176 research outputs found
Constraining very-high-energy and optical emission from FRB 121102 with the MAGIC telescopes
Fast radio bursts (FRBs) are bright flashes observed typically at GHz frequencies with millisecond duration, whose origin is likely extragalactic. Their nature remains mysterious, motivating searches for counterparts at other wavelengths. FRB 121102 is so far the only source known to repeatedly emit FRBs and is associated with a host galaxy at redshift z ≃ 0.193.We conducted simultaneous observations of FRB 121102 with the Arecibo and MAGIC telescopes during several epochs in 2016-2017. This allowed searches for millisecond time-scale burst emission in very-high-energy (VHE) gamma-rays as well as the optical band. While a total of five FRBs were detected during these observations, no VHE emission was detected, neither of a persistent nature nor burst-like associated with the FRBs. The average integral flux upper limits above 100 GeV at 95 per cent confidence level are 6.6 × 10 -12 photons cm -2 s -1 (corresponding to luminosity LVHE ≲ 10 45 erg s -1 ) over the entire observation period, and 1.2 × 10 -7 photons cm -2 s -1 (LVHE ≳ 10 49 erg s -1 ) over the total duration of the five FRBs. We constrain the optical U-band flux to be below 8.6 mJy at 5σ level for 1-ms intervals around the FRB arrival times. A bright burst with U-band flux 29 mJy and duration ~12 ms was detected 4.3 s before the arrival of one FRB. However, the probability of spuriously detecting such a signal within the sampled time space is 1.5 per cent (2.2, post-trial), i.e. consistent with the expected background. We discuss the implications of the obtained upper limits for constraining FRB models
TeV Gamma-ray Astronomy: A Summary
The field of TeV gamma-ray astronomy has produced many exciting results over
the last decade. Both the source catalogue, and the range of astrophysical
questions which can be addressed, continue to expand. This article presents a
topical review of the field, with a focus on the observational results of the
imaging atmospheric Cherenkov telescope arrays. The results encompass pulsars
and their nebulae, supernova remnants, gamma-ray binary systems, star forming
regions and starburst and active galaxies.Comment: 19 pages. Astroparticle Physics, in press. See published article for
higher resolution figures. Cite as: J. Holder, TeV gamma-ray astronomy: A
summary, Astropart. Phys. (2012),
http://dx.doi.org/10.1016/j.astropartphys.2012.02.01
Gamma-Ray Transients observed with the Fermi Large Area Telescope
Many observed phenomena in the universe are not static: this is why time- domain astrophysics is a key field of current astronomy and astrophysics. The temporal domain offers an important window on the understanding of extreme phases of stellar and galaxy evolution through studies of novae, supernovae, Gamma-Ray Bursts (GRBs), pulsars, Active Galactic Nuclei (AGN) to list only a few. Variable objects show some different characteristic variability and a lot of information on the physical processes at work comes from measuring luminosity and spectral variations over time.
Launched in June 2008, during its first eight years of operation the Fermi Gamma-Ray Space Telescope has confirmed that the gamma-ray sky is highly dynamic on all time scales, from \u3bcs to years, providing insight into extreme physical conditions.
My research activity is focused on the analysis of transient gamma-ray sources observed by the Large Area Telescope (LAT), the main instrument on-board Fermi.
The variable sources analyzed in this thesis spans different observing time scales:
- GRBs and solar flares show an impulsive and short phase that can last from 3c ms to some hundreds of seconds, and a time-extended phase observed at higher energies that can lasts several hours;\u2028- AGN show variability from hours to days;\u2028- novae, whose high-energy transient emission lasts for weeks.
In chapters number 2 and 3, I will present the spectral analysis of the impulsive phase of gamma-ray bursts and solar flares using data from the LAT and the GBM. The goal of of this work has been to develop a semi-automatic analysis-pipeline to optimize the source selection and the modelling of background emission in order to better constrain spectral features and infer important physical information on emission processes at work.
In chapter 4 and 5, I will show the analysis performed on LAT data for AGN and novae, in the context of coordinated very-high energy ( 3c TeV) observations with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes.
The aim of Chapter 1 is to present the main features of the observatories whose data have been used for my analyses
Very-high energy gamma-ray astronomy: A 23-year success story in high-energy astroparticle physics
Very-high energy (VHE) gamma quanta contribute only a minuscule fraction -
below one per million - to the flux of cosmic rays. Nevertheless, being neutral
particles they are currently the best "messengers" of processes from the
relativistic/ultra-relativistic Universe because they can be extrapolated back
to their origin. The window of VHE gamma rays was opened only in 1989 by the
Whipple collaboration, reporting the observation of TeV gamma rays from the
Crab nebula. After a slow start, this new field of research is now rapidly
expanding with the discovery of more than 150 VHE gamma-ray emitting sources.
Progress is intimately related with the steady improvement of detectors and
rapidly increasing computing power. We give an overview of the early attempts
before and around 1989 and the progress after the pioneering work of the
Whipple collaboration. The main focus of this article is on the development of
experimental techniques for Earth-bound gamma-ray detectors; consequently, more
emphasis is given to those experiments that made an initial breakthrough rather
than to the successors which often had and have a similar (sometimes even
higher) scientific output as the pioneering experiments. The considered energy
threshold is about 30 GeV. At lower energies, observations can presently only
be performed with balloon or satellite-borne detectors. Irrespective of the
stormy experimental progress, the success story could not have been called a
success story without a broad scientific output. Therefore we conclude this
article with a summary of the scientific rationales and main results achieved
over the last two decades.Comment: 45 pages, 38 figures, review prepared for EPJ-H special issue "Cosmic
rays, gamma rays and neutrinos: A survey of 100 years of research
MAGIC-II's central pixel system for simultaneous optical and gamma-ray observation
The MAGIC telescopes are a system of two imaging atmospheric Cherenkov telescopes designed to observe very-high-energy y rays. MAGIC utilizes a large reflective surface and photodetectors with ultrafast time response to capture Cherenkov photons. These features, together with the dedicated system installed in the central photomultiplier tube of their camera, so-called central pixel system (CPS), turn MAGIC into a suitable telescope to study high-speed optical astronomy in the millisecond (ms) regime. We report on the status of the CPS currently mounted in the MAGIC-II camera, its performance and calibration to demonstrate the sensitivity of MAGIC-II to ms optical pulses, for both transient and periodic signals, and discuss its potential over several science cases. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License
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