35 research outputs found
The central engine of GRB 130831A and the energy breakdown of a relativistic explosion
Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, yet
the nature and physical properties of their energy sources are far from
understood. Very important clues, however, can be inferred by studying the
afterglows of these events. We present optical and X-ray observations of GRB
130831A obtained by Swift, Chandra, Skynet, RATIR, Maidanak, ISON, NOT, LT and
GTC. This burst shows a steep drop in the X-ray light-curve at s
after the trigger, with a power-law decay index of . Such a rare
behaviour cannot be explained by the standard forward shock (FS) model and
indicates that the emission, up to the fast decay at s, must be of
"internal origin", produced by a dissipation process within an
ultrarelativistic outflow. We propose that the source of such an outflow, which
must produce the X-ray flux for day in the cosmological rest frame,
is a newly born magnetar or black hole. After the drop, the faint X-ray
afterglow continues with a much shallower decay. The optical emission, on the
other hand, shows no break across the X-ray steep decrease, and the late-time
decays of both the X-ray and optical are consistent. Using both the X-ray and
optical data, we show that the emission after s can be explained
well by the FS model. We model our data to derive the kinetic energy of the
ejecta and thus measure the efficiency of the central engine of a GRB with
emission of internal origin visible for a long time. Furthermore, we break down
the energy budget of this GRB into the prompt emission, the late internal
dissipation, the kinetic energy of the relativistic ejecta, and compare it with
the energy of the associated supernova, SN 2013fu.Comment: Accepted for publication by MNRAS. 21 pages, 3 figures, 8 tables.
Extra table with magnitudes in the sourc
Polarization and spectral energy distribution in OJ 287 during the 2016/17 outbursts
We report optical photometric and polarimetric observations of the blazar OJ 287 gathered during 2016/17. The high level of activity, noticed after the General Relativity Centenary flare, is argued to be part of the follow-up flares that exhibited high levels of polarization and originated in the primary black hole jet. We propose that the follow-up flares were induced as a result of accretion disk perturbations, travelling from the site of impact towards the primary SMBH. The timings inferred from our observations allowed us to estimate the propagation speed of these perturbations. Additionally, we make predictions for the future brightness of OJ 287. © 2017 by the authors
GRB 130831a: Rise and demise of a magnetar at z = 0.5
Open Access.--14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories; University of Rome "La Sapienza"Rome; Italy; 12 July 2015 through 18 July 2015; Code 142474.-- http://www.icra.it/mg/mg14/Gamma-ray bursts (GRBs) are the brightest explosions in the universe, yet the properties of their energy sources are far from understood. Very important clues, however, can be deduced by studying the afterglows of these events. We present observations of GRB 130831A and its afterglow obtained with Swift, Chandra, and multiple ground-based observatories. This burst shows an uncommon drop in the X-ray light curve at about 100 ks after the trigger, with a decay slope of α 7. The standard Forward Shock (FS) model offers no explanation for such a behaviour. Instead, a model in which a newly born magnetar outflow powers the early X-ray emission is found to be viable. After the drop, the X-ray afterglow resumes its decay with a slope typical of FS emission. The optical emission, on the other hand, displays no clear break across the X-ray drop and its decay is consistent with that of the late X-rays. Using both the X-ray and optical data, we show that the FS model can explain the emission after 100 ks. We model our data to infer the kinetic energy of the ejecta and thus estimate the efficiency of a magnetar âcentral engineâ of a GRB. Furthermore, we break down the energy budget of this GRB into prompt emission, late internal dissipation, kinetic energy of the relativistic ejecta, and compare it with the energy of the accompanying supernova, SN 2013fu. Copyright © 2018 by the Editors.All rights reserved.Peer reviewe
Polarization and spectral energy distribution in OJ 287 during the 2016/17 outbursts
