Cosmic Ray Acceleration in Superbubbles and the Composition of Cosmic Rays

We review the evidence for cosmic ray acceleration in the superbubble/hot phase of the interstellar medium, and discuss the implications for the composition of cosmic rays and the structure and evolution of the interstellar medium. We show that the bulk of the galactic supernovae, their expanding remnants, together with their metal-rich grain and gas ejecta, and their cosmic ray accelerating shocks, are all confined within the interiors of superbubbles, generated by the multiple supernova explosions of massive stars formed in giant OB associations. This superbubble/hot phase of the ISM provides throughout the age of the Galaxy a cosmic ray source of essentially constant metallicity for acceleration by the shocks of many supernovae over time scales of a few Myr, consistent with both the Be/Fe evolution and ACE observations of Ni-59/Co-59. We also show that if the refractory cosmic ray metals come from the sputtering of fast refractory grains then the accompanying scattering of ambient gas by these fast grains can also account for the relative abundance of cosmic ray volatiles.Comment: latex 8 pages, to appear in Proc. ACE-2000 Symp., AIP Conf. Pro

Redshifts from Spitzer Spectra for Optically Faint, Radio Selected Infrared Sources

Spectra have been obtained with the Infrared Spectrograph on the Spitzer Space Telescope for 18 optically faint sources (R > 23.9,mag) having f(nu) (24um) > 1.0,mJy and having radio detections at 20 cm to a limit of 115 microJy. Sources are within the Spitzer First Look Survey. Redshifts are determined for 14 sources from strong silicate absorption features (12 sources) or strong PAH emission features (2 sources), with median redshift of 2.1. Results confirm that optically faint sources of ~1 mJy at 24um are typically at redshifts z ~ 2, verifying the high efficiency in selecting high redshift sources based on extreme infrared to optical flux ratio, and indicate that 24um sources which also have radio counterparts are not systematically different than samples chosen only by their infrared to optical flux ratios. Using the parameter q = log[f(nu)(24um)/f(nu)(20 cm)] 17 of the 18 sources observed have values of 0<q<1, in the range expected for starburst-powered sources, but only a few of these show strong PAH emission as expected from starbursts, with the remainder showing absorbed or power-law spectra consistent with an AGN luminosity source. This confirms previous indications that optically faint Spitzer sources with f(nu)(24um) > 1.0mJy are predominately AGN and represent the upper end of the luminosity function of dusty sources at z ~ 2. Based on the characteristics of the sources observed so far, we predict that the nature of sources selected at 24um will change for f(nu)(24um) < 0.5 mJy to sources dominated primarily by starbursts.Comment: Accepted ApJ 20 February 2006, v638 2 issue, 10pages including 3 figure

Gamma ray burst size-frequency distributions: Spectral selection effects

The effects of spectral variation on the detection of gamma ray bursts were investigated. Selection biases resulting from these effects can account for the reported deviation of the observed size-frequency distribution in peak energy flux from that expected for a simple uniform distribution of sources. Thus these observations as yet provide no clear evidence for structure in the burst source distribution. Because of selection biases, the intrinsic average temperature of the bursts is much harder (kT approximately MeV) than the observed average (approximately 200 KeV)

A blackbody-pumped CO2-N2 transfer laser

A compact blackbody-pumped CO2-N2 transfer laser was constructed and the significant operating parameters were investigated. Lasing was achieved at 10.6 microns by passing preheated N2 through a 1.5-mm-diameter nozzle to a laser cavity where the N2 was mixed with CO2 and He. An intrinsic efficiency of 0.7 percent was achieved for an oven temperature of 1473 K and N2 oven pressure of 440 torr. The optimum laser cavity consisted of a back mirror with maximum reflectivity and an output mirror with 97.5-percent reflectivity. The optimum gas mixture was 1CO2/.5He/6N2. The variation of laser output was measured as a function of oven temperature, nozzle diameter, N2 oven pressure, He and CO2 partial pressures, nozzle-to-oven separation, laser cell temperature, and output laser mirror reflectivity. With these parameters optimized, outputs approaching 1.4 watts were achieved