@article{segura_lazzati_sankarasubramanian_2013, title={The use of broken power-laws to describe the distributions of daily flow above the mean annual flow across the conterminous U.S.}, volume={505}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/j.jhydrol.2013.09.016}, DOI={10.1016/j.jhydrol.2013.09.016}, abstractNote={A recent study employed a broken power-law (BPL) distribution for understanding the scaling frequency of bankfull discharge in snowmelt-dominated basins. This study, grounded from those findings, investigated the ability of a BPL function to describe the distribution of daily flows above the mean annual flow in 1217 sites across the conterminous U.S. (CONUS). The hydrologic regime in all the sites is unregulated and spans a wide range in drainage areas (2–120,000 km2) and elevation (0–3000 m). Available daily flow records in all sites varied between 15 and 108 years. Comparing the performance of BPL distribution and the traditionally used lognormal distribution, we found that BPL provides stronger fit in ∼80% of the sites. Thus the BPL function provides a suitable tool to model daily flows in most areas of the CONUS. The potential for developing a model for predicting the frequency distribution of daily flows in ungauged sites was analyzed. We found that such model is possible using drainage area, mean basin elevation, and mean annual precipitation as predicting variables for any site located above 600 m across the CONUS. We also found strong continental-wide correlations between 3 of the 4 parameters that describe the BPL and basin characteristics. Our results indicate that the BPL function provides a robust alternative to traditional functions such as the lognormal to model the statistical variation of daily flows above the mean annual in most basins of the CONUS.}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Segura, Catalina and Lazzati, Davide and Sankarasubramanian, Arumugam}, year={2013}, month={Nov}, pages={35–46} }
 @article{segura_james_lazzati_roulet_2012, title={Scaling relationships for event water contributions and transit times in small-forested catchments in Eastern Quebec}, volume={48}, journal={Water Resources Research}, author={Segura, C. and James, A. L. and Lazzati, D. and Roulet, N. T.}, year={2012} }
 @article{lazzati_2011, title={ASTROPHYSICS The awakening of a cosmic monster}, volume={476}, ISSN={["0028-0836"]}, DOI={10.1038/476405a}, abstractNote={Most galaxies harbour giant black holes; some are 'silent' whereas others produce copious amounts of radiation. The awakening of a silent monster has just been witnessed as it breaks apart and swallows a nearby star. See Letters p.421 & p.425 Two groups report observations of the X-ray source Swift J164449.3+573451, which was discovered when it triggered the Swift Burst Alert Telescope on 28 March 2011. Burrows et al. report that the source has increased in brightness in the X-ray band more than 10,000-fold since 1990, and by more than 100-fold since early 2010. They conclude that we are observing the onset of relativistic jet activity from a supermassive black hole. Zauderer et al. arrive at a similar conclusion based on their observation of a radio transient associated with the source, and extensive monitoring at centimetre to millimetre wavelengths during the first month of its evolution. They estimate the mass of the black hole at around 106 solar masses.}, number={7361}, journal={NATURE}, author={Lazzati, Davide}, year={2011}, month={Aug}, pages={405–406} }
 @article{lazzati_begelman_2010, title={NON-THERMAL EMISSION FROM THE PHOTOSPHERES OF GAMMA-RAY BURST OUTFLOWS. I. HIGH-FREQUENCY TAILS}, volume={725}, ISSN={["0004-637X"]}, DOI={10.1088/0004-637x/725/1/1137}, abstractNote={We study the spectrum of high-frequency radiation emerging from mildly dissipative photospheres of long-duration gamma-ray burst outflows. Building on the results of recent numerical investigations, we assume that electrons are heated impulsively to mildly relativistic energies by either shocks or magnetic dissipation at Thomson optical depths of several and subsequently cool by inverse Compton, scattering off the thermal photons of the photosphere. We show that even in the absence of magnetic field and non-thermal leptons, inverse Compton scattering produces power-law tails that extend from the peak of the thermal radiation, at several hundred keV, to several tens of MeV, and possibly up to GeV energies. The slope of the high-frequency power law is predicted to vary substantially during a single burst, and the model can easily account for the diversity of high-frequency spectra observed by BATSE. Our model works in baryonic as well as in magnetically dominated outflows, as long as the magnetic field component is not overwhelmingly dominant.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Lazzati, Davide and Begelman, Mitchell C.}, year={2010}, month={Dec}, pages={1137–1145} }
