Short-duration gamma-ray bursts from off-axis collapsars (2009)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
We present 2D high resolution hydrodynamic simulations of the relativistic outflows of long-duration gamma-ray burst progenitors. We analyze the properties of the outflows at wide off-axis angles,...
Polarization signature of gamma-ray bursts from fragmented fireballs (2009)
Lazzati, Davide, Begelman, Mitchell
We study the polarization properties of the prompt emission of gamma-ray bursts produced by fragmented fireballs. Such fireballs, known in the literature under various names, are made by the...
X-ray Polarization of Gamma-Ray Bursts (2009)
The degree and the temporal evolution of linear polarization in the prompt and afterglow emission of gamma-ray bursts is a very robust diagnostic of some key features of gamma-ray bursts jets and...
Very high efficiency photospheric emission in long duration gamma-ray bursts (2009)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitch
We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that...
Precursors in Swift Gamma Ray Bursts with Redshift (2008)
Burlon, Davide, Ghirlanda, Giancarlo, Ghisellini, Gabriele, Lazzati, Davide, Nava, Lara, Nardini, Marco, ...
We study a sample of Gamma-Ray Bursts detected by the Swift satellite with known redshift which show a precursor in the Swift-BAT light curve. We analyze the spectra of the precursors and compare...
Jitter radiation images, spectra, and light curves from a relativistic spherical blastwave (2008)
Morsony, Brian J., Workman, Jared C., Lazzati, Davide, Medvedev, Mikhail V.
We consider radiation emitted by the jitter mechanism in a Blandford-McKee self-similar blastwave. We assume the magnetic field configuration throughout the whole blastwave meets the condition for...
A direct measurement of the dust extinction curve in an intermediate-redshift galaxy (2008)
Heng, Kevin, Lazzati, Davide, Perna, Rosalba, Garnavich, Peter, Noriega-Crespo, Alberto, Bersier, David, ...
We present a proof-of-concept study that dust extinction curves can be extracted from the infrared (IR), optical, ultraviolet (UV), and X-ray afterglow observations of GRBs without assuming known...
X-ray flares, neutrino cooled disks, and the dynamics of late accretion in GRB engines (2008)
Lazzati, Davide, Perna, Rosalba, Begelman, Mitchell C.
We compute the average luminosity of X-ray flares as a function of time, for a sample of 10 long-duration gamma-ray burst afterglows. The mean luminosity, averaged over a timescale longer than the...
X-ray flares and their relation to the inner engine activity of GRBs (2008)
Lazzati, Davide, Morsony, Brian J., Perna, Rosalba, Begelman, Mitchell C.
Flares overlaid on the smooth power-law decay of Swift X-ray afterglows are rather common, appearing in roughly half the observed light curves. They are a manifestation of the late time activity of...
A Direct Measurement of the Dust Extinction Curve in an Intermediate-Redshift Galaxy (2008)
Heng, Kevin, Lazzati, Davide, Perna, Rosalba, Garnavich, Peter, Noriega-Crespo, Alberto, Bersier, David, ...
We present a proof-of-concept study that dust extinction curves can be extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow observations of GRBs without assuming known...
The unexpected clustering of the optical afterglow luminosities (2007)
Nardini, Marco, Ghisellini, Gabriele, Ghirlanda, Giancarlo, Tavecchio, Fabrizio, Firmani, Claudio, Lazzati, Davide
We studied the behaviour of the optical afterglow lightcurves of a sample of 24 Gamma--Ray Bursts (GRBs) with known redshift and published estimates of the optical extinction in the source frame,...
Non-LTE dust nucleation in sub-saturated vapors (2007)
We use the kinetic theory of nucleation to explore the properties of dust nucleation in sub-saturated vapors. Due to radiation losses, the sub-critical clusters have a smaller temperature compared to...
