Green Bank Telescope and Swift X-ray Telescope Observations of the Galactic Center Radio Magnetar SGR J1745-2900

We present results from eight months of Green Bank Telescope 8.7-GHz observations and nearly 18 months Swift X-ray telescope observations of the radio magnetar SGR J1745-2900, which is located 2.4" from Sgr A*. We tracked the magnetar's radio flux density, polarization properties, pulse profile evolution, rotation, and single-pulse behavior. We identified two main periods of activity in SGR J1745-2900. The first is characterized by approximately 5.5 months of relatively stable evolution in radio flux density, rotation, and profile shape, while in the second these properties varied substantially. Specifically, a third profile component emerged and the radio flux increased on average, but also became more variable. Bright single pulses are visible and are well described by a log-normal energy distribution at low to moderate energies, but with an excess at high energies. The 2-10 keV flux has decayed steadily since the initial X-ray outburst, in contrast with the radio flux. Our timing analysis includes Green Bank Telescope, Swift, and NuSTAR data. When we include the X-ray data in our analyses, we find that SGR J1745-2900 exhibited a level of timing noise unprecedented in a radio magnetar, though an analysis of only the radio data indicates timing noise at a level similar to that observed in other radio magnetars. We conclude that, while SGR J1745-2900 is similar to other radio magnetars in many regards, it differs by having experienced a period of relative stability in the radio band that now appears to have ended, while the X-ray properties have evolved independently.Comment: Submitted to ApJ; 10 pages (emulateapj style), 6 figures, 1 tabl

A Population Of Non-Recycled Pulsars Originating In Globular Clusters

We explore the enigmatic population of long-period, apparently non-recycled pulsars in globular clusters, building on recent work by Boyles et al. This population is difficult to explain if it formed through typical core-collapse supernovae, leading many authors to invoke electron capture supernovae. While Boyles et al. dealt only with non-recycled pulsars in clusters, we focus on the pulsars that originated in clusters but then escaped into the field of the Galaxy due to the kicks they receive at birth. The magnitude of the kick induced by electron capture supernovae is not well known, so we explore various models for the kick velocity distribution and size of the population. The most realistic models are those where the kick velocity is 10 km s–1 and where the number of pulsars scales with the luminosity of the cluster (as a proxy for cluster mass). This is in good agreement with other estimates of the electron capture supernovae kick velocity. We simulate a number of large-area pulsar surveys to determine if a population of pulsars originating in clusters could be identified as being separate from normal disk pulsars. We find that the spatial and kinematical properties of the population could be used, but only if large numbers of pulsars are detected. In fact, even the most optimistic surveys carried out with the future Square Kilometer Array are likely to detect \u3c10% of the total population, so the prospects for identifying these as a separate group of pulsars are presently poor

The Kinematic Evolution of Strong MgII Absorbers

We consider the evolution of strong (W_r(2796) > 0.3A) MgII absorbers, most of which are closely related to luminous galaxies. Using 20 high resolution quasar spectra from the VLT/UVES public archive, we examine 33 strong MgII absorbers in the redshift range 0.3 < z < 2.5. We compare and supplement this sample with 23 strong MgII absorbers at 0.4 < z < 1.4 observed previously with HIRES/Keck. We find that neither equivalent width nor kinematic spread (the optical depth weighted second moment of velocity) of MgII2796 evolve. However, the kinematic spread is sensitive to the highest velocity component, and therefore not as sensitive to additional weak components at intermediate velocities relative to the profile center. The fraction of absorbing pixels within the full velocity range of the system does show a trend of decreasing with decreasing redshift. Most high redshift systems (14/20) exhibit absorption over the entire system velocity range, which differs from the result for low redshift systems (18/36) at the 95% level. This leads to a smaller number of separate subsystems for high redshift systems because weak absorping components tend to connect the stronger regions of absorption. We hypothesize that low redshift MgII profiles are more likely to represent well formed galaxies, many of which have kinematics consistent with a disk/halo structure. High redshift MgII profiles are more likely to show evidence of complex protogalactic structures, with multiple accretion or outflow events. Although these results are derived from measurements of gas kinematics, they are consistent with hierarchical galaxy formation evidenced by deep galaxy surveys.Comment: Accepted to the Astrophysical Journa

A survey of weak MgII absorbers at redshift <z>=1.78

The exact nature of weak MgII absorbers (those with W_r(2796) < 0.3 A) is a matter of debate, but most are likely related to areas of local star formation or supernovae activity outside of giant galaxies. Using 18 QSO spectra obtained with the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT), we have conducted a survey for weak MgII absorbers at 1.4 < z < 2.4. We searched a redshift path length of 8.51, eliminating regions badly contaminated by atmospheric absorption so that the survey is close to 100% complete to W_r(2796) = 0.02 A. We found a total of 9 weak absorbers, yielding a number density of absorbers of dN/dz = 1.06 +/- 0.12 for 0.02 <= W_r(2796) < 0.3 A. Narayanan et al. (2005) found dN/dz = 1.00 +/- 0.20 at 0 < z < 0.3 and Churchill et al. (1999) found dN/dz = 1.74 +/- 0.10 at 0.4 < z < 1.4. Therefore, the population of weak MgII absorbers appears to peak at z~1. We explore the expected evolution of the absorber population subject to a changing extragalactic background radiation (EBR) from z = 0.9 to z = 1.78 (the median redshift of our survey), and find that the result is higher than the observed value. We point out that the peak epoch for weak MgII absorption at z~1 may coincide with the peak epoch of global star formation in the dwarf galaxy environment.Comment: 25 pages, 14 figures, to be published in ApJ 01 March 2006, v639,

A search for technosignatures from 14 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz

Analysis of Kepler mission data suggests that the Milky Way includes billions of Earth-like planets in the habitable zone of their host star. Current technology enables the detection of technosignatures emitted from a large fraction of the Galaxy. We describe a search for technosignatures that is sensitive to Arecibo-class transmitters located within ~420 ly of Earth and transmitters that are 1000 times more effective than Arecibo within ~13 000 ly of Earth. Our observations focused on 14 planetary systems in the Kepler field and used the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. Each source was observed for a total integration time of 5 minutes. We obtained power spectra at a frequency resolution of 3 Hz and examined narrowband signals with Doppler drift rates between +/-9 Hz/s. We flagged any detection with a signal-to-noise ratio in excess of 10 as a candidate signal and identified approximately 850 000 candidates. Most (99%) of these candidate signals were automatically classified as human-generated radio-frequency interference (RFI). A large fraction (>99%) of the remaining candidate signals were also flagged as anthropogenic RFI because they have frequencies that overlap those used by global navigation satellite systems, satellite downlinks, or other interferers detected in heavily polluted regions of the spectrum. All 19 remaining candidate signals were scrutinized and none were attributable to an extraterrestrial source.Comment: 15 pages, 5 figures, accepted for publication in the Astronomical Journa