752 research outputs found
A mercuric detector system for X-ray astronomy. 2. Results from flight tests of a balloon borne instrument
To establish the expected sensitivity of a new hard X-ray telescope design, an experiment was conducted to measure the background counting rate at balloon altitudes (40 km) of mercuric iodide, a room temperature solid state X-ray detector. The prototype detector consisted of two thin mercuric iodide (HgI2) detectors surrounded by a large bismuth germanate (Bi4Ge3O12) scintillator operated in anticoincidence. The bismuth germanate shield vetoed most of the background counting rate induced by atmospheric gamma-rays, neutrons and cosmic rays. A balloon-borne gondola containing a prototype detector assembly was designed, constructed and flown twice in the spring of 1982 from Palestine, Texas. The second flight of this instrument established a differential background counting rate of 4.2 O.7 x 10-5 counts/sec cm keV over the energy range of 40 to 80 keV. This measurement was within 50% of the predicted value. The measured rate is approx 5 times lower than previously achieved in shielded NaI/CsI or Ge systems operating in the same energy range. The prediction was based on a Monte Carlo simulation of the detector assembly in the radiation environment at float altitude
BATSE Observations of Gamma-Ray Burst Tails
I discuss in this paper the phenomenon of post-burst emission in BATSE
gamma-ray bursts at energies traditionally associated with prompt emission. By
summing the background-subtracted signals from hundreds of bursts, I find that
tails out to hundreds of seconds after the trigger may be a common feature of
long events (duration greater than 2s), and perhaps of the shorter bursts at a
lower and shorter-lived level. The tail component appears independent of both
the duration (within the long GRB sample) and brightness of the prompt burst
emission, and may be softer. Some individual bursts have visible tails at
gamma-ray energies and the spectrum in at least a few cases is different from
that of the prompt emission.Comment: 33 Pages from LaTex including 7 figures, with aastex. To appear in
Astrophysical Journa
Previously Claimed(/Unclaimed) X-ray Emission Lines in High Resolution Afterglow Spectra
We review the significance determination for emission lines in the Chandra
HETGS spectrum for GRB020813, and we report on a search for additional lines in
high resolution Chandra spectra. No previously unclaimed features are found. We
also discuss the significance of lines sets reportedly discovered using XMM
data for GRB011211 and GRB030227. We find that these features are likely of
modest, though not negligible, significance.Comment: 4 pages, 1 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Chandra Observations of the Optically Dark GRB030528
The X-ray-rich GRB030528 was detected by the HETE satellite and its
localization was rapidly disseminated. However, early optical observations
failed to detect a counterpart source. In a 2-epoch ToO observation with
Chandra, we discovered a fading X-ray source likely counterpart to GRB030528.
The source brightness was typical of X-ray afterglows observed at similar
epochs. Other observers detected an IR source at a location consistent with the
X-ray source. The X-ray spectrum is not consistent with a large absorbing
column.Comment: 4 pages, 1 figures, to appear in Santa Fe GRB Conference Proceedings,
200
TESS Discovery of an Ultra-short-period Planet around the Nearby M Dwarf LHS 3844
Data from the newly commissioned Transiting Exoplanet Survey Satellite has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of 1.303 ± 0.022 R⊕ and orbits the star every 11 hr. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy
Optical and X-ray Observations of the Afterglow to XRF030723
The X-ray-flash XRF030723 was detected by the HETE satellite and rapidly
disseminated, allowing for an optical transient to be detected ~1 day after the
burst. We discuss observations in the optical with Magellan, which confirmed
the fade of the optical transient. In a 2-epoch ToO observation with Chandra,
we discovered a fading X-ray source spatially coincident with the optical
transient. We present spectral fits to the X-ray data. We also discuss the
possibility that the source underwent a rebrightening in the X-rays, as was
observed in the optical. We find that the significance of a possible
rebrightening is very low (~1 sigma).Comment: 4 pages, 2 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Searching for Gravitational-Wave Counterparts using the Transiting Exoplanet Survey Satellite
In 2017, the LIGO and Virgo gravitational wave (GW) detectors, in conjunction
with electromagnetic (EM) astronomers, observed the first GW multi-messenger
astrophysical event, the binary neutron star (BNS) merger GW170817. This marked
the beginning of a new era in multi-messenger astrophysics. To discover further
GW multi-messenger events, we explore the synergies between the Transiting
Exoplanet Survey Satellite (TESS) and GW observations triggered by the
LIGO-Virgo-KAGRA Collaboration (LVK) detector network. TESS's extremely wide
field of view of ~2300 deg^2 means that it could overlap with large swaths of
GW localizations, which can often span hundreds of deg^2 or more. In this work,
we use a recently developed transient detection pipeline to search TESS data
collected during the LVK's third observing run, O3, for any EM counterparts. We
find no obvious counterparts brighter than about 17th magnitude in the TESS
bandpass. Additionally, we present end-to-end simulations of BNS mergers,
including their detection in GWs and simulations of light curves, to identify
TESS's kilonova discovery potential for the LVK's next observing run (O4). In
the most optimistic case, TESS will observe up to one GW-found BNS merger
counterpart per year. However, TESS may also find up to five kilonovae which
did not trigger the LVK network, emphasizing that EM-triggered GW searches may
play a key role in future kilonova detections. We also discuss how TESS can
help place limits on EM emission from binary black hole mergers, and rapidly
exclude large sky areas for poorly localized GW events.Comment: 16 pages, 7 figures, 2 tables. Submitted to AAS Journal
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