New VLT observations of the Fermi pulsar PSR J1048-5832

PSR J1048-5832 is a Vela-like (P=123.6 ms; tau~20.3 kyr) gamma-ray pulsar detected by Fermi, at a distance of ~2.7 kpc and with a rotational energy loss rate dot{E}_{SD} ~2 x 10^{36} erg/s. The PSR J1048-5832 field has been observed with the VLT in the V and R bands. We used these data to determine the colour of the object detected closest to the Chandra position (Star D) and confirm that it is not associated with the pulsar. For the estimated extinction along the line of sight, inferred from a re-analysis of the Chandra and XMM-Newton spectra, the fluxes of Star D (V~26.7; R~25.8) imply a -0.13 < (V-R)_0 < 0.6. This means that the PSR J1048-5832 spectrum would be unusually red compared to the Vela pulsar.Moreover, the ratio between the unabsorbed optical and X-ray flux of PSR J1048-5832 would be much higher than for other young pulsars. Thus, we conclude that Star D is not the PSR J1048-5832 counterpart. We compared the derived R and V-band upper limits (R>26.4; V>27.6) with the extrapolation of the X and gamma-ray spectra and constrained the pulsar spectrum at low-energies. In particular, the VLT upper limits suggest that the pulsar spectrum could be consistent with a single power-law, stretching from the gamma-rays to the optical.Comment: 5 pages, 2 figures, accepted for publication on Monthly Notices of the Royal Astronomical Society Main Journa

Analytic Kerr black hole lensing for equatorial observers in the strong deflection limit

In this paper we present an analytical treatment of gravitational lensing by Kerr black holes in the limit of very large deflection angles, restricting to observers in the equatorial plane. We accomplish our objective starting from the Schwarzschild black hole and adding corrections up to second order in the black hole spin. This is sufficient to provide a full description of all caustics and the inversion of lens mapping for sources near them. On the basis of these formulae we argue that relativistic images of Low Mass X-ray Binaries around Sgr A* are very likely to be seen by future X-ray interferometry missions.Comment: 19 pages, 9 figures, published on Phys. Rev.

Conformations Of A Model Protein Revealed By An Aggregating Cuᴵᴵ Porphyrin: Sensing The Difference

Aggregated t-CuP binds to poly-L-glutamate through supramolecular interactions, revealing itself to be an extremely sensitive probe for the major conformations of the polymeric scaffold

Target motion estimation via a multistatic FSR

The focus of this paper is on the estimation of the kinematic parameters of moving targets via a MIMO Forward Scatter Radar (FSR) system. A sub-optimum estimation technique is considered that exploits the information concerning the time instants at which the target crosses the individual baselines to retrieve the motion parameters. The accuracy of such technique is firstly investigated from a theoretical point of view and then the effectiveness of the proposed approach is demonstrated by applying it to live MIMO FSR data. Shown results prove the practical applicability of the proposed technique

Unifying Einstein and Palatini gravities

We consider a novel class of $f(\R)$ gravity theories where the connection is related to the conformally scaled metric $\hat g_{\mu\nu}=C(\R)g_{\mu\nu}$ with a scaling that depends on the scalar curvature $\R$ only. We call them C-theories and show that the Einstein and Palatini gravities can be obtained as special limits. In addition, C-theories include completely new physically distinct gravity theories even when $f(\R)=\R$. With nonlinear $f(\R)$, C-theories interpolate and extrapolate the Einstein and Palatini cases and may avoid some of their conceptual and observational problems. We further show that C-theories have a scalar-tensor formulation, which in some special cases reduces to simple Brans-Dicke-type gravity. If matter fields couple to the connection, the conservation laws in C-theories are modified. The stability of perturbations about flat space is determined by a simple condition on the lagrangian.Comment: 17 pages, no figure

A Characterization of Bispecial Sturmian Words

A finite Sturmian word w over the alphabet {a,b} is left special (resp. right special) if aw and bw (resp. wa and wb) are both Sturmian words. A bispecial Sturmian word is a Sturmian word that is both left and right special. We show as a main result that bispecial Sturmian words are exactly the maximal internal factors of Christoffel words, that are words coding the digital approximations of segments in the Euclidean plane. This result is an extension of the known relation between central words and primitive Christoffel words. Our characterization allows us to give an enumerative formula for bispecial Sturmian words. We also investigate the minimal forbidden words for the set of Sturmian words.Comment: Accepted to MFCS 201

La riforma monetaria dell’aġlabita Ibrāhīm II

Gli studi sulla ḫarrūba siciliana hanno ricevuto grande impulso nel secolo scorso dai contributi di P. Balog e di F. D’Angelo1. Questa precedente letteratura fornisce ancor oggi un imprescindibile punto di partenza e di supporto a chiunque desideri approfondire una frazione argentea, attestata esclusivamente in Sicilia, la cui origine e la cui evoluzione presentano però ancora numerosi punti oscuri. La mia ricerca, si prefigge appunto di sottoporre all’attenzione degli studiosi un evento poco documentato che potrebbe, a mio avviso, averne generato l’introduzione sul mercato, dapprima africano e poi siciliano. Lo spunto per queste mie considerazioni è nato dall’esame di un esemplare di frazione argentea battuta dall’aglabita Ibrāhīm II venuto alla luce, qualche anno fa, ad Agrigento. Concludendo, qualora le mie ipotesi risultassero fondate, il frammento agrigentino e tutte le altre piccole frazioni argentee di Ibrāhīm II altro non sarebbero che gli intriganti darāhim al-‘āširiyya menzionati da Ibn ‘Iḏārī: una minuscola moneta in grado di sfidare, almeno in Sicilia, i rivolgimenti politici, il passare dei secoli e la damnatio memoriae a cui fu invece condannato il suo ostinato ed “empio” promotore

Structural Properties of the Disordered Spherical and other Mean Field Spin Models

We extend the approach of Aizenman, Sims and Starr for the SK-type models to their spherical versions. Such an extension has already been performed for diluted spin glasses. The factorization property of the optimal structures found by Guerra for the SK model, which holds for diluted models as well, is verified also in the case of spherical systems, with the due modifications. Hence we show that there are some common structural features in various mean field spin models. These similarities seem to be quite paradigmatic, and we summarize the various techniques typically used to prove the structural analogies and to tackle the computation of the free energy per spin in the thermodynamic limit.Comment: 24 page