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.
    Astronomy and Astrophysics 07/2011; 533. DOI:10.1051/0004-6361/201117318 · 4.38 Impact Factor
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    ABSTRACT: Several newly discovered very-high-energy (VHE; E > 100 GeV) gamma-ray sources in the Galaxy are thought to be associated with energetic pulsars. Among them, middle-aged (> 1E+4 yr) systems exhibit large centre-filled VHE nebulae, offset from the pulsar position, which result from the complex relationship between the pulsar wind and the surrounding medium, and reflect the past evolution of the pulsar. Imaging Atmospheric Cherenkov Telescopes (IACTs) have been successful in revealing extended emission from these sources in the VHE regime. Together with radio and X-ray observations, this observational window allows one to probe the energetics and magnetic field inside these large-scale nebulae. H.E.S.S., with its large field of view, angular resolution of < 0.1deg and unprecedented sensitivity, has been used to discover a large population of such VHE sources. In this paper, the H.E.S.S. data from the continuation of the Galactic Plane Survey (-80deg < l < 60deg, |b| < 3deg), together with the existing multi-wavelength observations, are used. A new VHE gamma-ray source was discovered at R.A. (J2000) = 13h56m00s, Dec. (J2000) = -64d30m00s with a 2' statistical error in each coordinate, namely HESS J1356-645. The source is extended, with an intrinsic Gaussian width of (0.20 +/- 0.02)deg. Its integrated energy flux between 1 and 10 TeV of 8E-12 erg cm-2 s-1 represents ~ 11% of the Crab Nebula flux in the same energy band. The energy spectrum between 1 and 20 TeV is well described by a power law dN/dE ~ E-Gamma with photon index Gamma = 2.2 +/- 0.2stat +/- 0.2sys. The inspection of archival radio images at three frequencies and the analysis of X-ray data from ROSAT/PSPC and XMM-Newton/MOS reveal the presence of faint non-thermal diffuse emission coincident with HESS J1356-645. HESS J1356-645 is most likely associated with the young and energetic pulsar PSR J1357-6429 (Abridged)
    Astronomy and Astrophysics 09/2011; 533:103. DOI:10.1051/0004-6361/201117445 · 4.38 Impact Factor
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    ABSTRACT: We observed the young pulsar J1357—6429 with the Chandra and XMM-Newton observatories. The pulsar spectrum fits well a combination of an absorbed power-law model (Γ = 1.7 ± 0.6) and a blackbody model (kT = 140+60– 40 eV, R ~ 2 km at the distance of 2.5 kpc). Strong pulsations with pulsed fraction of 42% ± 5%, apparently associated with the thermal component, were detected in 0.3-1.1 keV. Surprisingly, the pulsed fraction at higher energies, 1.1-10 keV, appears to be smaller, 23% ± 4%. The small emitting area of the thermal component either corresponds to a hotter fraction of the neutron star surface or indicates inapplicability of the simplistic blackbody description. The X-ray images also reveal a pulsar wind nebula (PWN) with complex, asymmetric morphology comprised of a brighter, compact PWN surrounded by the fainter, much more extended PWN whose spectral slopes are Γ = 1.3 ± 0.3 and Γ = 1.7 ± 0.2, respectively. The extended PWN with the observed flux of ~7.5 × 10–13 erg s–1 cm–2 is a factor of 10 more luminous then the compact PWN. The pulsar and its PWN are located close to the center of the extended TeV source HESS J1356-645, which strongly suggests that the very high energy emission is powered by electrons injected by the pulsar long ago. The X-ray to TeV flux ratio, ~0.1, is similar to those of other relic PWNe. We found no other viable candidates to power the TeV source. A region of diffuse radio emission, offset from the pulsar toward the center of the TeV source, could be synchrotron emission from the same relic PWN rather than from the supernova remnant.
    The Astrophysical Journal 12/2011; 744(2):81. DOI:10.1088/0004-637X/744/2/81 · 5.99 Impact Factor
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