Infrared to Ultraviolet Wavelength-Dependent Variations Within the Pulse Profile Peaks of the Crab Nebula Pulsar

We present evidence of wavelength-dependent variations within the infrared, optical, and ultraviolet pulse profile peaks of the Crab Nebula pulsar. The leading and trailing edge half-width half-maxima of the peaks display clear differences in their wavelength dependences. In addition, phase-resolved infrared-to-ultraviolet color spectra show significant variations from the leading to trailing edges of the peaks. The color variations between the leading and trailing edges remain significant over phase differences smaller than 0.0054, corresponding to timescales of $<180 \mu$s. These results are not predicted by any current models of the pulsar emission mechanism and offer new challenges for the development of such models.Comment: 12 pages, 4 figure

Pulsar Science with the Green Bank 43m Telescope

The 43m telescope at the NRAO site in Green Bank, WV has recently been outfitted with a clone of the Green Bank Ultimate Pulsar Processing Instrument (GUPPI \cite{Ransom:2009}) backend, making it very useful for a number of pulsar related studies in frequency ranges 800-1600 MHz and 220-440 MHz. Some of the recent science being done with it include: monitoring of the Crab pulsar, a blind search for transient sources, pulsar searches of targets of opportunity, and an all-sky mapping project. For the Crab monitoring project, regular observations are searched for giant pulses (GPs), which are then correlated with $\gamma$-ray photons from the \emph{Fermi} spacecraft. Data from the all-sky mapping project are first run through a pipeline that does a blind transient search, looking for single pulses over a DM range of 0-500 pc~cm$^{-3}$. These projects are made possible by MIT Lincoln Labs.Comment: 2 pages, 1 figure, to appear in AIP Conference Proceedings of Pulsar Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe", Sardinia, October 201

No detectable radio emission from the magnetar-like pulsar in Kes 75

The rotation-powered pulsar PSR J1846-0258 in the supernova remnant Kes 75 was recently shown to have exhibited magnetar-like X-ray bursts in mid-2006. Radio emission has not yet been observed from this source, but other magnetar-like sources have exhibited transient radio emission following X-ray bursts. We report on a deep 1.9 GHz radio observation of PSR J1846-0258 with the 100-m Green Bank Telescope in late 2007 designed to search for radio pulsations or bursts from this target. We have also analyzed three shorter serendipitous 1.4 GHz radio observations of the source taken with the 64-m Parkes telescope during the 2006 bursting period. We detected no radio emission from PSR J1846-0258 in either the Green Bank or Parkes datasets. We place an upper limit of 4.9 \mu Jy on coherent pulsed emission from PSR J1846-0258 based on the 2007 November 2 observation, and an upper limit of 27 \mu Jy around the time of the X-ray bursts. Serendipitously, we observed radio pulses from the nearby RRAT J1846-02, and place a 3\sigma confidence level upper limit on its period derivative of 1.7 * 10^{-13}, implying its surface dipole magnetic field is less than 2.6 * 10^{13} G.Comment: 15 pages, 2 figures, submitted to Ap

Is the Compact Source at the Center of Cas A Pulsed?

A 50 ksec observation of the Supernova Remnant Cas A was taken using the Chandra X-Ray Observatory High Resolution Camera (HRC) to search for periodic signals from the compact source located near the center. Using the HRC-S in imaging mode, problems with correctly assigning times to events were overcome, allowing the period search to be extended to higher frequencies than possible with previous observations. In an extensive analysis of the HRC data, several possible candidate signals are found using various algorithms, including advanced techniques developed by Ransom to search for low significance periodic signals. Of the candidate periods, none is at a high enough confidence level to be particularly favored over the rest. When combined with other information, however (e.g., spectra, total energetics, and the historical age of the remnant), a 12 ms candidate period seems to be more physically plausible than the others, and we use it for illustrative purposes in discussing the possible properties of a putative neutron star in the remnant. We emphasize that this is not necessarily the true period, and that a follow-up observation, scheduled for the fall of 2001, is required. A 50 ksec Advanced CCD Imaging Spectrometer (ACIS) observation was taken, and analysis of these data for the central object shows that the spectrum is consistent with several forms, and that the emitted X-ray luminosity in the 0.1 -10 keV band is 10^{33}-10^{35}erg cm^{-2}sec^{-1} depending on the spectral model and the interstellar absorption along the line of sight to the source.Comment: 14 pages, 3 figures Submitted to ApJ 2001 June 2

Correlation of Fermi photons with high-frequency radio giant pulses from the Crab pulsar

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov (2007) for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at gamma-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hours of simultaneous observations we obtained a sample of 2.1x10^4 giant pulses, observed at a radio frequency of 9 GHz, and 77 Fermi photons, with energies between 100 MeV and 5 GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120 s windows at lags of up to +-40 min of observed gamma-ray photons. The 95% upper limit for a gamma-ray flux enhancement in pulsed emission phase window around all GPs is 4 times the average pulsed gamma-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed gamma-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density.Comment: 9 pages, 6 figures; to appear in The Astrophysical Journal, February 201

VLA Observations of Single Pulses from the Galactic Center Magnetar

We present the results of a 7-12 GHz phased-array study of the Galactic center magnetar J1745-2900 with the Karl G. Jansky Very Large Array (VLA). Using data from two 6.5 hour observations from September 2014, we find that the average profile is comprised of several distinct components at these epochs and is stable over $\sim$day timescales and $\sim$GHz frequencies. Comparison with additional phased VLA data at 8.7 GHz shows significant profile changes on longer timescales. The average profile at 7-12 GHz is dominated by the jitter of relatively narrow pulses. The pulses in each of the four main profile components seen in September 2014 are uncorrelated in phase and amplitude, though there is a small but significant correlation in the occurrence of pulses in two of the profile components. Using the brightest pulses, we measure the dispersion and scattering parameters of J1745-2900. A joint fit of 38 pulses gives a 10 GHz pulse broadening time of $\tau_{\rm sc, 10} = 0.09 \pm 0.03~\rm ms$ and a dispersion measure of ${\rm DM} = 1760^{+2.4}_{-1.3}~{\rm pc~cm}^{-3}$. Both of these results are consistent with previous measurements, which suggests that the scattering and dispersion measure of J1745-2900 may be stable on timescales of several years.Comment: 20 pages, 10 figures, published in Ap

Pulsars in Globular Clusters with the SKA

Globular clusters are highly efficient radio pulsar factories. These pulsars can be used as precision probes of the clusters' structure, gas content, magnetic field, and formation history; some of them are also highly interesting in their own right because they probe exotic stellar evolution scenarios as well as the physics of dense matter, accretion, and gravity. Deep searches with SKA1-MID and SKA1-LOW will plausibly double to triple the known population. Such searches will only require one to a few tied-array beams, and can be done during early commissioning of the telescope - before an all-sky pulsar survey using hundreds to thousands of tied-array beams is feasible. With SKA2 it will be possible to observe most of the active radio pulsars within a large fraction of the Galactic globular clusters, an estimated population of 600 - 3700 observable pulsars (those beamed towards us). This rivals the total population of millisecond pulsars that can be found in the Galactic field; fully characterizing it will provide the best-possible physical laboratories as well as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04