusters (2008)
Ramirez-Ruiz, Enrico, Rosswog, Stephan
The dynamics of stars in the inner regions of nearby globular clusters (GCs) such as M15 and G1 indicate the presence of central concentrated dark masses, and one would like to know whether these are...
The Hydrodynamics of Gamma-Ray Burst Remnants (2008)
Ramirez-Ruiz, Enrico, MacFadyen, Andrew I.
This paper reports on the results of a numerical investigation designed to address how the initially anisotropic appearance of a GRB remnant is modified by the character of the circumburst medium and...
Gamma Ray Burst Production and Supernova Signatures in Slowly Rotating Collapsars (2008)
Lopez-Camara, Diego, Lee, William H., Ramirez-Ruiz, Enrico
We consider accretion onto newborn black holes following the collapse of rotating massive stellar cores, at the threshold where a centrifugally supported disk gives way to nearly radial inflow for...
Prochaska, Jason X., Dessauges-Zavadsky, Miroslava, Ramirez-Ruiz, Enrico, Chen, Hsiao-Wen
We survey NV absorption in the afterglow spectra of long-duration gamma-ray bursts (GRBs) with the intent to study highly ionized gas in the galaxies hosting these events. We identify a high...
Broadband observations of the naked-eye y-ray burst GRB 080319B (2008)
Racusin, Judith L., Karpov, S. V., Sokolowski, M., Granot, Jonathan, Wu, Xiao Feng, Pal'shin, V., ...
Long-duration y-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse of...
Broadband observations of the naked-eye y-ray burst GRB 080319B (2008)
Racusin, Judith L., Karpov, S. V., Sokolowski, M., Granot, Jonathan, Wu, Xiao Feng, Pal'shin, V., ...
Long-duration y-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse of...
Electron-Positron Pair Loading and the Origin of the Upstream Magnetic Field in GRB Shocks (2007)
Ramirez-Ruiz, Enrico, Nishikawa, Ken-Ichi, Hededal, Christian B.
We investigate here the effects of plasma instabilities driven by rapid electron/positron pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed...
The Progenitors of Short Gamma-Ray Bursts (2007)
Lee, William H., Ramirez-Ruiz, Enrico
Recent months have witnessed dramatic progress in our understanding of SGRBs. There is now general agreement that SGRBs can produce directed outflows of relativistic matter with a kinetic luminosity...
Chen, Hsiao-Wen, Prochaska, Jason X., Ramirez-Ruiz, Enrico, Bloom, Joshua S., Dessauges-Zavadsky, Miroslava, Foley, Ryan J.
We investigate available constraints on the circumstellar medium (CSM) around long-duration gamma-ray burst (GRB) progenitors from afterglow spectra. We first establish a statistical sample of five...
Socrates, Aristotle, Davis, Shane W., Ramirez-Ruiz, Enrico
We show that the luminosity of a star forming galaxy is capped by the production and subsequent expulsion of cosmic rays from its interstellar medium. By defining an Eddington luminosity in cosmic...
A Simple Test of the External Shock Model for the Prompt Emission in Gamma-Ray Bursts (2006)
Ramirez-Ruiz, Enrico, Granot, Jonathan
It is demonstrated here that if the prompt GRB emission is produced by the simplest version of the external shock model, a specific relation should prevail between the observed duration, isotropic...
No supernovae associated with two long-duration gamma ray bursts (2006)
Fynbo, Johan P. U., Watson, Darach, Thoene, Christina C., Sollerman, Jesper, Bloom, Joshua S., Davis, Tamara M., ...
It is now accepted that long duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. The standard "collapsar" model predicts that a broad-lined and luminous Type Ic...
Deducing the Lifetime of Short Gamma-Ray Burst Progenitors from Host Galaxy Demography (2006)
Zheng, Zheng, Ramirez-Ruiz, Enrico
The frequency of short gamma-ray bursts (GRBs) in galaxies with distinct star formation histories can be used to constrain the lifetime of the progenitor systems. As an illustration, we consider here...
No supernovae associated with two long-duration gamma-ray bursts (2006)
Fynbo, Johan P. U., Watson, Darach, Thöne, Christina C., Sollerman, Jesper, Bloom, Joshua S., Davis, Tamara M., ...
No supernovae associated with two long-duration gamma-ray bursts (2006)
Fynbo, Johan P. U., Watson, Darach, Thöne, Christina C., Sollerman, Jesper, Bloom, Joshua S., Davis, Tamara M., ...
