18216611
A Modified Synchrotron Model for Knots in the M87 Jet
To explain the broadband spectral shape of knots in the M87 jet from radio through optical to X-rays, we propose a modified synchrotron model that considers the integrated effect of particle injection from different acceleration sources in the thin acceleration region. This results in two break frequencies at two sides of which the spectral index of knots in the M87 jet changes. We discuss the possible implications of these results for the physical properties in the M87 jet. The observed flux of the knots in the M87 jet from radio to X-rays can be satisfactorily explained by the model, and the predicted spectra from ultraviolet to X-rays could be further tested by future observations. The model implies that knots D, E, F, A, B, and C1 are unlikely to be candidates for the TeV emission recently detected in M87.
119253614
AN HOURGLASS MODEL FOR THE FLARE OF HST-1 IN M87
To explain the multi-wavelength light curves (from radio to X-ray) of HST-1 in the M87 jet, we propose an hourglass model that is a modified two-zone system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or Laval-nozzle-shaped layer connected by two revolving exponential surfaces surrounding a fast spine through which plasma blobs flow. Based on the conservation of magnetic flux, the magnetic field changes along the axis of the hourglass. We adopt the result of TG08-the high-energy emission from GeV to TeV can be produced through inverse Compton by the two-zone system, and the photons from radio to X-ray are mainly radiated by the fast inner zone system. Here, we only discuss the light curves of the fast inner blob from radio to X-ray. When a compressible blob travels down the axis of the first bulb in the hourglass, because of magnetic flux conservation, its cross section experiences an adiabatic compression process, which results in particle acceleration and the brightening of HST-1. When the blob moves into the second bulb of the hourglass, because of magnetic flux conservation, the dimming of the knot occurs along with an adiabatic expansion of its cross section. A similar broken exponential function could fit the TeV peaks in M87, which may imply a correlation between the TeV flares of M87 and the light curves from radio to X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1 verifies our prediction based on the model fit to the main peak of the VLA 15 GHz radio one.
16598807
A modified stratified model for the 3C 273 jet
We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in the 3C 273 jet. Based on the hypothesis of the single index of the particle energy spectrum at injection and identical emission processes among all the knots, the observed difference of spectral shape among different 3C 273 knots can be understood as a manifestation of the deviation of the equivalent Doppler factor of stratified emission regions in an individual knot from a characteristic one. The summed spectral energy distributions of all ten knots in the 3C 273 jet can be well fitted by two components: a low-energy component (radio to optical) dominated by synchrotron radiation and a high-energy component (UV, X-ray and γ-ray) dominated by inverse Compton scattering of the cosmic microwave background. This gives a consistent spectral index of α = 0.88 (Sv ∝ v−α) and a characteristic Doppler factor of 7.4. Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C 273 jet, we further get a distribution of Doppler factors. We discuss the possible implications of these results for the physical properties in the 3C 273 jet. Future GeV observations with GLAST could separate the γ-ray emission of 3C 273 from the large scale jet and the small scale jet (i.e. the core) through measuring the GeV spectrum.
108286294
PROPOSALS FOR ELECTRON BEAM TRANSPORTATION CHANNEL TO PROVIDE HOMOGENEOUS BEAM DENSITY DISTRIBUTION AT A TARGET SURFACE *
NSC KIPT neutron source will use 64x64 mm rectangular tungsten or uranium target. To generate maximum neutron flux, prevent overheating of the target and reduce thermal stress one should provide homogeneous electron beam distribution at the target surface. In the facility transportation channel three different possibilities of electron beam density redistribution along the target surface can be realized. It can be the fast beam scanning with two dimensional scanning magnets; the method of uniform beam distribution formation with linear focusing elements (dipole and quadrupole magnets) and nonlinear focusing elements (octupole magnets), when final required rectangular beam shape with homogeneous beam density is formed at target; and combined method, when one forms the small rectangular beam with homogeneous beam density distribution and scan it over the target surface with scanning magnets. In the report the all tree methods are considered and discussed considering the layout of the NSC KIPT transportation channel. Calculation results show that the proposed transportation channel lattice can provide uniform beam of rectangular shape with sizes 64x64 mm without target overheating. INTRODUCTION In National Science Center “Kharkov Institute of Physics and Technology” (NSC KIPT, Kharkov, Ukraine) a neutron source based on the subcritical assembly driven by electron linear accelerator are under design and development [1]. Neutron source is a hybrid facility. The main facility components are an electron linear accelerator, a system for electron beam transportation from linear accelerator to the target, neutron production target, subcritical assembly, biological shield, neutron channels and auxiliary supporting systems. Photonuclear reactions, induced by hard electromagnetic radiation emerging at retarding of the beam of relativistic electrons in the target from heavy element, are used to generate primary neutrons. Two options of the target are under consideration: tungsten and natural uranium. Energy of electrons in driven beam is 100 MeV. It is expected that facility will provide neutron flux of about 2.4×10 neutron/s. All activity is supported by Argon National Laboratory, Chicago, USA. 100 MeV/100 kW electron linear accelerator is under design and manufacture in IHEP, Beijing, China [2]. For generation of maximum neutron flux without overheating of the target and with minor thermal stress one should provide accurate beam transportation with homogeneous electron beam distribution at the target surface. Figure 1: Layout of the NSC KIPT neutron sour ce on the base of subcritical assembly driven by linear electron accelerator. ___________________________________________ *Work supported by ANL, Chicago, USA contract #9J-30123... gohar@anl.gov TUPC039 Proceedings of IPAC2011, San Sebastián, Spain 1084 C op yr ig ht c ○ 20 11 by IP A C ’1 1/ E PS -A G — cc C re at iv e C om m on sA tt ri bu tio n 3. 