Implications of the VHE Gamma-Ray Detection of the Quasar 3C279

The MAGIC collaboration recently reported the detection of the quasar 3C279 at > 100 GeV gamma-ray energies. Here we present simultaneous optical (BVRI) and X-ray (RXTE PCA) data from the day of the VHE detection and discuss the implications of the snap-shot spectral energy distribution for jet models of blazars. A one-zone synchrotron-self-Compton origin of the entire SED, including the VHE gamma-ray emission can be ruled out. The VHE emission could, in principle, be interpreted as Compton upscattering of external radiation (e.g., from the broad-line regions). However, such an interpretation would require either an unusually low magnetic field of B ~ 0.03 G or an unrealistically high Doppler factor of Gamma ~ 140. In addition, such a model fails to reproduce the observed X-ray flux. This as well as the lack of correlated variability in the optical with the VHE gamma-ray emission and the substantial gamma-gamma opacity of the BLR radiation field to VHE gamma-rays suggests a multi-zone model. In particular, an SSC model with an emission region far outside the BLR reproduces the simultaneous X-ray -- VHE gamma-ray spectrum of 3C279. Alternatively, a hadronic model is capable of reproducing the observed SED of 3C279 reasonably well. However, the hadronic model requires a rather extreme jet power of L_j ~ 10^{49} erg s^{-1}, compared to a requirement of L_j ~ 2 X 10^{47} erg s^{-1} for a multi-zone leptonic model.Comment: Accepted for pulication. Several clarifications and additions to the manuscript to match the accepted versio

Nonthermal Synchrotron and Synchrotron Self-Compton Emission from GRBs: Predictions for {\em Swift} and {\em GLAST}

Results of a leptonic jet model for the prompt emission and early afterglows of GRBs are presented. The synchrotron component is modeled with the canonical Band spectrum and the synchrotron self-Compton component is calculated from the implied synchrotron-emitting electron spectrum in a relativistic plasma blob. In the comoving frame the magnetic field is assumed to be tangled and the electron and photon distributions are assumed to be isotropic. The Compton-scattered spectrum is calculated using the full Compton cross-section in the Thomson through Klein-Nishina using the Jones formula. Pair production photoabsorption, both from ambient radiation in the jet and from the extragalactic background light (EBL), is taken into account. Results are presented as a function of a small set of parameters: the Doppler factor, the observed variability timescale, the comoving magnetic field, the peak synchrotron flux, and the redshift of the burst. Model predictions will be tested by multiwavelength observations, including the {\em Swift} and {\em GLAST} satellites, which will provide unprecedented coverage of GRBs.Comment: 4 pages, 2 figures. Poster at GRB 2007, Santa Fe, New Mexic

Thermally Activated D₂ Emission upon Decomposition of Thin Deuterofullerene Films on Au(111)

We have studied the formation and thermal properties of thin, deuterofullerene-containing films on Au(111) under ultrahigh vacuum conditions. The films were prepared in situ by exposure of predeposited C₆₀ layers to a flux of atomic deuterium. With increasing deuterium dose, a D + C₆₀ → C₆₀D_<i>x</i> reaction front propagates through the fullerene film toward the gold surface. Heating the resulting deuterofullerene-containing films to >600 K leads to desorption of predominantly C₆₀ and C₆₀D_<i>x</i>. Interestingly, some D₂ is also evolved while a significant fraction of the carbon initially deposited is left on the surface as nondesorbable residue. This is in contrast to analogous deuterofullerene-containing films prepared on graphite, which sublime completely but do not measurably evolve D₂, suggesting that the gold surface can act as a catalyst for D₂ formation. To explore this further, we have systematically studied (i) the thermal properties of C₆₀/Au­(111) reference films, (ii) the reaction of C₆₀/Au­(111) films with D atoms, and (iii) the heating-induced degradation of deuterofullerene-containing films on Au(111). In particular, we have recorded temperature-resolved mass spectra of the desorbing species (sublimation maps) as well as performed ultraviolet photoionization spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning tunneling microscopy measurements of the surfaces at various stages of study. We infer that heating deuterofullerene-containing films generates mobile deuterium atoms which can recombine to form molecular deuterium either at the gold surface or on fullerene oligomers in direct contact with it

IR, NIR, and UV Absorption Spectroscopy of C₆₀²⁺ and C₆₀³⁺ in Neon Matrixes

C₆₀²⁺ and C₆₀³⁺ were produced by electron-impact ionization of sublimed C₆₀ and charge-state-selectively codeposited onto a gold mirror substrate held at 5 K together with neon matrix gas containing a few percent of the electron scavengers CO₂ or CCl₄. This procedure limits charge-changing of the incident fullerene projectiles during matrix isolation. IR, NIR, and UV–vis spectra were then measured. Ten IR absorptions of C₆₀²⁺ were identified. C₆₀³⁺ was observed to absorb in the NIR region close to the known vibronic bands of C₆₀⁺. UV spectra of C₆₀, C₆₀⁺, and C₆₀²⁺ were almost indistinguishable, consistent with a plasmon-like nature of their UV absorptions. The measurements were supported by DFT and TDDFT calculations, revealing that C₆₀²⁺ has a singlet <i>D</i>_5<i>d</i> ground state whereas C₆₀³⁺ forms a doublet of <i>C</i>_<i>i</i> symmetry. The new results may be of interest regarding the presence of C₆₀²⁺ and C₆₀³⁺ in space

IR Absorptions of C₆₀⁺ and C₆₀^– in Neon Matrixes

C₆₀⁺ ions were produced by electron-impact ionization of sublimed C₆₀, collimated into an ion beam, turned 90° by an electrostatic deflector to separate them from neutrals, mass filtered by a radio frequency quadrupole, and co-deposited with Ne on a cold 5 K gold-coated sapphire substrate. Infrared absorption spectroscopy revealed the additional presence of C₆₀ and C₆₀^– in the as-prepared cryogenic matrixes. To change the C₆₀⁺/C₆₀^– ratio, CCl₄ or CO₂ electron scavengers were added to the matrix gas. Also taking into account DFT calculations, we have identified nine new previously unpublished IR absorptions of C₆₀⁺ and seven of C₆₀^– in Ne matrixes. Our measurements are in very good agreement with DFT calculations, predicting <i>D</i>_5<i>d</i> C₆₀⁺ and <i>D</i>_3<i>d</i> C₆₀^– ground states. The new results may be of interest regarding the presence of C₆₀ and C₇₀ (as well as ions thereof) in Space