RFI Identification and Mitigation Using Simultaneous Dual Station Observations

RFI mitigation is a critically important issue in radio astronomy using existing instruments as well as in the development of next-generation radio telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA involve multiple stations with spacings of up to a few thousands of kilometers and thus can exploit the drastically different RFI environments at different stations. As demonstrator observations and analysis for SKA-like instruments, and to develop RFI mitigation schemes that will be useful in the near term, we recently conducted simultaneous observations with Arecibo Observatory and the Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and using the mostly uncorrelated RFI between the two sites to excise RFI from several generic kinds of measurements such as giant pulses from Crab-like pulsars and weak HI emission from galaxies in bands heavily contaminated by RFI. This paper presents observations, analysis, and RFI identification and excision procedures that are effective for both time series and spectroscopy applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for publication in Radio Scienc

A Survey of 56 Mid-latitude EGRET Error Boxes for Radio Pulsars

We have conducted a radio pulsar survey of 56 unidentified gamma-ray sources from the 3rd EGRET catalog which are at intermediate Galactic latitudes (5 deg. < |b| < 73 deg.). For each source, four interleaved 35-minute pointings were made with the 13-beam, 1400-MHz multibeam receiver on the Parkes 64-m radio telescope. This covered the 95% error box of each source at a limiting sensitivity of about 0.2 mJy to pulsed radio emission for periods P > 10 ms and dispersion measures < 50 pc cm-3. Roughly half of the unidentified gamma-ray sources at |b| > 5 deg. with no proposed active galactic nucleus counterpart were covered in this survey. We detected nine isolated pulsars and four recycled binary pulsars, with three from each class being new. Timing observations suggest that only one of the pulsars has a spin-down luminosity which is even marginally consistent with the inferred luminosity of its coincident EGRET source. Our results suggest that population models, which include the Gould belt as a component, overestimate the number of isolated pulsars among the mid-latitude Galactic gamma-ray sources and that it is unlikely that Gould belt pulsars make up the majority of these sources. However, the possibility of steep pulsar radio spectra and the confusion of terrestrial radio interference with long-period pulsars (P > 200 ms) having very low dispersion measures (< 10 pc cm-3, expected for sources at a distance of less than about 1 kpc) prevent us from strongly ruling out this hypothesis. Our results also do not support the hypothesis that millisecond pulsars make up the majority of these sources. Non-pulsar source classes should therefore be further investigated as possible counterparts to the unidentified EGRET sources at intermediate Galactic latitudes.Comment: 24 pages, including 4 figures and 3 tables. Accepted for publication in Ap

Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5

We report on the determination of astrometric, spin and orbital parameters for PSR J1518+0204C, a "black widow" binary millisecond pulsar in the globular cluster M5. The accurate position and orbital parameters obtained from radio timing allowed us to search for the optical companion. By using WFC3/HST images we identified a very faint variable star (m_F390W > 24.8, m_F606W > 24.3, m_F814W > 23.1) located at only 0.25" from the pulsar's timing position. Due to its strong variability, this star is visible only in a sub-sample of images. However, the light curve obtained folding the available data with the orbital parameters of the pulsar shows a maximum at the pulsar inferior conjunction and a possible minimum at the pulsar superior conjunction. Furthermore, the shape of the optical modulation indicates a heating process possibly due to the pulsar wind. This is the first identification of an optical companion to a black widow pulsar in the dense stellar environment of a globular cluster.Comment: Accepted for publication by ApJ; 24 Pages, 5 Figures, 1 Tabl

Twenty-One Millisecond Pulsars in Terzan 5 Using the Green Bank Telescope

We have discovered 21 millisecond pulsars (MSPs) in the globular cluster Terzan 5 using the Green Bank Telescope, bringing the total of known MSPs in Terzan 5 to 24. These discoveries confirm fundamental predictions of globular cluster and binary system evolution. Thirteen of the new MSPs are in binaries, of which two show eclipses and two have highly eccentric orbits. The relativistic periastron advance for the two eccentric systems indicates that at least one of these pulsars has a mass >1.68 Msun at 95% confidence. Such large neutron star masses constrain the equation of state of matter at or beyond the nuclear equilibrium density.Comment: 12 pages, 2 figures. Accepted by Science. Published electronically via Science Express 13 Jan 200

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

A Strong Upper Limit on the Pulsed Radio Luminosity of the Compact Object 1RXS J141256.0+792204

The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as a likely compact object whose properties suggest it could be a very nearby radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by searching for radio pulsations using the Westerbork Synthesis Radio Telescope. We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time and frequency resolution in order to maintain sensitivity to millisecond pulsations. These data were searched both for dispersed single pulses and using Fourier techniques sensitive to constant and orbitally modulated periodicities. No radio pulsations were detected in these observations, resulting in pulsed radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03 (d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable radio pulsations from 1RXS J141256.0+792204 brings into question its identification as a nearby radio pulsar, though, because the pulsar could be beamed away from us, this hypothesis cannot be strictly ruled out.Comment: To appear in A&A. 3 page