125 research outputs found
Cosmic rays in early star-forming galaxies and their effects on the interstellar medium
Galaxies at high redshifts with strong star formation are sources of
high-energy cosmic rays. These cosmic rays interact with the baryon and
radiation fields of the galactic environment via photo-pair, photo-pion and
proton-proton processes to produce charged and neutral pions, neutrons and
protons. The cosmic rays thereby deposit energy into the interstellar medium
(ISM) as they propagate. We show how energy transport and deposition by ultra
high-energy cosmic rays is regulated by the evolution of the galaxy, in
particular by the development of the galactic magnetic field. We show how the
particle-driven energy deposition can influence the thermal evolution of the
host and its surroundings. Using a parametric protogalaxy model, we calculate
the heating effect on the ISM as the cosmic rays are increasingly confined by
the magnetic evolution of the galaxy.Comment: 8 pages, 2 figures; Proceedings of the 35th International Cosmic Ray
Conference (ICRC2017), 10-20 July 2017, Bexco, Busan, Korea -
PoS(ICRC2017)28
Interactions between Ultra-High-Energy Particles and Protogalactic Environments
We investigate the interactions of energetic hadronic particles (cosmic ray
protons) with photons and baryons in protogalactic environments, where the
target photons are supplied by the first generations of stars to form in the
galaxy and the cosmological microwave background, while the target baryons are
the interstellar and circumgalactic medium. We show that pair-production and
photo-pion processes are the dominant interactions at particle energies above
, while -interaction pion-production dominates
at the lower energies in line with expectations from, for example -ray
observations of star-forming galaxies and dense regions of our own galaxy's
interstellar medium. We calculate the path lengths for the interaction channels
and determine the corresponding rates of energy deposition. We have found that
protogalactic magnetic fields and their evolution can significantly affect the
energy transport and energy deposition processes of cosmic rays. Within a Myr
after the onset of star-formation the magnetic field in a protogalaxy could
attain a strength sufficient to confine all but the highest energy particles
within the galaxy. This enhances the cosmic ray driven self-heating of the
protogalaxy to a rate of around for a galaxy with strong star-forming activity that yields 1 core
collapse SN event per year. This heating power exceeds even that due to
radiative emission from the protogalaxy's stellar populations. However, in a
short window before the protogalaxy is fully magnetised, energetic particles
could stream across the galaxy freely, delivering energy into the
circumgalactic and intergalactic medium.Comment: 24 pages, 8 figures, 2 tables, accepted for publication in MNRA
Constraining the Ratio in TeV Cosmic Rays with Observations of the Moon Shadow by HAWC
An indirect measurement of the antiproton flux in cosmic rays is possible as
the particles undergo deflection by the geomagnetic field. This effect can be
measured by studying the deficit in the flux, or shadow, created by the Moon as
it absorbs cosmic rays that are headed towards the Earth. The shadow is
displaced from the actual position of the Moon due to geomagnetic deflection,
which is a function of the energy and charge of the cosmic rays. The
displacement provides a natural tool for momentum/charge discrimination that
can be used to study the composition of cosmic rays. Using 33 months of data
comprising more than 80 billion cosmic rays measured by the High Altitude Water
Cherenkov (HAWC) observatory, we have analyzed the Moon shadow to search for
TeV antiprotons in cosmic rays. We present our first upper limits on the
fraction, which in the absence of any direct measurements, provide
the tightest available constraints of on the antiproton fraction for
energies between 1 and 10 TeV.Comment: 10 pages, 5 figures. Accepted by Physical Review
Measurement of the Crab Nebula Spectrum Past 100 TeV with HAWC
We present TeV gamma-ray observations of the Crab Nebula, the standard
reference source in ground-based gamma-ray astronomy, using data from the High
Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory. In this analysis we use
two independent energy-estimation methods that utilize extensive air shower
variables such as the core position, shower angle, and shower lateral energy
distribution. In contrast, the previously published HAWC energy spectrum
roughly estimated the shower energy with only the number of photomultipliers
triggered. This new methodology yields a much improved energy resolution over
the previous analysis and extends HAWC's ability to accurately measure
gamma-ray energies well beyond 100 TeV. The energy spectrum of the Crab Nebula
is well fit to a log parabola shape with emission up to at least 100 TeV. For the first
estimator, a ground parameter that utilizes fits to the lateral distribution
function to measure the charge density 40 meters from the shower axis, the
best-fit values are
=(2.350.04)10 (TeV cm
s), =2.790.02, and
=0.100.01. For the second estimator, a neural
network which uses the charge distribution in annuli around the core and other
variables, these values are
=(2.310.02)10 (TeV cm
s), =2.730.02, and
=0.060.010.02. The first set of uncertainties are statistical;
the second set are systematic. Both methods yield compatible results. These
measurements are the highest-energy observation of a gamma-ray source to date.Comment: published in Ap
Daily monitoring of TeV gamma-ray emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC
We present results from daily monitoring of gamma rays in the energy range
to TeV with the first 17 months of data from the High
Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2
steradians and duty cycle of % are unique features compared to other TeV
observatories that allow us to observe every source that transits over HAWC for
up to hours each sidereal day. This regular sampling yields
unprecedented light curves from unbiased measurements that are independent of
seasons or weather conditions. For the Crab Nebula as a reference source we
find no variability in the TeV band. Our main focus is the study of the TeV
blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a
power law index and
an exponential cut-off
TeV. For Mrk 501, we find an index and exponential cut-off TeV. The light curves for both sources show clear
variability and a Bayesian analysis is applied to identify changes between flux
states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab
Nebula flux by a factor of approximately five. For Mrk 501, several transits
show fluxes in excess of three times the Crab Nebula flux. In a comparison to
lower energy gamma-ray and X-ray monitoring data with comparable sampling we
cannot identify clear counterparts for the most significant flaring features
observed by HAWC.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical
Journa
The 2HWC HAWC Observatory Gamma Ray Catalog
We present the first catalog of TeV gamma-ray sources realized with the
recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the
most sensitive wide field-of-view TeV telescope currently in operation, with a
1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an
instantaneous field of view >1.5 sr and >90% duty cycle, it continuously
surveys and monitors the sky for gamma ray energies between hundreds GeV and
tens of TeV.
HAWC is located in Mexico at a latitude of 19 degree North and was completed
in March 2015. Here, we present the 2HWC catalog, which is the result of the
first source search realized with the complete HAWC detector. Realized with 507
days of data and represents the most sensitive TeV survey to date for such a
large fraction of the sky. A total of 39 sources were detected, with an
expected contamination of 0.5 due to background fluctuation. Out of these
sources, 16 are more than one degree away from any previously reported TeV
source. The source list, including the position measurement, spectrum
measurement, and uncertainties, is reported. Seven of the detected sources may
be associated with pulsar wind nebulae, two with supernova remnants, two with
blazars, and the remaining 23 have no firm identification yet.Comment: Submitted 2017/02/09 to the Astrophysical Journa
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