0 (C C B Y 3. 0) 03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques A08 Linear Accelerators LAYOUT OF THE FACILITY AND TRANSPORTATIONCHANNEL The layout of the facility is shown in Fig. 1. After long discussions it was decided to simplify the facility scheme and put linear accelerator to the second floor of the neutron source building. In such configuration transportation channel became much shorter and simpler compare with previous channel version. [3] but should meet the same requirements:  transportation of the high current electron beam from the driving linear accelerator to the subcritical assembly without particle losses;  electron beam size at the subcritical assembly should be of about ±32 mm in both transversal directions with small value of the beam divergence;  electron beam density distribution at the targetshould be uniform. The sketch of the transport line is shown in Fig. 2. Two 45° vertical sector bending magnets of 0.51 m radius, B1 and B2 are used to bend the beam from the linac to the target. A quadrupole (Q11) is placed at the middle point of the arc to cancel the dispersion. A triplet (Q6, Q7 and Q8) and another two quadrupoles (Q9, Q10) are used to form the beam size on the target. Because of the uncertainty of the beam twiss parameters at the linac exit, the triplet is also used for the emittance measurement together with the profile monitor PR3 by the quadrupole scanning method. The distance between the last bending magnet B2 and the target is about 2.5 m. Figure 2: Layout transport line. Figure 3 is the beta function and dispersion function along the transport line calculated with MAD code [4] with the assumption that ε=0.5 mm⋅mrad, β=10 m and α=0. Fig. 4 is the MAD calculation result assumed β=55 m on the target that shows the flexibility of the lattice. Figure 3: Beta function and dispersion along the transport line. Figure 4: Beta function and dispersion along the transport line with β=55 m. ELECTRON BEAM HOMOGENEITY AT THE TARGET Three different ways to provide homogeneous electron beam distribution at the target surface were considered during design of the transportation channel such as:  the fast beam scanning with two dimensional scanning magnets;  the method of uniform beam distribution formation with linear focusing elements (dipole and quadrupole magnets) and nonlinear focusing elements (octupole magnets), when final required rectangular beam shape with homogeneous beam density is formed at target;  combined method, when one forms the small rectangular beam with homogeneous beam density distribution and scan it over the target surface with scanning magnets.
119226741
Spectroscopic factors for low-lying $^{16}$N levels and the astrophysical $^{15}$N $(n,\gamma)^{16}$N reaction rate
Fluorine is a key element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site to produce fluorine is suggested to be asymptotic giant branch (AGB) stars. In these stars the 15N(n, g)16N reaction could affect the abundance of fluorine by competing with 15N(a, g)19F. The 15N(n, g)16N reaction rate depends directly on the neutron spectroscopic factors of the low-lying states in 16N. The angular distributions of the 15N(7Li, 6Li)16N reaction populating the ground state and the first three excited states in 16N are measured using a Q3D magnetic spectrograph and are used to derive the spectroscopic factors of these states based on distorted wave Born approximation (DWBA) analysis. The spectroscopic factors of these four states are extracted to be 0.96+-0.09, 0.69+-0.09, 0.84+-0.08 and 0.65+-0.08, respectively. Based on the new spectroscopic factors we derive the 15N(n,g)16N reaction rate. The accuracy and precision of the spectroscopic factors are enhanced due to the first application of high-precision magnetic spectrograph for resolving the closely-spaced 16N levels which can not be achieved in most recent measurement. The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in 16N are not so good single-particle levels although 15N is a closed neutron-shell nucleus. This finding is contrary to the shell model expectation. The present work also provides an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the 15N(n, g)16N rate.
119331816
An Equilibrium Dark Matter Halo with the Burkert Profile
In this paper a prescription for generating an equilibrium spherical system depicted with cuspy density profiles is extended to a core density profile, the Burkert profile, which is observationally more suitable to dwarfs. By using a time-saving Monte Carlo method instead of N-body simulations, we show that the Burkert halo, which is initialized with a distribution function that depends only on energy, is in a practically stable equilibrium. The one generated with the local Maxwellian approximation is unstable, where the flat core density structure tends to steepen. This is fundamentally different from a previous study on a halo with a cuspy density profile. The deviation of the unstable “Burkert” from the initial Burkert profile is found to be closely related to taking a Gaussian as the velocity distribution at any given point. The significance of not using the local Maxwellian approximation is further demonstrated by exploring the dynamical evolution of compact super star clusters (SSCs) in the Burkert halo. In particular, the local Maxwellian approximation results in underestimating the dynamical friction and overestimating sinking time scale. Accordingly, this leads to a lower probability of forming massive bulges and young nuclear star clusters in bulgeless galaxies.