30 research outputs found
e-MERLIN and VLBI observations of the luminous infrared galaxy IC883: a nuclear starburst and an AGN candidate revealed
The high star formation rates of luminous infrared galaxies (LIRGs) make them
ideal places for core-collapse supernova (CCSN) searches. At radio frequencies,
free from dust extinction, it is possible to detect compact components within
the innermost LIRG nuclear regions, such as SNe and SN remnants, as well as AGN
buried deep in the LIRG nuclei. We studied the LIRG IC883 aiming at: (i)
investigating its (circum-)nuclear regions using the e-EVN at 5GHz, and
e-MERLIN at 6.9GHz, complemented by archival VLBI data; (ii) detecting at radio
frequencies the two recently reported circumnuclear SNe 2010cu and 2011hi,
which were discovered by near-IR (NIR) adaptive optics observations of IC883;
and (iii) further investigating the nature of SN2011hi at NIR by means of
observations with Gemini-North. The circumnuclear regions traced by e-MERLIN at
6.9GHz have an extension of ~1kpc, and show a striking double-sided structure,
which very likely corresponds to a warped rotating ring, in agreement with
previous studies. Our e-EVN observations at 5GHz and complementary archival
VLBI data at 5GHz and 8.4GHz, reveal the presence of various milliarcsec
compact components in the nucleus of IC883. A single compact source, an AGN
candidate, dominates the emission at both nuclear and circumnuclear scales, as
imaged with the e-EVN and e-MERLIN, respectively. The other milliarcsec
components are very suggestive of ongoing nuclear CCSN activity. Our e-EVN
observations also resulted in upper limits to the radio luminosity of the two
SNe in IC883 recently discovered at NIR. We refine the classification of
SN2011hi as a Type IIP SN according to our latest Gemini-North epoch from 2012,
in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate
lower limit of 1.1_{-0.6}^{+1.3} yr^{-1} for the entire galaxy, based on three
nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi. (abridged)Comment: 9 pages, 5 figures and 2 tables. Accepted for publication in A&
LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A
Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon {} RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of {gt}5 from two independent LOFAR data sets. The derived line velocities (v ~{} - 50 km s) and integrated optical depths (~{}13 s) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of ~{}1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 { imes} 10 on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band
Etude experimentale d'un moyen de commande en aeronautique integrant un clavier a labels variables et une commande vocale
SIGLECNRS RP 174 (138) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Etude des effets d'une nouvelle forme galenique de cafeine a liberation prolongee chez 24 sujets soumis a une privation de sommeil de 34 heures
Available from INIST (FR), Document Supply Service, under shelf-number : RP 15189 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc
Influence de frequences spatiales sur l'extraction de cibles
SIGLECNRS RP 174 (216) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
LOFAR calibration and wide-field imaging
LOFAR is a revolutionary instrument, operating at low frequencies (nu less than or similar to 240 MHz). It will drive major breakthroughs in the area of observational cosmology, but its use requires the development of challenging techniques and algorithms. Since its field of view and sensitivity are increased by orders of magnitude as compared to the older generation of instruments, new technical problems have to be addressed. The LOFAR survey team is in charge of commissioning the first LOFAR data produced in the imager mode as part of building the imaging pipeline. We are developing algorithms to tackle the problems associated with calibration (ionosphere, beam, etc.) and wide-field imaging for the achievement of the deep extragalactic surveys. New types of problems arise in that context, and notions such as algorithmic complexity and parallelism become fundamental. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved