214 research outputs found
Nowcast model for lowâenergy electrons in the inner magnetosphere
We present the nowcast model for lowâenergy (<200 keV) electrons in the inner magnetosphere, which is the version of the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) for electrons. Lowâenergy electron fluxes are very important to specify when hazardous satellite surfaceâcharging phenomena are considered. The presented model provides the lowâenergy electron flux at all L shells and at all satellite orbits, when necessary. The model is driven by the realâtime solar wind and interplanetary magnetic field (IMF) parameters with 1 h time shift for propagation to the Earth's magnetopause and by the real time Dst index. Realâtime geostationary GOES 13 or GOES 15 (whenever each is available) data on electron fluxes in three energies, such as 40 keV, 75 keV, and 150 keV, are used for comparison and validation of IMPTAM running online. On average, the model provides quite reasonable agreement with the data; the basic level of the observed fluxes is reproduced. The best agreement between the modeled and the observed fluxes are found for <100 keV electrons. At the same time, not all the peaks and dropouts in the observed electron fluxes are reproduced. For 150 keV electrons, the modeled fluxes are often smaller than the observed ones by an order of magnitude. The normalized rootâmeanâsquare deviation is found to range from 0.015 to 0.0324. Though these metrics are buoyed by large standard deviations, owing to the dynamic nature of the fluxes, they demonstrate that IMPTAM, on average, predicts the observed fluxes satisfactorily. The computed binary event tables for predicting high flux values within each 1 h window reveal reasonable hit rates being 0.660â0.318 for flux thresholds of 5 ·104â2 ·105 cmâ2 sâ1 srâ1 keVâ1 for 40 keV electrons, 0.739â0.367 for flux thresholds of 3 ·104â1 ·105 cmâ2 sâ1 srâ1 keVâ1 for 75 keV electrons, and 0.485â0.438 for flux thresholds of 3 ·103â3.5 ·103 cmâ2 sâ1 srâ1 keVâ1 for 150 keV electrons but rather small Heidke Skill Scores (0.17 and below). This is the first attempt to model lowâenergy electrons in real time at 10 min resolution. The output of this model can serve as an input of electron seed population for realâtime higherâenergy radiation belt modeling.Key PointsNowcast model for lowâenergy electronsOnline nearârealâtime comparison to GOES MAGED dataFirst successful model for lowâenergy electrons in real timePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110719/1/swe20196.pd
Lowâenergy electrons (5â50 keV) in the inner magnetosphere
Transport and acceleration of the 5â50 keV electrons from the plasma sheet to geostationary orbit were investigated. These electrons constitute the lowâenergy part of the seed population for the highâenergy MeV particles in the radiation belts and are responsible for surface charging. We modeled one nonstorm event on 24â30 November 2011, when the presence of isolated substorms was seen in the AE index. We used the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) with the boundary at 10 R E with moment values for the electrons in the plasma sheet. The output of the IMPTAM modeling was compared to the observed electron fluxes in 10 energy channels (from 5 to 50 keV) measured on board the AMC 12 geostationary spacecraft by the Compact Environmental Anomaly Sensor II with electrostatic analyzer instrument. The behavior of the fluxes depends on the electron energy. The IMPTAM model, driven by the observed parameters such as Interplanetary Magnetic Field (IMF) B y and B z , solar wind velocity, number density, dynamic pressure, and the Dst index, was not able to reproduce the observed peaks in the electron fluxes when no significant variations are present in those parameters. We launched several substormâassociated electromagnetic pulses at the substorm onsets during the modeled period. The observed increases in the fluxes can be captured by IMPTAM when substormâassociated electromagnetic fields are taken into account. Modifications of the pulse front velocity and arrival time are needed to exactly match the observed enhancements. Key Points Electron flux peaks due to substorm activity Solar wind driven inner magnetosphere model does not work for quiet times Substormâassociated fields to explain electron flux peaksPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106068/1/jgra50735.pd
Implications for the origin of GRB 051103 from LIGO observations
We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed ĂÂł-ray emission with a jet semi-angle of 30Ă°, we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with \u3e99% confidence. If the event occurred in M81, then our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it one of the most distant extragalactic magnetars observed to date. Ă© 2012 The American Astronomical Society. All rights reserved
Search for gravitational waves from binary black hole inspiral merger and ringdown in LIGO-Virgo data from 2009-2010
We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20,20)MĂÂąĂ
ĂąâÂą coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28M ĂÂąĂ
ĂąâÂą of 3.3Ăâ10-7 mergers Mpc -3 yr-1. Ă© 2013 American Physical Society
All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run
We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration -1s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc3 for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range ĂąËÂŒ5Ăâ10-22Hz-1/2 to ĂąËÂŒ1Ăâ10-20Hz-1/2. The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors. Ă© 2012 American Physical Society
Search for gravitational waves from intermediate mass binary black holes
We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450M and with the component mass ratios between 11 and 41. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88+88M, for nonspinning sources, the rate density upper limit is 0.13 per Mpc3 per Myr at the 90% confidence level. Ă© 2012 American Physical Society
First low-latency LIGO+Virgo search for binary inspirals and their electromagnetic counterparts
Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results. Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data. Ă© 2012 ESO
All-sky search for periodic gravitational waves in the full S5 LIGO data
We report on an all-sky search for periodic gravitational waves in the frequency band 50-800Hz and with the frequency time derivative in the range of 0 through -6Ăâ10-9Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10Ăâ increase in computational efficiency, we have searched in two years of data collected during LIGO\u27s fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150Hz our upper limit on worst-case linearly polarized strain amplitude h0 is 1Ăâ10-24, while at the high end of our frequency range we achieve a worst-case upper limit of 3.8Ăâ10-24 for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion. Ă© 2012 American Physical Society
All-Sky Search for Periodic Gravitational Waves in the Full S5 LIGO Data
We report on an all-sky search for periodic gravitational waves in the frequency band 50-800 Hz and with the frequency time derivative in the range of 0 through -6 x 10(exp -9) Hz/s. Such a signal could be produced by a nearby spinning and slightly non-axisymmetric isolated neutron star in our galaxy. After recent improvements in the search program that yielded a 10x increase in computational efficiency, we have searched in two years of data. collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude h(sub 0) is 1 x 10(exp -24), while at the high end of our frequency ra.nge we achieve a worst-case upper limit of 3.8 x 10(exp -24) for all polarizations and sky locations. These results constitute a factor of two improvement upop. previously published data. A new detection pipeline utilizing a Loosely Coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long.period binary companion
- âŠ