Showing 1–31 of 31 results for author: Barraud, C

Financial markets as a Le Bonian crowd during boom-and-bust episodes: A complementary theoretical framework in behavioural finance

Authors: Claire Barraud

Abstract: This article proposes a complementary theoretical framework in behavioural finance by interpreting financial markets during boom-and-bust episodes as a Le Bonian crowd. While behavioural finance has documented the limits of individual rationality through biases and heuristics, these contributions remain primarily microeconomic. A second, more macroeconomic strand appears to treat market instabilit… ▽ More This article proposes a complementary theoretical framework in behavioural finance by interpreting financial markets during boom-and-bust episodes as a Le Bonian crowd. While behavioural finance has documented the limits of individual rationality through biases and heuristics, these contributions remain primarily microeconomic. A second, more macroeconomic strand appears to treat market instability as the aggregated result of individual biases, although it generally does so without an explicit theoretical account of how such aggregation operates. In contrast, this paper adopts a macro-psychological -and therefore macroeconomic -perspective, drawing on classical crowd psychology (Le Bon, 1895; Tarde, 1901; Freud, 1921). The central claim is that during speculative booms and crashes, markets behave as psychological crowds governed by unconscious processes, suggestion, emotional contagion, and impulsive action. These episodes cannot be understood merely as the sum of individual departures from rationality, but as the emergence of a collective mental state that follows its own psychological laws. By reintroducing crowd psychology into behavioural finance, this paper clarifies the mechanisms through which market-wide irrationality arises and offers a theoretical foundation for a macrobehavioural understanding of financial instability. △ Less

Submitted 27 October, 2025; originally announced October 2025.

Decoupling thermoelectric coefficients of multilayer graphene by nanomeshing

Authors: Mehrdad Rahimi, Nunzia Lubertino, Roberto Bellelli, Linsai Chen, François Mallet, Philippe Lafarge, Clément Barraud, PAscal Marti, Julien Chaste, Danièle Fournier, Maria Luisa Della Rocca

Abstract: Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional (2D) materials, where surface effects dominate, and has been applied in the thermoelectric field. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomesh… ▽ More Nanostructuring materials at small scales enables control over their physical properties, revealing behaviors not observed at larger dimensions. This strategy is particularly effective in two-dimensional (2D) materials, where surface effects dominate, and has been applied in the thermoelectric field. Here, we use multilayer graphene (4-6 nm thick) as a test platform to study the effect of nanomeshing on its thermoelectric properties. The nanomesh consists of a hexagonal array of holes, with a measured diameter and neck-width of ~360 nm and ~160 nm, respectively. The multilayer graphene is integrated into field-effect transistor-like devices supported by hexagonal boron nitride (hBN), allowing simultaneous electric and thermoelectric measurements, with nanomeshing applied to only part of the material. We use modulated thermoreflectance to investigate thermal transport in equivalent nanomeshed and pristine graphene flakes, extracting key parameters that affect thermoelectric performance. The nanomesh geometry suppresses thermal transport without significantly impacting charge transport, highlighting the different scattering lengths of phonons and electrons while enhancing the thermopower response. We observe a twofold improvement in the device power factor, PF = S^2 sigma (with S the Seebeck coefficient and sigma the electrical conductivity), at room temperature, along with a nearly threefold reduction in thermal conductivity k. The results show that nanomeshing can significantly improve the thermoelectric performance of multilayer graphene, paving the way for novel energy conversion strategies using 2D materials. △ Less

Submitted 7 October, 2025; v1 submitted 4 July, 2025; originally announced July 2025.

Comments: 10 pages, 4 figures

Rb2Ti2O5 : a layered ionic conductor at the sub-micrometer scale

Authors: Valerio Digiorgio, Karen Sobnath, Maria Luisa Della Rocca, Clément Barraud, Rémi Federicci, Armel Descamps-Mandine, Brigitte Leridon

Abstract: Over the past few years, ionic conductors have gained a lot of attention given the possibility to implement them in various applications such as supercapacitors, batteries or fuel cells as well as for resistive memories. Especially, layered two-dimensional (2D) crystals such as h-BN, graphene oxide and MoSe2 have shown to provide unique properties originating from the specific 2D confinement of mo… ▽ More Over the past few years, ionic conductors have gained a lot of attention given the possibility to implement them in various applications such as supercapacitors, batteries or fuel cells as well as for resistive memories. Especially, layered two-dimensional (2D) crystals such as h-BN, graphene oxide and MoSe2 have shown to provide unique properties originating from the specific 2D confinement of moving ions. Two important parameters are the ion conductivity and the chemical stability over a wide range of operating conditions. In this vein, Rb2Ti2O5 has been recently found displaying remarkable properties such as superionic conduction and colossal equivalent dielectric constant. Here, a first approach to the study of the electrical properties of layered Rb2Ti2O5 at the 100-nanometer scale is presented. Characterizations by means of micro-Raman spectroscopy and atomic force microscope (AFM) measurements of mechanically exfoliated RTO nanocrystals via the so-called adhesive-tape technique are reported. Finally, the results of electrical measurements performed on an exfoliated RTO nanocrystals are presented, and are found to be consistent with the results obtained on macroscopic crystals. 4 △ Less

Submitted 22 July, 2024; originally announced July 2024.

