37 research outputs found
The detection rate of early UV emission from supernovae: A dedicated GALEX/PTF survey and calibrated theoretical estimates
The radius and surface composition of an exploding massive star,as well as
the explosion energy per unit mass, can be measured using early UV observations
of core collapse supernovae (SNe). We present the first results from a
simultaneous GALEX/PTF search for early UV emission from SNe. Six Type II SNe
and one Type II superluminous SN (SLSN-II) are clearly detected in the GALEX
NUV data. We compare our detection rate with theoretical estimates based on
early, shock-cooling UV light curves calculated from models that fit existing
Swift and GALEX observations well, combined with volumetric SN rates. We find
that our observations are in good agreement with calculated rates assuming that
red supergiants (RSGs) explode with fiducial radii of 500 solar, explosion
energies of 10^51 erg, and ejecta masses of 10 solar masses. Exploding blue
supergiants and Wolf-Rayet stars are poorly constrained. We describe how such
observations can be used to derive the progenitor radius, surface composition
and explosion energy per unit mass of such SN events, and we demonstrate why UV
observations are critical for such measurements. We use the fiducial RSG
parameters to estimate the detection rate of SNe during the shock-cooling phase
(<1d after explosion) for several ground-based surveys (PTF, ZTF, and LSST). We
show that the proposed wide-field UV explorer ULTRASAT mission, is expected to
find >100 SNe per year (~0.5 SN per deg^2), independent of host galaxy
extinction, down to an NUV detection limit of 21.5 mag AB. Our pilot GALEX/PTF
project thus convincingly demonstrates that a dedicated, systematic SN survey
at the NUV band is a compelling method to study how massive stars end their
life.Comment: See additional information including animations on
http://www.weizmann.ac.il/astrophysics/ultrasa
Hippocampal-Dependent Spatial Memory in the Water Maze is Preserved in an Experimental Model of Temporal Lobe Epilepsy in Rats
Cognitive impairment is a major concern in temporal lobe epilepsy (TLE). While different experimental models have been used to characterize TLE-related cognitive deficits, little is known on whether a particular deficit is more associated with the underlying brain injuries than with the epileptic condition per se. Here, we look at the relationship between the pattern of brain damage and spatial memory deficits in two chronic models of TLE (lithium-pilocarpine, LIP and kainic acid, KA) from two different rat strains (Wistar and Sprague-Dawley) using the Morris water maze and the elevated plus maze in combination with MRI imaging and post-morten neuronal immunostaining. We found fundamental differences between LIP- and KA-treated epileptic rats regarding spatial memory deficits and anxiety. LIP-treated animals from both strains showed significant impairment in the acquisition and retention of spatial memory, and were unable to learn a cued version of the task. In contrast, KA-treated rats were differently affected. Sprague-Dawley KA-treated rats learned less efficiently than Wistar KA-treated animals, which performed similar to control rats in the acquisition and in a probe trial testing for spatial memory. Different anxiety levels and the extension of brain lesions affecting the hippocampus and the amydgala concur with spatial memory deficits observed in epileptic rats. Hence, our results suggest that hippocampal-dependent spatial memory is not necessarily affected in TLE and that comorbidity between spatial deficits and anxiety is more related with the underlying brain lesions than with the epileptic condition per se