X-ray flares following short gamma-ray bursts from shock heating of binary stellar companions (2005)
MacFadyen, Andrew I., Ramirez-Ruiz, Enrico, Zhang, Weiqun
The discovery of long-lasting (~100 s) X-ray flares following short gamma-ray bursts initially called into question whether they were truly classical short-hard bursts. Opinion over the last few...
Accretion modes in collapsars - prospects for GRB production (2005)
Lee, William H., Ramirez-Ruiz, Enrico
We explore low angular momentum accretion flows onto black holes formed after the collapse of massive stellar cores. In particular, we consider the state of the gas falling quasi-spherically onto...
Photospheric signatures imprinted on the gamma-ray burst spectra (2005)
A solution is presented for the spectrum of high-energy gamma-ray burst photons confined to a quasi-thermal baryonic photosphere. The solution is valid in the steady-state limit assuming the region...
Lee, William H., Ramirez-Ruiz, Enrico, Page, Dany
We present a detailed, two dimensional numerical study of the microphysical conditions and dynamical evolution of accretion disks around black holes when neutrino emission is the main source of...
A compact binary merger model for the short, hard GRB 050509b (2005)
Lee, William H., Ramirez-Ruiz, Enrico, Granot, Jonathan
The first X-ray afterglow for a short (~30 ms), hard gamma-ray burst was detected by Swift on 9 May 2005 (GRB 050509b). No optical or radio counterpart was identified in follow-up observations. The...
The redshift distribution of gamma-ray bursts revisited (2005)
Natarajan, Priyamvada, Albanna, Badr, Hjorth, Jens, Ramirez-Ruiz, Enrico, Tanvir, Nial, Wijers, Ralph
In this letter, we calculate the redshift distribution of gamma-ray bursts assuming that they trace (i) the globally averaged star formation rate or (ii) the average metallicity in the Universe....
Supernovae and Gamma-Ray Bursts Powered by Hot Neutrino-Cooled Coronae (2005)
Ramirez-Ruiz, Enrico, Socrates, Aristotle
Cosmological explosions such as core-collapse supernovae (SNe) and gamma-ray bursts (GRBs) are thought to be powered by the rapid conversion of roughly a solar mass' worth of gravitational binding...
Afterglow Observations Shed New Light on the Nature of X-ray Flashes (2005)
Granot, Jonathan, Ramirez-Ruiz, Enrico, Perna, Rosalba
X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRGRBs) share many observational characteristics with long duration GRBs, but the reason for which their prompt emission peaks at lower photon...
An asymmetric energetic type Ic supernova viewed off-axis, and a link to gamma ray bursts (2005)
Mazzali, Paolo A., Kawabata, Koji S., Maeda, Keiichi, Nomoto, Ken'ichi, Filippenko, Alexei V., Ramirez-Ruiz, Enrico, ...
Ramirez-Ruiz, Enrico, Garcia-Segura, Guillermo, Salmonson, Jay D., Perez-Rendon, Brenda
We present a numerical investigation of the contribution of the presupernova ejecta of Wolf-Rayet stars to the environment surrounding gamma-ray bursts (GRBs), and describe how this external matter...
An Off-Axis Model for GRB 031203 (2004)
Ramirez-Ruiz, Enrico, Granot, Jonathan, Kouveliotou, Chryssa, Woosley, S. E., Patel, Sandy K., Mazzali, Paolo A.
The low luminosity radio emission of the unusually faint GRB 031203 has been argued to support the idea of a class of intrinsically sub-energetic gamma-ray bursts (GRBs), currently comprising two...
Levan, Andrew, Patel, Sandeep, Kouveliotou, Chryssa, Fruchter, Andrew, Rhoads, James, Rol, Evert, ...
X-ray Flashes (XRFs) are, like Gamma-Ray Bursts (GRBs), thought to signal the collapse of massive stars in distant galaxies. Many models posit that the isotropic equivalent energies of XRFs are lower...
Implications of the Measured Image Size for the Radio Afterglow of GRB 030329 (2004)
Granot, Jonathan, Ramirez-Ruiz, Enrico, Loeb, Abraham
We use data on the image size of the radio afterglow of GRB 030329 (Taylor et al. 2004) to constrain the physical parameters of this explosion. Together with the observed broad band spectrum, this...
Supernova 1993J: a veiled pulsar in a binary system? (2004)
Ramirez-Ruiz, Enrico, Serenelli, Aldo M.
The recent report of a binary companion to the progenitor of supernova 1993J may provide important clues for identifying the nature of the nascent compact object. Given the estimates of the...
