1,143 research outputs found
Estimating the Explosion Time of Core-Collapse Supernovae from Their Optical Light Curves
Core-collapse supernovae are among the prime candidate sources of high energy
neutrinos. Accordingly, the IceCube collaboration has started a program to
search for such a signal. IceCube operates an online search for neutrino
bursts, forwarding the directions of candidate events to a network of optical
telescopes for immediate follow-up observations. If a supernova is identified
from the optical observations, in addition to a directional coincidence a
temporal photon-neutrino coincidence also needs to be established. To achieve
this, we present a method for estimating the supernova explosion time from its
light curve using a simple model. We test the model with supernova light curve
data from SN1987A, SN2006aj and SN2008D and show that the explosion times can
be determined with an accuracy of better than a few hours.Comment: Version accepted for publication by Astroparticle Physics; 13 pages,
5 figure
Systematic search for gamma-ray periodicity in active galactic nuclei detected by the Fermi Large Area Telescope
We use nine years of gamma-ray data provided by the Fermi Large Area
Telescope (LAT) to systematically study the light curves of more than two
thousand active galactic nuclei (AGN) included in recent Fermi-LAT catalogs.
Ten different techniques are used, which are organized in an automatic
periodicity-search pipeline, in order to search for evidence of periodic
emission in gamma rays. Understanding the processes behind this puzzling
phenomenon will provide a better view about the astrophysical nature of these
extragalactic sources. However, the observation of temporal patterns in
gamma-ray light curves of AGN is still challenging. Despite the fact that there
have been efforts on characterizing the temporal emission of some individual
sources, a systematic search for periodicities by means of a full likelihood
analysis applied to large samples of sources was missing. Our analysis finds 11
AGN, of which 9 are identified for the first time, showing periodicity at more
than 4sigma in at least four algorithms. These findings will help in solving
questions related to the astrophysical origin of this periodic behavior.Comment: 16 pages, 5 figures, 4 tables. Accepted by Ap
The total assessment profile, volume 2
Appendices are presented which include discussions of interest formulas, factors in regionalization, parametric modeling of discounted benefit-sacrifice streams, engineering economic calculations, and product innovation. For Volume 1, see
The total assessment profile, volume 1
A methodology is described for the evaluation of societal impacts associated with the implementation of a new technology. Theoretical foundations for the methodology, called the total assessment profile, are established from both the economic and social science perspectives. The procedure provides for accountability of nonquantifiable factors and measures through the use of a comparative value matrix by assessing the impacts of the technology on the value system of the society
Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
It is widely accepted that cosmic rays (CRs) up to at least PeV energies are
Galactic in origin. Accelerated particles are injected into the interstellar
medium where they propagate to the farthest reaches of the Milky Way, including
a surrounding halo. The composition of CRs coming to the solar system can be
measured directly and has been used to infer the details of CR propagation that
are extrapolated to the whole Galaxy. In contrast, indirect methods, such as
observations of gamma-ray emission from CR interactions with interstellar gas,
have been employed to directly probe the CR densities in distant locations
throughout the Galactic plane. In this article we use 73 months of data from
the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV
to search for gamma-ray emission produced by CR interactions in several high-
and intermediate-velocity clouds located at up to ~ 7 kpc above the Galactic
plane. We achieve the first detection of intermediate-velocity clouds in gamma
rays and set upper limits on the emission from the remaining targets, thereby
tracing the distribution of CR nuclei in the halo for the first time. We find
that the gamma-ray emissivity per H atom decreases with increasing distance
from the plane at 97.5% confidence level. This corroborates the notion that CRs
at the relevant energies originate in the Galactic disk. The emissivity of the
upper intermediate-velocity Arch hints at a 50% decline of CR densities within
2 kpc from the plane. We compare our results to predictions of CR propagation
models.Comment: Accepted for publication in the Astrophysical Journa
The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
The origin of the extragalactic -ray background (EGB) has been
debated for some time. { The EGB comprises the -ray emission from
resolved and unresolved extragalactic sources, such as blazars, star-forming
galaxies and radio galaxies, as well as radiation from truly diffuse
processes.} This letter focuses on the blazar source class, the most numerous
detected population, and presents an updated luminosity function and spectral
energy distribution model consistent with the blazar observations performed by
the {\it Fermi} Large Area Telescope (LAT). We show that blazars account for
50\,\% of the EGB photons (0.1\,GeV), and that {\it Fermi}-LAT
has already resolved 70\,\% of this contribution. Blazars, and in
particular low-luminosity hard-spectrum nearby sources like BL Lacs, are
responsible for most of the EGB emission above 100\,GeV. We find that the
extragalactic background light, which attenuates blazars' high-energy emission,
is responsible for the high-energy cut-off observed in the EGB spectrum.
Finally, we show that blazars, star-forming galaxies and radio galaxies can
naturally account for the amplitude and spectral shape of the background in the
0.1--820\,GeV range, leaving only modest room for other contributions. This
allows us to set competitive constraints on the dark-matter annihilation cross
section.Comment: On behalf of the Fermi-LAT collaboration. Contact authors: M. Ajello,
D. Gasparrini, M. Sanchez-Conde, G. Zaharijas, M. Gustafsson. Accepted for
publication on ApJ
The Antares Neutrino Telescope and Multi-Messenger Astronomy
Antares is currently the largest neutrino telescope operating in the Northern
Hemisphere, aiming at the detection of high-energy neutrinos from astrophysical
sources. Such observations would provide important clues about the processes at
work in those sources, and possibly help solve the puzzle of ultra-high energy
cosmic rays. In this context, Antares is developing several programs to improve
its capabilities of revealing possible spatial and/or temporal correlations of
neutrinos with other cosmic messengers: photons, cosmic rays and gravitational
waves. The neutrino telescope and its most recent results are presented,
together with these multi-messenger programs.Comment: 10 pages, 7 figures. Proceedings of the 14th Gravitational Wave Data
Analysis Workshop (GWDAW-14) in Roma - January 26th-29th, 201
Multi-Frequency Observations of the Candidate Neutrino Emitting Blazar BZB J0955+3551
The recent spatial and temporal coincidence of the blazar TXS 0506+056 with
the IceCube detected neutrino event IC-170922A has opened up a realm of
multi-messenger astronomy with blazar jets as a plausible site of cosmic-ray
acceleration. After TXS 0506+056, a second blazar, BZB J0955+3551, has recently
been found to be spatially coincident with the IceCube detected neutrino event
IC-200107A and undergoing its brightest X-ray flare measured so far. Here, we
present the results of our multi-frequency campaign to study this peculiar
event that includes observations with the NuSTAR, Swift, NICER, and 10.4 m Gran
Telescopio Canarias (GTC). The optical spectroscopic observation from GTC
secured its redshift as and the central black
hole mass as 10. Both NuSTAR and NICER data reveal a
rapid flux variability albeit at low-significance (). We
explore the origin of the target photon field needed for the photo-pion
production using analytical calculations and considering the observed
optical-to-X-ray flux level. We conclude that seed photons may originate from
outside the jet, similar to that reported for TXS 0506+056, although a scenario
invoking a co-moving target photon field (e.g., electron-synchrotron) can not
be ruled out. The electromagnetic output from the neutrino-producing
photo-hadronic processes are likely to make only a sub-dominant contribution to
the observed spectral energy distribution suggesting that the X-ray flaring
event may not be directly connected with IC-200107A.Comment: Accepted for publication in the Astrophysical journa
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