Detection Techniques of Microsecond Gamma-Ray Bursts using Ground-Based Telescopes

Gamma-ray observations above 200 MeV are conventionally made by satellite-based detectors. The EGRET detector on the Compton Gamma Ray Observatory (CGRO) has provided good sensitivity for the detection of bursts lasting for more than 200 ms. Theoretical predictions of high-energy gamma-ray bursts produced by quantum-mechanical decay of primordial black holes (Hawking 1971) suggest the emission of bursts on shorter time scales. The final stage of a primordial black hole results in a burst of gamma-rays, peaking around 250 MeV and lasting for a tenth of a microsecond or longer depending on particle physics. In this work we show that there is an observational window using ground-based imaging Cherenkov detectors to measure gamma-ray burst emission at energies E greater than 200 MeV. This technique, with a sensitivity for bursts lasting nanoseconds to several microseconds, is based on the detection of multi-photon-initiated air showers.Comment: accepted for publication in the Astrophysical Journa

Improved energy resolution for VHE gamma-ray astronomy with systems of Cherenkov telescopes

We present analysis techniques to improve the energy resolution of stereoscopic systems of imaging atmospheric Cherenkov telescopes, using the HEGRA telescope system as an example. The techniques include (i) the determination of the height of the shower maximum, which is then taken into account in the energy determination, and (ii) the determination of the location of the shower core with the additional constraint that the direction of the gamma rays is known a priori. This constraint can be applied for gamma-ray point sources, and results in a significant improvement in the localization of the shower core, which translates into better energy resolution. Combining both techniques, the HEGRA telescopes reach an energy resolution between 9% and 12%, over the entire energy range from 1 TeV to almost 100 TeV. Options for further improvements of the energy resolution are discussed.Comment: 13 Pages, 7 figures, Latex. Astroparticle Physics, in pres

Towards micro-arcsecond spatial resolution with Air Cherenkov Telescope arrays as optical intensity interferometers

In this poster contribution we highlight the equivalence between an Imaging Air Cherenkov Telescope (IACT) array and an Intensity Interferometer for a range of technical requirements. We touch on the differences between a Michelson and an Intensity Interferometer and give a brief overview of the current IACT arrays, their upgrades and next generation concepts (CTA, AGIS, completion 2015). The latter are foreseen to include 30-90 telescopes that will provide 400-4000 different baselines that range in length between 50m and a kilometre. Intensity interferometry with such arrays of telescopes attains 50 micro-arcseconds resolution for a limiting V magnitude of ~8.5. This technique opens the possibility of a wide range of studies, amongst others, probing the stellar surface activity and the dynamic AU scale circumstellar environment of stars in various crucial evolutionary stages. Here we discuss possibilities for using IACT arrays as optical Intensity Interferometers.Comment: Appeared in the proceedings of "The Universe under the Microscope - Astrophysics at High Angular Resolution", Journal of Physics:Conference Series (IOP; http://www.iop.org/EJ/toc/1742-6596/131/1

Effects of Individual Pre-Fledging Traits and Environmental Conditions on Return Patterns in Juvenile King Penguins

Despite the importance of early life stages in individuals' life history and population dynamics, very few studies have focused on the constraints to which these juvenile traits are subjected. Based on 10 years of automatic monitoring of over 2500 individuals, we present the first study on the effects of environmental conditions and individual pre-fledging traits on the post-fledging return of non-banded king penguins to their natal colony. Juvenile king penguins returned exclusively within one of the three austral summers following their departure. A key finding is that return rates (range 68–87%) were much higher than previously assumed for this species, importantly meaning that juvenile survival is very close to that of adults. Such high figures suggest little juvenile dispersal, and selection occurring mostly prior to fledging in king penguins. Pre-fledging conditions had a strong quadratic impact on juvenile return rates. As expected, cohorts reared under very unfavourable years (as inferred by the breeding success of the colony) exhibited low return rates but surprisingly, so did those fledged under very favourable conditions. Juvenile sojourns away from the colony were shorter under warm conditions and subsequent return rates higher, suggesting a positive effect of climate warming. The longer the post-fledging trip (1, 2 or 3 years), the earlier in the summer birds returned to their natal colony and the longer they stayed before leaving for the winter journey. The presence of juveniles in the colony was more than twice the duration required for moulting purposes, yet none attempted breeding in the year of their first return. Juvenile presence in the colony may be important for acquiring knowledge on the social and physical colonial environment and may play an important part in the learning process of mating behaviour. Further studies are required to investigate its potential implications on other life-history traits such as recruitment age