Ramirez-Ruiz, Enrico, Madau, Piero
There is now compelling evidence of a link between long-duration gamma-ray bursts (GRBs) and Type Ib/c supernovae (SNe). These core-collapse explosions are conjectured to radiate an anisotropic,...
The Case for a Misaligned Relativistic Jet from SN 2001em (2004)
Granot, Jonathan, Ramirez-Ruiz, Enrico
SN 2001em, identified as a Type Ic supernova, has recently been detected in the radio and X-rays, $\gtrsim$ 2 yr after the explosion. The high luminosities at such late times might arise from a...
Identifying young gamma-ray burst fossils (2004)
The recent reports of temporal and spectral peculiarities in the early stages of some afterglows suggest that we may be wrong in postulating a central engine which becomes dormant after the burst...
Dynamos, Super-pulsars and Gamma-ray bursts (2003)
Rosswog, Stephan, Ramirez-Ruiz, Enrico
The remnant of a neutron star binary coalescence is expected to be temporarily stabilised against gravitational collapse by its differential rotation. We explore the possibility of dynamo activity in...
Formation rates of core collapse SNe and GRBs (2003)
Izzard, Robert G., Ramirez-Ruiz, Enrico, Tout, Christopher A.
We study the evolution of stars that may be the progenitors of long-soft gamma-ray burst (GRBs) -- rotating naked helium stars presumed to have lost their envelopes to winds or companions. Our aim is...
On the Central Engine of short Gamma-ray Bursts (2003)
Rosswog, Stephan, Ramirez-Ruiz, Enrico
We assess two mechanisms to produce a short GRB from a neutron star coalescence: the annihilation of neutrino and anti-neutrino pairs and magnetic processes within the remnant. We find that the...
High Resolution Calculations of Merging Neutron Stars III: Gamma-Ray Bursts (2003)
Rosswog, Stephan, Ramirez-Ruiz, Enrico, Davies, Melvyn B.
Recent three dimensional, high-resolution simulations of neutron star coalescences are analysed to assess whether short gamma-ray bursts (GRBs) could originate from such encounters. The two most...
On the diversity of short GRBs (2003)
Rosswog, Stephan, Ramirez-Ruiz, Enrico
Hydrodynamical simulations of the last inspiral stages and the final coalescence of a double neutron star system are used to investigate the power of the neutrino-driven wind, the energy and momentum...
Accretion disk assembly and survival during the disruption of a neutron star by a black hole (2003)
Ramirez-Ruiz, Enrico, Lee, William H.
We study the formation of accretion disks resulting from dynamical three dimensional binary coalescence calculations, where a neutron star is tidally disrupted before being swallowed by its black...
Jets, winds and bursts from coalescing neutron stars (2002)
Rosswog, Stephan, Ramirez-Ruiz, Enrico
Recent high-resolution calculations of neutron star coalescences are used to investigate whether nu bar{nu} annihilation can provide sufficient energy to power gamma-ray bursts, especially those...
Lee, William H., Ramirez-Ruiz, Enrico
We study the hydrodynamical evolution of massive accretion disks around black holes, formed when a neutron star is disrupted by a black hole in a binary system. Initial conditions are taken from 3D...
On The Spectral Energy Dependence of Gamma-Ray Burst Variability (2002)
Lloyd-Ronning, Nicole M., Ramirez-Ruiz, Enrico
The variable activity of a gamma-ray burst (GRB) source is thought to be correlated with its absolute peak luminosity - a relation that, if confirmed, can be used to derive an independent estimate of...
Events in the life of a cocoon surrounding a light, collapsar jet (2002)
Ramirez-Ruiz, Enrico, Celotti, Annalisa, Rees, Martin J.
According to the collapsar model, gamma-ray bursts are thought to be produced in shocks that occur after the relativistic jet has broken free from the stellar envelope. If the mass density of the...
Gamma-ray bursts in normal and extreme star-forming galaxies (2002)
Trentham, Neil, Ramirez-Ruiz, Enrico, Blain, A. W.
We discuss how gamma-ray burst (GRB) optical afterglows and multiwavelength observations of their host galaxies can be used to obtain information about the relative amounts of star formation...
Soft X-ray emission lines in the early afterglow of gamma-ray bursts (2002)
Lazzati, Davide, Ramirez-Ruiz, Enrico, Rees, Martin J.
We compute the luminosity of K_alpha emission lines produced by astrophysically abundant elements in the soft X-ray spectra of the early afterglow of gamma-ray bursts. We find that the detection of...
