D. A. Smith

Eight gamma-ray pulsars discovered in blind frequency searches of Fermi LAT data

We report the discovery of eight gamma-ray pulsars in blind frequency searches using the LAT, onboard the Fermi Gamma-ray Space Telescope. Five of the eight pulsars are young (tau_c 10^36 erg/s), and located within the Galactic plane (|b|<3 deg). The remaining three are older, less energetic, and located off the plane. Five pulsars are associated with sources included in the LAT bright gamma-ray source list, but only one, PSR J1413-6205, is clearly associated with an EGRET source. PSR J1023-5746 has the smallest characteristic age (tau_c=4.6 kyr) and is the most energetic (Edot=1.1E37 erg/s) of all gamma-ray pulsars discovered so far in blind searches. PSRs J1957+5033 and J2055+25 have the largest characteristic ages (tau_c~1 Myr) and are the least energetic (Edot~5E33 erg/s) of the newly-discovered pulsars. We present the timing models, light curves, and detailed spectral parameters of the new pulsars. We used recent XMM observations to identify the counterpart of PSR J2055+25 as XMMU J205549.4+253959. In addition, publicly available archival Chandra X-ray data allowed us to identify the likely counterpart of PSR J1023-5746 as a faint, highly absorbed source, CXOU J102302.8-574606. The large X-ray absorption indicates that this could be among the most distant gamma-ray pulsars detected so far. PSR J1023-5746 is positionally coincident with the TeV source HESS J1023-575, located near the young stellar cluster Westerlund 2, while PSR J1954+2836 is coincident with a 4.3 sigma excess reported by Milagro at a median energy of 35 TeV. Deep radio follow-up observations of the eight pulsars resulted in no detections of pulsations and upper limits comparable to the faintest known radio pulsars, indicating that these can be included among the growing population of radio-quiet pulsars in our Galaxy being uncovered by the LAT, and currently numbering more than 20.

Three Millisecond Pulsars in FERMI LAT Unassociated Bright Sources

We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and γ-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind γ-ray pulsation searches. They seem to be relatively normal, nearby (≤2 kpc) MSPs. These observations, in combination with the Fermi detection of γ-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient γ-ray producers. The γ-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of ~1030-1031 erg s–1 are typical of the rare radio MSPs seen in X-rays.

RADIO DETECTION OF LAT PSRs J1741-2054 AND J2032+4127: NO LONGER JUST GAMMA-RAY PULSARS

Sixteen pulsars have been discovered so far in blind searches of photons collected with the Large Area Telescope on the Fermi Gamma-ray Space Telescope. We here report the discovery of radio pulsations from two of them. PSR J1741-2054, with period P = 413 ms, was detected in archival Parkes telescope data and subsequently has been detected at the Green Bank Telescope (GBT). Its received flux varies greatly due to interstellar scintillation and it has a very small dispersion measure of DM = 4.7 pc cm{sup -3}, implying a distance of approx0.4 kpc and possibly the smallest luminosity of any known radio pulsar. At this distance, for isotropic emission, its gamma-ray luminosity above 0.1 GeV corresponds to 28% of the spin-down luminosity of E-dot=9.4x10{sup 33} erg s{sup -1}. The gamma-ray profile occupies 1/3 of pulse phase and has three closely spaced peaks with the first peak lagging the radio pulse by delta = 0.29 P. We have also identified a soft Swift source that is the likely X-ray counterpart. In many respects PSR J1741-2054 resembles the Geminga pulsar. The second source, PSR J2032+4127, was detected at the GBT. It has P = 143 ms, and its DM = 115 pc cm{supmorexa0» -3} suggests a distance of approx3.6 kpc, but we consider it likely that it is located within the Cyg OB2 stellar association at half that distance. The radio emission is nearly 100% linearly polarized, and the main radio peak precedes by delta = 0.15 P the first of two narrow gamma-ray peaks that are separated by DELTA = 0.50 P. The second peak has a harder spectrum than the first one, following a trend observed in young gamma-ray pulsars. Faint, diffuse X-ray emission in a Chandra image is possibly its pulsar wind nebula. The wind of PSR J2032+4127 is responsible for the formerly unidentified HEGRA source TeV J2032+4130. PSR J2032+4127 is coincident in projection with MT91 213, a Be star in Cyg OB2, although apparently not a binary companion of it.«xa0less

OBSERVATIONS OF ENERGETIC HIGH MAGNETIC FIELD PULSARS WITH THE FERMI LARGE AREA TELESCOPE

We report the detection of γ-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119 6127 using data from the Fermi Large Area Telescope. The γ-ray light curve of PSR J1119 6127 shows a single, wide peak offset from the radio peak by 0.43±0.02 in phase. Spectral analysis suggests a power law of index 1.0 ± 0.3 +0.4 −0.2 with an energy cut-off at 0.8 ± 0.2 +2.0 −0.5 GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119 6127 and demonstrate that despite the object’s high surface magnetic field—near that of magnetars—the field strength and structure in the γ-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the γ-ray pulsed emission for the magnetically active PSR J1846 0258 in the supernova remnant Kesteven 75 and two other energetic high-B pulsars, PSRs J1718 3718 and J1734 3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry. Subject headings: gamma rays: stars — pulsars: general — pulsars: individual (PSR J1119 6127, PSR J1718 3718, PSR J1734 3333, PSR J1846 0258)

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

Context. 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 ( u E = 3.1 × 10 36 erg s −1 ), 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 (E > 100 GeV), 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. Aims. We search for gamma- and X-ray pulsations from this pulsar, characterize the neutron star emission and explore the environment of PSR J1357−6429. Methods. 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 the Large Area Telescope on-board Fermi as well as those collected withXMM-Newton, and perform gamma-ray spectral modeling. Results. 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 previous work. Upper limits on the gamma-ray emission from its potential pulsar wind nebula (PWN) are also reported. Conclusions. Assuming a distance of 2.4 kpc, the Fermi LAT energy flux yields a gamma-ray luminosity for PSR J1357−6429 of Lγ = (2.13 ± 0.25stat ± 0.83syst) × 10 34 erg s −1 , consistent with an Lγ ∝ √ u E 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.

GeV Gamma-Ray Pulsar Detection

Detecting more gamma ray pulsars will boost our understanding of pulsars in general. This article reviews the two principal types of high energy gamma ray instruments, ground-based atmospheric Cherenkov light detectors, and orbital telescopes, focussing on the strengths and limitations of each with respect to the key performance topics of sensitivity and imaging, and of energy range and spectroscopy. The pulsar results and prospects for the leading Cherenkov imager arrays (HESS, VERITAS, and MAGIC) are summarized, as are those of the space missions AGILE, AMS, and GLAST. The Large Area Telescope (LAT) on the GLAST satellite should see dozens of pulsars emitting GeV gamma rays. Special attention is paid to preparations for launch in 2008, including data analysis as well as the correlated efforts in radio observations for timing.

“Garden-variety” Gamma-ray Pulsars J0248+6021 & J2240+5832

PSRs J0248+6021 & J2240+5832 are “typical” young, radio-loud pulsars detected in GeV gamma rays using the Large Area Telescope (LAT) on the Fermi satellite. “Typical” because their P, P lie mid-range of those of the new gamma-ray pulsars, but also because of some nagging little observational problems. This paper focusses on the observables available to help interpret the wave of new gamma-ray pulsar findings, and some of their limitations.