Engineering topics

Wilson-Hodge, Colleen A.

Publications and source records attributed to Wilson-Hodge, Colleen A..

65 records · Page 4

NASA NTRS2010

Fermi GBM Observations of Terrestrial Gamma Flashes

In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed more than 77 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds. The energy spectra of some TGFs have strong 511 keV positron annihilation lines, indicating that these TGFs contain a large fraction of positrons

Wilson-Hodge, Colleen A.↗

NASA NTRS2010

Fermi GBM Observations of Terrestrial Gamma Flashes

In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed 79 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds.

Wilson-Hodge, Colleen A.↗

NASA NTRS2010

Fermi GBM Observations of Terrestrial Gamma-Ray Flashes

This slide presentation explores the relationship between Terrestrial Gamma-Ray Flashes (TGF) and lightning. Using data from the World-Wide Lightning Location Network (WWLLN), and the gamma ray observations from Fermi's Gamma-ray Burst Monitor (GBM), the study reviews any causal relationship between TGFs and lightning. The conclusion of the study is that the TGF and lightning are simultaneous with out a causal relationship.

Wilson-Hodge, Colleen A.↗

NASA NTRS2010

All-Sky Monitoring with the Fermi Gamma Ray Burst Monitor

We are currently monitoring the transient hard X-ray/soft gamma ray sky using the Gamma Ray Burst Monitor (GBM) on-board Fermi. The twelve GBM NaI detectors span 8 keV to 1MeV, while the two GBM BGO detectors span about 150 keV to 40 MeV. With GBM, we detect transient events on multiple timescales. Brief events, such as Gamma Ray Bursts, Solar flares, and magnetar bursts are detected with on-board triggers. On longer timescales, we use the Earth occultation technique to monitor a number of sources, including X-ray binaries, AGN, and solar flaring activity. To date we have detected 7 sources above 100 keV. Transient activity from accretion-powered pulsars is monitored using epoch-folding techniques. With GBM we track the pulsed flux and frequency for a number of pulsars. We will present highlights of GBM observations on various timescales.

Wilson-Hodge, Colleen A.↗

NASA NTRS2010

AXTAR: Mission Design Concept

The Advanced X-ray Timing Array (AXTAR) is a mission concept for X-ray timing of compact objects that combines very large collecting area, broadband spectral coverage, high time resolution, highly flexible scheduling, and an ability to respond promptly to time-critical targets of opportunity. It is optimized for sub-millisecond timing of bright Galactic X-ray sources in order to study phenomena at the natural time scales of neutron star surfaces and black hole event horizons, thus probing the physics of ultra-dense matter, strongly curved spacetimes, and intense magnetic fields. AXTAR s main instrument, the Large Area Timing Array (LATA) is a collimated instrument with 2 50 keV coverage and over 3 square meters effective area. The LATA is made up of an array of super-modules that house 2-mm thick silicon pixel detectors. AXTAR will provide a significant improvement in effective area (a factor of 7 at 4 keV and a factor of 36 at 30 keV) over the RXTE PCA. AXTAR will also carry a sensitive Sky Monitor (SM) that acts as a trigger for pointed observations of X-ray transients in addition to providing high duty cycle monitoring of the X-ray sky. We review the science goals and technical concept for AXTAR and present results from a preliminary mission design study

Ray, Paul S.↗

NASA NTRS2009

Fermi GBM: Highlights from the First Year

The Fermi Gamma ray Burst Monitor is an all-sky instrument sensitive to photons from about 8 keV to 40 MeV. I will summarize highlights from the first year, including triggered observations of gamma ray bursts, soft gamma ray repeaters, and terrestrial gamma flashes, and observations in the continuous data of X-ray binaries and accreting X-ray pulsars. GBM provides complementary observations to Swift/BAT, observing many of the same sources, but over a wider energy range.

Wilson-Hodge, Colleen A.↗

NASA NTRS2009

Fermi GBM: Results from the First Year +

Gamma-ray Burst Monitor (GBM) has performed well in the first year+. GBM triggers 353 Gamma-ray Bursts (GRBs), 168 SGR events, 18 TGFs, and 1 solar flare to date. Short GRBs appear contracted in time and shifted to higher energy than long GRBs. Pulsed persistent emission from SGR 1550-5418 detected. TGFs are shorter, have higher average photon energies, and much higher count rates than GRBs. GBM monitoring of accreting pulsars provides long-term spin-histories. GBM Earth occultation monitoring complements Swift.

Wilson-Hodge, Colleen A.↗

NASA NTRS2009

Accreting X-ray Pulsars

This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magnetic field measurements are obtained by measuring the lowest cyclotron absorption line energy, observing the cutoff of accretion due to centrifugal inhibition and measuring the spin-up rate at high luminosity.

Wilson-Hodge, Colleen A.↗

NASA NTRS2008

All Sky Observations with BATSE and GBM

The Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) monitored the entire sky from 1991-2000. I will review highlights of BATSE observations including gamma ray bursts, black hole candidates, accreting pulsars, and active galaxies. On 2008 June 11, the Fermi Gamma Ray Space Telescope was launched. The Gamma ray Burst Monitor (GBM) on board Fermi continues the all-sky monitoring legacy started with BATSE. I will review early results and planned observations with GBM.

Wilson-Hodge, Colleen A.↗

NASA NTRS2004

The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog

The hard X-ray sky was continuously monitored with the BATSE experiment on the Compton Gamma Ray observatory using the Earth Occultation method. Known sources were monitored twice every orbit and transients could be detected at about the approx. 50 mCrab level on a daily basis. I will summarize the results from our catalog of 179 monitored sources, highlighting observations of black holes and energy spectra for the 83 firmly detected sources and FITS files for all 179 sources. This web database can serve as a guide and comparison tool for future observations with EXIST.

Wilson-Hodge, Colleen A.↗

NASA NTRS2001

The Ever Changing X-ray Sky: X-ray Transients Observed With BATSE

X-ray transients are typically sources in our own galaxy. They are called "transient" because they usually spend more time in quiescence than in outburst. These transients consist of a compact object and a "normal" star in a binary system. The compact objects in some of these systems are known to be neutron stars because they exhibit X-ray bursts or periodic pulsations, Other systems are believed to contain black holes based upon their outburst behavior and in some cases, optical measurements of their masses. The Burst and Transient Source Experiment (BATSE), one of 4 instruments on the Compton Gamma Ray Observatory, was an all-sky instrument sensitive to photons from about 20 keV to 2 MeV, designed primarily to detect gamma-ray bursts. Transient and persistent hard X-ray point sources were extracted from the data using the Earth occultation method to measure source intensities. In this method, the change in count rate in a BATSE detector was measured just before and just after a source location was occulted by the Earth. For long period pulsars (>1 second) Fourier transforms and epoch-folded searches were used to measure pulse frequency and pulsed flux. Using these methods, 3 black hole candidates and 6 X-ray pulsars were discovered with BATSE during its 9 years in orbit. BATSE provided unprecedented temporal coverage in the 20 keV - 2 MeV band, allowing detection of numerous new outbursts of X-ray transients. In this talk, I will describe the BATSE instrument, discuss methods we use to detect hard X-ray sources, and describe observations of X-ray transients.

Wilson-Hodge, Colleen A.↗