Ramirez-Ruiz, Enrico, Lloyd-Ronning, Nicole M.
The variety of gamma-ray burst phenomenology could be largely attributable to differences in the opening angle of an isotropic outflow or to a standard type of event viewed from different...
Constraints on the Bulk Lorentz Factor of GRB 990123 (2002)
Soderberg, Alicia M., Ramirez-Ruiz, Enrico
GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We present the collective constraints on the bulk Lorentz factor for this burst based on estimates...
Hard X-ray afterglows of short GRBs (2002)
Lazzati, Davide, Ramirez-Ruiz, Enrico, Ghisellini, Gabriele
We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of the four channel BATSE light curves of 76...
The birth place of gamma-ray bursts: abundance gradients and constraints on progenitors (2001)
Ramirez-Ruiz, Enrico, Lazzati, Davide, Blain, Andrew W.
The physics of gamma-ray bursts (GRBs) and their offsets from the centers of their host galaxies are used to investigate the evolutionary state of their progenitors, motivated by the popular idea...
Precursors and electron-positron pair loading from erupting fireballs (2001)
Ramirez-Ruiz, Enrico, MacFadyen, Andrew I., Lazzati, Davide
Recent observations suggest that long-duration gamma-ray bursts and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. As the jet makes its way out of the...
Was GRB 990123 a unique optical flash? (2001)
Soderberg, Alicia M., Ramirez-Ruiz, Enrico
GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation...
Possible detection of hard X-ray afterglows of short gamma-ray bursts (2001)
Lazzati, Davide, Ramirez-Ruiz, Enrico, Ghisellini, Gabriele
We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of the four channel BATSE light curves of 76...
Iron K-alpha Emission from X-ray Reflection: Predictions for Gamma-Ray Burst Models (2001)
Ballantyne, David R., Ramirez-Ruiz, Enrico
Recent observations of several gamma-ray burst (GRB) afterglows have shown evidence for a large amount of X-ray line emitting material, possibly arising from ionized iron. A significant detection of...
Lloyd-Ronning, Nicole M., Fryer, Chris L., Ramirez-Ruiz, Enrico
Using 220 Gamma-Ray Burst (GRB) redshifts and luminosities derived from the luminosity-variability relationship of Fenimore & Ramirez-Ruiz (2000), we show that there exists a significant correlation...
Ramirez-Ruiz, Enrico, Trentham, Neil, Blain, A. W.
The properties of gamma-ray bursts (GRBs) and their afterglows are used to investigate the location of star formation activity through the history of the Universe. This approach is motivated by the...
Winds from massive stars: implications for the afterglows of gamma-ray bursts (2000)
Ramirez-Ruiz, Enrico, Dray, Lynnette M., Madau, Piero, Tout, Christopher A.
Recent observations suggest that long-duration gamma-ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. The pre-explosive ambient...
Cosmic Gamma-Ray Bursts as a Probe of Star Formation History (2000)
Ramirez-Ruiz, Enrico, Fenimore, Edward E., Trentham, Neil
The cosmic gamma-ray burst (GRB) formation rate, as derived from the variability-luminosity relation for long-duration GRBs, is compared with the cosmic star formation rate. If GRBs are related to...
Completely dark galaxies: their existence, properties, and strategies for finding them (2000)
Trentham, Neil, Moeller, Ole, Ramirez-Ruiz, Enrico
There are a number of theoretical and observational hints that large numbers of low-mass galaxies composed entirely of dark matter exist in the field. The theoretical considerations follow from the...
Ramirez-Ruiz, Enrico, Merloni, Andrea
Although more than 2000 astronomical gamma-ray bursts (GRBs) have been detected, the precise progenitor responsible for these events is unknown. The temporal phenomenology observed in GRBs can...
Quiescent times in gamma-ray bursts: II. Dormant periods in the central engine? (2000)
Ramirez-Ruiz, Enrico, Merloni, Andrea, Rees, Martin J.
Within the framework of the internal-external shocks model for gamma-ray bursts, we study the various mechanisms that can give rise to quiescent times in the observed gamma-ray light-curves. In...
A Possible Cepheid-Like Luminosity Estimator for the Long Gamma-Ray Bursts (2000)
Reichart, Daniel E., Lamb, Donald Q., Fenimore, Edward E., Ramirez-Ruiz, Enrico, Cline, Thomas L., Hurley, Kevin
We present a possible Cepheid-like luminosity estimator for the long gamma-ray bursts based on the variability of their light curves. To construct the luminosity estimator, we use CGRO/BATSE data for...