 @article{morsony_lazzati_begelman_2010, title={THE ORIGIN AND PROPAGATION OF VARIABILITY IN THE OUTFLOWS OF LONG-DURATION GAMMA-RAY BURSTS}, volume={723}, ISSN={["1538-4357"]}, DOI={10.1088/0004-637x/723/1/267}, abstractNote={We present the results of hydrodynamical simulations of gamma-ray burst (GRB) jets propagating through their stellar progenitor material and subsequently through the surrounding circumstellar medium. We consider both jets that are injected with constant properties in the center of the star and jets injected with a variable luminosity. We show that the variability properties of the jet outside the star are a combination of the variability injected at the base of the jet and the variability caused by the jet propagation through the star. Comparing power spectra for the two cases shows that the variability injected by the engine is preserved even if the jet is heavily shocked inside the star. Such shocking produces additional variability at long timescales, of order several seconds. Within the limited number of progenitors and jets investigated, our findings suggest that the broad pulses of several seconds duration typically observed in GRBs are due to the interaction of the jet with the progenitor, while the short-timescale variability, characterized by fluctuations on timescales of milliseconds, has to be injected at the base of the jet. Studying the properties of the fast variability in GRBs may therefore provide clues to the nature of the inner engine and the mechanisms of energy extraction from it.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Morsony, Brian J. and Lazzati, Davide and Begelman, Mitchell C.}, year={2010}, month={Nov}, pages={267–276} }
 @article{keith_lazzati_2011, title={Thermal fluctuations and nanoscale effects in the nucleation of carbonaceous dust grains}, volume={410}, ISSN={["0035-8711"]}, DOI={10.1111/j.1365-2966.2010.17478.x}, abstractNote={We investigate the role of thermal fluctuations and of the finite number of monomers in small clusters of carbon atoms on the nucleation rate of carbonaceous grains. Thermal fluctuations are due to the quantized nature of the energy exchanges between the clusters, the gas and the radiation field. Nanoscale effects modify the spontaneous detachment of monomers due to the finite amount of internal energy contained in small clusters. We find that both corrections have a big impact on the stability of the clusters and on the rate of nucleation. We implement our model within a Monte Carlo code to derive the new stability conditions for clusters as well as nucleation rates. Due to computing limitations, we can explore the consequences of this approach only at high temperatures, at which particle interactions are not much less frequent than photon interactions. We found that the combined effect of the detachment correction and the temperature fluctuations produces faster nucleation. We also found that the nucleation rate depends on the composition of the gas and not only on the partial pressure of the compound that condensates into grains. This is a unique result of this model that can be used to prove or disprove it.}, number={1}, journal={MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY}, author={Keith, Adam C. and Lazzati, Davide}, year={2011}, month={Jan}, pages={685–693} }
 @article{lazzati_blackwell_morsony_begelman_2011, title={X-ray flares from propagation instabilities in long gamma-ray burst jets}, volume={411}, ISSN={["0035-8711"]}, DOI={10.1111/j.1745-3933.2010.00984.x}, abstractNote={Abstract
               We present a numerical simulation of a gamma-ray burst jet from a long-lasting engine in the core of a 16 solar mass Wolf–Rayet star. The engine is kept active for 6000 s with a luminosity that decays in time as a power law with index −5/3. Even though there is no short time-scale variability in the injected engine luminosity, we find that the jet's kinetic luminosity outside the progenitor star is characterized by fluctuations with relatively short time-scale. We analyse the temporal characteristics of those fluctuations and we find that they are consistent with the properties of observed flares in X-ray afterglows. The peak-to-continuum flux ratio of the flares in the simulation is consistent with some, but not all, the observed flares. We propose that propagation instabilities, rather than variability in the engine luminosity, are responsible for the X-ray flares with moderate contrast. Strong flares such as the one detected in GRB 050502B, instead, cannot be reproduced by this model and require strong variability in the engine activity.}, number={1}, journal={MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY}, author={Lazzati, D. and Blackwell, C. H. and Morsony, B. J. and Begelman, M. C.}, year={2011}, month={Feb}, pages={L16–L20} }