Comments: 4 figures

Strong electronic winds blowing under liquid flows on carbon surfaces

Authors: Mathieu Lizée, Alice Marcotte, Baptiste Coquinot, Nikita Kavokine, Karen Sobnath, Clément Barraud, Ankit Bhardwaj, Boya Radha, Antoine Niguès, Lydéric Bocquet, Alessandro Siria

Abstract: The interface between a liquid and a solid is the location of plethora of intrincate mechanisms at the nanoscale, at the root of their specific emerging properties in natural processes or technological applications. However, while the structural properties and chemistry of interfaces have been intensively explored, the effect of the solid-state electronic transport at the fluid interface has been… ▽ More The interface between a liquid and a solid is the location of plethora of intrincate mechanisms at the nanoscale, at the root of their specific emerging properties in natural processes or technological applications. However, while the structural properties and chemistry of interfaces have been intensively explored, the effect of the solid-state electronic transport at the fluid interface has been broadly overlooked up to now. It has been reported that water flowing against carbon-based nanomaterials, such as carbon nanotubes or graphene sheets, does induce electronic currents, but the mechanism at stake remains controversial. Here, we unveil the molecular mechanisms underlying the hydro-electronic couplings by investigating the electronic conversion under flow at the nanoscale. We use a tuning fork-Atomic Force Microscope (AFM) to deposit and displace a micrometric droplet of both ionic and non-ionic liquids on a multilayer graphene sample, while recording the electrical current across the carbon flake. We report measurements of an oscillation-induced current which is several orders of magnitude larger than previously reported for water on carbon , and further boosted by the presence of surface wrinkles on the carbon layer. Our results point to a peculiar momentum transfer mechanism between fluid molecules and charge carriers in the carbon walls mediated by phonon excitations in the solid. Our findings pave the way for active control of fluid transfer at the nanoscale by harnessing the complex interplay between collective excitations in the solid and the molecules in the fluid. △ Less

Submitted 12 January, 2023; v1 submitted 10 May, 2022; originally announced May 2022.

Comments: Accepted for publication at PRX

Rectification effect in organic junctions based on aryl thin films covalently attached to a multilayer graphene electrode

Authors: Clément Barraud, Matthieu Lemaitre, Roméo Bonnet, Jacko Rastikian, Chloé Salhani, Stéphanie Lau, Quyen Van Nguyen, Philippe Decorse, Jean-Christophe Lacroix, Maria Luisa Della Rocca Philippe Lafarge, Pascal Martin

Abstract: The quantum interaction between molecules and electrode s material at molecules-electrode interfaces is a major ingredient in the electronic transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in a broadening and an energy shift of the interacting molecular orbitals. Using new electrodes materials, such as the recent semi-conducti… ▽ More The quantum interaction between molecules and electrode s material at molecules-electrode interfaces is a major ingredient in the electronic transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in a broadening and an energy shift of the interacting molecular orbitals. Using new electrodes materials, such as the recent semi-conducting two-dimensional nanomaterials, has become a recent challenge in the field of molecular-organic electronics that opens new possibilities for controlling the interfacial electronic properties and thus the charge injection properties. In this article, we report the use of atomically thin two-dimensional multilayer graphene films as base electrode in organic junctions with a vertical architecture. The interfacial electronic structure dominated by the covalent bonding between bis-thienyl benzene diazonium-based molecules and the multilayer graphene electrode has been probed by ultraviolet photoelectron spectroscopy and the results compared with those obtained on junctions with standard Au electrodes. Room temperature injection properties of such interfaces have been also explored by electronic transport measurements. We find that, despite strong variations of the density of states, the Fermi energy and the injection barriers, both organic junctions with Au base electrodes and multilayer graphene base electrodes show similar electronic responses. We explain this observation by the strong orbital coupling occurring at the bottom electrode-bis(thienyl) benzene molecules interface and by the pinning of the hybridized molecular orbitals. △ Less

Submitted 4 May, 2018; originally announced May 2018.

Comments: 14 pages, 4 figures

Boundary flow of viscoelastic polyelectrolyte solutions

Authors: Chloé Barraud, Benjamin Cross, Cyril Picard, Frédéric Restagno, Liliane Léger, Elisabeth Charlaix

Abstract: We report an investigation of the equilibrium and dynamic properties of polyelectrolyte solutions confined between platinum surfaces with a dynamic Surface Force Apparatus. The polyelectrolyte adsorbs on the surfaces in a dense compact layer bearing a surface charge in good agreement with the theoretical predictions. The flow of the solution on this charged adsorbed layer is probed over four decad… ▽ More We report an investigation of the equilibrium and dynamic properties of polyelectrolyte solutions confined between platinum surfaces with a dynamic Surface Force Apparatus. The polyelectrolyte adsorbs on the surfaces in a dense compact layer bearing a surface charge in good agreement with the theoretical predictions. The flow of the solution on this charged adsorbed layer is probed over four decades of spatial scales and one decade of frequency by dynamic measurements. At distances larger than the hundredth of nanometers, the flow of the viscoelastic solution is well described by a partial slip boundary condition. We show that the wall slip is quantitatively described by an interfacial friction coefficient, according to the original Navier's formulation, and not by a slip length. At smaller distance the partial slip model overestimates the solution mobility, and we observe the presence of a low viscosity layer coating the surfaces. The viscosity and thickness of this boundary layer are directly resolved, and found to be independent on shear-rate, frequency, and confinement. We discuss the thickness of the low viscosity layer in terms of the structural length of the semi-dilute solution and the Debye length screening the adsorbed layer charge. △ Less

Submitted 9 March, 2018; originally announced March 2018.

Comments: 11 pages, 11 figures

Wall slip of complex fluids: interfacial friction or slip length?

Authors: Benjamin Cross, Chloé Barraud, Cyril Picard, Liliane Léger, Frédéric Restagno, Elisabeht Charlaix

Abstract: Using a dynamic Surface Force Apparatus, we demonstrate that the notion of slip length used to describe the boundary flow of simple liquids, is not appropriate for viscoelastic liquids. Rather, the appropriate description lies in the original Navier's partial slip boundary condition, formulated in terms of an interfacial friction coefficient. We establish an exact analytical expression to extract… ▽ More Using a dynamic Surface Force Apparatus, we demonstrate that the notion of slip length used to describe the boundary flow of simple liquids, is not appropriate for viscoelastic liquids. Rather, the appropriate description lies in the original Navier's partial slip boundary condition, formulated in terms of an interfacial friction coefficient. We establish an exact analytical expression to extract the interfacial friction coefficient from oscillatory drainage forces between a sphere and a plane, suitable for dynamic SFA or Atomic Force Microscopy non-contact measurements. We use this model to investigate the boundary friction of viscoelastic polymer solutions over 5 decades of film thicknesses and one decade in frequency. The proper use of the original Navier's condition describes accurately the complex hydrodynamic force up to scales of tens of micrometers, with a simple "Newtonian-like" friction coefficient, not frequency dependent, and reflecting closely the dynamics of an interfacial depletion layer at the solution/solid interface. △ Less

Submitted 23 May, 2018; v1 submitted 9 March, 2018; originally announced March 2018.

