arXiv subjects

R. Preece

Publications and source records attributed to R. Preece.

At least 55 records · Page 3Linked to original sources

arXiv2005

Particle acceleration in electron-ion jets

Weibel instability created in collisionless shocks is responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-ion jet fronts propagating into an ambient plasma without initial magnetic fields with a longer simulation system in order to investigate nonlinear stage of the Weibel instability and its acceleration mechanism. The current channels generated by the Weibel instability induce the radial electric fields. The z component of the Poynting vector (E x B) become positive in the large region along the jet propagation direction. This leads to the acceleration of jet electrons along the jet. In particular the E x B drift with the large scale current channel generated by the ion Weibel instability accelerate electrons effectively in both parallel and perpendicular directions.

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arXiv2005

INTEGRAL and XMM-Newton observations of the low-luminosity and X-ray rich burst GRB 040223

GRB 040223 was observed by INTEGRAL and XMM-Newton. GRB 040223 has a peak flux of (1.6+/-0.13) x10^-8 ergs cm^-2 s^-1, a fluence of (4.4+/-0.4)x10^-7 ergs cm^-2 and a steep photon power law index of -2.3+/-0.2, in the energy range 20-200 keV. The steep spectrum implies it is an x- ray rich GRB with emission up to 200 keV and E_peak < 20 keV. If E_peak is < 10 keV, it would qualify as an x-ray flash with high energy emission. The x-ray data has a spectral index beta_x = -1.7+/-0.2, a temporal decay of t^(-0.75+/-0.25) and a large column density of (1.8 x 10^22) cm^-2. The luminosity-lag relationship was used to obtain a redshift (z = 0.1+0.04-0.02). The isotropic energy radiated in gamma-rays and x-ray luminosity after 10 hours are factors of 1000 and 100 less than classical GRBs. GRB 040223 is consistent with the extrapolation of the Amati relation into the region that includes XRF 030723 and XRF 020903.

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arXiv2005

Weibel Instability Driven by Relativistic Pair Jets: Particle Acceleration, Magnetic Field Generation, and Emission

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find that the growth times of the Weibel instability in electron-positron jets are not affected by the (electron-positron or electron-ion) ambient plasmas. However, the amplitudes of generated local magnetic fields in the electron-ion ambient plasma are significantly larger than those in the electron-positron ambient plasma.

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arXiv2005

Particle acceleration, magnetic field generation, and emission in relativistic pair jets

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find that the growth times of Weibel instability are proportional to the Lorentz factors of jets. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction.

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arXiv2005

Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks

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arXiv2004

Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head.

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arXiv2004

INTEGRAL and XMM-Newton Observations of GRB040106

On January 6th 2004, the IBAS burst alert system triggered the 8th gamma-ray burst (GRB) to be located by the INTEGRAL satellite. The position was determined and publicly distributed within 12s, prompting ESA's XMM-Newton to execute a ToO observation just 5 hours later, during which an X-ray afterglow was detected. The GRB had a duration ~52s with two distinct pulses separated by \~42s. Here we present the results of imaging and spectral analyses of the prompt emission from INTEGRAL data and the X-ray afterglow from XMM-Newton data. The gamma-ray spectrum is consistent with a single power-law of photon index -1.72 +/- 0.15. The fluence (20-200 keV) was 8.2 x 10^-7 erg cm^-2. The X-ray afterglow (F_nu (t) propto nu^-beta_X t^-delta) was extremely hard with beta_X = 0.47 +/- 0.01 and delta = 1.46 +/- 0.04. The 2-10 keV flux 11 hours after the burst was 1.1 x 10^-12 erg cm^-2 s^-1. The time profile of the GRB is consistent with the observed trends from previous analysis of BATSE GRBs. We find that the X-ray data are not well-fit by either a simple spherical fireball or by a speading jet, expanding into a homogeneous medium or a wind environment. Based on previously determined correlations between GRB spectra and redshift, we estimate a redshift of ~0.9^+0.5_-0.4 (1 sigma) and a lower limit on the isotropic radiated energy of ~5 x 10^51 erg in this burst.

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arXiv2004

Relativistic Shocks: Particle Acceleration and Magnetic Field Generation, and Emission

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g.,Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma with and without initial magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock at the same simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale (mainly transverse) magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation of ``jitter'' radiation from deflected electrons (positrons) as opposed to synchrotron radiation.

