30 research outputs found
Molecular environment, reverberation, and radiation from the pulsar wind nebula in CTA 1
We estimate the molecular mass around CTA 1 using data from Planck and the
Harvard CO survey. We observe that the molecular mass in the vicinity of the
complex is not enough to explain the TeV emission observed by VERITAS, even
under favorable assumptions for the cosmic-ray acceleration properties of the
supernova remnant. This supports the idea that the TeV emission comes from the
PWN. Here, we model the spectrum of the PWN at possible different stages of its
evolution, including both the dynamics of the PWN and the SNR and their
interaction via the reverse shock. We have included in the model the energy
lost via radiation by particles and the particles escape when computing the
pressure produced by the gas. This leads to an evolving energy partition, since
for the same instantaneous sharing of the injection of energy provided by the
rotational power, the field and the particles are affected differently by
radiation and losses. We present the model, and study in detail how the
spectrum of a canonical isolated PWN is affected during compression and
re-expansion and how this may impact on the CTA 1 case. By exploring the
phase-space of parameters that lead to radii in agreement with those observed,
we then analyze different situations that might represent the current stage of
the CTA 1 PWN, and discuss caveats and requirements of each one.Comment: 13 pages, 8 figures, accepted for publication in MNRA
Very High Energy Emission from Passive Supermassive Black Holes
The H.E.S.S. experiment, an array of four Imaging Cherenkov Telescopes, widened the horizon of Very High Energy (VHE) astronomy. Its unprecedented sensitivity is well suited for the study of new classes of expected VHE emitters, such as passive galactic nuclei that are the main focus of the work presented in this thesis. Acceleration of particles up to Ultra High Energies is expected in the magnetosphere of supermassive black holes (SMBH). The radiation losses of these accelerated particles are expected to reach the VHE regime in which H.E.S.S. operates. Predicted fluxes exceed the sensitivity of the array. However, strong photon fields in the surrounding of the acceleration region might absorb the produced radiation. Therefore observations focus on those galactic nuclei that are underluminous at lower photon energies. This work presents data collected by the H.E.S.S. telescopes on the test candidate NGC 1399 and their interpretation. While no detection has been achieved, important constraints can be derived from the obtained upper limits on the maximum energy attainable by the accelerated particles and on the magnetic field strength in the acceleration region. A limit on the magnetic field of B<74 Gauss is given. The limit is model dependent and a scaling of the result with the assumptions is given. This is the tightest empirical constraint to date. Because of the lack of signal from the test candidate, a stacking analysis has been performed on similar sources in three cluster fields. A search for signal from classes of active galactic nuclei has also been made in the same three fields. None of the analyzed samples revealed a significant signal. Also presented are the expectations for the next generation of Cherenkov Telescopes and an outlook on the relativistic effects expected on the VHE emission close to SMBH
Estimating Galactic gas content using different tracers: Compatibility of results, dark gas, and unidentified TeV sources
A large fraction of Galactic very-high energy (VHE; E100 GeV)
-ray sources is cataloged as unidentified. In this work we explore the
possibility that these unidentified sources are located in ambients
particularly rich in material content unaccounted by traditional tracers. In a
scenario where the VHE emission is due to the interaction of the accelerated
particles with a target mass, a large mass of untraced material could be
substantially contributing to the VHE emission from these regions. Here, we use
three tracers for the commonly explored components: intensity of the
CO(10) line to trace the molecular material, HI
hyperfine transition at 21cm to trace atomic hydrogen, and dust emission to
trace the total hydrogen content. We show that the estimates of material
content from these three tracers are compatible if the uncertainty on the
respective conversion factors is taken into account. No additional gas
component is found in these regions. However, a simple mass estimation from the
CO(10) line intensity might underestimate the total
mass component in some locations.Comment: 9 pages, 4 figures, accepted for publication in JHEA
The high-energy gamma-ray detection of G73.9+0.9, a supernova remnant interacting with a molecular cloud
We have analysed the Fermi Large Area Telescope (LAT) data on the SNR G73.9+0.9. We have confirmed a previous detection of high-energy γ-rays from this source at a high significance of ≃12σ. The observed spectrum shows a significant curvature, peaking in EFE at ∼1 GeV. We have also calculated the flux upper limits in the mm-wavelength and X-ray ranges from Planck and XMM-Newton, respectively. We have inspected the intensity of the CO (1→0) emission line and found a large peak at a velocity range corresponding to the previously estimated source distance of ∼4kpc, which may indicate an association between a molecular cloud and the supernova remnant (SNR). The γ-ray emission appears due to interaction of accelerated particles within the SNR with the matter of the cloud. The most likely radiative process responsible for the γ-ray emission is decay of neutral pions produced in ion-ion collisions. While a dominant leptonic origin of this emission can be ruled out, the relativistic electron population related to the observed radio flux will necessarily lead to a certain level of bremsstrahlung γ-ray emission. Based on this broad-band modelling, we have developed a method to estimate the magnetic field, yielding B ≳ 80 μG at our best estimate of the molecular cloud density (or less at a lower density). G73.9+0.9 appears similar, though somewhat weaker, to other SNRs interacting with a local dense medium detected by the LA
35th International Cosmic Ray Conference, ICRC 2017
PKS1510-089 is a flat spectrum radio quasar located at a redshift of 0.36. It is one of only a few such sources detected in very-high-energy (VHE, >100 GeV) gamma rays. Though PKS1510-089 is highly variable at GeV energies, until recently no variability has been observed in the VHE band. In 2015 May PKS1510-089 showed a high state in optical and in the GeV range. A VHE gamma-ray flare was detected with MAGIC at that time, showing the first instance of VHE gamma-ray flux variability on the time scale of days in this source. We will present the MAGIC results from this observation, discuss their temporal and spectral properties in the multi-wavelength context and present modelling of such emission in the external Compton scenario.</p
Multiwavelength Picture of the Blazar S5 0716+714 during Its Brightest Outburst
S5 0716+714 is a well known BL Lac object, and one of the brightest and
most active blazars. The discovery in the Very High Energy band (VHE, E
> 100 GeV) by MAGIC happened in 2008. In January 2015, the source
went through the brightest optical state ever observed, triggering MAGIC
follow-up and a VHE detection with ∼ 13σ significance (ATel ♯6999 ).
Rich multiwavelength coverage of the flare allowed us to construct the
broad-band spectral energy distribution of S5 0716+714 during its
brightest outburst. In this work, we will present the preliminary
analysis of MAGIC and Fermi-LAT data of the flaring activity in
January and February 2015 for the HE (0.1 < HE < 300 GeV) and VHE
band, together with radio (Metsähovi, OVRO, VLBA, Effelsberg),
sub-millimeter (SMA), optical (Tuorla, Perkins, Steward, AZT-8+ST7,
LX-200, Kanata), X-ray and UV (Swift-XRT and UVOT), in the same
time-window and discuss the time variability of the multiwavelength
light curves during this impressive outburst.</p