Academic literature on the topic 'HESS J1616-508'

The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.

AbstractHESS J1614–518 and HESS J1616–508 are two tera-electron volt γ-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the tera-electron volt γ-ray sources using results from a 7-mm-wavelength Mopra study, the Mopra Southern Galactic Plane CO Survey, the Millimetre Astronomer’s Legacy Team-45 GHz survey and [C i] data from the HEAT telescope. Data in the CO(1–0) transition lines reveal diffuse gas overlapping the two tera-electron volt sources at several velocities along the line of sight, while observations in the CS(1–0) transition line reveal several interesting dense gas features. To account for the diffuse atomic gas, archival H i data was taken from the Southern Galactic Plane Survey. The observations reveal gas components with masses ~103 to 105 M⊙ and with densities ~102 to 103 cm−3 overlapping the two tera-electron volt sources. Several origin scenarios potentially associated with the tera-electron volt γ-ray sources are discussed in light of the distribution of the local interstellar medium. We find no strong convincing evidence linking any counterpart with HESS J1614–518 or HESS J1616–508.

One of the most intriguing problems in galactic astronomy is the observation of the highest energy photons. Very high energy (VHE) gamma-ray telescopes such as HESS have located sources of TeV (10¹² eV) gamma-rays which are not associated with any known objects. Whilst these could be a new type of particle accelerator, it is more likely that they are related to supernova remnants (SNRs), pulsar wind nebula (PWN) or massive stellar regions. They may result from high energy cosmic-ray (CR) interactions with interstellar gas (ISM). This project used new radio data which provided information on molecular clouds to model the production of gamma-rays from CR interactions. The densities of protons in these clouds were used in models to determine if potential particle accelerators surrounding the two HESS sources, HESS J1616-508 and HESS J1614-518 were capable of producing the emission. The potential accelerators surrounding HESS J1616-508 were all found to have insufficient gas within their diffusion radius. Thus, it was not possible for those sources to produce gamma-rays through hadronic interactions despite only requiring modest CR energy budgets compared to that provided from a SNR. The same result was also found for WR 73-1 and PSR J1613-5211 near HESS J1614-518. However, Pismis 22 and WR 74 contained CO RoI CO1, CO2 and CO25 within their diffusion radii. The energy in CRs required for each region to generate the overlapping gamma-ray emission was compared to the available energy if a SNR was assumed to be the accelerator. The required energy was found to be less than the energy available. Thus, WR 74 and Pismis 22 could still generate the hadronic gamma-ray emission from HESS J1614-518.
Thesis (M.Phil.) -- University of Adelaide, School of Physical Sciences, 2016.