Comments: 7 pages, 5 figures

Journal ref: Phys. Rev. Fluids 3, 062001 (2018)

Reactive-Ion-Etched Graphene Nanoribbons on a Hexagonal Boron Nitride Substrate

Authors: Dominik Bischoff, Tobias Krähenmann, Susanne Dröscher, Michelle A. Gruner, Clément Barraud, Thomas Ihn, Klaus Ensslin

Abstract: We report on the fabrication and electrical characterization of both single layer graphene micron-sized devices and nanoribbons on a hexagonal boron nitride substrate. We show that the micron-sized devices have significantly higher mobility and lower disorder density compared to devices fabricated on silicon dioxide substrate in agreement with previous findings. The transport characteristics of th… ▽ More We report on the fabrication and electrical characterization of both single layer graphene micron-sized devices and nanoribbons on a hexagonal boron nitride substrate. We show that the micron-sized devices have significantly higher mobility and lower disorder density compared to devices fabricated on silicon dioxide substrate in agreement with previous findings. The transport characteristics of the reactive-ion-etched graphene nanoribbons on hexagonal boron nitride, however, appear to be very similar to those of ribbons on a silicon dioxide substrate. We perform a detailed study in order to highlight both similarities as well as differences. Our findings suggest that the edges have an important influence on transport in reactive ion-etched graphene nanodevices. △ Less

Submitted 5 February, 2013; originally announced February 2013.

Journal ref: APPLIED PHYSICS LETTERS 101, 203103 (2012)

Electron flow in split-gated bilayer graphene

Authors: S. Dröscher, C. Barraud, K. Watanabe, T. Taniguchi, T. Ihn, K. Ensslin

Abstract: We present transport measurements on a bilayer graphene sheet with homogeneous back gate and split top gate. The electronic transport data indicates the capability to direct electron flow through graphene nanostructures purely defined by electrostatic gating. By comparing the transconductance data recorded for different top gate geometries - continuous barrier and split-gate - the observed transpo… ▽ More We present transport measurements on a bilayer graphene sheet with homogeneous back gate and split top gate. The electronic transport data indicates the capability to direct electron flow through graphene nanostructures purely defined by electrostatic gating. By comparing the transconductance data recorded for different top gate geometries - continuous barrier and split-gate - the observed transport features for the split-gate can be attributed to interference effects inside the narrow opening. △ Less

Submitted 20 July, 2012; originally announced July 2012.

Journal ref: New J. Phys. 14 (2012) 103007

Unravelling the role of the interface for spin injection into organic semiconductors

Authors: Clément Barraud, Pierre Seneor, Richard Mattana, Stéphane Fusil, Karim Bouzehouane, Cyrile Deranlot, Patrizio Graziosi, Luis Hueso, Ilaria Bergenti, Valentin Dediu, Frédéric Petroff, Albert Fert

Abstract: Whereas spintronics brings the spin degree of freedom to electronic devices, molecular/organic electronics adds the opportunity to play with the chemical versatility. Here we show how, as a contender to commonly used inorganic materials, organic/molecular based spintronics devices can exhibit very large magnetoresistance and lead to tailored spin polarizations. We report on giant tunnel magnetores… ▽ More Whereas spintronics brings the spin degree of freedom to electronic devices, molecular/organic electronics adds the opportunity to play with the chemical versatility. Here we show how, as a contender to commonly used inorganic materials, organic/molecular based spintronics devices can exhibit very large magnetoresistance and lead to tailored spin polarizations. We report on giant tunnel magnetoresistance of up to 300% in a (La,Sr)MnO3/Alq3/Co nanometer size magnetic tunnel junction. Moreover, we propose a spin dependent transport model giving a new understanding of spin injection into organic materials/molecules. Our findings bring a new insight on how one could tune spin injection by molecular engineering and paves the way to chemical tailoring of the properties of spintronics devices. △ Less

Submitted 11 May, 2010; originally announced May 2010.

Comments: Original version. Revised version to appear in Nature Physics.

The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs

Authors: K. Hurley, C. Guidorzi, F. Frontera, E. Montanari, F. Rossi, M. Feroci, E. Mazets, S. Golenetskii, D. D. Frederiks, V. D. Pal'shin, R. L. Aptekar, T. Cline, J. Trombka, T. McClanahan, R. Starr, J. -L. Atteia, C. Barraud, A. Pelangeon, M. Boer, R. Vanderspek, G. Ricker, I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak , et al. (9 additional authors not shown)

Abstract: Between 1996 July and 2002 April, one or more spacecraft of the interplanetary network detected 787 cosmic gamma-ray bursts that were also detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera experiments aboard the BeppoSAX spacecraft. During this period, the network consisted of up to six spacecraft, and using triangulation, the localizations of 475 bursts were obtained. We pre… ▽ More Between 1996 July and 2002 April, one or more spacecraft of the interplanetary network detected 787 cosmic gamma-ray bursts that were also detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera experiments aboard the BeppoSAX spacecraft. During this period, the network consisted of up to six spacecraft, and using triangulation, the localizations of 475 bursts were obtained. We present the localization data for these events. △ Less

Submitted 9 April, 2010; originally announced April 2010.

