GRB 970228 Revisited: Evidence for a Supernova in the Light Curve and La te Spectral Energy Distribution of the Afterglow

At the time of its discovery, the optical and X-ray afterglow of GRB 970228 appeared to be a ringing endorsement of the previously untried relativistic fireball model of gamma-ray burst (GRB) afterglows, but now that nearly a dozen optical afterglows to GRBs have been observed, the wavering light curve and reddening spectrum of this afterglow make it perhaps the most difficult of the observed afterglows to reconcile with the fireball model. In this Letter, we argue that this afterglow's unusual temporal and spectral properties can be attributed to a supernova that overtook the light curve nearly two weeks after the GRB. This is the strongest case yet for a GRB/supernova connection. It strengthens the case that a supernova also dominated the late afterglow of GRB 980326, and the case that GRB 980425 is related to SN 1998bw.Comment: Accepted to The Astrophysical Journal (Letters), 14 pages, LaTe

Geosynchronous continental land-atmosphere sensing system (g-class): persistent radar imaging for earth science

More frequent imaging of Earth system processes is recognised as one of the emerging needs in Earth observation. Conventional low Earth orbit satellites are limited in their ability to provide this, whereas satellites in geosynchronous orbit can in principle provide continuous imaging. A new mission de- sign has been developed from studies for a previous geosynchronous radar mission concept (GeoSTARe) to improve its technical feasibility and geographical coverage, and to rein- force its science focus. This new mission (Geosynchronous - Continental Land Atmosphere Sensing System (G-CLASS)) is presented. G-CLASS is in fact a family of missions: we present a version focussed on the diurnal water cycle - G-CLASS:H2O - for which geosynchronous radar has great potential. G-CLASS:H2O is being developed as a proposal for ESA’s Earth Explorer programme

A Photometric Investigation of the GRB970228 Afterglow and the Associated Nebulosity

We carefully analyze the WFPC2 and STIS images of GRB970228. We measure magnitudes for the GRB970228 point source component in the WFPC2 images of $V=26.20^{+0.14}_{-0.13}$, $I_c=23.94^{+0.10}_{-0.09}$ and $V=26.52^{+0.16}_{-0.18}$, $I_c=24.31^{+0.15}_{-0.11}$ on March 26 and April 7, respectively; and $R_c=27.09^{+0.14}_{-0.14}$ on September 4 in the STIS image. For the extended component, we measure magnitudes of $R_c=25.48^{+0.22}_{-0.20}$ in the combined WFPC2 images and $R_c=25.54^{+0.33}_{-0.22}$ in the STIS image, which are consistent with no variation. This value is fainter than previously reported (Galama et al. 98) and modifies the previously assumed magnitudes for the optical transient when it faded to a level where the extended source component contribution was not negligible, alleviating the discrepancy to a power-law temporal behavior. We also measure a color of $V_{606}-I_{814}=-0.18^{+0.51}_{-0.61}$ for the extended source component. Taking into account the extinction measured in this field (Castander & Lamb 1998), this color implies that the extended source is most likely a galaxy with ongoing star formation.Comment: 21 pages, including 8 figures. Submitted to Ap

Learning activation functions from data using cubic spline interpolation

Neural networks require a careful design in order to perform properly on a given task. In particular, selecting a good activation function (possibly in a data-dependent fashion) is a crucial step, which remains an open problem in the research community. Despite a large amount of investigations, most current implementations simply select one fixed function from a small set of candidates, which is not adapted during training, and is shared among all neurons throughout the different layers. However, neither two of these assumptions can be supposed optimal in practice. In this paper, we present a principled way to have data-dependent adaptation of the activation functions, which is performed independently for each neuron. This is achieved by leveraging over past and present advances on cubic spline interpolation, allowing for local adaptation of the functions around their regions of use. The resulting algorithm is relatively cheap to implement, and overfitting is counterbalanced by the inclusion of a novel damping criterion, which penalizes unwanted oscillations from a predefined shape. Experimental results validate the proposal over two well-known benchmarks.Comment: Submitted to the 27th Italian Workshop on Neural Networks (WIRN 2017

ASCA and BeppoSAX observations of the peculiar X-ray source 4U1700+24/HD154791

The X-ray source 4U1700+24/HD154791 is one of the few galactic sources whose counterpart is an evolved M star. In X-rays the source shows extreme erratic variability and a complex and variable spectrum. While this strongly suggests accretion onto a compact object, no clear diagnosis of binarity was done up to now. We report on ASCA and BeppoSAX X-ray broad band observations of this source and on ground optical observations from the Loiano 1.5 m telescope.Comment: 5 pages, 4 figures, uses aipproc.sty, to appear in Proceedings of the Fifth Compton Symposiu