arXiv subjects

Roberto Mignani

Publications and source records attributed to Roberto Mignani.

23 records · Page 2Linked to original sources

arXiv2004

Multiwavelength Study Of Two Unidentified Gamma-ray Sources

Most counterparts of the identified low-latitude gamma-ray sources are Isolated Neutron Stars (INSs). They are characterized by an extremely high value of the X/optical flux ratio, therefore a systematic X-ray/optical coverage of the fields of unidentified low-latitude gamma-ray sources is the best way to unveil possible INS counterparts. Since the low-latitude sources are heavily affected by the interstellar absorption in both the X-ray and optical bands, we decided to apply the above strategy to two middle-latitude EGRET sources, which could belong to a local galactic population: 3EG J0616-3310 and 3EG J1249-8330. Here we report on the global X-ray characterisation of about 300 objects, on their candidate optical counterparts and on the preliminary results of their identification.

astro-ph↗

arXiv2003

Unveiling the multi-wavelength phenomenology of Anomalous X-ray Pulsars

During 2002-2003 the number of IR-identified counterparts to the Anomalous X-ray Pulsars (AXPs) has grown to four (4U0142+614, 2E2259+584, 1E 1048-59 and 1RXS J170849-400910) out of the six assessed objects of this class, plus two candidates. More importantly, some new common observational characteristics have been identified, such as the IR variability, the IR flattening in the broad band energy spectrum, the X-ray spectral variability as a function of pulse phase (which are not predicted by the magnetar model), and the SGR-like bursts (which can not be explained in terms of standard accretion models). We present the results obtained from an extensive multi-wavelength observational campaign carried out collecting data from the NTT, CFHT for the optical/IR bands, and XMM, Chandra (plus BeppoSAX archival data) in the X-rays. Based on these results and those reported in the literature, the IR-to-X-ray band emission of AXPs has been compared and studied.

astro-ph↗

arXiv2000

On the solutions of the Cartan equation in Metric Affine Gravity

In the Tucker-Wang approach to Metric Affine gravity we review some particular solutions of the Cartan equation for the non-riemannian part of the connection. As application we show how a quite general non Riemannian model gives a Proca type equation for the trace of the nonmetricity 1-forms Q.

gr-qc↗

arXiv1999

Non-Invariant Ground States, Thermal Average, and generalized Fermionic Statistics

We present an approach to generalised fermionic statistics which relates the existence of a generalised statistical behaviour to non-invariant ground states. Considering the thermal average of an operatorial generalization of the Heisenberg algebra, we get an occupation number which depends on the degree of mixing between symmetric and antisymmetric sectors of the ground state. A natural prescription is given for the construction of a supersymmetric statistics. We also show that the structure of the vacuum, and therefore the statistical behaviour of the system, can be accounted for in terms of a second order phase transition.

cond-mat.stat-mech↗

arXiv1998

Pre-Supernova Ring Around PSR0540-69

SNR0540-69 is a supernova remnant in the LMC, harbouring a young (~1600 yrs) radio/optical/X-ray pulsar (P=50 ms). Ground based Halpha imaging of the region has shown a unique spiral-like structure centered around the pulsar. In narrow band HST imaging, the feature seems resolved in a ring-like structure, probably ejected by the progenitor star in a pre-supernova phase (> 10^4 yrs ago).

astro-ph↗