5 research outputs found
Constraints on cosmic rays, magnetic fields, and dark matter from gamma-ray observations of the coma cluster of galaxies with veritas andfermi
Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated and, on account of weak energy losses, can accumulate, suggesting that clusters may also be sources of very high energy (VHE; E > 100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cerenkov telescopes, with complementing Fermi Large Area Telescope observations at GeV energies. No significant gamma-ray emission from the Coma Cluster was detected. Integral flux upper limits at the 99% confidence level were measured to be on the order of (2-5) x 10(-8) photonsm(-2) s(-1) (VERITAS, >220 GeV) and similar to 2 x 10(-6) photonsm(-2) s(-1) (Fermi, 1-3GeV), respectively. We use the gamma-ray upper limits to constrain cosmic rays (CRs) and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be < 16% from VERITAS data and <1.7% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be <50%. Alternatively, this may argue for non-negligible CR transport processes such as CR streaming and diffusion into the outer cluster regions. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of similar to(2-5.5) mu G, depending on the radial magnetic field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this renders the hadronic model a very plausible explanation of the Coma radio halo. Finally, since galaxy clusters are dark matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, <sigma nu >
Constraints on Cosmic Rays, Magnetic Fields, and Dark Matter from Gamma-Ray Observations of the Coma Cluster of Galaxies with VERITAS and Fermi.
Observations of radio halos and relics in galaxy clusters indicate efficient
electron acceleration. Protons should likewise be accelerated, suggesting that
clusters may also be sources of very high-energy (VHE; E>100 GeV) gamma-ray
emission. We report here on VHE gamma-ray observations of the Coma galaxy
cluster with the VERITAS array of imaging Cherenkov telescopes, with
complementing Fermi-LAT observations at GeV energies. No significant gamma-ray
emission from the Coma cluster was detected. Integral flux upper limits at the
99% confidence level were measured to be on the order of (2-5)*10^-8\ ph. m^-2
s^-1 (VERITAS, >220 GeV} and ~2*10^-6 ph. m^-2 s^-1 (Fermi, 1-3 GeV),
respectively. We use the gamma-ray upper limits to constrain CRs and magnetic
fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio
is constrained to be < 16% from VERITAS data and < 1.7% from Fermi data
(averaged within the virial radius). These upper limits are starting to
constrain the CR physics in self-consistent cosmological cluster simulations
and cap the maximum CR acceleration efficiency at structure formation shocks to
be <50%. Assuming that the radio-emitting electrons of the Coma halo result
from hadronic CR interactions, the observations imply a lower limit on the
central magnetic field in Coma of (2 - 5.5) muG, depending on the radial
magnetic-field profile and on the gamma-ray spectral index. Since these values
are below those inferred by Faraday rotation measurements in Coma (for most of
the parameter space), this {renders} the hadronic model a very plausible
explanation of the Coma radio halo. Finally, since galaxy clusters are
dark-matter (DM) dominated, the VERITAS upper limits have been used to place
constraints on the thermally-averaged product of the total self-annihilation
cross section and the relative velocity of the DM particles, . (abr.)Comment: ApJ in pres
Nonlinear stress analysis of plates under thermo-mechanical loads
We report on simultaneous broadband observations of the TeV-emitting blazar
Markarian 501 between 1 April and 10 August 2013, including the first detailed
characterization of the synchrotron peak with Swift and NuSTAR. During the
campaign, the nearby BL Lac object was observed in both a quiescent and an
elevated state. The broadband campaign includes observations with NuSTAR,
MAGIC, VERITAS, the Fermi Large Area Telescope (LAT), Swift X-ray Telescope and
UV Optical Telescope, various ground-based optical instruments, including the
GASP-WEBT program, as well as radio observations by OVRO, Mets\"ahovi and the
F-Gamma consortium. Some of the MAGIC observations were affected by a sand
layer from the Saharan desert, and had to be corrected using event-by-event
corrections derived with a LIDAR (LIght Detection And Ranging) facility. This
is the first time that LIDAR information is used to produce a physics result
with Cherenkov Telescope data taken during adverse atmospheric conditions, and
hence sets a precedent for the current and future ground-based gamma-ray
instruments. The NuSTAR instrument provides unprecedented sensitivity in hard
X-rays, showing the source to display a spectral energy distribution between 3
and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability
on hour timescales. None (of the four extended NuSTAR observations) shows
evidence of the onset of inverse-Compton emission at hard X-ray energies. We
apply a single-zone equilibrium synchrotron self-Compton model to five
simultaneous broadband spectral energy distributions. We find that the
synchrotron self-Compton model can reproduce the observed broadband states
through a decrease in the magnetic field strength coinciding with an increase
in the luminosity and hardness of the relativistic leptons responsible for the
high-energy emission.Comment: Accepted for publication in Ap