Discovery of gamma and X-ray pulsations from the young and energetic PSR J1357-6429 with Fermi and XMM-Newton

Astronomy and Astrophysics (Impact Factor: 4.38). 07/2011; 533. DOI: 10.1051/0004-6361/201117413
Source: arXiv


Since the launch of the Fermi satellite, the number of known gamma-ray
pulsars has increased tenfold. Most gamma-ray detected pulsars are young and
energetic, and many are associated with TeV sources. PSR J1357-6429 is a high
spin-down power pulsar (Edot = 3.1 * 10^36 erg/s), discovered during the Parkes
multibeam survey of the Galactic plane, with significant timing noise typical
of very young pulsars. In the very-high-energy domain, H.E.S.S. has reported
the detection of the extended source HESS J1356-645 (intrinsic Gaussian width
of 12') whose centroid lies 7' from PSR J1357-6429. Using a rotational
ephemeris obtained with 74 observations made with the Parkes telescope at 1.4
GHz, we phase-fold more than two years of gamma-ray data acquired by Fermi-LAT
as well as those collected with XMM-Newton, and perform gamma-ray spectral
modeling. Significant gamma and X-ray pulsations are detected from PSR
J1357-6429. The light curve in both bands shows one broad peak. Gamma-ray
spectral analysis of the pulsed emission suggests that it is well described by
a simple power-law of index 1.5 +/- 0.3stat +/- 0.3syst with an exponential
cut-off at 0.8 +/- 0.3stat +/- 0.3syst GeV and an integral photon flux above
100 MeV of (6.5 +/- 1.6stat +/- 2.3syst) * 10^-8 cm^-2 s^-1. The X-ray spectra
obtained from the new data provide results consistent with those reported by
Zavlin (2007). Upper limits on the gamma-ray emission from its potential pulsar
wind nebula (PWN) are also reported. Assuming a distance of 2.4 kpc, the Fermi
LAT energy flux yields a gamma-ray luminosity for PSR J1357-6429 of L_gamma =
(2.13 +/- 0.25stat +/- 0.83syst) * 10^34 erg/s, consistent with an L_gamma
\propto sqrt(Edot) relationship. The Fermi non-detection of the pulsar wind
nebula associated with HESS J1356-645 provides new constraints on the electron
population responsible for the extended TeV emission.

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    ABSTRACT: Optical observations of pulsars are crucial to study the neutron star properties, from the structure and composition of the interior, to the properties and geometry of the magnetosphere. Historically, X and gamma-ray observations have paved the way to the pulsar optical identifications. The launch of Fermi opened new perspectives in the optical-to-gamma-ray studies of neutron stars, with the detection of more than 80 pulsars. Here, we aim to search for optical emission from two Fermi pulsars which are interesting targets on the basis of their spin-down age, energetics, and distance: PSR J1357-6429and PSR J1048-5832. The two pulsars and their pulsar wind nebulae (PWNe) are also detected in X-rays by Chandra and XMM. No deep optical observations of these two pulsars have been reported so far. We used multi-band optical images (V,R,I) taken with the VLT and available in the European Southern Observatory (ESO) archive to search for, or put tight constraints to, their optical emission. We re-assessed the positions of the two pulsars from the analyses of all the available Chandra observations and the comparison with the published radio coordinates. For PSR J1357-6429, this yielded a tentative proper motion mu=0.17+/-0.055 "/yr (70+/-15 deg position angle). We did not detect candidate counterparts to PSR J1357-6429 and PSR J1048-5832 down to V~27 and ~27.6, respectively, although for the former we found a possible evidence for a faint, unresolved object at the Chandra position. Our limits imply an efficiency in converting spin-down power into optical luminosity <7x10^{-7} and <6x10^{-6}, respectively, possibly close to that of the Vela pulsar.
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