A molecular shell with star formation toward the supernova remnant G349.7+0.2

A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO, using the On-The-Fly technique. The resolution of the observations is 54". We have found that this remnant is interacting with a small CO cloud which, in turn, is part of a much larger molecular complex, which we call the ``Large CO Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of 930,000 solar masses, and a density of 35 cm-3. We investigate the origin of this structure and suggest that an old supernova explosion ocurred about 4 million years ago, as a suitable hypothesis. Analyzing the interaction between G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock front currently driven into the molecular gas is a non-dissociative shock (C-type), in agreement with the presence of OH 1720 MHz masers. The positional and kinematical coincidence among one of the CO clouds that constitute the Large CO Shell, an IRAS point-like source and an ultracompact H II region, indicate the presence of a recently formed star. We suggest that the formation of this star was triggered during the expansion of the Large CO Shell, and suggest the possibility that the same expansion also created the progenitor star of G349.7+0.2. The Large CO Shell would then be one of the few observational examples of supernova-induced star formation.Comment: accepted in Astronomical Journal, corrected typo in the abstract (in first line, 38' instead of 38"

The neutral gas in the environs of the Geminga gamma-ray pulsar

We present a high-resolution (24 arcsec) study of the HI interstellar gas distribution around the radio-quiet neutron star Geminga. Based on Very Large Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field around Geminga. These observations have revealed the presence of a neutral gas shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which surrounds Geminga at a radial velocity compatible with the kinematical distance of the neutron star. In addition, morphological agreement is observed between the internal face of the HI shell and the brightest structure of Geminga's tail observed in X-rays.We explore the possibility that this morphological agreement is the result of a physical association.Comment: One tarfile including a Latex file (7 pages) and two figures. Paper accepted for publication in Advances in Space Research; typos corrected; changes in section Results and Discussion after referee's suggestions. S. Johnston's affilation correcte

Magnetic field effects on neutrino production in microquasars

We investigate the effects of magnetic fields on neutrino production in microquasars. We calculate the steady particle distributions for the pions and muons generated in p-gamma and p-p interactions in the jet taking the effects of all energy losses into account. The obtained neutrino emission is significantly modified due to the synchrotron losses suffered by secondary pions and muons. The estimates made for neutrino fluxes arriving on the Earth imply that detection of high-energy neutrinos from the vicinity of the compact object can be difficult. However, in the case of windy microquasars, the interaction of energetic protons in the jet with matter of dense clumps of the wind could produce detectable neutrinos. This is because the pions and muons at larger distances from the compact object will not be affected by synchrotron losses.Comment: 12 pages, 11 figures, accepted for publication in A&

Imaging transverse electron focusing in semiconducting heterostructures with spin-orbit coupling

Transverse electron focusing in two-dimensional electron gases (2DEGs) with strong spin-orbit coupling is revisited. The transverse focusing is related to the transmission between two contacts at the edge of a 2DEG when a perpendicular magnetic field is applied. Scanning probe microscopy imaging techniques can be used to study the electron flow in these systems. Using numerical techniques we simulate the images that could be obtained in such experiments. We show that hybrid edge states can be imaged and that the outgoing flux can be polarized if the microscope tip probe is placed in specific positions.Comment: Contribution to the Book/Proceedings of the PITP Les Houches School on "Quantum Magnetism" held on June, 2006. Final forma

The antenna DSA 3 and its potential use for Radio Astronomy

The European Space Agency (ESA) will inaugurate its third Deep Space Antenna (DSA 3) by the end of 2012. DSA 3 will be located in Argentina near the city of Malarg"ue in the Mendoza province. While the instrument will be primarily dedicated to communications with interplanetary missions, the characteristics of its antenna and receivers will also enable standalone leading scientific contributions, with a high scientific-technological return. We outline here scientific proposals for a radio astronomical use of DSA 3.Comment: 4 pages, submitted as Proceedings for the BAA

High resolution CO observations towards the Bright Eastern Knot of the SNR Puppis A

