K. S. Wood

The HEAO A-1 X-ray source catalog

The catalog of X-ray sources detected during the NRL Large Area Sky Survey (LASS) with the HEAO 1 satellite is presented. The catalog is derived from the first six months of data from HEAO 1 and includes sources detected during one full scan. Positions and intensities for a total of 842 different sources are included, with a limiting flux of 250 nJy at 5 keV. The catalog is more than 90 percent complete at a flux level equivalent to 1.5 microjoules at 5 keV for a Crab-like spectrum. Cross-references with published literature are provided and coincidental identifications are proposed for some of the sources which have been never studied before. A cross-sectional line drawing of the sensor module of HEAO I is also provided.

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.

Searches for millisecond pulsations on low-mass x-ray binaries

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DISCOVERY OF TWO MILLISECOND PULSARS IN FERMI SOURCES WITH THE NANÇAY RADIO TELESCOPE

We report the discovery of two millisecond pulsars in a search for radio pulsations at the positions of \emph{Fermi Large Area Telescope} sources with no previously known counterparts, using the Nancay radio telescope. The two millisecond pulsars, PSRs J2017+0603 and J2302+4442, have rotational periods of 2.896 and 5.192 ms and are both in binary systems with low-eccentricity orbits and orbital periods of 2.2 and 125.9 days respectively, suggesting long recycling processes. Gamma-ray pulsations were subsequently detected for both objects, indicating that they power the associated \emph{Fermi} sources in which they were found. The gamma-ray light curves and spectral properties are similar to those of previously-detected gamma-ray millisecond pulsars. Detailed modeling of the observed radio and gamma-ray light curves shows that the gamma-ray emission seems to originate at high altitudes in their magnetospheres. Additionally, X-ray observations revealed the presence of an X-ray source at the position of PSR J2302+4442, consistent with thermal emission from a neutron star. These discoveries along with the numerous detections of radio-loud millisecond pulsars in gamma rays suggest that many \emph{Fermi} sources with no known counterpart could be unknown millisecond pulsars.

Further X-ray observations of EXO 0748-676 in quiescence: evidence for a cooling neutron star crust

In late 2008, the quasi-persistent neutron star X-ray transient and eclipsing binary EXO 0748−676 started a transition from outburst to quiescence, after it actively accreted for more than 24 yr. In a previous work, we discussed Chandra and Swift observations obtained during the first 5 months of this transition. Here, we report on further X-ray observations of EXO 0748−676, extending the quiescent monitoring to 1.6 yr. Chandra and XMM–Newton data reveal quiescent X-ray spectra composed of a soft, thermal component that is well fitted by a neutron star atmosphere model. An additional hard power-law tail is detected that changes non-monotonically over time, contributing between 4 and 20 per cent to the total unabsorbed 0.5–10 keV flux. The combined set of Chandra, XMM–Newton and Swift data reveals that the thermal bolometric luminosity fades from ∼1 × 10 34 to 6 × 10 33 (D/7.4 kpc) 2 erg s −1 , whereas the inferred neutron star effective temperature decreases from ∼124 to 109 eV. We interpret the observed decay as cooling of the neutron star crust and show that the fractional quiescent temperature change of EXO 0748−676 is markedly smaller than observed for three other neutron star X-ray binaries that underwent prolonged accretion outbursts.

Five New Millisecond Pulsars from a Radio Survey of 14 Unidentified Fermi-LAT Gamma-Ray Sources

We have discovered five millisecond pulsars (MSPs) in a survey of 14unidentified Fermi Large Area Telescope sources in the southern skyusing the Parkes radio telescope. PSRs J0101-6422, J1514-4946, andJ1902-5105 reside in binaries, while PSRs J1658-5324 and J1747-4036 areisolated. Using an ephemeris derived from timing observations of PSRJ0101-6422 (P = 2.57 ms, DM = 12 pc cm

On the nature of soft gamma repeaters

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USA Experiment and RXTE Observations of a Variable Low-Frequency Quasi-periodic Oscillation in XTE J1118+480

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Radio and X-ray states in the X-ray binary Scorpius X-1

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