© 2017 by the authors. We report optical photometric and polarimetric observations of the blazar OJ 287 gathered during 2016/17. The high level of activity, noticed after the General Relativity Centenary flare, is argued to be part of the follow-up flares that exhibited high levels of polarization and originated in the primary black hole jet. We propose that the follow-up flares were induced as a result of accretion disk perturbations, travelling from the site of impact towards the primary SMBH. The timings inferred from our observations allowed us to estimate the propagation speed of these perturbations. Additionally, we make predictions for the future brightness of OJ 287
GRB 130831a: Rise and demise of a magnetar at z = 0.5
Gamma-ray bursts (GRBs) are the brightest explosions in the universe, yet the properties of their energy sources are far from understood. Very important clues, however, can be deduced by studying the afterglows of these events. We present observations of GRB 130831A and its afterglow obtained with Swift, Chandra, and multiple ground-based observatories. This burst shows an uncommon drop in the X-ray light curve at about 100 ks after the trigger, with a decay slope of α 7. The standard Forward Shock (FS) model offers no explanation for such a behaviour. Instead, a model in which a newly born magnetar outflow powers the early X-ray emission is found to be viable. After the drop, the X-ray afterglow resumes its decay with a slope typical of FS emission. The optical emission, on the other hand, displays no clear break across the X-ray drop and its decay is consistent with that of the late X-rays. Using both the X-ray and optical data, we show that the FS model can explain the emission after 100 ks. We model our data to infer the kinetic energy of the ejecta and thus estimate the efficiency of a magnetar âcentral engineâ of a GRB. Furthermore, we break down the energy budget of this GRB into prompt emission, late internal dissipation, kinetic energy of the relativistic ejecta, and compare it with the energy of the accompanying supernova, SN 2013fu
Pulmonary artery enlargement in schistosomiasis associated pulmonary arterial hypertension
Polarization and Spectral Energy Distribution in OJ 287 during the 2016/17 Outbursts
We report optical photometric and polarimetric observations of the
blazar OJ 287 gathered during 2016/17. The high level of activity,
noticed after the General Relativity Centenary flare, is argued to be
part of the follow-up flares that exhibited high levels of polarization
and originated in the primary black hole jet. We propose that the
follow-up flares were induced as a result of accretion disk
perturbations, traveling from the site of impact towards the primary
SMBH. The timings inferred from our observations allowed us to estimate
the propagation speed of these perturbations. Additionally, we make
predictions for the future brightness of OJ 287.</p
Oberflaechenpolysacchrid-Synthese in Xanthomonas campestris pathovar campestris Genetische Analyse und Untersuchung ihrer Rolle im Pathogenitaetsverhalten
Available from TIB Hannover: DW 7567 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Skynet Junior Scholars: From Idea to Enactment--Tales from the Trenches II Implementation with Blind and Low Vision Youth
Skynet Junior Scholars is an ambitious program that aims to:--Develop online tools that enable middle school and high school aged youth to use robotic optical and radio telescopes to do astronomy--Create an inquiry-based curriculum that promotes critical thinking and scientific habits of mind--Proactively incorporate Principles of Universal Design in all SJS development tasks to ensure access by blind/low vision and deaf/hard of hearing youth--Prepare 180 adult youth leaders from diverse backgrounds including 4-H leaders, museum educators, amateur astronomers and teachers to facilitate SJS activities in a variety of settings.In this paper we describe the work of staff and volunteers at the Wisconsin School for the Blind and Visually Impaired who have implemented SJS activities in school and camp environments, as well as ways in which they have empowered their students to take on leadership roles. Students from the Wisconsin School for the Blind and Visually Impaired planned and co-hosted a Magic of Astronomy (Harry Potter Themed) star party that incorporated topics learned as part of the SJS program; filters, exposure time, locating objects in the sky, as well as, how to make an image request from the Skynet network. Their experiences in successfully doing active astronomy will provide insight into how anyone can engage everyone in programs like Skynet Junior Scholars.Skynet Junior Scholars is supported by the National Science Foundation under Grant Numbers 1223687, 1223235 and 1223345