This paper reports molecular observations towards the Bright Eastern Knot (BEK) in the SNR Puppis A, a feature where radio and X-ray studies suggest that the shock front is interacting with a dense molecular clump. We performed high-resolution millimetric observations towards the BEK of Puppis A using the SEST telescope in the 12CO J=1-0 and 2-1 lines (beams of 45" and 23" respectively). More extended, lower angular resolution 12CO J=1-0 observations taken from NANTEN archival data were also analyzed to obtain a complete picture. In the velocity range near 16 km/s, the Puppis A systemic velocity, our study revealed two important properties: (i) no dense molecular gas is detected immediately adjacent to the eastern border of the BEK and (ii) the molecular clump detected very close to the radiocontinuum maximum is probably located in the foreground along the line of sight and has not yet been reached by the SNR shock front. We propose two possible scenarios to explain the absence of molecular emission eastwards of the BEK border of Puppis A. Either the shock front has completely engulfed and destroyed a molecular clump or the shock front is interacting with part of a larger cloud and we do not detect CO emission immediately beyond it because the molecules have been dissociated by photodissociation and by reactions with photoionized material due to the radiative precursor.Comment: 10 pages, 7 figures. Accepted for publication in A&

Gravitational radiation from precessing accretion disks in gamma-ray bursts

We study the precession of accretion disks in the context of gamma-ray burst inner engines. Our aim is to quantitatively estimate the characteristics of gravitational waves produced by the precession of the transient accretion disk in gamma-ray bursts. We evaluate the possible periods of disk precession caused by the Lense-Thirring effect using an accretion disk model that allows for neutrino cooling. Assuming jet ejection perpendicular to the disk plane and a typical intrinsic time-dependence for the burst, we find gamma-ray light curves that have a temporal microstructure similar to that observed in some reported events. The parameters obtained for the precession are then used to evaluate the production of gravitational waves. We find that the precession of accretion disks of outer radius smaller than $10^8$ cm and accretion rates above 1 solar mass per second could be detected by Advanced LIGO if they occur at distances of less than 100 Mpc. We conclude that the precession of a neutrino-cooled accretion disk in long gamma-ray bursts can be probed by gravitational wave astronomy. Precession of the disks in short gamma-ray events is undetectable with the current technology.Comment: 5 pages, 5 figures, accepted for publication in A&

A two-component model for the high-energy variability of blazars. Application to PKS 2155-304

We study the production of VHE emission in blazars as a superposition of a steady component from a baryonic jet and a time- dependent contribution from an inner e-e+ beam launched by the black hole. Both primary relativistic electrons and protons are injected in the jet, and the particle distributions along it are found by solving a one-dimensional transport equation that accounts for convection and cooling. The short-timescale variability of the emission is explained by local pair injections in turbulent regions of the inner beam. For illustration, we apply the model to the case of PKS 2155-304, reproducing a quiescent state of emission with inverse Compton and synchrotron radiation from primary electrons, as well as proton-proton interactions in the jet. The latter also yield an accompanying neutrino flux that could be observed with a new generation km-scale detector in the northern hemisphere such as KM3NeT.Comment: 9 pages, 12 figures, published in A&A (final version

Magnetic Field Amplification in Tycho and other Shell-type Supernova Remnants

It is shown that amplification of the magnetic field in supernova remnants (SNRs) occurs in all six objects where morphological measurements are presently available in the hard X-ray continuum at several keV. For the three archetypical objects (SN 1006, Cas A and Tycho's SNR) to which nonlinear time-dependent acceleration theory has been successfully applied up to now, the global theoretical and the local observational field strengths agree very well, suggesting in addition that all young SNRs exhibit the amplification effect as a result of very efficient acceleration of nuclear cosmic rays (CRs) at the outer shock. Since this appears to be empirically the case, we may reverse the argument and consider field amplification as a measure of nuclear CR acceleration and it has indeed been argued that acceleration in the amplified fields allows the CR spectrum from SNRs to reach the knee in the spectrum or, in special objects, even beyond. The above results are furthermore used to investigate the time evolution of field amplification in young SNRs. Although the uncertainties in the data do not allow precise conclusions regarding this point, they rather clearly show that the ratio of the magnetic field energy density and the kinetic energy density of gas flow into the shock is of the order of a few percent if the shock speed is high enough V_s > 10^3 km/s, and this ratio remains nearly constant during the SNR evolution. The escape of the highest energy nuclear particles from their sources becomes progressively important with age, reducing also the cutoff in the \pi^0 -decay gamma-ray emission spectrum with time after the end of the sweep-up phase. Simultaneously the leptonic gamma-ray channels will gain in relative importance with increasing age of the sources.Comment: 13 pages, 8 figures, accepted for publication in A&