Deep infrared observations of the puzzling central X-ray source in RCW103

1E 161348-5055 (1E 1613) is a point-like, soft X-ray source originally identified as a radio-quiet, isolated neutron star, shining at the center of the 2000 yr old supernova remnant RCW103. 1E 1613 features a puzzling 6.67 hour periodicity as well as a dramatic variability over a time scale of few years. Such a temporal behavior, coupled to the young age and to the lack of an obvious optical counterpart, makes 1E 1613 a unique source among all compact objects associated to SNRs. It could either be the first low-mass X-ray binary system discovered inside a SNR, or a peculiar isolated magnetar with an extremely slow spin period. Analysis of archival IR observations, performed in 2001 with the VLT/ISAAC instrument, and in 2002 with the NICMOS camera onboard HST unveils a very crowded field. A few sources are positionally consistent with the refined X-ray error region that we derived from the analysis of 13 Chandra observations. To shed light on the nature of 1E 1613, we have performed deep IR observations of the field with the NACO instrument at the ESO/VLT, searching for variability. We find no compelling reasons to associate any of the candidates to 1E 1613. On one side, within the frame of the binary system model for the X-ray source, it is very unlikely that one of the candidates be a low-mass companion star to 1E 1613. On the other side, if the X-ray source is an isolated magnetar surrounded by a fallback disc, we cannot exclude that the IR counterpart be hidden among the candidates. If none of the potential counterparts is linked to the X-ray source, 1E 1613 would remain undetected in the IR down to Ks>22.1. Such an upper limit is consistent only with an extremely low-mass star (an M6-M8 dwarf) at the position of 1E 1613, and makes rather problematic the interpretation of 1E 1613 as an accreting binary system.Comment: 26 pages, 5 figures. Accepted for publication in Ap

Spatio-temporal analysis of prodelta dynamics by means of new satellite generation: the case of Po river by Landsat-8 data

Abstract This paper describes a procedure to perform spatio-temporal analysis of river plume dispersion in prodelta areas by multi-temporal Landsat-8-derived products for identifying zones sensitive to water discharge and for providing geostatistical patterns of turbidity linked to different meteo-marine forcings. In particular, we characterized the temporal and spatial variability of turbidity and sea surface temperature (SST) in the Po River prodelta (Northern Adriatic Sea, Italy) during the period 2013–2016. To perform this analysis, a two-pronged processing methodology was implemented and the resulting outputs were analysed through a series of statistical tools. A pixel-based spatial correlation analysis was carried out by comparing temporal curves of turbidity and SST hypercubes with in situ time series of wind speed and water discharge, providing correlation coefficient maps. A geostatistical analysis was performed to determine the spatial dependency of the turbidity datasets per each satellite image, providing maps of correlation and variograms. The results show a linear correlation between water discharge and turbidity variations in the points more affected by the buoyant plumes and along the southern coast of Po River delta. Better inverse correlation was found between turbidity and SST during floods rather than other periods. The correlation maps of wind speed with turbidity show different spatial patterns depending on local or basin-scale wind effects. Variogram maps identify different spatial anisotropy structures of turbidity in response to ambient conditions (i.e. strong Bora or Scirocco winds, floods). Since the implemented processing methodology is based on open source software and free satellite data, it represents a promising tool for the monitoring of maritime ecosystems and to address water quality analyses and the investigations of sediment dynamics in estuarine and coastal waters

Search for the Optical Counterpart of the Vela Pulsar X-ray Nebula

Observations of the Vela pulsar region with the Chandra X-ray observatory have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN), which showed an overall similarity with the Crab PWN. However, contrary to the Crab, no firm detection of the Vela PWN in optical has been reported yet. To search for the optical counterpart of the X-ray PWN, we analyzed deep optical observations performed with different telescopes. We compared the optical images with those obtained with the Chandra ACIS to search for extended emission patterns which could be identified as counterparts of the X-ray nebula elements. Although some features are seen in the optical images, we find no correlation with the X-ray structure. Thus, we conclude that the diffuse optical emission is more likely associated with filaments in the host Vela SNR. The derived upper limits on the optical flux from the PWN are compatibile, within the uncertainties, with the values expected on the basis of the extrapolations of the X-ray data.Comment: 19 pages, 6 figures. Accepted for publication in Ap