Jitter radiation in gamma-ray bursts and their afterglows: emission and self-absorption (2007)
Workman, Jared, Morsony, Brian, Lazzati, Davide, Medvedev, Mikhail
Relativistic electrons moving into a highly tangled magnetic field emit jitter radiation. We present a detailed computation of the jitter radiation spectrum, including self-absorption, for electrons...
Medvedev, Mikhail V., Lazzati, Davide, Morsony, Brian C., Workman, Jared C.
The standard model of GRB afterglows assumes that the radiation observed as a delayed emission is of synchrotron origin, which requires the shock magnetic field to be relatively homogeneous on small...
Dust Echoes from the Ambient Medium of Gamma-Ray Bursts (2007)
Heng, Kevin, Lazzati, Davide, Perna, Rosalba
Long gamma-ray bursts (GRBs) are likely associated with the collapse of massive stars, which produce dust and are born in dusty environments. Absorption and scattering of ultraviolet/X-ray photons...
The physics of GRB jets and their interaction with the progenitor star (2006)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
It is now generally accepted that long gamma-ray bursts are associated with the final evolutionary stages of massive stars. As a consequence, their jets must propagate through the stellar progenitor...
GRB progenitors and their environments (2006)
The detection of supernova features in the late spectra of several gamma-ray burst afterglows has shown that at least a fraction of long-duration gamma-ray bursts are associated to the final...
Gamma-Ray Burst jet dynamics and their interaction with the progenitor star (2006)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
The association of at least some long gamma-ray bursts with type Ic supernova explosions has been established beyond reasonable doubt. Theoretically, the challenge is to explain the presence of a...
X-ray flares and the duration of engine activity in gamma-ray bursts (2006)
Lazzati, Davide, Perna, Rosalba
The detection of bright X-ray flares superimposed on the regular afterglow decay in Swift gamma-ray bursts has triggered theoretical speculations on their origin. We study the temporal properties of...
Temporal and Angular Properties of GRB Jets Emerging from Massive Stars (2006)
Morsony, Brian J., Lazzati, Davide, Begelman, Mitchell C.
We study the long-term evolution of relativistic jets in collapsars and examine the effects of viewing angle on the subsequent gamma ray bursts. We carry out a series of high-resolution simulations...
Polarization in the prompt emission of gamma-ray bursts and their afterglows (2006)
Synchrotron is considered the dominant emission mechanism in the production of gamma-ray burst photons in the prompt as well as in the afterglow phase. Polarization is a characteristic feature of...
Thick fireballs and the steep decay in the early X-ray afterglow of gamma-ray bursts (2005)
Lazzati, Davide, Begelman, Mitchell C.
We study the early afterglows of gamma-ray bursts produced by geometrically thick fireballs, following the development of the external shock as energy is continually supplied to the shocked material....
GRB Progenitors and Environment (2005)
The study and knowledge of the environment of Gamma-Ray Bursts is of great interest from many points of view. For high redshift (z>0.5) events, the structure of the ambient medium is one of the best...
SGR giant flares in the BATSE short GRB catalogue: constraints from spectroscopy (2005)
Lazzati, Davide, Ghirlanda, Giancarlo, Ghisellini, Gabriele
The giant flare observed on Dec. 27th 2004 from SGR 1806-20 has revived the idea that a fraction of short (
Universal GRB jets from jet-cocoon interaction in massive stars (2005)
Lazzati, Davide, Begelman, Mitchell
We consider the time-dependent evolution of a relativistic jet following its breakout through the surface of a massive compact star, as envisaged in the collapsar model of gamma-ray bursts. At...
Gamma-Ray Bursts and Afterglow Polarisation (2004)
Covino, Stefano, Rossi, Elena, Lazzati, Davide, Malesani, Daniele, Ghisellini, Gabriele
Polarimetry of Gamma-Ray Burst (GRB) afterglows in the last few years has been considered one of the most effective tool to probe the geometry, energetic, dynamics and the environment of GRBs. We...
