56 research outputs found
Measuring the Cosmic X-ray Background accurately
Measuring the Cosmic X-ray Background (CXB) is a key to understand the Active
Galactic Nuclei population, their absorption distribution and their average
spectra. However, hard X-ray instruments suffer from time-dependent backgrounds
and cross-calibration issues. The uncertainty of the CXB normalization remain
of the order of 20%. To obtain a more accurate measurement, the Monitor Vsego
Neba (MVN) instrument was built in Russia but not yet launched to the ISS
(arXiv:1410.3284). We follow the same ideas to develop a CXB detector made of
four collimated spectrometers with a rotating obturator on top. The collimators
block off-axis photons below 100 keV and the obturator modulates on-axis
photons allowing to separate the CXB from the instrumental background. Our
spectrometers are made of 20 mm thick CeBr crystals on top of a SiPM
array. One tube features a 20 cm effective area and more energy
coverage than MVN, leading to a CXB count rate improved by a factor of 10
and a statistical uncertainty 0.5% on the CXB flux. A prototype is being
built and we are seeking for a launch opportunity.Comment: 8 pages, 5 figures, 37th International Cosmic Ray Conference
(ICRC2021
Urban monitoring using NetKDE and VGI: network based kernel density estimation on volunteered geographic information applied to Baghdad, Iraq
This paper presents a methodology for urban monitoring using volunteered geographic information (VGI) and journalism data Iraq war logs with network based kernel density estimation (NetKDE). It investigates, using spatio-temporal analysis, the evolution of urban events in Baghdad between 2004 and 2009. The extracted street network is based on the data distributed by OpenStreetMap (OSM). A total of 21,876 logged events, 66,648 network segments, 22,644 gridpoints (200m resolution grid) and 362,304 gridpoints (50m resolution grid) are used for the analysis. The methodology combines and adapts these VGI data and is mainly based on open source and/or publicly available software. It handles very large datasets with multiscale, multi-resolution and temporal perspectives. Fuzzy-set map comparison (FMC) is used to identify level of changes between each period of time. The methodology is already used in other fields of research being biology, urban planning, criminology or economic evelopment. It should help stakeholders in respective domain to analyze the evolution of network constrained events in multiple contexts. This paper is divided in three parts. Firstly, conceptual background of VGI, NetKDE and FMC is presented. Secondly, the methodology is illustrated using data Iraq war logs, OSM data and grids with two different resolutions. Thirdly, spatio-temporal analysis results are presented and discussed.Peer Reviewe
Adding Gamma-ray Polarimetry to the Multi-Messenger Era
The last decade has seen the emergence of two new fields within astrophysics:
gamma ray polarimetry and GW astronomy. The former, which aims to measure the
polarization of gamma rays in the energy range of 10s to 100s of keV, from
astrophysical sources, saw the launch of the first dedicated polarimeters such
as GAP and POLAR. On the other hand, GW astronomy started with the detection of
the first black hole mergers by LIGO in 2015, followed by the first multi
messenger detection in 2017. While the potential of the two individual fields
has been discussed in detail in the literature, the potential for joint
observations has thus far been ignored. In this article, we aim to define how
GW observations can best contribute to gamma ray polarimetry and study the
scientific potential of joint analyses. In addition we aim to provide
predictions on feasibility of such joint measurements in the near future. We
study which GW observables can be combined with measurements from gamma ray
polarimetry to improve the discriminating power regarding GRB emission models.
We then provide forecasts for the joint detection capabilities of current and
future GW detectors and polarimeters. Our results show that by adding GW data
to polarimetry, a single precise joint detection would allow to rule out the
majority of emission models. We show that in the coming years joint detections
between GW and gamma ray polarimeters might already be possible. Although these
would allow to constrain part of the model space, the probability of highly
constraining joint detections will remain small in the near future. However,
the scientific merit held by even a single such measurement makes it important
to pursue such an endeavour. Furthermore, we show that using the next
generation of GW detectors, such as the Einstein Telescope, joint detections
for which GW data can better complement the polarization data become possible.Comment: 19 pages, 10 figures, Accepted for publication in A&
Measuring the Cosmic X-ray Background accurately
Synthesis models of the diffuse Cosmic X-ray Background (CXB) suggest that it
can be resolved into discrete sources, primarily Active Galactic Nuclei (AGNs).