Ship-Induced Depression Wakes and Shoreline Erosion

Shoreline retreat as an effect of ship wakes was studied in a navigation channel of the industrial port of Venice, Italy: the Malamocco -Marghera Channel. The investigation revealed unprecedented erosion rates, up to 4 m y , that determined a total loss of about 1.2 million of m of soil in the period 1970 -2015. This interaction between navigation and the channel margins must be considered in order to understand the past evolution of the central Venice Lagoon and for a sustainable management of the port traffic in the future sea -level rise scenario

VLT observations of the Central Compact Object in the Vela Jr. supernova remnant

X-ray observations have unveiled the existence of enigmatic point-like sources at the center of young (a few kyrs) supernova remnants. These sources, known as Central Compact Objects (CCOs), are thought to be neutron stars produced by the supernova explosion, although their X-ray phenomenology makes them markedly different from all the other young neutron stars discovered so far.The aim of this work is to search for the optical/IR counterpart of the Vela Junior CCO and to understand the nature of the associated Halpha nebula discovered by Pellizzoni et al. (2002).}{We have used deep optical (R band) and IR (J,H,Ks bands) observations recently performed by our group with the ESO VLT to obtain the first deep, high resolution images of the field with the goal of resolving the nebula structure and pinpointing a point-like source possibly associated with the neutron star.Our R-band image shows that both the nebula's flux and its structure are very similar to the Halpha ones, suggesting that the nebula spectrum is dominated by pure Halpha line emission. However, the nebula is not detected in our IR observations, whick makes it impossible to to constrain its spectrum. A faint point-like object (J>22.6, H~21.6, Ks ~ 21.4) compatible with the neutron star's Chandra X-ray position is detected in our IR images (H and Ks) but not in the optical one (R > 25.6), where it is buried by the nebula background. The nebula is most likely a bow-shock produced by the neutron star motion through the ISM or, alternatively, a photo-ionization nebula powered by UV radiation from a hot neutron star.Comment: 8 pages, 4 figures, A&Aaccepte

The Effects of Ship Wakes in the Venice Lagoon and Implications for the Sustainability of Shipping in Coastal Waters

We analyse the impact of ship traffic in the vicinity of navigation channels in a wide shallow waterbody. The crucial hydrodynamic driver in this situation is the depression (Bernoulli) wake that may be transferred into a long-living solitary wave of depression over the shoals. The analysis considers navigation channels in the Venice Lagoon using a new large dataset of approximately 600 measured wake events associated to specific ships whose data are provided by the AIS system. Since the development of the modern industrial port and the opening of the Malamocco–Marghera channel in the late 1960s, growing pressure on the lagoon caused by ship traffic has raised concerns about its physical integrity and habitat survival. The transit of large vessels has been shown to have serious impacts on the shallow water areas adjacent to waterways. Depression wakes created by such vessels can reach significant dimensions (water level dropdown of up to 2.45 m at the channel margin), causing unusually large retreat rates of several sections of the shoreline and which may adversely affect the lagoon morphology. The wakes are analysed in relation to ship and morphological parameters. A formulation is proposed to predict wake amplitude on the basis of ship characteristics and motion

Fast Shoreline Erosion Induced by Ship Wakes in a Coastal Lagoon: Field Evidence and Remote Sensing Analysis

An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3˗4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968˗2015 (1.19×106 m3). The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide

Morphology of the Veneto Coast

A considerable amount of the North Adriatic coast is currently eroding despite the development of a wide range of measures to protect shorelines from eroding and flooding. The management of Northern Adriatic coast need a multidisciplinary, updating and modular approach. We must understand how natural and man-induced dynamics act on littoral areas. This motivated to initiate a specific research program concerning these issues started in 2003 by a cooperation among CNR-ISMAR, the Autorità di Bacino dei fiumi dell’Alto Adriatico and APAT, Servizio Laguna di Venezia. This paper shows first results of such program in progress

VLT observations of Compact Central Objects

We present the first results of our VLT observation campaign of the Central Compact Objects (CCOs) in SNRs RX J085201.4-461753 (Vela Jr), 1E 1648-5051 (RCW 103) and RX J171328.4-394955 (G347.3-0.5). For Vela Jr., we found that the source is embedded in a compact optical nebulosity, possibly a bow-shock or a photo-ionization nebula, and we identified a candidate IR counterpart to the CCO. For RCW 103, we found no convincing evidence neither for 6 hrs IR modulation nor for variability on any time scale from the proposed counterpart, as well as for the other candidates close to the revised Chandra position. For G347.3-0.5, we identified few possible IR counterparts but none of them is apparently associated with the CCO.Comment: 4 pages, in Proc. of ``40 Years of Pulsars: Millisecond Pulsars, Magnetars and More'', AIP, in pres