O. Tibolla

Fermi large area telescope detection of the young supernova remnant tycho

After almost three years of data taking in sky-survey mode, the Fermi Large Area Telescope has detected γ-ray emission toward Tychos supernova remnant (SNR). The Tycho SNR is among the youngest remnants in the Galaxy, originating from a Type Ia Supernova in AD 1572. The γ-ray integral flux from 400 MeV up to 100 GeV has been measured to be (3.5 ± 1.1stat ± 0.7syst)× 10–9 cm–2 s–1 with a photon index of 2.3 ± 0.2stat ± 0.1syst. A simple model consistent with TeV, X-ray, and radio data is sufficient to explain the observed emission as originating from π0 decays as a result of cosmic-ray acceleration and interaction with the ambient medium.

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE CYGNUS LOOP SUPERNOVA REMNANT

We present an analysis of the gamma-ray measurements by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) Cygnus Loop (G74.0-8.5). We detect significant gamma-ray emission associated with the SNR in the energy band 0.2-100 GeV. The gamma-ray spectrum shows a break in the range 2-3 GeV. The gamma-ray luminosity is {approx} 1 x 10{sup 33} erg s{sup -1} between 1-100 GeV, much lower than those of other GeV-emitting SNRs. The morphology is best represented by a ring shape, with inner/outer radii 0{sup o}.7 {+-} 0{sup o}.1 and 1{sup o}.6 {+-} 0{sup o}.1. Given the association among X-ray rims, H{alpha} filaments and gamma-ray emission, we argue that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields adjacent to the shock regions. The decay of neutral pions produced in nucleon-nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray spectrum.

TIME-DEPENDENT MODELING OF PULSAR WIND NEBULAE

A spatially independent model that calculates the time evolution of the electron spectrum in a spherically expanding pulsar wind nebula (PWN) is presented, allowing one to make broadband predictions for the PWN’s non-thermal radiation. The source spectrum of electrons injected at the termination shock of the PWN is chosen to be a broken power law. In contrast to previous PWN models of a similar nature, the source spectrum has a discontinuity in intensity at the transition between the low- and high-energy components. To test the model, it is applied to the young PWN G21.5−0.9, where it is found that a discontinuous source spectrum can model the emission at all wavelengths better than a continuous one. The model is also applied to the unidentified sources HESS J1427−608 and HESS J1507−622. Parameters are derived for these two candidate nebulae that are consistent with the values predicted for other PWNe. For HESS J1427−608, a present day magnetic field of Bage = 0.4 μG is derived. As a result of the small present day magnetic field, this source has a low synchrotron luminosity, while remaining bright at GeV/TeV energies. It is therefore possible to interpret HESS J1427−608 within the ancient PWN scenario. For the second candidate PWN HESS J1507−622, a present day magnetic field of Bage = 1.7 μG is derived. Furthermore, for this candidate PWN a scenario is favored in the present paper in which HESS J1507−622 has been compressed by the reverse shock of the supernova remnant.

Dark Matter Limits from Dwarf Spheroidal Galaxies with the HAWC Gamma-Ray Observatory

The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field of view observatory sensitive to 500 GeV - 100 TeV gamma rays and cosmic rays. It can also perform diverse indirect searches for dark matter (DM) annihilation and decay. Among the most promising targets for the indirect detection of dark matter are dwarf spheroidal galaxies. These objects are expected to have few astrophysical sources of gamma rays but high dark matter content, making them ideal candidates for an indirect dark matter detection with gamma rays. Here we present individual limits on the annihilation cross section and decay lifetime for 15 dwarf spheroidal galaxies within the HAWC field-of-view, as well as their combined limit. These are the first limits on the annihilation cross section and decay lifetime using data collected with HAWC.

New developments in the ancient PulsarWind Nebulae scenario

In a Pulsar Wind Nebula (PWN), the lifetime of inverse Compton emitting electrons exceeds the lifetime of its progenitor pulsar, but it exceeds also the age of the electrons that emit via synchrotron radiation; i.e. while the PWN grows older, it can remain bright in IC, whereas its GeV-TeV gamma-ray (for

Extended X-ray jet and TeV emission in a low frequency peaked BL Lac object

10^5-10^6

FACT: A novel camera for Cherenkov telescopes for ground-based gamma-ray astronomy

years) flux remains high for timescales much larger than the Pulsar lifetime and the PWN visible in X-rays. The shell-type remnant of the supernova explosion that led to the formation of the pulsar also has a much shorter lifetime. In this scenario, the magnetic field in the cavity induced by the wind of the progenitor star plays a crucial role, but also the magnetic field in the interstellar medium cannot be negligible and its outward decrease away from the Galactic disk further reduces their X-ray brightness. This is in line with the discovery of several unidentified sources in the TeV gamma-ray band without X-ray counterparts. Moreover, the consequences are important also in order to reinterprete the detection of starburst galaxies in the TeV gamma-ray band considering a leptonic origin of the gamma-ray signal.

Gamma-Ray Observations of the Supernova Remnant RX J0852.0-4622 with the Fermi LAT

BL Lac objects are known to have very energetic jets pointing towards the observer under small viewing angles. Many of these show high luminosity over the whole energy range up to TeV, mostly classified as high-energy peaked BL Lac objects. Recently, TeV gamma-ray emission was detected from a low-energy peaked BL Lac object. Interestingly, this source has also a clear detection of an X-ray jet. We present a detailed study of this X-ray jet and its connection to the radio jet as well as a study of the underlying physical processes in the energetic jet, producing emission from the radio to the TeV range.

GAMMA-RAY OBSERVATIONS OF THE SUPERNOVA REMNANT RX J0852.0–4622 WITH THEFERMILARGE AREA TELESCOPE

The field of gamma-ray astronomy has expanded rapidly during the last decade. In the energy regime from 100 GeV up to several TeV, Imaging Atmospheric Cherenkov Telescopes (IACT) are the most sensitive detectors. Presently all IACTs use photomultiplier tubes for light detection, but for future projects Geiger-mode Avalanche Photodiodes (G-APD) are very promising alternatives. In order to demonstrate their potential, the First G-APD Cherenkov Telescope (FACT) collaboration has constructed an IACT camera comprising 1440 G-APDs. By means of specially designed light concentrators the collection area of each sensor is enlarged. The entire electronics for analog signal processing, digitization and triggering is fully integrated into the camera body. Event data are sent via Ethernet to the counting house. The FACT camera was installed during fall 2011 at the Observatorio del Roque de los Muchachos on La Palma, Canary Islands (Spain), on a refurbished telescope mount.

The X‐/VHE γ‐ray connection of BL Lac objects

We report on gamma-ray observations of the supernova remnant (SNR) RX J0852.0–4622 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. In the Fermi-LAT data, we find a spatially extended source at the location of the SNR. The extension is consistent with the SNR size seen in other wavelengths such as X-rays and TeV gamma rays, leading to the identification of the gamma-ray source with the SNR. The spectrum is well described as a power law with a photon index of Γ = 1.85 ± 0.06 (stat)+0.18 – 0.19 (sys), which smoothly connects to the H.E.S.S. spectrum in the TeV energy band. We discuss the gamma-ray emission mechanism based on multiwavelength data. The broadband data can be fit well by a model in which the gamma rays are of hadronic origin. We also consider a scenario with inverse Compton scattering of electrons as the emission mechanism of the gamma rays. Although the leptonic model predicts a harder spectrum in the Fermi-LAT energy range, the model can fit the data considering the statistical and systematic errors.