Comments: 89 pages, 3 figures. Submitted to the Astrophysical Journal Supplement Series

The Interplanetary Network Supplement to the HETE-2 Gamma-Ray Burst Catalog

Authors: K. Hurley, J. -L. Atteia, C. Barraud, A. Pelangeon, M. Boer, R. Vanderspek, G. Ricker, E. Mazets, S. Golenetskii, D. D. Frederiks, V. D. Pal'shin, R. L. Aptekar, D. M. Smith, C. Wigger, W. Hajdas, A. Rau, A. von Kienlin, I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak, A. B. Sanin, W. Boynton, C. Fellows, K. Harshman S. Barthelmy , et al. (21 additional authors not shown)

Abstract: Between 2000 November and 2006 May, one or more spacecraft of the interplanetary network (IPN) detected 226 cosmic gamma-ray bursts that were also detected by the FREGATE experiment aboard the HETE-II spacecraft. During this period, the IPN consisted of up to nine spacecraft, and using triangulation, the localizations of 157 bursts were obtained. We present the IPN localization data on these event… ▽ More Between 2000 November and 2006 May, one or more spacecraft of the interplanetary network (IPN) detected 226 cosmic gamma-ray bursts that were also detected by the FREGATE experiment aboard the HETE-II spacecraft. During this period, the IPN consisted of up to nine spacecraft, and using triangulation, the localizations of 157 bursts were obtained. We present the IPN localization data on these events. △ Less

Submitted 22 September, 2010; v1 submitted 15 July, 2009; originally announced July 2009.

Comments: 37 pages, 3 figures. To be submitted to ApJSS. Table 5 was truncated in the original version, and has been replaced. Revised 9/2010 to correct errors in some ecliptic latitudes in table 5. Also, 3 bursts were added to the catalog

On the nature of X-Ray Flashes

Authors: C. Barraud, F. Daigne, R. Mochkovitch, J. L. Atteia

Abstract: We discuss the origin of X-Ray Flashes (XRFs), a recently discovered class of Gamma-Ray Bursts (GRBs). Using a simplified model for internal shocks we check if XRFs can be intrinsically soft due to some specific values of the parameters describing the relativistic outflow emerging from the central engine. We generate a large number of synthetic events and find that XRFs are obtained when the con… ▽ More We discuss the origin of X-Ray Flashes (XRFs), a recently discovered class of Gamma-Ray Bursts (GRBs). Using a simplified model for internal shocks we check if XRFs can be intrinsically soft due to some specific values of the parameters describing the relativistic outflow emerging from the central engine. We generate a large number of synthetic events and find that XRFs are obtained when the contrast Gamma_max/Gamma_min of the Lorentz factor distribution is small while the average Lorentz factor Gamma is large. A few XRFs may be GRBs at large redshifts but we exclude this possibility for the bulk of the population. If outflows with a small contrast are commonly produced, even a large population of XRFs could be explained. If conversely the Lorentz factor distribution within the wind is broad, one should then rely on extrinsic causes, such as viewing angle effects or high redshift. △ Less

Submitted 7 July, 2005; originally announced July 2005.

Comments: 9 pages, 8 figures, to appear in A&A

Report number: aaa-07-05

HETE-2 Observation of two gamma-ray bursts at z > 3

Authors: J. -L. Atteia, N. Kawai, R. Vanderspek, G. Pizzichini, G. R. Ricker, C. Barraud, M. Boer, J. Braga, N. Butler, T. Cline, G. B. Crew, J. -P. Dezalay, T. Q. Donaghy, J. Doty, E. E. Fenimore, M. Galassi, C. Graziani, K. Hurley, J. G. Jernigan, D. Q. Lamb, A. Levine, R. Manchanda, F. Martel, M. Matsuoka, E. Morgan , et al. (14 additional authors not shown)

Abstract: GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with a measured redshift greater than 3. This paper presents the temporal and spectral properties of these two gamma-ray bursts detected and localized with HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in fluence, thus s… ▽ More GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with a measured redshift greater than 3. This paper presents the temporal and spectral properties of these two gamma-ray bursts detected and localized with HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in fluence, thus sampling distinct regions of the GRB luminosity function. The properties of these two bursts are compared with those of the bulk of the GRB population detected by HETE-2. We also discuss the energetics of GRB 020124 and GRB 030323 and show that they are compatible with the Epeak - Eiso relation discovered by Amati et al. (2002). Finally, we compute the maximum redshifts at which these bursts could have been detected by HETE-2 and we address various issues connected with the detection and localization of high-z GRBs. △ Less

Submitted 23 February, 2005; originally announced February 2005.

Comments: 19 pages, 4 figures, submitted to ApJ

Journal ref: Astrophys.J. 626 (2005) 292-297

Global Characteristics of X-Ray Flashes and X-Ray-Rich GRBs Observed by HETE-2

Authors: T. Sakamoto, D. Q. Lamb, C. Graziani, T. Q. Donaghy, M. Suzuki, G. Ricker, J-L. Atteia, N. Kawai, A. Yoshida, Y. Shirasaki, T. Tamagawa, K. Torii, M. Matsuoka, E. E. Fenimore, M. Galassi, J. Doty, R. Vanderspek, G. B. Crew, J. Villasenor, N. Butler, G. Prigozhin, J. G. Jernigan, C. Barraud, M. Boer, J-P. Dezalay , et al. (13 additional authors not shown)

Abstract: We describe and discuss the global properties of 45 gamma-ray bursts (GRBs) observed by HETE-2 during the first three years of its mission, focusing on the properties of X-Ray Flashes (XRFs) and X-ray-rich GRBs (XRRs). We find that the numbers of XRFs, XRRs, and GRBs are comparable. We find that the durations and the sky distributions of XRFs and XRRs are similar to those of GRBs. We also find t… ▽ More We describe and discuss the global properties of 45 gamma-ray bursts (GRBs) observed by HETE-2 during the first three years of its mission, focusing on the properties of X-Ray Flashes (XRFs) and X-ray-rich GRBs (XRRs). We find that the numbers of XRFs, XRRs, and GRBs are comparable. We find that the durations and the sky distributions of XRFs and XRRs are similar to those of GRBs. We also find that the spectral properties of XRFs and XRRs are similar to those of GRBs, except that the values of the peak energy $E^{\rm obs}_{\rm peak}$ of the burst spectrum in $νF_ν$, the peak energy flux $\Fp$, and the energy fluence $S_E$ of XRFs are much smaller -- and those of XRRs are smaller -- than those of GRBs. Finally, we find that the distributions of all three kinds of bursts form a continuum in the [$S_E$(2-30 keV),$S_E$(30-400) keV]-plane, the [$S_E$(2-400 keV), $E_{\rm peak}$]-plane, and the [$F_{\rm peak}$(50-300 keV), $E_{\rm peak}$]-plane. These results provide strong evidence that all three kinds of bursts arise from the same phenomenon. △ Less

Submitted 6 September, 2004; originally announced September 2004.