Precursor activity in bright long BATSE gamma-Ray Bursts (2004)
We study a sample of bright long BATSE GRB light curves in the 200 s before the detection of the GRB prompt emission. We find that in a sizable fraction of cases (20 %) there is evidence of emission...
Internal shocks and the blazar sequence. Low and intermediate power BL Lac objects (2004)
Guetta, Dafne, Ghisellini, Gabriele, Lazzati, Davide, Celotti, Annalisa
We consider internal shocks as the main dissipation mechanism responsible for the emission in blazars and show that it can satisfactorily account for the properties of all blazars. In particular, we...
Gamma-Ray Burst Progenitors Confront Observations (2004)
The discovery of a supernova emerging at late times in the afterglow of GRB 030329 has apparently settled the issue on the nature of the progenitor of gamma-ray bursts. We now know that at least a...
Internal shocks and the blazar sequence. Low and intermediate power BL Lac objects (2004)
Guetta, Dafne, Ghisellini, Gabriele, Lazzati, Davide, Celotti, Annalisa
We consider internal shocks as the main dissipation mechanism responsible for the emission in blazars and show that it can satisfactorily account for the properties of all blazars. In particular, we...
Linear polarization on Gamma-Ray Bursts: from the prompt to the late afterglow (2003)
The past year has witnessed a large increase in our knowledge of the polarization properties of Gamma-Ray Burst (GRB) radiation. In the prompt phase, the measurement (albeit highly debated) of a...
Compton drag as a mechanism for very high linear polarization in Gamma-Ray Bursts (2003)
Lazzati, Davide, Rossi, Elena, Ghisellini, Gabriele, Rees, Martin J.
The recent claim by Coburn & Boggs to have detected a very high degree of linear polarization in the prompt emission of GRB 021206 has stimulated interest in how much polarization could arise in...
Reconsidering the origin of the X-ray emission lines in GRB 011211 (2003)
Tavecchio, Fabrizio, Ghisellini, Gabriele, Lazzati, Davide
We reanalyze the XMM--Newton data of GRB 011211 showing that the spectral features, interpreted by Reeves et al. (2002, 2003) as due thermal emission from a collisionally ionized plasma, can be also...
Polarization of Gamma--Ray Burst Optical and Near-Infrared Afterglows (2003)
Covino, Stefano, Ghisellini, Gabriele, Lazzati, Davide, Malesani, Daniele
Gamma-Ray Burst afterglow polarization measurements, in spite of their intrinsic difficulties, have been carried out for a number of events that begins to be adequate to draw some general statistical...
Gamma-Ray Bursts environment and progenitors (2003)
The properties of the ambient medium in which GRBs go off are an important piece of the puzzle, not only as an issue in itself, but because of their link with the nature of the progenitor. In this...
Lazzati, Davide, Perna, Rosalba
We use the time-dependent photoionization and dust destruction code developed by Perna & Lazzati (2002) to study the time evolution of the medium in a dusty gaseous cloud illuminated by a bright...
Perna, Rosalba, Lazzati, Davide, Fiore, Fabrizio
The interaction of a radiation field with a dusty medium is a relevant issue in several astrophysical contexts. We use the time-dependent photoionization code in a dusty medium developed by Perna &...
X-ray lines, progenitor and beaming of Gamma-Ray Bursts (2002)
X-ray emission features have been detected in at least five GRB afterglows. Their detection and properties are of great importance in our understanding of the nature of the GRB progenitor. Moreover,...
Thermal components in the early X-ray afterglow of GRBs (2002)
The possible presence of thermal components in the early X-ray afterglows of gamma-ray bursts is investigated. We discuss both the presence of a thermal continuum and, in particular, of collisional...
Time-Dependent Photoionization in a Dusty Medium I: Code Description and General Results (2002)
Perna, Rosalba, Lazzati, Davide
We present a time-dependent photoionization code that combines self-consistently metal evolution and dust destruction under an intense X-ray UV radiation field. Firstly, we extend the mathematical...
