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Context. Dust emission at sub-millimeter to centimeter wavelengths is often simply the Rayleigh-Jeans tail of dust particles at thermal equilibrium and is used as a cold mass tracer in various environments, including nearby galaxies. However, well-sampled spectral energy distributions of the nearby, star-forming Magellanic Clouds have a pronounced (sub-)millimeter excess. Aims. This study attempts to confirm the existence of this millimeter excess above expected dust, free-free and synchrotron emission and to explore different possibilities for its origin. Methods. We model near-infrared to radio spectral energy distributions of the Magellanic Clouds with dust, free-free, and synchrotron emission. A millimeter excess emission is confirmed above these components and its spectral shape and intensity are analyzed in light of different scenarios: very cold dust, cosmic microwave background (CMB) fluctuations, a change of the dust spectral index and spinning dust emission. Results. We show that very cold dust or CMB fluctuations are very unlikely explanations for the observed excess in these two galaxies. The excess in the Large Magellanic Cloud can be satisfactorily explained either by a change of the spectral index related to intrinsic properties of amorphous grains, or by spinning dust emission. In the Small Magellanic Cloud, however, the excess is larger and the dust grain model including TLS/DCD effects cannot reproduce the observed emission in a simple way. A possible solution was achieved with spinning dust emission, but many assumptions on the physical state of the interstellar medium had to be made. Conclusions. Further studies, with higher resolution data from Planck and Herschel are needed to probe the origin of this observed submillimeter-centimeter excess more definitely. Our study shows that the different possible origins will be best distinguished where the excess is the highest, as is the case in the Small Magellanic Cloud.

We have created a map of the large-scale infrared surface brightness in excess of that associated with the atomic interstellar medium, using region-by-region correlations between the far-infrared and 21-cm line surface brightness. Our study updates and extends a previous attempt with the Infrared Astronomical Satellite and Berkeley/Parkes H I surveys. The far-infrared observations used here are from the Cosmic Background Explorer Diffuse Infrared Background Experiment, which extends far-infrared wavelength coverage to 240 µm, so that we are reliably sampling the emission of large, thermal-equilibrium grains that dominate the dust mass. The H I data are from the combined Leiden-Dwingeloo and Parkes 21-cm line surveys. Using the maps of excess infrared emission at 100, 140, and 240 µm, we created an atlas and identified the coherent structures.These infrared excess clouds can be caused both by dust that is warmer than average, or by dust associated with gas other than the atomic interstellar medium. We find very few warm clouds, such as the H II region around the high-latitude B-type star α Vir. The majority of the infrared excess clouds are colder than the average atomic interstellar medium. These clouds are peaks of column density, and their excess infrared emission is due to dust associated with molecular gas. We identify essentially all known high-latitude molecular clouds in the infrared excess maps, and further identify a sample of new clouds with similar infrared properties. The infrared excess was correlated with CO line brightness, allowing us to measure the ratio of H 2 column density to CO line integral (i.e. the N(H 2 )/W (CO) conversion factor) for high-latitude clouds. The atlas of infrared excess clouds may be useful as a guide to regions of relatively higher interstellar column density, which might cause high extinction toward extragalactic objects at optical and ultraviolet wavelengths and confusion toward -3structures in the cosmic background at infrared and microwave frequencies.

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Aims. Our goal is to determine and study the global emission from the Magellanic Clouds over the full radio to ultraviolet spectral range. Methods. We have selected from the literature those flux densities that include the entire LMC and SMC respectively, and we have complemented these with maps extracted from the WMAP and COBE databases covering the missing 23−90 GHz (13-3.2 mm) and the poorly sampled 1.25-250 THz (240-1.25 μm) spectral ranges in order to reconstruct the global SEDs of the Magellanic Clouds over eight decades in frequency or wavelength. Results. A major result is the discovery of a pronounced excess of emission from the Magellanic Clouds at millimeter and submillimeter wavelengths. We also confirm global mid-infrared (12 μm) emission suppression, and determine accurate thermal radio fluxes and very low global extinctions for both LMC and SMC, the latter being the most extreme in all these respects. Conclusions. These and other dust properties such as the far-UV extinction curve appear to be correlated with (low) metallicity. Possible explanations are briefly considered. As long as the nature of the excess emission is unknown, the total dust masses and gas-to-dust ratios of the Magellanic Clouds cannot reliably be determined

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles

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