The electromagnetic (EM) emission associated with a gravitational wave (GW) signal is one of the main goal of future astronomy. Merger of neutron stars and/or black holes and core-collapse of massive stars are expected to cause rapid transient electr
omagnetic signals. The EM follow-up of GW signals will have to deal with large position uncertainties. The gravitational sky localization is expected to be tens to hundreds of square degrees. Wide-field cameras and rapid follow-up observations will be crucial to characterize the EM candidates for the first EM counterpart identification. We present some of the activities that we are currently carrying on to optimize the response of the INAF network of facilities to expected GW triggers. The INAF network will represent an efficient operational framework capable of fast reaction on large error box triggers and direct identification and characterization of the candidates.
Pioneering efforts aiming at the development of multi-messenger gravitational wave and electromagnetic astronomy have been made. An electromagnetic observation follow-up program of candidate gravitational wave events has been performed (Dec 17 2009 t
o Jan 8 2010 and Sep 4 to Oct 20 2010) during the recent runs of the LIGO and Virgo gravitational wave detectors. It involved ground-based and space electromagnetic facilities observing the sky at optical, X-ray and radio wavelengths. The joint gravitational wave and electromagnetic observation study requires the development of specific image analysis procedures able to discriminate the possible electromagnetic counterpart of gravitational wave triggers from contaminant/background events. The paper presents an overview of the electromagnetic follow-up program and the image analysis procedures.
A pioneering electromagnetic (EM) observation follow-up program of candidate gravitational wave (GW) triggers has been performed, Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010, during the recent LIGO/Virgo run. The follow-up program involved gro
und-based and space EM facilities observing the sky at optical, X-ray and radio wavelengths. The joint GW/EM observation study requires the development of specific image analysis procedures able to discriminate the possible EM counterpart of GW trigger from background events. The paper shows an overview of the EM follow-up program and the developing image analysis procedures as they are applied to data collected with TAROT and Zadko.
In this paper we re-visit the observational relation between X-ray luminosity and temperature for high-z galaxy clusters and compare it with the local L_X-T and with theoretical models. To these ends we use a sample of 17 clusters extracted from the
Chandra archive supplemented with additional clusters from the literature, either observed by Chandra or XMM-Newton, to form a final sample of 39 high redshift (0.25 < z < 1.3) objects. Different statistical approaches are adopted to analyze the L_X-T relation. The slope of the L_X-T relation of high redshift clusters is steeper than expected from the self-similar model predictions and steeper, even though still compatible within the errors, than the local L_X-T slope. The distant cluster L_X-T relation shows a significant evolution with respect to the local Universe: high-z clusters are more luminous than the local ones by a factor ~2 at any given temperature. The evolution with redshift of the L_X-T relation cannot be described by a single power law nor by the evolution predicted by the self-similar model. We find a strong evolution, similar or stronger than the self-similar model, from z = 0 to z <0.3 followed by a much weaker, if any, evolution at higher redshift. The weaker evolution is compatible with non-gravitational models of structure formation. According to us a statistically significant sample of nearby clusters (z < 0.25) should be observed with the current available X-ray telescopes to completely exclude observational effects due to different generation detectors and to understand this novel result.
The current generation of X-ray observatories like Chandra allows studies with very fine spatial details. It is now possible to resolve X-ray point sources projected into the cluster diffuse emission and exclude them from the analysis to estimate the
``correct X-ray observables. In order to verify the incidence of point sources on the cluster thermal emission and to evaluate the impact of their non-thermal emission on the determination of cluster properties, we used a sample of 18 high-z (0.25 < z < 1.01) clusters from the Chandra archive. We performed a detailed analysis of the cluster properties and compared the changes observed in the X-ray observables, like temperature and luminosity or their inter-relation, when one keeps the point sources in the analysis. The point sources projected into the cluster extended emission affect the estimates of cluster temperature or luminosity considerably (up to 13% and 17% respectively). These percentages become even larger for clusters with z > 0.7 where temperature and luminosity increase up to 24% and 22%, respectively. Thus the point sources should be removed to correctly estimate the cluster properties. However the inclusion of the point sources does not impact significantly the slope and normalization of the L-T relationship since for each cluster the correction to be applied to T and L produces a moderate shift in the L-T plane almost parallel to the best-fit of the ``correct L-T relation.