Measuring the CXB accurately offers a unique probe to study the AGN population
in the nearby Universe. Current hard X-ray instruments suffer from the
time-dependent background and cross-calibration issues. As a result, their
measurements of the CXB normalization have an uncertainty of the order of
15%. In this paper, we present the concept and simulated performances of
a CXB detector, which could be operated on different platforms. With a 16-U
CubeSat mission running for more than two years in space, such a detector could
measure the CXB normalization with 1% uncertainty
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Crowdsourcing the georeferencing of historical pictures
Countless organizations own archive pictures which are not used due to the difficulty of localizing them. Only the participation of volunteers can help to identify the image content. Through an accessible web interface called smapshot, citizens are able to georeference historical images without any prior specific competence. To avoid the volunteers to face the complexity of 3D digitization and navigation, we implemented a state of the art photogrammetry camera orientation algorithm in the platform. Currently several thousand images from all around Switzerland have been georeferenced by the crowd. At this time the tool is mainly used by the population for the visualization experience and the nostalgia behind it. The ambition is to support scientists to analyze landscape evolution
Perspectives on Gamma-Ray Burst Physics and Cosmology with Next Generation Facilities
High-redshift Gamma-Ray Bursts (GRBs) beyond redshift are potentially
powerful tools to probe the distant early Universe. Their detections in large
numbers and at truly high redshifts call for the next generation of high-energy
wide-field instruments with unprecedented sensitivity at least one order of
magnitude higher than the ones currently in orbit. On the other hand, follow-up
observations of the afterglows of high-redshift GRBs and identification of
their host galaxies, which would be difficult for the currently operating
telescopes, require new, extremely large facilities of at multi-wavelengths.
This chapter describes future experiments that are expected to advance this
exciting field, both being currently built and being proposed. The legacy of
Swift will be continued by SVOM, which is equipped with a set of space-based
multi-wavelength instruments as well as and a ground segment including a wide
angle camera and two follow-up telescopes. The established Lobster-eye X-ray
focusing optics provides a promising technology for the detection of faint GRBs
at very large distances, based on which the {THESEUS}, {Einstein Probe} and
other mission concepts have been proposed. Follow-up observations and
exploration of the reionization era will be enabled by large facilities such as
{SKA} in the radio, the 30m class telescopes in the optical/near-IR, and the
space-borne {WFIRST} and {JWST} in the optical/near-IR/mid-IR. In addition, the
X-ray and -ray polarization experiment POLAR is also introduced.Comment: accepted for publication in Space Science Review; reprinted as a
chapter in a book of the Space Sciences Series of ISSI for the proceedings of
the ISSI-Beijing workshop " Gamma-Ray Bursts: a Tool to Explore the Young
Universe
POLAR-2, the next generation of GRB polarization detector
The POLAR-2 Gamma-Ray Burst (GRB) Polarimetry mission is a follow-up to the
successful POLAR mission. POLAR collected six months of data in 2016-2017 on
board the Tiangong-2 Chinese Space laboratory. From a polarization study on 14
GRBs, POLAR measured an overall low polarization and a hint for an unexpected
complexity in the time evolution of polarization during GRBs. Energy-dependent
measurements of the GRB polarization will be presented by N. de Angelis in
GA21-09 (August 2nd). These results demonstrate the need for measurements with
significantly improved accuracy. Moreover, the recent discovery of
gravitational waves and their connection to GRBs justifies a high-precision GRB
polarimeter that can provide both high-precision polarimetry and detection of
very faint GRBs. The POLAR-2 polarimeter is based on the same Compton
scattering measurement principle as POLAR, but with an extended energy range
and an order of magnitude increase in total effective area for polarized
events. Proposed and developed by a joint effort of Switzerland, China, Poland
and Germany, the device was selected for installation on the China Space
Station and is scheduled to start operation for at least 2 years in 2025.Comment: Proceeding from the 38th International Cosmic Ray Conference
(ICRC2023), 8 pages, 6 figure
Energy-dependent polarization of Gamma-Ray Bursts' prompt emission with the POLAR and POLAR-2 instruments
Gamma-Ray Bursts are among the most powerful events in the Universe. Despite
half a century of observations of these transient sources, many open questions
remain about their nature. Polarization measurements of the GRB prompt emission
have long been theorized to be able to answer most of these questions. With the
aim of characterizing the polarization of these prompt emissions, a compact
Compton polarimeter, called POLAR, has been launched to space in September
2016. Time integrated polarization analysis of the POLAR GRB catalog have shown
that the prompt emission is lowly polarized or fully unpolarized. However, time
resolved analysis depicted strong hints of an evolving polarization angle
within single pulses, washing out the polarization degree in time integrated
analyses. Here we will for the first time present energy resolved polarization
measurements with the POLAR data. The novel analysis, performed on several
GRBs, will provide new insights and alter our understanding of GRB
polarization. The analysis was performed using the 3ML framework to fit
polarization parameters versus energy in parallel to the spectral parameters.
Although limited by statistics, the results could provide a very relevant input
to disentangle between existing theoretical models. In order to gather more
statistics per GRB and perform joint time and energy resolved analysis, a
successor instrument, called POLAR-2, is under development with a launch window
early 2025 to the CSS. After presenting the first energy resolved polarization
results of the POLAR mission, we will present the prospects for such
measurements with the upcoming POLAR-2 mission.Comment: Proceeding from the 38th International Cosmic Ray Conference
(ICRC2023), 9 pages, 6 figure
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