D. J. Macomb

Point sources of GeV gamma rays

A catalog of c-ray sources based on photons with energies greater than 1 GeV has been developed from observations taken by the EGRET instrument of the Compton Gamma Ray Observatory. The data are taken from the 4.5 yr of observation available in the public data archives. We emphasize sources that are detected using the entire database, without regard to any possible transient or variable behavior. Ten of the 57 sources reported here have not previously been reported in the catalogs developed using photons above 100 MeV in energy. Twenty-seven sources have identiÐcations with objects seen at other wavelengths: the Large Magellanic Cloud, Ðve pulsars, and 21 blazars. The remaining 30 sources are classiÐed as unidentiÐed; however, seven may be associated with Galactic supernova remnants and one source may be a Galactic X-ray binary (LSI 61 303). The 30 unidentiÐed sources are distributed nearly uniformly along the Galactic plane and are symmetric about it. Only one of the unidentiÐed sources has a Galactic latitude in excess of 30i, whereas, if the sources were distributed uniformly, D12 would be expected on the basis of the combined EGRET exposure. A scatter plot of the Nux from the unidentiÐed sources versus Galactic latitude reveals two rather distinct categories of source: ““ bright II sources with Nuxes greater than or equal to 4.0]10~8 photons cm~2 s~1 and ““ dim II sources with Nuxes of less than 4.0]10~8 photons cm~2 s~1. The absence of high-latitude bright sources is striking. The bright unidentiÐed sources have an average Galactic latitude of 2i.7, which is consistent with a Population I distribution at distances of 1E5 kpc. The dim unidentiÐed sources have a broader latitude distribution with an average o b o\13i.8, indicating that if they are at the same average distance from the Galactic plane as the bright sources, they are paradoxically approximately 5 times closer than the bright objects on average and therefore roughly 2 orders of magnitude less luminou

Rossi X-Ray Timing Explorer Absolute Timing Results for the Pulsars B1821–24 and B1509–58

Observations with the Rossi X-Ray Timing Explorer and the Jodrell Bank, Parkes, and Green Bank telescopes have enabled us to determine the time delay between radio and X-ray pulses in the two isolated pulsars B1821-24 and B1509-58. For the former we find that the narrow X-ray and radio pulse components are close to being coincident in time, with the radio peak leading by 0.02 period (60 ± 20 μs), while the wide X-ray pulse component lags the last of the two wider radio components by about 0.08 period. For the latter pulsar we find, using the standard value for the dispersion measure, that the X-ray pulse lags the radio by about 0.27 period, with no evidence for any energy dependence in the range 2-100 keV. However, uncertainties in the history of the dispersion measure for this pulsar make a comparison to previous results difficult. It is clear that there are no perceptible variations in either the lag or the dispersion measure at timescales of a year or less.

The x-ray spectrum of the plerionic system psr b1509-58/msh 15-52

We present the results of observations of the PSR B1509

High-Energy Spectral and Temporal Characteristics of GRO J1008–57

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Discovery of Pulsed X-Ray Emission from the Small Magellanic Cloud Transient RX J0117.6–7330

58/MSH 15

DISCOVERY OF PULSED X-RAYS FROM THE SMC TRANSIENT RX J0052.1(7319

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A Gamma-Ray Flare from PKS 2255–282

52 system in X-rays (

A Search for Radio-quiet Gamma-Ray Pulsars

2-250

Addendum: “Discovery of a Possible Anomalous X-Ray Pulsar in the Small Magellanic Cloud” (ApJ, 574, L29 [2002])

keV) by the Rossi X-ray Timing Explorer. The spectra of the peak of the pulsed component (radio phase

Absolute Timing of X-Ray Emission from Pulsars with RXTE

0.17-0.53