Comments: 33 pages, 15 figures, submitted to ApJ

Journal ref: Astrophys.J. 629 (2005) 311-327

High Energy Observations of XRF 030723: Evidence for an Off-axis Gamma-Ray Burst?

Authors: N. R. Butler, T. Sakamoto, M. Suzuki, N. Kawai, D. Q. Lamb, C. Graziani, T. Q. Donaghy, A. Dullighan, R. Vanderspek, G. B. Crew, P. Ford, G. Ricker, J-L. Atteia, A. Yoshida, Y. Shirasaki, T. Tamagawa, K. Torii, M. Matsuoka, E. E. Fenimore, M. Galassi, J. Doty, J. Villasenor, G. Prigozhin, J. G. Jernigan, C. Barraud , et al. (12 additional authors not shown)

Abstract: We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray Monitor/French Gamma Telescope observations of XRF030723 along with observations of the XRF afterglow made using the 6.5m Magellan Clay telescope and the Chandra X-ray Observatory. The observed peak energy E_pk_obs of the nu F_nu burst spectrum is found to lie within (or below) the WXM 2-25 keV passband at 98.5% confidence, and… ▽ More We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray Monitor/French Gamma Telescope observations of XRF030723 along with observations of the XRF afterglow made using the 6.5m Magellan Clay telescope and the Chandra X-ray Observatory. The observed peak energy E_pk_obs of the nu F_nu burst spectrum is found to lie within (or below) the WXM 2-25 keV passband at 98.5% confidence, and no counts are detected above 30 keV. Our best fit value is E_pk_obs=8.4+3.5/-3.4 keV. The ratio of X-ray to Gamma-ray flux for the burst follows a correlation found for GRBs observed with HETE-2, and the duration of the burst is similar to that typical of long-duration GRBs. If we require that the burst isotropic equivalent energy E_iso and E_pk_rest satisfy the relation discovered by Amati et al. (2002), a redshift of z=0.38+0.36/-0.18 can be determined, in agreement with constraints determined from optical observations. We are able to fit the X-ray afterglow spectrum and to measure its temporal fade. Although the best-fit fade is shallower than the concurrent fade in the optical, the spectral similarity between the two bands indicates that the X-ray fade may actually trace the optical fade. If this is the case, the late time rebrightening observed in the optical cannot be due to a supernova bump. We interpret the prompt and afterglow X-ray emission as arising from a jetted GRB observed off-axis and possibly viewed through a complex circumburst medium due to a progenitor wind. △ Less

Submitted 13 January, 2005; v1 submitted 24 August, 2004; originally announced August 2004.

Comments: 14 pages, 9 figures, to appear in ApJ

Journal ref: Astrophys.J. 621 (2005) 884-893

Time-resolved X-ray spectral modeling of an intermediate burst from SGR1900+14 observed by HETE-2/FREGATE and WXM

Authors: J. -F. Olive, K. Hurley, T. Sakamoto, J. -L. Atteia, G. Crew, G. Ricker, G. Pizzichini, C. Barraud, N. Kawai

Abstract: We present a detailed analysis of a 3.5 s long burst from SGR1900+14 which occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well described by the sum of two blackbodies whose temperatures are approximately 4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fit by the sum of two blackbodies. The higher temperature blackbody evolves with time in a manner… ▽ More We present a detailed analysis of a 3.5 s long burst from SGR1900+14 which occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well described by the sum of two blackbodies whose temperatures are approximately 4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fit by the sum of two blackbodies. The higher temperature blackbody evolves with time in a manner consistent with a shrinking emitting surface. The interpretation of these results in the context of the magnetar model suggests that the two blackbody fit is an approximation of an absorbed, multi-temperature spectrum expected on theoretical grounds rather than a physical description of the emission. If this is indeed the case, our data provide further evidence for a strong magnetic field, and indicate that the entire neutron was radiating during most of the burst duration. △ Less

Submitted 19 August, 2004; v1 submitted 5 March, 2004; originally announced March 2004.

Comments: Accepted for publication in the Astrophysical Journal

Journal ref: Astrophys.J. 616 (2004) 1148-1158

HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component

Authors: R. Vanderspek, T. Sakamoto, C. Barraud, T. Tamagawa, C. Graziani, M. Suzuki, Y. Shirasaki, G. Prigozhin, J. Villasenor, J. G. Jernigan, G. B. Crew, J. -L. Atteia, K. Hurley, N. Kawai, D. Q. Lamb, G. R. Ricker, S. E. Woosley, N. Butler, J. P. Doty, A. Dullighan, T. Q. Donaghy, E. E. Fenimore, M. Galassi, G. Pizzichini, M . Matsuoka , et al. (8 additional authors not shown)

Abstract: An exceptionally intense gamma-ray burst, GRB030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two \~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making GRB030329 one of the bright… ▽ More An exceptionally intense gamma-ray burst, GRB030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two \~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst lightcurves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We present details of the HETE observations of GRB030329. △ Less

Submitted 8 December, 2004; v1 submitted 15 January, 2004; originally announced January 2004.