The role of photon scattering in shaping the lightcurves and spectra of gamma-ray bursts (2002)
We analyze the power spectra of the lightcurves of long gamma-ray bursts, dividing the sample in bins of luminosity, using the recently discovered variability-luminosity correlation. We find that the...
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...
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...
X-ray spectroscopy of gamma-ray bursts: the path to the progenitor (2002)
Lazzati, Davide, Perna, Rosalba, Ghisellini, Gabriele
Despite great observational and theoretical effort, the burst progenitor is still a mysterious object. It is generally accepted that one of the best ways to unveil its nature is the study of the...
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...
Lazzati, Davide, Perna, Rosalba
We investigate through dedicated numerical simulations the evolution of the soft X-ray absorption properties of a cloud surrounding a gamma-ray burst source. We show that the absorption properties of...
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...
Time dependent photoionization opacities in dense Gamma-Ray Burst environments (2001)
Lazzati, Davide, Perna, Rosalba, Ghisellini, Gabriele
The recent detection of a transient absorption feature in the X-ray prompt emission of GRB 990705 showed the importance of such observations in the understanding of gamma-ray bursts and their...
Internal shocks in the jets of radio-loud quasars (2001)
Spada, Maddalena, Ghisellini, Gabriele, Lazzati, Davide, Celotti, Annalisa
The central engine causing the production of jets in radio sources may work intermittently, accelerating shells of plasma with different mass, energy and velocity. Faster but later shells can then...
The BMW X-ray Cluster Survey (2001)
Moretti, Alberto, Guzzo, Luigi, Campana, Sergio, Covino, Stefano, Lazzati, Davide, Longhetti, Marcella, ...
We describe the main features of the BMW survey of serendipitous X-ray clusters, based on the still unexploited ROSAT-HRI archival observations. The sky coverage, surface density and first deep...
Early afterglows as probes for the reionization epoch (2001)
Lazzati, Davide, Ghisellini, Gabriele, Haardt, Francesco, Fernandez-Soto, Alberto
The nature of Gamma-Ray Burst progenitors is still a debated issue, but consensus is growing on the association of GRBs with massive stars. Furthermore, current models for the reionization of the...
Illuminated, and enlightened, by GRB 991216 (2000)
Vietri, Mario, Ghisellini, Gabriele, Lazzati, Davide, Fiore, Fabrizio, Stella, Luigi
We consider models for the generation of the emission line recently discovered in the X-ray afterglow spectrum of several bursts, and especially of GRB 991216 observed by Chandra. These observations...
Internal shocks in the jets of blazars (2000)
Spada, Maddalena, Lazzati, Davide, Ghisellini, Gabriele, Celotti, Annalisa
The development of instabilities leading to the formation of internal shocks is expected in the relativistic outflows of both gamma-ray bursts and blazars. The shocks heat the expanding ejecta,...
Constraints on the emission mechanisms of gamma-ray bursts (1999)
Ghisellini, Gabriele, Celotti, Annalisa, Lazzati, Davide
If the emission of gamma-ray bursts were due to the synchrotron process in the standard internal shock scenario, then the typical observed spectrum should have a slope F(nu) \propto nu^{-1/2}, which...
Compton Dragged Gamma--Ray Bursts associated with Supernovae (1999)
Lazzati, Davide, Ghisellini, Gabriele, Celotti, Annalisa, Rees, Martin J.
It is proposed that the gamma-ray photons that characterize the prompt emission of Gamma-Ray Bursts are produced through the Compton drag process, caused by the interaction of a relativistic fireball...
Constraints on the bulk Lorentz factor in the internal shock scenario for gamma-ray bursts (1999)
Lazzati, Davide, Ghisellini, Gabriele
We investigate, independently of specific emission models, the constraints on the value of the bulk Lorentz factor Gamma of a fireball. We assume that the burst emission comes from internal shocks in...
