* Astronomy

Title: VLT Suzaku observations of the Fermi pulsar PSR J1028-5819
Authors: R. P. Mignani (MSSL-UCL, Kepler Institute of Astronomy, University of Zielona Gora), M. Razzano (Istituto Nazionale di Fisica Nucleare, Pisa, Dipartimento di Fisica "E. Fermi", Universita' di Pisa, and Santa Cruz Institute for Particle Physics, University of California), P. Esposito (INAF Osservatorio Astronomico di Cagliari), A. De Luca (IUSS - Istituto Universitario di Studi Superiori, Pavia, and INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano, INFN - Istituto Nazionale di Fisica Nucleare, Pavia), M. Marelli (INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano, and Universit`a degli Studi dell'Insubria, Varese), S. R. Oates (MSSL-UCL), P. Saz-Parkinson (Santa Cruz Institute for Particle Physics, University of California)

We used optical images taken with the Very Large Telescope (VLT) in the B and V bands to search for the optical counterpart of PSR J1028-5819 or constrain its optical brightness. At the same time, we used an archival Suzaku observation to confirm the preliminary identification of the pulsar's X-ray counterpart obtained by Swift. Due to the large uncertainty on the pulsar's radio position and the presence of a bright (V = 13.2) early F-type star at < 4", we could not detect its counterpart down to flux limits of B~25.4 and V ~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku observations, we found that the X-ray spectrum of the pulsar's candidate counterpart is best-fit by a power-law with spectral index 1.7 ±0.2 and an absorption column density NH < 10^21 cm-2, which would support the proposed X-ray identification. Moreover, we found possible evidence for the presence of diffuse emission around the pulsar. If real, and associated with a pulsar wind nebula (PWN), its surface brightness and angular extent would be compatible with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.

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