Comments: 22 pages, 5 figures, to be published in ApJ 617, no. 2 (10 December 2004). Referee comments have been incorporated; results of improved spectral analysis are included

Journal ref: Astrophys.J. 617 (2004) 1251-1257

GRB 020531: A Short, Hard Gamma-Ray Burst Localized and Observed by HETE-2

Authors: D. Q. Lamb, G. R. Ricker, J. -L. Atteia, K. Hurley, N. Kawai, Y. Shirasaki, T. Sakamoto, T. Tamagawa, T. Donaghy, C. Graziani, C. Barraud, J. -F. Olive, A. Yoshida, K. Torii, E. E. Fenimore, M. Galassi, R. Vanderspek, the HETE-2 Science Team

Abstract: The HETE-2 FREGATE and WXM instruments detected a short, hard GRB at 00:26:18.72 UT on 31 May 2002. A preliminary localization was reported as a GCN Position Notice 88 min after the burst, and a refined localization was disseminated 123 minutes later. An IPN localization of the burst was reported 18 hours after the GRB, and a refined IPN localization was disseminated ~5 days after the burst. The… ▽ More The HETE-2 FREGATE and WXM instruments detected a short, hard GRB at 00:26:18.72 UT on 31 May 2002. A preliminary localization was reported as a GCN Position Notice 88 min after the burst, and a refined localization was disseminated 123 minutes later. An IPN localization of the burst was reported 18 hours after the GRB, and a refined IPN localization was disseminated ~5 days after the burst. The final IPN localization, disseminated on 25 July 2002, is a diamond-shaped region centered on RA=15h 15m 11.18s, Dec=-19o 24' 27.08" (J2000), and has an area of ~9 square arcminutes (99.7% confidence region). The prompt localization of the burst by HETE-2, coupled with the refinement of the localization by the IPN, made possible the most sensitive follow-up observations to date of a short, hard GRB at radio, optical, and X-ray wavelengths. The time history of GRB020531 at high (>30 keV) energies consists of a short, intense spike followed by a much less intense secondary peak, which is characteristic of many short, hard bursts. The duration of the burst increases with decreasing energy and the spectrum of the burst evolves from hard to soft, behaviors which are similar to those of long GRBs. This suggests that short, hard GRBs are closely related to long GRBs. △ Less

Submitted 18 December, 2003; originally announced December 2003.

Comments: 4 pages, 3 figures, to appear in proc. 3rd Rome Workshop on Gamma-Ray Bursts in the Afterglow Era, 2002

Observation and implications of the Epeak - Eiso correlation in Gamma-Ray Bursts

Authors: J-L. Atteia, G. R. Ricker, D. Q. Lamb, T. Sakamoto, C. Graziani, T. Donaghy, C. Barraud, the HETE-2 Science Team

Abstract: The availability of a few dozen GRB redshifts now allows studies of the intrinsic properties of these high energy transients. Amati et al. recently discovered a correlation between Epeak, the intrinsic peak energy of the $νf ν$ spectrum, and Eiso, the isotropic equivalent energy radiated by the source. Lamb et al. have shown that HETE-2 data confirm and extend this correlation. We discuss here o… ▽ More The availability of a few dozen GRB redshifts now allows studies of the intrinsic properties of these high energy transients. Amati et al. recently discovered a correlation between Epeak, the intrinsic peak energy of the $νf ν$ spectrum, and Eiso, the isotropic equivalent energy radiated by the source. Lamb et al. have shown that HETE-2 data confirm and extend this correlation. We discuss here one of the consequences of this correlation: the existence of a 'spectral standard candle', which can be used to construct a simple redshift indicator for GRBs. △ Less

Submitted 15 December, 2003; originally announced December 2003.

Comments: Proceedings of the GRB 2003 Conference in SantaFe, 5 pages, 4 figures

Spectral analysis of 50 GRBs detected by HETE-2

Authors: C. Barraud, the HETE-2 team

Abstract: FREGATE, the gamma-ray detector of HETE-2 is entirely dedicated to the study of GRBs. Its main characteristic is its broad energy range, from 7 keV to 400 keV. This energy range can be further extended down to 2 keV using the data from the WXM, the X-ray detector of HETE-2. Such a large energy range allows to study in details the prompt emission of GRBs, determining with a high precision their s… ▽ More FREGATE, the gamma-ray detector of HETE-2 is entirely dedicated to the study of GRBs. Its main characteristic is its broad energy range, from 7 keV to 400 keV. This energy range can be further extended down to 2 keV using the data from the WXM, the X-ray detector of HETE-2. Such a large energy range allows to study in details the prompt emission of GRBs, determining with a high precision their spectral parameters. Moreover, because this energy range extends at low energies, the sample of GRBs detected by both FREGATE and WXM contains a significant fraction of X-Ray Rich GRBs and X-Ray Flashes. We present here the distributions of the spectral parameters mesured for the time integrated spectra of 50 GRBs. We put emphasis on the distribution of the low energy spectral index alpha. Because FREGATE and WXM detected all classes of GRBs, we also discuss the connection between GRBs, X-Ray Rich GRBs and X-Ray Flashes. △ Less

Submitted 28 November, 2003; originally announced November 2003.

Comments: 4 pages aipTEX, contribution to the 2003 GRB Conference, held at Santa Fe,NM

Highlights of the HETE-2 Mission

Authors: D. Q. Lamb, G. R. Ricker, J. -L. Atteia, C. Barraud, M. Boer, J. Braga, N. Butler, T. Cline, G. B. Crew, J. -P. Dezalay, T. Q. Donaghy, J. P. Doty, A. Dullighan, E. E. Fenimore, M. Galassi, C. Graziani, K. Hurley, J. G. Jernigan, N. Kawai, A. Levine, R. Manchanda, M. Matsuoka, F. Martel, G. Monnelly, E. Morgan , et al. (15 additional authors not shown)

Abstract: The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have redshift determinations. HETE-2 has also observed more than 45 bursts… ▽ More The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have redshift determinations. HETE-2 has also observed more than 45 bursts from soft gamma-ray repeaters, and more than 700 X-ray bursts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs may be correlated with redshift; such a correlation would imply that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It has made it possible to explore the previously unknown behavior optical afterglows at very early times, and has opened up the era of high-resolution spectroscopy of GRB optical afterglows. It is also solving the mystery of "optically dark" GRBs, and revealing the nature of X-ray flashes (XRFs). △ Less

Submitted 18 December, 2003; v1 submitted 15 October, 2003; originally announced October 2003.