Polarization lightcurves and position angle variation of beamed gamma-ray bursts (1999)
Ghisellini, Gabriele, Lazzati, Davide
The recently detected linear polarization in the optical lightcurve of GRB 990510 renewed the interest on how polarization can be produced in gamma-ray burst fireballs. Here we present a model based...
GRB Redshift determination in the X-ray band (1999)
Campana, Sergio, Ghisellini, Gabriele, Lazzati, Davide, Haardt, Francesco, Covino, Stefano
If gamma-ray bursts originate in dense stellar forming regions, the interstellar material can imprint detectable absorption features on the observed X-ray spectrum. Such features can be detected by...
Iron line in the afterglow: a key to the progenitor (1999)
Lazzati, Davide, Ghisellini, Gabriele, Campana, Sergio
The discovery of a powerful and transient iron line feature in the X-ray afterglow spectrum of GRB 970508 and GRB 970828, if confirmed, would be a major breakthrough for understanding the nature the...
Iron line afterglows: general constraints (1999)
Ghisellini, Gabriele, Lazzati, Davide, Campana, Sergio
The discovery of a powerful and transient iron line feature in the X-ray afterglow spectra of gamma-ray bursts would be a major breakthrough for understanding the nature of their progenitors,...
Iron line afterglows: how to produce them (1999)
Lazzati, Davide, Campana, Sergio, Ghisellini, Gabriele
We discuss how a powerful iron line emission can be produced if ~1-5 iron rich solar masses are concentrated in the close vicinity of the burst. Recombination, thermal and fluorescent reflection are...
The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. I: the algorithm (1999)
Lazzati, Davide, Campana, Sergio, Rosati, Piero, Panzera, Maria Rosa, Tagliaferri, Gianpiero
We present a new detection algorithm based on the wavelet transform for the analysis of high energy astronomical images. The wavelet transform, due to its multi-scale structure, is suited for the...
Campana, Sergio, Lazzati, Davide, Panzera, Maria Rosa, Tagliaferri, Gianpiero
The wavelet detection algorithm (WDA) described in the accompanying paper by Lazzati et al. is made suited for a fast and efficient analysis of images taken with the High Resolution Imager (HRI)...
Iron line in the afterglow: a key to unveil Gamma-Ray Burst progenitors (1999)
Lazzati, Davide, Campana, Sergio, Ghisellini, Gabriele
The discovery of a powerful and transient iron line feature in the X-ray afterglow spectra of gamma-ray bursts would be a major breakthrough for understanding the nature of their progenitors. Piro et...
Constraints on the bulk Lorentz factor in the internal shock scenario for gamma-ray bursts (1999)
Lazzati, Davide, Ghisellini, Gabriele, Celotti, Annalisa
We investigate, independently of specific emission models, the constraints on the value of the bulk Lorentz factor Gamma of a fireball. We assume that the burst emission comes from internal shocks in...
EISily looking for distant galaxy clusters (1998)
Lobo, Catarina, Lazzati, Davide, Iovino, Angela, Guzzo, Luigi, Chincarini, Guido
We present a new algorithm to search for distant clusters of galaxies on catalogues deriving from imaging data, as those of the ESO Imaging Survey. We discuss the advantages of our technique relative...
On the location of X-ray peaks and dominant galaxies in clusters (1998)
Lazzati, Davide, Chincarini, Guido
We analyze the structure of the X-ray emission of a sample of 22 Abell clusters of galaxies with a cD in their centre, observed with the ROSAT PSPC. Utilizing the multi-scale power of the Wavelet...
On the relationship between the periodic and aperiodic variability of accreting X-ray pulsars (1996)
Lazzati, Davide, Stella, Luigi
Besides the narrow peaks originating from the periodic signal, the power spectra of accreting X-ray pulsars display continuum components usually increasing towards low frequencies; these arise from...