 @article{lazzati_begelman_2009, title={POLARIZATION SIGNATURE OF GAMMA-RAY BURSTS FROM FRAGMENTED FIREBALLS}, volume={700}, ISSN={["2041-8205"]}, DOI={10.1088/0004-637X/700/2/L141}, abstractNote={We study the polarization properties of the prompt emission of gamma-ray bursts (GRBs) produced by fragmented fireballs. Such fireballs, known in the literature under various names, are made by the superposition of many individual blobs, each of which produces a spike in the light curve. The differences between pulses are due both to the intrinsic diversity in the blobs' properties and to their orientation with respect to the line of sight. We show that the peak flux and the polarization of each pulse are connected through the orientation of the blob that produces the pulse, while the position angle fluctuates randomly from one pulse to the next and is constant within an individual pulse. The most polarized pulses are those with approximately one-tenth the peak flux of the brightest pulse. These conclusions do not depend on the assumed radiation mechanism nor on the energy and Lorentz factor of the blobs. We compare the prediction of this model to a simulated set of observations, showing that a limited sample of GRBs with time-resolved polarization measurements would provide a crucial test for this model. We finally show that a hint of the predicted correlation may have been already observed.}, number={2}, journal={ASTROPHYSICAL JOURNAL LETTERS}, author={Lazzati, Davide and Begelman, Mitchell C.}, year={2009}, month={Aug}, pages={L141–L144} }
 @article{robinson_perna_lazzati_marle_2010, title={The rest-frame ultraviolet spectra of GRBs from massive rapidly rotating stellar progenitors}, volume={401}, ISSN={["0035-8711"]}, DOI={10.1111/j.1365-2966.2009.15672.x}, abstractNote={The properties of a massive star prior to its final explosion are imprinted in the circumstellar medium (CSM) created by its wind and termination shock. We perform a detailed, comprehensive calculation of the time-variable and angle-dependent transmission spectra of an average-luminosity gamma-ray burst (GRB) which explodes in the CSM structure produced by the collapse of a 20 M ⊙ , rapidly rotating, Z = 0.001 progenitor star. We study both the case in which metals are initially in the gaseous phase and the situation in which they are heavily depleted into dust. We find that high-velocity lines from low-ionization states of silicon, carbon and iron are initially present in the spectrum only if the metals are heavily depleted into dust prior to the GRB explosion. However, such lines disappear on time-scales of a fraction of a second for a burst observed on-axis, and of a few seconds for a burst seen at high latitude, making their observation virtually impossible. Rest-frame lines produced in the termination shock are instead clearly visible in all conditions. We conclude that time-resolved, early-time spectroscopy is not a promising way in which the properties of the GRB progenitor wind can be routinely studied. Previous detections of high-velocity features in GRB ultraviolet spectra must have been either due to a superposition of a physically unrelated absorber or due to a progenitor star with very unusual properties.}, number={1}, journal={MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY}, author={Robinson, Peter B. and Perna, Rosalba and Lazzati, Davide and Marle, Allard J.}, year={2010}, month={Jan}, pages={88–98} }
 @article{lazzati_morsony_begelman_2009, title={VERY HIGH EFFICIENCY PHOTOSPHERIC EMISSION IN LONG-DURATION gamma-RAY BURSTS}, volume={700}, DOI={10.1088/0004-637X/700/1/L47}, abstractNote={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 the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very efficient radiator, capable of converting more than half of the total energy of the jet into radiation. We show that bright photospheres are a common feature of jets born inside massive progenitor stars and that this effect can explain the high radiative efficiency observed in long-duration bursts.}, number={1}, journal={ASTROPHYSICAL JOURNAL LETTERS}, author={Lazzati, Davide and Morsony, Brian J. and Begelman, Mitchell C.}, year={2009}, month={Jul}, pages={L47–L50} }
 @article{piranomonte_d'avanzo_covino_antonelli_beardmore_campana_chincarini_d'elia_della valle_fiore_et al._2008, title={The short GRB 070707 afterglow and its very faint host galaxy}, volume={491}, number={1}, journal={Astronomy and Astrophysics (Berlin, Germany : West)}, author={Piranomonte, S. and D'Avanzo, P. and Covino, S. and Antonelli, L. A. and Beardmore, A. P. and Campana, S. and Chincarini, G. and D'Elia, V. and Della Valle, M. and Fiore, F. and et al.}, year={2008}, pages={183–188} }