Pulsar Discovery by Global Volunteer Computing Knispel, B; Allen, B; Cordes, J.M ...
Science (American Association for the Advancement of Science),
09/2010, Letnik:
329, Številka:
5997
Journal Article
Recenzirano
Odprti dostop
Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to mine large data sets. It has now found a 40.8-hertz isolated pulsar in radio survey data from ...the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.
ABSTRACT We present Clusterrank, a new algorithm for identifying dispersed astrophysical pulses. Such pulses are commonly detected from Galactic pulsars and rotating radio transients (RRATs), which ...are neutron stars with sporadic radio emission. More recently, isolated, highly dispersed pulses dubbed fast radio bursts (FRBs) have been identified as the potential signature of an extragalactic cataclysmic radio source distinct from pulsars and RRATs. Clusterrank helped us discover 14 pulsars and 8 RRATs in data from the Arecibo 327 MHz Drift Pulsar Survey (AO327). The new RRATs have DMs in the range 23.5-86.6 pc cm−3 and periods in the range 0.172-3.901 s. The new pulsars have DMs in the range 23.6-133.3 pc cm−3 and periods in the range 1.249-5.012 s, and include two nullers and a mode-switching object. We estimate an upper limit on the all-sky FRB rate of 105 day−1 for bursts with a width of 10 ms and flux density 83 mJy. The DMs of all new discoveries are consistent with a Galactic origin. In comparing statistics of the new RRATs with sources from the RRATalog, we find that both sets are drawn from the same period distribution. In contrast, we find that the period distribution of the new pulsars is different from the period distributions of canonical pulsars in the ATNF catalog or pulsars found in AO327 data by a periodicity search. This indicates that Clusterrank is a powerful complement to periodicity searches and uncovers a subset of the pulsar population that has so far been underrepresented in survey results and therefore in Galactic pulsar population models.
We present the discovery of the Vela-like radio pulsar J1856+0245 in the Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81 ms, a characteristic age of 21 kyr, and a spin-down luminosity E ...= 4.6 x 10 super(36) ergs s sub(-1). It is positionally coincident with the TeV gamma -ray source HESS J1857+026, which has no other known counterparts. Young, energetic pulsars create wind nebulae, and more than a dozen pulsar wind nebulae have been associated with very high energy (100 GeV-100 TeV) gamma -ray sources discovered with the HESS telescope. The gamma -ray emission seen from HESS J1857+026 is potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint X-ray emission detected by ASCA at the pulsar's position supports this hypothesis. The inferred gamma -ray efficiency is = / =3.1% (1-10 TeV, for a distance of 9 kpc), comparable to that observed in similar associations.
ABSTRACT We compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9 year data set from the North American Nanohertz Observatory for ...Gravitational Waves (NANOGrav) collaboration. Well-tested Bayesian techniques are used to set upper limits on the dimensionless strain amplitude (at a frequency of 1 yr−1) for a GWB from supermassive black hole binaries of A gw < 1.5 × 10 − 15 . We also parameterize the GWB spectrum with a broken power-law model by placing priors on the strain amplitude derived from simulations of Sesana and McWilliams et al. Using Bayesian model selection we find that the data favor a broken power law to a pure power law with odds ratios of 2.2 and 22 to one for the Sesana and McWilliams prior models, respectively. Using the broken power-law analysis we construct posterior distributions on environmental factors that drive the binary to the GW-driven regime including the stellar mass density for stellar-scattering, mass accretion rate for circumbinary disk interaction, and orbital eccentricity for eccentric binaries, marking the first time that the shape of the GWB spectrum has been used to make astrophysical inferences. Returning to a power-law model, we place stringent limits on the energy density of relic GWs, gw ( f ) h 2 < 4.2 × 10 − 10 . Our limit on the cosmic string GWB, gw ( f ) h 2 < 2.2 × 10 − 10 , translates to a conservative limit on the cosmic string tension with G < 3.3 × 10 − 8 , a factor of four better than the joint Planck and high-l cosmic microwave background data from other experiments.
We present an analysis of high-precision pulsar timing data taken as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We have observed 17 pulsars for a ...span of roughly five years using the Green Bank and Arecibo radio telescopes. We analyze these data using standard pulsar timing models, with the addition of time-variable dispersion measure and frequency-variable pulse shape terms. Sub-microsecond timing residuals are obtained in nearly all cases, and the best rms timing residuals in this set are ~30-50 ns. We present methods for analyzing post-fit timing residuals for the presence of a gravitational wave signal with a specified spectral shape. These optimally take into account the timing fluctuation power removed by the model fit, and can be applied to either data from a single pulsar, or to a set of pulsars to detect a correlated signal. We apply these methods to our data set to set an upper limit on the strength of the nHz-frequency stochastic supermassive black hole gravitational wave background of h sub(c)(1 yr super(-1)) < 7 x 10 super(-15) (95%). This result is dominated by the timing of the two best pulsars in the set, PSRs J1713+0747 and J1909-3744.
This paper summarizes a search for radio-wavelength counterparts to candidate gravitational-wave events. The identification of an electromagnetic counterpart could provide a more complete ...understanding of a gravitational-wave event, including such characteristics as the location and the nature of the progenitor. We used the Expanded Very Large Array (EVLA) to search six galaxies which were identified as potential hosts for two candidate gravitational-wave events. We summarize our procedures and discuss preliminary results.
Traditional astronomy has focused on properties of the steady-state universe. Recent discoveries of strong, isolated radio pulses have, however, invigorated interest in transient phenomena. These ...radio transient events are rare, necessitating long observing times to give reasonable statistics. The National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) Deep Space Network (DSN) tracks spacecraft continuously with several large antennas having low system noise temperature. The DSN also returns substantial predetection bandwidth from the antennas (400 MHz at X-band), currently processing only a fraction of that band for spacecraft tracking. This unused wideband capability is ideal for study of the radio transient sky. Here we describe and show initial performance results of a prototype receiver to search for such transients. This prototype is implemented as a firmware change in an operational DSN tracking receiver and can thus run in parallel with operational spacecraft tracks using existing spare receiver hardware. An operational version of this system could be deployed throughout the DSN to acquire data over extended periods and substantially improve the statistics of rare radio transient events.
PDF
