537 research outputs found
An improved redshift indicator for Gamma-Ray Bursts, based on the prompt emission
We propose an improved version of the redshift indicator developed by Atteia
(2003), which gets rid of the dependence on the burst duration and provides
better estimates for high-redshift GRBs. We present the derivation and the
definition of this redshift indicator, then its calibration with 17 GRBs with
known redshifts detected by HETE-2 and 2 more detected by Konus-Wind. We also
provide an estimation of the redshift for 59 bursts, and we finally discuss the
redshift distribution of HETE-bursts and the possible other applications of
this redshift indicator.Comment: To appear in the proceedings of the 16th Annual October Astrophysics
Conference in Maryland, "Gamma Ray Bursts in the Swift Era", Washington DC.,
November 29-December 2, 2005, 4 pages, 3 figure
The Space System for the High Energy Transient Experiment
The High Energy Transient Experiment (HETE) is an astrophysics project funded by NASA and led by the Center for Space Research (CSR) at the Massachusetts Institute of Technology (MIT). It has for principal goal the detection and precise localization of the still mysterious sources of gamma ray bursts. The project is original in many respects. HETE will provide simultaneous observations of bursts in the gamma, X-ray and UV ranges from the same small (250 Ibms) space platform. A network of ground stations around the world will diffuse in real time key information derived from HETE observations to many ground observatories, allowing quick follow-on observations with ground instruments. The whole project is entirely managed by MIT, under top level NASA supervision, and satellite and ground stations will be remotely operated from CSA. The HETE system development is conducted with a small budget and under a short schedule
Event-driven charge-coupled device design and applications therefor
An event-driven X-ray CCD imager device uses a floating-gate amplifier or other non-destructive readout device to non-destructively sense a charge level in a charge packet associated with a pixel. The output of the floating-gate amplifier is used to identify each pixel that has a charge level above a predetermined threshold. If the charge level is above a predetermined threshold the charge in the triggering charge packet and in the charge packets from neighboring pixels need to be measured accurately. A charge delay register is included in the event-driven X-ray CCD imager device to enable recovery of the charge packets from neighboring pixels for accurate measurement. When a charge packet reaches the end of the charge delay register, control logic either dumps the charge packet, or steers the charge packet to a charge FIFO to preserve it if the charge packet is determined to be a packet that needs accurate measurement. A floating-diffusion amplifier or other low-noise output stage device, which converts charge level to a voltage level with high precision, provides final measurement of the charge packets. The voltage level is eventually digitized by a high linearity ADC
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
Quick-Look Pipeline Light Curves for 5.7 Million Stars Observed Over the Second Year of TESS' First Extended Mission
We present High-Level Science Products (HLSPs) containing light curves from
MIT's Quick-Look Pipeline (QLP) from the second year of TESS' first Extended
Mission (Sectors 40 - 55; 2021 July - 2022 September). In total, 12.2 million
per-sector light curves for 5.7 million unique stars were extracted from
10-minute cadence Full-Frame Images (FFIs) and are made available to the
community. As in previous deliveries, QLP HLSPs include both raw and detrended
flux time series for all observed stars brighter than TESS magnitude T = 13.5
mag. Starting in Sector 41, QLP also produces light curves for select fainter M
dwarfs. QLP has provided the community with one of the largest sources of
FFI-extracted light curves to date since the start of the TESS mission.Comment: 3 pages, 1 figur
Particle formation and surface processes on atmospheric aerosols: a review of applied quantum chemical calculations
Aerosols significantly influence atmospheric processes such as cloud nucleation, het- erogeneous chemistry, and heavy-metal transport in the troposphere. The chemical and physical complexity of atmospheric aerosols results in large uncertainties in their climate and health effects. In this article, we review recent advances in scientific understanding of aerosol processes achieved by the application of quantum chemical calculations. In particular, we emphasize recent work in two areas: new particle for- mation and heterogeneous processes. Details in quantum chemical methods are pro- vided, elaborating on computational models for prenucleation, secondary organic aerosol formation, and aerosol interface phenomena. Modeling of relative humidity effects, aerosol surfaces, and chemical kinetics of reaction pathways is discussed. Because of their relevance, quantum chemical calculations and field and laboratory experiments are compared. In addition to describing the atmospheric relevance of the computational models, this article also presents future challenges in quantum chemical calculations applied to aerosols
Time-resolved X-ray spectral modeling of an intermediate burst from SGR1900+14 observed by HETE-2/FREGATE and WXM
We present a detailed analysis of a 3.5 s long burst from SGR 1900+14 that occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well described by the sum of two blackbodies whose temperatures are approximately 4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fitted by the sum of two blackbodies. The higher temperature blackbody evolves with time in a manner consistent with a shrinking emitting surface. The interpretation of these results in the context of the magnetar model suggests that the two-blackbody fit is an approximation of an absorbed, multitemperature spectrum expected on theoretical grounds rather than a physical description of the emission. If this is indeed the case, our data provide further evidence for a strong magnetic field and indicate that the entire neutron star was radiating during most of the burst duration
Securing the legacy of TESS through the care and maintenance of TESS planet ephemerides
Much of the science from the exoplanets detected by the TESS mission relies
on precisely predicted transit times that are needed for many follow-up
characterization studies. We investigate ephemeris deterioration for simulated
TESS planets and find that the ephemerides of 81% of those will have expired
(i.e. 1 mid-transit time uncertainties greater than 30 minutes) one
year after their TESS observations. We verify these results using a sample of
TESS planet candidates as well. In particular, of the simulated planets that
would be recommended as JWST targets by Kempton et al. (2018), 80% will
have mid-transit time uncertainties 30 minutes by the earliest time JWST
would observe them. This rapid deterioration is driven primarily by the
relatively short time baseline of TESS observations. We describe strategies for
maintaining TESS ephemerides fresh through follow-up transit observations. We
find that the longer the baseline between the TESS and the follow-up
observations, the longer the ephemerides stay fresh, and that 51% of simulated
primary mission TESS planets will require space-based observations. The
recently-approved extension to the TESS mission will rescue the ephemerides of
most (though not all) primary mission planets, but the benefits of these new
observations can only be reaped two years after the primary mission
observations. Moreover, the ephemerides of most primary mission TESS planets
(as well as those newly discovered during the extended mission) will again have
expired by the time future facilities such as the ELTs, Ariel and the possible
LUVOIR/OST missions come online, unless maintenance follow-up observations are
obtained.Comment: 16 pages, 10 figures, accepted to AJ; main changes are cross-checking
results against the sample of real TOIs, and addressing the impact of the
TESS extended missio
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