A Matemática Natural na Instrução Primária, 1978

Este livro possui 223 páginas, com dimensões de 18,5 cm x 12 cm, e encadernação tipo lombada quadrada. Possui ilustrações. O exemplar original pertence ao acervo pessoal do prof. Marcus Vinicius Basso. Item digitalizado por Bárbara Cardoso Kayser.O livro faz parte da coleção "Técnicas de Educação" e descreve duas experiências do ensino da Matemática em sala de aula dos primeiros anos do ensino primário: "Primeiros passos para uma matemática natural no 1º ano" e "Primeira experiência de matemática livre no 2º ano". Em cada parte é retratada a experiência vivida por professores lidando com novos conceitos de Matemática e novos conceitos sobre o ensino. Além disso, propõem um programa concreto de ensino dessa disciplina

Search for TeV Gamma-Rays from Shell-Type Supernova Remnants

If cosmic rays with energies <100 TeV originate in the galaxy and are accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays will be produced as the result of proton and electron interactions with the local interstellar medium, and by inverse Compton emission from electrons scattering soft photon fields. We report on observations of two supernova remnants with the Whipple Observatory's 10 m gamma-ray telescope. No significant detections have been made and upper limits on the >500 GeV flux are reported. Non-thermal X-ray emission detected from one of these remnants (Cassiopeia A) has been interpreted as synchrotron emission from electrons in the ambient magnetic fields. Gamma-ray emission detected from the Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray acceleration. We interpret our results in the context of these observations.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999

Stellar Intensity Interferometry with Air Cherenkov Telescope arrays

The present generation of ground-based Very High Energy (VHE) gamma-ray observatories consist of arrays of up to four large (> 12m diameter) light collectors quite similar to those used by R. Hanbury Brown to measure stellar diameters by Intensity Interferometry in the late 60's. VHE gamma-ray observatories to be constructed over the coming decade will involve several tens of telescopes of similar or greater sizes. Used as intensity interferometers, they will provide hundreds of independent baselines. Now is the right time to re-assess the potential of intensity interferometry so that it can be taken into consideration in the design of these large facilities.Comment: 11 pages, 9 figures, in procedings of the High Time Resolution Astrophysics conferenc

Very High Energy Gamma-ray spectral properties of Mrk 501 from CAT Cerenkov telescope observations in 1997

The BL Lac object Mrk 501 went into a very high state of activity during 1997, both in VHE gamma-rays and X-rays. We present here results from observations at energies above 250 GeV carried out between March and October 1997 with the CAT Cerenkov imaging Telescope. The average differential spectrum between 30 GeV and 13 TeV shows significant curvature and is well represented by phi_0 * E_TeV^{-(alpha + beta*log10(E_TeV))}, with: phi_0 = 5.19 +/- 0.13 {stat} +/- 0.12 {sys-MC} +1.66/-1.04 {sys-atm} * 10^-11 /cm^2/s/TeV alpha = 2.24 +/- 0.04 {stat} +/- 0.05 {sys} beta = 0.50 +/- 0.07 {stat} (negligible systematics). The TeV spectral energy distribution of Mrk 501 clearly peaks in the range 500 GeV-1 TeV. Investigation of spectral variations shows a significant hardness-intensity correlation with no measurable effect on the curvature. This can be described as an increase of the peak TeV emission energy with intensity. Simultaneous and quasi-simultaneous CAT VHE gamma-ray and BeppoSAX hard X-ray detections for the highest recorded flare on 16th April and for lower-activity states of the same period show correlated variability with a higher luminosity in X-rays than in gamma-rays. The observed spectral energy distribution and the correlated variability between X-rays and gamma-rays, both in amplitude and in hardening of spectra, favour a two-component emission scheme where the low and high energy components are attributed to synchrotron and inverse Compton (IC) radiation, respectively.Comment: Submitted to Astronomy and Astrophysics, 8 pages including 6 figures. Published with minor change