A search of the SAS-2 data for pulsed gamma-ray emission from radio pulsars

Data from the SAS-2 high energy gamma ray experiment were examined for pulsed emission from each of 75 radio pulsars which were viewed by the instrument and which have sufficiently well defined period and period derivative information from radio observations to allow for gamma ray periodicity searches. When gamma ray arrival times were converted to pulsar phase using the radio reference timing information, two pulsars, PSR 1747-46 and PSR 1818-04, showed positive effects, each with a probability less than 0.0001 of being a random fluctuation in the data for that pulsar. These are in addition to PSR 0531+21 and PSR 0833-45, previously reported. The results of this study suggest that gamma-ray astronomy has reached the detection threshold for gamma ray pulsars and that work in the near future should give important information on the nature of pulsars

Recognition of compact astrophysical objects

NASA's Laboratory for High Energy Astrophysics and the Dept. of Physics and Astrophysics at the Univ. of Md. collaberated on a graduate level course with this title. This publication is an edited version of notes used as the course text. Topics include stellar evolution, pulsars, binary stars, X-ray signatures, gamma ray sources, and temporal analysis of X-ray data

ROSAT Observations of the Vela Pulsar

The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six observations span 2-1/2 years and 3 glitches. The summed data yield a determination of the pulse shape, and X-ray emission from the pulsar is found to be 12 % pulsed with one broad and two narrow peaks. One observation occurred 15 days after a large glitch. No change in pulse structure was observed and any change in X-ray luminosity, if present, was less than 3 %. Implications for neutron star structure are discussed.Comment: To be publisned in the Astrophysical Journa

XMM-Newton observations of Nova Sgr 1998

We report on X-ray observations of Nova Sagittarius 1998 (V4633 Sgr), performed with XMM-Newton at three different epochs, 934, 1083 and 1265 days after discovery. The nova was detected with the EPIC cameras at all three epochs, with emission spanning the whole energy range from 0.2 to 10 keV. The X-ray spectra do not change significantly at the different epochs, and are well fitted for the first and third observations with a multi-temperature optically thin thermal plasma, while lower statistics in the second observations lead to a poorer fit. The thermal plasma emission is most probably originated in the shock heated ejecta, with chemical composition similar to that of a CO nova. However, we can not completely rule out reestablished accretion as the origin of the emission. We also obtain upper limits for the temperature and luminosity of a potential white dwarf atmospheric component, and conclude that hydrogen burning had already turned-off by the time of our observations.Comment: 18 pages, 3 figures. Accepted in Astrophysical Journa

Variability of the Vela Pulsar-wind Nebula Observed with Chandra

The observations of the pulsar-wind nebula (PWN) around the Vela pulsar with the Advanced CCD Imaging Spectrometer aboard the Chandra X-ray Observatory, taken on 2000 April 30 and November 30, reveal its complex morphology reminiscent of that of the Crab PWN. Comparison of the two observations shows changes up to 30% in the surface brightness of the PWN features. Some of the PWN elements show appreciable shifts, up to a few arcseconds (about 10^{16} cm), and/or spectral changes. To elucidate the nature of the observed variations, further monitoring of the Vela PWN is needed.Comment: 7 pages (incl. 3 embedded PS figures), AASTEX, uses emulateapj5.sty. Submitted to ApJ Lett. For a high-resolution color PS image of Figure 3 (6.3 Mby), see http://www.astro.psu.edu/users/divas/velaneb_fig3.p

ASCA observations of the young rotation-powered pulsars PSR B1046-58 and PSR B1610-50

We present X-ray observations of two young energetic radio pulsars, PSRs B1046-58 and B1610-50, and their surroundings, using archival data from the Advanced Satellite for Cosmology and Astrophysics (ASCA). The energetic pulsar PSR B1046-58 is detected in X-rays with a significance of 4.5 sigma. The unabsorbed flux, estimated assuming a power-law spectrum and a neutral hydrogen column density N_H of 5E21 cm^-2 is (2.5 +/- 0.3) x 10E-13 ergs/cm^2/s in the 2-10 keV band. Pulsed emission is not detected; the pulsed fraction is less than 31% at the 90% confidence level for a 50% duty cycle. We argue that the emission is best explained as originating from a pulsar-powered synchrotron nebula. The X-ray counterpart of the pulsar is the only hard source within the 95% error region of the previously unidentified gamma-ray source 3EG J1048-5840. This evidence supports the results of Kaspi et al. (1999), who in a companion paper, suggest that PSR B1046-58 is the counterpart to 3EG J1048-5840. X-ray emission from PSR B1610-50 is not detected. Using similar assumptions as above, the derived 3 sigma upper limit for the unabsorbed 2-10 keV X-ray flux is 1.5E-13 ergs/cm^2/s. We use the flux limit to estimate the pulsar's velocity to be less than ~170 km/s, casting doubt on a previously reported association between PSR B1610-50 and supernova remnant Kes 32. Kes 32 is detected, as is evident from the correlation between X-ray and radio emission. The ASCA images of PSR B1610-50 are dominated by mirror-scattered emission from the X-ray-bright supernova remnant RCW 103, located 33' away. We find no evidence for extended emission around either pulsar, in contrast to previous reports of large nebulae surrounding both pulsars.Comment: Accepted for publication in the ApJ (v.528, pp.436-444) Correcting typo in abstract of .tex fil

Discovery of Gamma-ray Emission from M31 via FERMI-LAT

2 years worth of archival FERMI-LAT data was used to search for the gamma-ray emission from the Andromeda galaxy. The data show no noticeable elliptical image. Subsequent on-off source aperture photometry analysis using a CO image template show a 7 sigma excess in the number of on-source apertures in comparison to the off-source apertures, yielding a flux of (4.95+/-0.71)x10-8 photons cm-2 s-1 for E>100 MeV.Comment: 7 pages, 5 figure

Analyzing X-Ray Pulsar Profiles: Geometry and Beam Pattern of Her X-1

We report on our analysis of a large sample of energy dependent pulse profiles of the X-ray binary pulsar Hercules X-1. We find that all data are compatible with the assumption of a slightly distorted magnetic dipole field as sole cause of the asymmetry of the observed pulse profiles. Further the analysis provides evidence that the emission from both poles is equal. We determine an angle of 20 deg between the rotation axis and the local magnetic axis. One pole has an offset of 5 deg from the antipodal position of the other pole. The beam pattern shows structures that can be interpreted as pencil- and fan-beam configurations. Since no assumptions on the polar emission are made, the results can be compared with various emission models. A comparison of results obtained from pulse profiles of different phases of the 35-day cycle indicates different attenuation of the radiation from the poles being responsible for the change of the pulse shape during the main-on state. These results also suggest the resolution of an ambiguity within a previous analysis of pulse profiles of Cen X-3, leading to a unique result for the beam pattern of this pulsar as well. The analysis of pulse profiles of the short-on state indicates that a large fraction of the radiation cannot be attributed to the direct emission from the poles. We give a consistent explanation of both the evolution of the pulse profile and the spectral changes with the 35-day cycle in terms of a warped precessing accretion disk.Comment: 24 pages, 12 figures. To appear in ApJ 529 #2, 1 Feb 200