Comments: 12 pages, 6 figures, to appear in proc. 2nd VERITAS Symposium on TeV Astrophysics, Chicago, Illinois; revised text, added refs

Scientific Highlights of the HETE-2 Mission

Authors: D. Q. Lamb, G. R. Ricker, J-L. Atteia, C. Barraud, M. Boer, J. Braga, N. Butler, T. Cline, G. B. Crew, J. -P. Dezalay, T. Q. Donaghy, J. P. Doty, A. Dullighan, E. E. Fenimore, M. Galassi, C. Graziani, K. Hurley, J. G. Jernigan, N. Kawai, A. Levine, R. Manchanda, M. Matsuoka, F. Martel, G. Monnelly, G. Morgan , et al. (15 additional authors not shown)

Abstract: The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and… ▽ More The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs are correlated with redshift, implying that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It is also solving the mystery of "optically dark' GRBs, and revealing the nature of X-ray flashes. △ Less

Submitted 18 December, 2003; v1 submitted 16 September, 2003; originally announced September 2003.

Comments: 10 pages, 9 figures, to appear in proc. "The Restless High-Energy Universe", Royal Tropical Institute, Amsterdam; revised text, added refs

Journal ref: New Astron.Rev.48:423-430,2004; Nucl.Phys.Proc.Suppl.132:279-288,2004

HETE-2 Observations of the Extremely Soft X-Ray Flash XRF 020903

Authors: T. Sakamoto, D. Q. Lamb, C. Graziani, T. Q. Donaghy, M. Suzuki, G. Ricker, J-L. Atteia, N. Kawai, A. Yoshida, Y. Shirasaki, T. Tamagawa, K. Torii, M. Matsuoka, E. E. Fenimore, M. Galassi, T. Tavenner, J. Doty, R. Vanderspek, G. B. Crew, J. Villasenor, N. Butler, G. Prigozhin, J. G. Jernigan, C. Barraud, M. Boer , et al. (14 additional authors not shown)

Abstract: We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S_X/S_gamma) = 0.7, where S_X and S_gamma are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E^{obs}_{peak} < 5.0 keV (99.7 % probability upper limit) and no photons… ▽ More We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S_X/S_gamma) = 0.7, where S_X and S_gamma are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E^{obs}_{peak} < 5.0 keV (99.7 % probability upper limit) and no photons were detected above ~10 keV. The burst is shorter at higher energies, which is similar to the behavior of long GRBs. We consider the possibility that the burst lies at very high redshift and that the low value of E^{obs}_{peak} is due to the cosmological redshift, and show that this is very unlikely. We find that the properties of XRF 020903 are consistent with the relation between the fluences S(7-30 keV) and S(30-400 keV) found by Barraud et al. for GRBs and X-ray-rich GRBs, and are consistent with the extension by a decade of the hardness-intensity correlation (Mallozzi et al. 1995) found by the same authors. Assuming that XRF 020903 lies at a redshift z = 0.25 as implied by the host galaxy of the candidate optical and radio afterglows of this burst, we find that the properties of XRF 020903 are consistent with an extension by a factor ~300 of the relation between the isotropic-equivalent energy E_iso and the peak E_peak of the nu F_nu spectrum (in the source frame of the burst) found by Amati et al. for GRBs. The results presented in this paper therefore provide evidence that XRFs, X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon. The results also impose strong constraints on models of XRFs and X-ray-rich GRBs. △ Less

Submitted 10 November, 2003; v1 submitted 16 September, 2003; originally announced September 2003.

Comments: 32 pages, 12 figures, revised, accepted by ApJ

Journal ref: AIP Conf.Proc.727:106-110,2004

HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211

Authors: G. B. Crew, D. Q. Lamb, G. R. Ricker, J. -L. Atteia, N. Kawai, R. Vanderspek, J. Villasenor, J. Doty, G. Prigozhin, J. G. Jernigan, C. Graziani, Y. Shirasaki, T. Sakamoto, M. Suzuki, N. Butler, K. Hurley, T. Tamagawa, A. Yoshida, M. Matsuoka, E. E. Fenimore, M. Galassi, C. Barraud, M. Boer, J. -P. Dezalay, J. -F. Olive , et al. (13 additional authors not shown)

Abstract: A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon en… ▽ More A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1 and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211 is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt localization allowed the detection of an optical afterglow for what would otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that some fraction of burst afterglows are ``optically dark'' because their optical afterglows at times > 1 hr after the burst are very faint, and thus have often escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have very bright afterglows at times < 20 min after the burst. △ Less

Submitted 2 September, 2003; v1 submitted 20 March, 2003; originally announced March 2003.

Comments: 21 pages, 4 figures, accepted by ApJ, abstract. condensed; revised

Report number: CSR-03-27

Journal ref: Astrophys.J. 599 (2003) 387-393

On the nature of X-ray Flashes

Authors: Robert Mochkovitch, Frederic Daigne, Celine Barraud, Jean-Luc Atteia

Abstract: We have developed a toy model for internal shocks which has been used to generate a large number of synthetic GRBs in order to find in the parameter space the conditions which can lead to the formation of X-ray flashes. The key condition appears to be a small contrast of the Lorentz factor in the relativistic wind emitted by the central engine. We have developed a toy model for internal shocks which has been used to generate a large number of synthetic GRBs in order to find in the parameter space the conditions which can lead to the formation of X-ray flashes. The key condition appears to be a small contrast of the Lorentz factor in the relativistic wind emitted by the central engine. △ Less

Submitted 13 March, 2003; originally announced March 2003.

Comments: 4 pages, 4 figures, to appear in "Gamma-ray bursts in the afterglow era", 3rd workshop, Rome 17-20 Sept. 2002

Are X-ray flashes a peculiar class of (soft) gamma-ray bursts ?

