Gamma-Ray Bursts, witnessing the birth of stellar mass black holes

Gamma-ray bursts are associated with catastrophic cosmic events. They appear when a new black hole, created after the explosion of a massive star or the merger of two compact stars, quickly accretes the matter around it and ejects a transient relativistic jet in our direction. This review discusses the various types of gamma-ray bursts, their progenitors, their beaming and their rate in the local universe. We emphasize the broad astrophysical interest of GRB studies, and the crucial role of high-energy satellites as exclusive suppliers of GRB alerts and initial locations.Comment: 8 pages, 2 figures, invited review at the conference "An INTEGRAL view of the high-energy sky (the first 10 years) - 9th INTEGRAL Workshop and celebration of the 10th anniversary of the launch" - to appear in Proceedings of Science - PoS(INTEGRAL 2012)11

Choosing a measure of GRB brightness that approaches a standard candle

Studies using the GRB brightness as a distance indicator require a measure of brightness with a small intrinsic dispersion (close to a standard candle). There is unfortunately no general agreement on the definition of such a quantity. We show here that the comparison of the size-frequency curves obtained with various measures of brightness can be used to select the quantity which is closer to a standard candle. Our method relies on a few general assumptions on the burster spatial distribution, namely that nearby bursters are homogeneously distributed in an Euclidean space with no density or luminosity evolution. We apply it to 5 measures of GRB brightness in the Current BATSE Catalog and we find that the GRB size-frequency distribution depends significantly on the energy window used to measure the GRB brightness. The influence of the time window being, in comparison, negligible. Our method suggests that the best distance indicator in this Catalog is the fluence measured below 100 keV, indicating that GRB luminosities have a smaller intrinsic dispersion below 100 keV than above.Comment: 5 pages (LateX), 2 Postscript figures, Proceedings of the 4th Huntsville GRB Worksho

Employees’ Satisfaction Is It an Antecedent of Customers’ Satisfaction: An Empirical Study on the Five and Four Star Hotels in the Kingdom of Bahrain

Along eras, customers were considered the single reason for hotel properties to remain in business, and due to the fact that their satisfaction remained to be a crucial issue, both practitioners and academics address it with a special concern. Because customers can easily perceive the enthusiasm and the positive energy of those employees in terms of their willingness to provide them with an enjoyable memorable experience, the founder of Marriott hotel chain stated “You can’t make happy guests with unhappy employees”. Therefore this study aims to investigate whether employees’ satisfaction can be viewed as an antecedent of customers’ satisfaction. An empirical study was conducted on the hotel industry in the Kingdom of Bahrain to investigate the relationship between employee and customer satisfaction as the impact of such relation in the hospitality industry is not quiet evidenced yet. The research adopts the analytical descriptive approach, utilizing two questionnaires addressed towards employees and customers to identify the impact of employees’ satisfaction on customers’ satisfaction. Data for this study was collected from employees and customers of five and four star hotels. The study traced the impact of employees’ satisfaction on customers’ satisfaction and results revealed high correlation between these variables. Empirical findings confirmed that pay and award as well as promotion have significant effect on customers’ satisfaction. Drawing from this finding, the research suggests for hotel practitioners to create employee engagement’s score and to correlate it to customer satisfaction score in one chart to manage this relationship. Keywords: Employees’ satisfaction, pay and award, supervision, working conditions, promotion, customers’ satisfaction, five and four star hotels