GRBs in the Era of Swift and Fermi

Utilizing both Swift and Fermi to study GRBs provides us with a unique broad spectral and temporal window into both prompt emission and afterglow studies. Swift has provided key information from GRB follow-up of LAT detected bursts) that has led to ground-based redshift measurements and afterglow broadband light curves and SEDs. We study the X-ray and optical afterglows of Fermi-LAT detected bursts in the context of the hundreds of GRBs discovered by Swift over the last 7 years) in order to better understand the origin of the high-energy gamma-rays. We also briefly describe the efforts to best facilitate joint Swift-Fermi observations. These initial results demonstrate the synergy between Swift and Fermi) and hint at the many interesting discoveries to come

Fermi-LAT Gamma-ray Bursts and Insight from Swift

A new revolution in GRB observation and theory has begun over the last 3 years since the launch of the Fermi gamma-ray space telescope. The new window into high energy gamma-rays opened by the Fermi-LAT is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts. In this talk I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by Swift over the last 7 years and how through comparisons between the Swift, GBM, and LAT GRB samples, we can learn about the unique characteristics and relationships between each population

Locked In: the Silent Siege of Dubrovnik by the Tourism Industry

This thesis argues that Yugoslavia and an independent Croatia used Dubrovnik's cultural heritage to define and substantiate themselves as they emerged from political upheaval, disrupted economies, and nascent institutional foundations and thus firmly embedded the tourism industry within their political economies as more than an economic tool. Through the tourism industry, the cultural heritage of Dubrovnik played a fundamental role, symbolically and economically, in their process of nation building. As an emblematic site of historic and national significance, Dubrovnik represented the freedom and wealth of culture that both Yugoslavia and Croatia as new unsteady political institutions sought to evoke. Within bolstering the tourism industry, Yugoslavia and Croatia cultivated Dubrovnik's path dependency in the sector, which resulted in its contemporary "lock-in" and mono-economy. This study of Dubrovnik will elucidate the role of path dependency in shaping Dubrovnik's economy, political actors, and social fabric, while portraying the extent that tourism has pervaded throughout all spectrums of society and distorted its local heritage. Thus, I seek to answer the following questions: How did the State's focus on the tourism industry as an economic and political engine engender Dubrovnik's path dependency in the sector? How does Dubrovnik's lock-in the tourism industry represent the State's failure to regulate the industry? How does a lock-in the tourism industry facilitate the erosion of a site's cultural heritage? Using Dubrovnik as a case study to answer these questions, this research will evaluate path dependency's potential use as an ex-ante planning and preservation tool to predict if a state is advancing towards an irreconcilable lock-in and how to intervene if it does. Path dependency makes meaningful intervention all the more difficult, because it increasingly diminishes the agency of political actors to switch paths. Therefore, as will be demonstrated, planners need to increase means for effective participatory planning to counter a potential lack of political will that can prevent developing alternative, more optimal paths

Optical afterglows of Gamma-Ray Bursts: peaks, plateaus, and possibilities

The optical light-curves of GRB afterglows display either peaks or plateaus. We identify 16 afterglows of the former type, 17 of the latter, and 4 with broad peaks, that could be of either type. The optical energy release of these two classes is similar and is correlated with the GRB output, the correlation being stronger for peaky afterglows, which suggests that the burst and afterglow emissions of peaky afterglows are from the same relativistic ejecta and that the optical emission of afterglows with plateaus arises more often from ejecta that did not produce the burst emission. Consequently, we propose that peaky optical afterglows are from impulsive ejecta releases and that plateau optical afterglows originate from long-lived engines, the break in the optical light-curve (peak or plateau end) marking the onset of the entire outflow deceleration. In the peak luminosity--peak time plane, the distribution of peaky afterglows displays an edge with L_p \propto t_p^{-3}, which we attribute to variations (among afterglows) in the ambient medium density. The fluxes and epochs of optical plateau breaks follow a L_b \propto t_b^{-1} anticorrelation. Sixty percent of 25 afterglows that were well-monitored in the optical and X-rays show light-curves with comparable power-law decays indices and achromatic breaks. The other 40 percent display three types of decoupled behaviours: i) chromatic optical light-curve breaks (perhaps due to the peak of the synchrotron spectrum crossing the optical), ii) X-ray flux decays faster than in the optical (suggesting that the X-ray emission is from local inverse-Compton scattering), and iii) chromatic X-ray light-curve breaks (indicating that the X-ray emission is from external up-scattering).Comment: 11 pages, table with afterglows added, to appear in MNRA

Do Fermi-LAT observations really imply very large Lorentz factors in GRB outflows ?

Recent detections of GeV photons in a few GRBs by Fermi-LAT have led to strong constraints on the bulk Lorentz factor in GRB outflows. To avoid a large gamma gamma optical depth, minimum values of the Lorentz factor are estimated to be as high as 800-1200 in some bursts. Here we present a detailed calculation of the gamma gamma optical depth taking into account both the geometry and the dynamics of the jet. In the framework of the internal shock model, we compute lightcurves in different energy bands and the corresponding spectrum and we show how the limits on the Lorentz factor can be significantly lowered compared to previous estimates.Comment: 4 pages, 3 figures, proceedings of the Gamma Ray Bursts 2010 Conference, Annapolis, USA. Editors: McEnery, Racusin, Gehrel

Fermi-LAT Gamma-Ray Bursts and Insights from Swift

A new revolution in Gamma-ray Burst (GRB) observations and theory has begun over the last two years since the launch of the Fermi Gamma-ray Space Telescope. The new window into high energy gamma-rays opened by the Fermi-Large Area Telescope (LAT) is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts compared to the large sample detected by Swift over the last 6 years. In this talk, I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by the Swift X-ray Telescope (XRT) and UV/Optical Telescope (UVOT). Through comparisons between the GRBs detected by Swift-BAT, G8M, and LAT, we can learn about the unique characteristics, physical differences, and the relationships between each population. These population characteristics provide insight into the different physical parameters that contribute to the diversity of observational GRB properties

Chandra Observations of WR147 Reveal a Double X-ray Source

We report the first results from deep X-ray observations of the Wolf-Rayet binary system WR147 with the Chandra HETG. Analysis of the zeroth order data reveals that WR147 is a double X-ray source. The northern counterpart is likely associated with the colliding wind region, while the southern component is certainly identified with the WN star in this massive binary. The latter is the source of high energy X-rays (including the Fe K_alpha complex at 6.67 keV) whose production mechanism is yet unclear. For the first time, X-rays are observed directly from a WR star in a binary system.Comment: 15 pages, 3 figures, To Appear in The Astrophysical Journal Letter