32 research outputs found
Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles
We revise the bound from the supernova SN1987A on the coupling of ultralight
axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs
would be emitted via the Primakoff process, and eventually convert into gamma
rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in
the GRS instrument of the SMM satellite in coincidence with the observation of
the neutrinos emitted from SN1987A therefore provides a strong bound on their
coupling to photons. Due to the large uncertainty associated with the current
bound, we revise this argument, based on state-of-the-art physical inputs both
for the supernova models and for the Milky-Way magnetic field. Furthermore, we
provide major amendments, such as the consistent treatment of
nucleon-degeneracy effects and of the reduction of the nuclear masses in the
hot and dense nuclear medium of the supernova. With these improvements, we
obtain a new upper limit on the photon-ALP coupling: g_{a\gamma} < 5.3 x
10^{-12} GeV^{-1}, for m_a < 4.4 x 10^{-10} eV, and we also give its dependence
at larger ALP masses. Moreover, we discuss how much the Fermi-LAT satellite
experiment could improve this bound, should a close-enough supernova explode in
the near future.Comment: Accepted for publication in JCAP (December 22nd, 2014
Magnetic Fields in the Milky Way
This chapter presents a review of observational studies to determine the
magnetic field in the Milky Way, both in the disk and in the halo, focused on
recent developments and on magnetic fields in the diffuse interstellar medium.
I discuss some terminology which is confusingly or inconsistently used and try
to summarize current status of our knowledge on magnetic field configurations
and strengths in the Milky Way. Although many open questions still exist, more
and more conclusions can be drawn on the large-scale and small-scale components
of the Galactic magnetic field. The chapter is concluded with a brief outlook
to observational projects in the near future.Comment: 22 pages, 5 figures, to appear in "Magnetic Fields in Diffuse Media",
eds. E.M. de Gouveia Dal Pino and A. Lazaria
The surface detector array of the Telescope Array experiment
The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector.Comment: 32 pages, 17 figure
New air fluorescence detectors employed in the Telescope Array experiment
Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been
observing ultra high energy cosmic rays to understand their origins. The
experiment involves a surface detector (SD) array and three fluorescence
detector (FD) stations. FD stations, installed surrounding the SD array,
measure the air fluorescence light emitted from extensive air showers (EASs)
for precise determination of their energies and species. The detectors employed
at one of the three FD stations were relocated from the High Resolution Fly's
Eye experiment. At the other two stations, newly designed detectors were
constructed for the TA experiment. An FD consists of a primary mirror and a
camera equipped with photomultiplier tubes. To obtain the EAS parameters with
high accuracies, understanding the FD optical characteristics is important. In
this paper, we report the characteristics and installation of new FDs and the
performances of the FD components. The results of the monitored mirror
reflectance during the observation time are also described in this report.Comment: 44 pages, 23 figures, submitted to NIM-