Authors: Frederic Daigne, Celine Barraud, Robert Mochkovitch

Abstract: Heise et al. (2001) have reported the identification of a new class of sources by Beppo-SAX, the so-called X-ray flashes (XRFs), which have many common properties with gamma-ray bursts (GRBs) but are not detected in the gamma-ray range. In the framework of the internal shock model, we investigate the possibility that XRFs have the same origin than GRBs but are intrinsically softer due to differe… ▽ More Heise et al. (2001) have reported the identification of a new class of sources by Beppo-SAX, the so-called X-ray flashes (XRFs), which have many common properties with gamma-ray bursts (GRBs) but are not detected in the gamma-ray range. In the framework of the internal shock model, we investigate the possibility that XRFs have the same origin than GRBs but are intrinsically softer due to different shock parameters. △ Less

Submitted 2 December, 2002; originally announced December 2002.

Comments: 2 pages. To appear in SF2A-2002: Semaine de l'Astrophysique Francaise, meeting held in Paris, France, June 24-29, 2002

Spectral analysis of 35 GRBs/XRFs observed with HETE-2/FREGATE

Authors: C. Barraud, J-F. Olive, J. P. Lestrade, J-L. Atteia, K. Hurley, G. Ricker, D. Q. Lamb, N. Kawai, M. Boer, J-P. Dezalay, G. Pizzichini, R. Vanderspek, G. Crew, J. Doty, G. Monelly, J. Villasenor, N. Butler, A. Levine, A. Yoshida, Y. Shirasaki, T. Sakamoto, T. Tamagawa, K. Torii, M. Matsuoka, E. E. Fenimore , et al. (5 additional authors not shown)

Abstract: We present a spectral analysis of 35 GRBs detected with the HETE-2 gamma-ray detectors (the FREGATE instrument) in the energy range 7-400 keV. The GRB sample analyzed is made of GRBs localized with the Wide Field X-ray Monitor onboard HETE-2 or with the GRB Interplanetary Network. We derive the spectral parameters of the time-integrated spectra, and present the distribution of the low-energy pho… ▽ More We present a spectral analysis of 35 GRBs detected with the HETE-2 gamma-ray detectors (the FREGATE instrument) in the energy range 7-400 keV. The GRB sample analyzed is made of GRBs localized with the Wide Field X-ray Monitor onboard HETE-2 or with the GRB Interplanetary Network. We derive the spectral parameters of the time-integrated spectra, and present the distribution of the low-energy photon index, alpha, and of the peak energy, e_peak . We then discuss the existence and nature of the recently discovered X-Ray Flashes and their relationship with classical GRBs. △ Less

Submitted 13 January, 2003; v1 submitted 21 June, 2002; originally announced June 2002.

Comments: 14 pages, 43 figures, accepted for publication in Astronomy and Astrophysics

The E-peak distribution of the GRBs detected by HETE FREGATE instrument

Authors: C. Barraud, J. L. Atteia, J. F. Olive, J. P. Dezalay

Abstract: The FREGATE gamma ray detector of HETE-2 is sensitive to photons between 6 and 400 keV. This sensitivity range, extended towards low energies, allows us to explore the emission of GRBs in hard X-rays. We fit the spectra of 23 GRBs with Band's spectral function in order to derive the distribution of their peak energies (E-peak). This distribution is then compared with the E-peak distributions mea… ▽ More The FREGATE gamma ray detector of HETE-2 is sensitive to photons between 6 and 400 keV. This sensitivity range, extended towards low energies, allows us to explore the emission of GRBs in hard X-rays. We fit the spectra of 23 GRBs with Band's spectral function in order to derive the distribution of their peak energies (E-peak). This distribution is then compared with the E-peak distributions measured by BATSE and GINGA. △ Less

Submitted 24 April, 2002; originally announced April 2002.

Comments: 3 pages, Woods Hole Proceedings

Journal ref: AIP Conf.Proc. 662 (2003) 59-62

FREGATE observation of a strong burst from SGR1900+14

Authors: J-F. Olive, K. Hurley, J-P. Dezalay, J-L. Atteia, C. Barraud, N. Butler, G. B. Crew, J. Doty, G. Ricker, R. Vanderspek

Abstract: After a long period of quiescence, the soft gamma repeater SGR1900+14 was suddenly reactivated on April 2001. On July 2, 2001, a bright flare emitted by this source triggerred the WXM and FREGATE instruments onboard the HETE-2 satellite. Unlike typical short (0.1 s) and spiky SGRs recurrent bursts, this event features a 4.1 s long main peak, with a sharp rise (50 ms) and a slower cutoff (250 ms)… ▽ More After a long period of quiescence, the soft gamma repeater SGR1900+14 was suddenly reactivated on April 2001. On July 2, 2001, a bright flare emitted by this source triggerred the WXM and FREGATE instruments onboard the HETE-2 satellite. Unlike typical short (0.1 s) and spiky SGRs recurrent bursts, this event features a 4.1 s long main peak, with a sharp rise (50 ms) and a slower cutoff (250 ms). This main peak is followed by a 2 sec decreasing tail. We found no evidence of any precursor or any extended `afterglow' tail to this burst. We present the preliminary spectral fits of the total emission of this flare as observed by the FREGATE instrument between 7 and 150 keV. The best fit is obtained with a model consisting of two blackbody components of temperatures 4.15 keV and 10.4 keV. A thermal bremsstrahlung can not be fitted to this spectrum. We compare these features and the burst energetics with the other strong or giant flares from SGR1900+14. △ Less

Submitted 6 March, 2002; originally announced March 2002.

Comments: 5 pages, Latex, Woods Hole 2001 GRB conference

Journal ref: AIP Conf.Proc. 662 (2003) 82-87

In-flight verification of the FREGATE spectral response

Authors: J-F. Olive, J-P. Dezalay, J-L. Atteia, C. Barraud, N. Butler, G. B. Crew, J. Doty, G. Ricker, R. Vanderspek

Abstract: We present the first results of the in-flight validation of the spectral response of the FREGATE X/gamma detectors on-board the HETE-2 satellite. This validation uses the Crab pulsar and nebula as reference spectra. We present the first results of the in-flight validation of the spectral response of the FREGATE X/gamma detectors on-board the HETE-2 satellite. This validation uses the Crab pulsar and nebula as reference spectra. △ Less

Submitted 6 March, 2002; originally announced March 2002.

Comments: 3 pages, Latex, Woods Hole 2001 GRB conference