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arXiv2004

Measurements of Gamma-Ray Bursts (GRBs) with Glast

One of the scientific goals of the main instrument of GLAST is the study of Gamma-Ray Bursts (GRBs) in the energy range from ~20 MeV to ~300 GeV. In order to extend the energy measurement towards lower energies a secondary instrument, the GLAST Burst Monitor (GBM), will measure GRBs from ~10 keV to ~25 MeV and will therefore allow the investigation of the relation between the keV and the MeV-GeV emission from GRBs over six energy decades. These unprecedented measurements will permit the exploration of the unknown aspects of the high-energy burst emission and the investigation of their connection with the well-studied low-energy emission. They will also provide ne insights into the physics of GRBs in general. In addition the excellent localization of GRBs by the LAT will stimulate follow-up observations at other wavelengths which may yield clues about the nature of the burst sources.

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arXiv2004

Preliminary INTEGRAL Analysis of GRB040106

On January 6th 2004, the IBAS burst alert system triggered the 8th gamma-ray burst (GRB) to be detected by the INTEGRAL satellite. The position was determined and publicly distributed within 12s, enabling ESA's XMM-Newton to take advantage of a ToO observation just 5 hours later during which the x-ray afterglow was detected. Observations at optical wavelengths also revealed the existence of a fading optical source. The GRB is ~52s long with 2 distinct peaks separated by ~24s. At gamma-ray energies the burst was the weakest detected by INTEGRAL up to that time with a flux in the 20-200 keV band of 0.57 photons/cm^2/s. Nevertheless, it was possible to determine its position and extract spectra and fluxes. Here we present light curves and the results of imaging, spectral and temporal analyses of the prompt emission and the onset of the afterglow from INTEGRAL data.

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arXiv2004

INTEGRAL Spectrometer Analysis of GRB030227 & GRB030131

The spectrometer SPI on board INTEGRAL is capable of high-resolution spectroscopic studies in the energy range 20keV to 8MeV for GRBs which occur within the fully coded field of view (16 degrees corner to corner). Six GRBs occurred within the SPI field of view between October 2002 and November 2003. We present results of the analysis of the first two GRBs detected by SPI after the payload performance and verification phase of INTEGRAL.

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arXiv2003

GLAST's GBM Burst Trigger

The GLAST Burst Monitor (GBM) will detect and localize bursts for the GLAST mission, and provide the spectral and temporal context in the traditional 10 keV to 25 MeV band for the high energy observations by the Large Area Telescope (LAT). The GBM will use traditional rate triggers in up to three energy bands, and on a variety of timescales between 16 ms and 16 s.

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arXiv2003

Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

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arXiv2003

INTEGRAL Spectrometer SPI's GRB detection capabilities. GRBs detected inside SPI's FoV and with the anticoincidence system ACS

The spectrometer SPI, one of the two main instruments of the INTEGRAL spacecraft, offers significant gamma-ray burst detection capabilities. In its 35 deg (full width) field of view SPI is able to localise gamma-ray bursts at a mean rate of ~ 0.8/month. With its large anticoincidence shield of 512 kg of BGO crystals SPI is able to detect gamma-ray bursts quasi omni-directionally with a very high sensitivity. Burst alerts of the anticoincidence shield are distributed by the INTEGRAL Burst Alert System. In the first 8 months of the mission about 0.8/day gamma-ray burst candidates and 0.3/day gamma-ray burst positions were obtained with the anticoincidence shield by interplanetary network triangulations with other spacecrafts.

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arXiv2003

Particle Acceleration in Relativistic Jets due to Weibel Instability

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation (Medvedev 2000) from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

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arXiv2003

Triggers and alerts with GLAST

We present preliminary results on Gamma Ray Burst (GRB) triggers with the Gamma-ray Large Area Space Telescope (GLAST). After a brief summary of the detector layout, GLAST expected performances on GRB detection are recalled. Status report on the simulation software and preliminary triggers studies are then reported, already showing significant improvement on EGRET results.

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arXiv2001

The GLAST Burst Monitor (GBM)

The selection of the GLAST burst monitor (GBM) by NASA will allow the investigation of the relation between the keV and the MeV-GeV emission from gamma-ray bursts. The GBM consists of 12 NaI and 2 BGO crystals allowing a continuous measurement of the energy spectra of gamma-ray bursts from ~5 keV to \~30 MeV. One feature of the GBM is its high time resolution for time-resolved gamma-ray spectroscopy. Moreover the arrangement of the NaI crystals allows a rapid on-board location (<15 degrees) of a gamma-ray burst within a FoV of ~8.6 sr. This position will be communicated to the main instrument of GLAST making follow-up observations at high energies possible.

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arXiv1997

The Statistics of the BATSE Spectral Features

The absence of a BATSE line detection in a gamma-ray burst spectrum during the mission's first six years has led to a statistical analysis of the occurrence of lines in the BATSE burst database; this statistical analysis will still be relevant if lines are detected. We review our methodology, and present new simulations of line detectability as a function of the line parameters. We also discuss the calculation of the number of ``trials'' in the BATSE database, which is necessary for our line detection criteria.

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