(Abridged) The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV. This paper describes the LAT, its pre-flight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4x4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 x,y tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an 8 layer hodoscopic configuration with a total depth of 8.6 radiation lengths. The aspect ratio of the tracker (height/width) is 0.4 allowing a large field-of-view (2.4 sr). Data obtained with the LAT are intended to (i) permit rapid notification of high-energy gamma-ray bursts (GRBs) and transients and facilitate monitoring of variable sources, (ii) yield an extensive catalog of several thousand high-energy sources obtained from an all-sky survey, (iii) measure spectra from 20 MeV to more than 50 GeV for several hundred sources, (iv) localize point sources to 0.3 - 2 arc minutes, (v) map and obtain spectra of extended sources such as SNRs, molecular clouds, and nearby galaxies, (vi) measure the diffuse isotropic gamma-ray background up to TeV energies, and (vii) explore the discovery space for dark matter.

The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission

Gamma-ray bursts (GRB's), short and intense pulses of low-energy $\ensuremath{\gamma}$ rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions---BATSE (Burst and Transient Source Experiment) on the Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer)---together with ground-based optical, infrared, and radio observatories have revolutionized our understanding of GRB's, showing that they are cosmological, that they are accompanied by long-lasting afterglows, and that they are associated with core-collapse supernovae. At the same time a theoretical understanding has emerged in the form of the fireball internal-external shocks model. According to this model GRB's are produced when the kinetic energy of an ultrarelativistic flow is dissipated in internal collisions. The afterglow arises when the flow is slowed down by shocks with the surrounding circumburst matter. This model has had numerous successful predictions, like the predictions of the afterglow itself, of jet breaks in the afterglow light curve, and of the optical flash that accompanies the GRB's. This review focuses on the current theoretical understanding of the physical processes believed to take place in GRB's.

/pdf/the-physics-of-gamma-ray-bursts-2v7vwfzv9l.pdf

The physics of gamma-ray bursts

https://ned.ipac.caltech.edu/level5/March04/Piran2/paper.pdf

Gamma-ray bursts and the fireball model

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin and mechanism are the focus of intense research and debate. More than three decades after their discovery, and after pioneering breakthroughs from space and ground experiments, their study is entering a new phase with the recently launched Swift satellite. The interplay between these observations and theoretical models of the prompt gamma-ray burst and its afterglow is reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/69/8/R01/pdf

Gamma-ray bursts

Formation and evolution of binary and millisecond radio pulsars

Energetic Radiation from Rapidly Spinning Pulsars. 1. Outer Magnetosphere Gaps. 2. Vela and Crab

L'augmentation des regions (trous) a depletion de charge dans la magnetosphere exterieure d'etoiles a neutrons magnetisees en rotation rapide est limitee par la production de e ± . On applique les resultats obtenus aux pulsars Vela et Crab en mettant en evidence ce qui differencie les deux pulsars

Energetic radiation from rapidly spinning pulsars. II: Vela and Crab

Assuming that the speed up of the Vela pulsar was caused by a “starquake”, a number of predictions can be made, and the event can be taken as evidence that the interior of the pulsar is a superfluid.

Spin up in neutron stars: the future of the vela pulsar.

A three-dimensional pulsar magnetosphere model is used to study the geometry of outer magnetospheric gap accelerators, following seminal work of Romani and coworkers. The size of the outer gap is self-consistently limited by pair production from collisions of thermal photons from polar cap heating of backflow outer gap current with curvature photons emitted by gap-accelerated charged particles. In principle, there could be two topologically disconnected outer gaps. Conditions for local pair production such as local field line curvature, soft X-ray density, electric field, etc., support pair production inside an outer gap only between rin() (the radius of the null surface at azimuthal angle ) and rlim() ≈ 6rin( = 0) RL (the light cylinder radius). Secondary pairs, on the other hand, are produced almost everywhere outside the outer gap by collisions between curvature photons and synchrotron X-rays emitted by these secondary pairs. These processes produce a wide X-ray fan beam in the outgoing direction and a very narrow beam in the incoming direction for each outer gap. For pulsars with a large magnetic dipole inclination angle, part of the incoming γ-ray beam will be absorbed by the stellar magnetic field. If the surface magnetic field is dominated by a far off-center dipole moment (e.g., as in a proposed "plate tectonic" model), gravitational bending of photons from polar cap accelerators and their ultimate conversion into outflowing e± pairs can result in the quenching of one of these two outer gaps. Various emission morphologies for the pulsar (depending on magnetic inclination angle and viewing angle) are presented. Double-peak light curves with strong bridges are most common. From the three-dimensional structure of the outer gap and its local properties, we calculate phase-resolved spectra of gamma-ray pulsars and apply them to observed spectra of the Crab pulsar.

/pdf/a-three-dimensional-outer-magnetospheric-gap-model-for-gamma-2x55v35aat.pdf

A three-dimensional outer magnetospheric gap model for gamma-ray pulsars: Geometry, pair production, emission morphologies, and phase-resolved spectra

Spinning superfluid neutrons in the core of a neutron star interact strongly with coexisting superconducting protons. One consequence is that the outward (inward) motion of core superfluid neutron vortices during spin-down (spin-up) of a neutron star may alter the core's magnetic field. Such core field changes are expected to result in movements of the stellar crust and changes in the star's surface magnetic field that reflect those in the core below. Observed magnitudes and evolution of the spin-down indices of canonical pulsars are understood as a consequence of such surface field changes. If the growing crustal strains caused by the changing core magnetic field configuration in canonical spinning-down pulsars are relaxed by large-scale crust-cracking events, special properties are predicted for the resulting changes in spin period. These agree with various glitch observations, including glitch activity, permanent shifts in spin-down rates after glitches in young pulsars, the intervals between glitches, families of glitches with different magnitudes in the same pulsar, the sharp drop in glitch intervals and magnitudes as pulsar spin periods approach 0.7 s, and the general absence of glitching beyond this period.

https://cds.cern.ch/record/333024/files/9709008.pdf

Malvin Ruderman

Papers

Energetic Radiation from Rapidly Spinning Pulsars. 1. Outer Magnetosphere Gaps. 2. Vela and Crab

Energetic radiation from rapidly spinning pulsars. II: Vela and Crab

Spin up in neutron stars: the future of the vela pulsar.

A three-dimensional outer magnetospheric gap model for gamma-ray pulsars: Geometry, pair production, emission morphologies, and phase-resolved spectra

Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches