Calibration of X-ray absorption in our Galaxy
01 May 2013-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 431, Iss: 1, pp 394-404
TL;DR: In this paper, a simple function, dependent on the product of the atomic hydrogen column density, N(HI), and dust extinction, E(B-V), was derived to estimate the variation of the molecular hydrogen column densities over the sky.
Abstract: Prediction of the soft X-ray absorption along lines of sight through our Galaxy is crucial for understanding the spectra of extragalactic sources, but requires a good estimate of the foreground column density of photoelectric absorbing species. Assuming uniform elemental abundances this reduces to having a good estimate of the total hydrogen column density, N(Htot)=N(HI)+2N(H2). The atomic component, N(HI), is reliably provided using the mapped 21 cm radio emission but estimating the molecular hydrogen column density, N(H2), expected for any particular direction, is difficult. The X-ray afterglows of GRBs are ideal sources to probe X-ray absorption in our Galaxy because they are extragalactic, numerous, bright, have simple spectra and occur randomly across the entire sky. We describe an empirical method, utilizing 493 afterglows detected by the Swift XRT, to determine N(Htot) through the Milky Way which provides an improved estimate of the X-ray absorption in our Galaxy and thereby leads to more reliable measurements of the intrinsic X-ray absorption and, potentially, other spectral parameters, for extragalactic X-ray sources. We derive a simple function, dependent on the product of the atomic hydrogen column density, N(HI), and dust extinction, E(B-V), which describes the variation of the molecular hydrogen column density, N(H2), of our Galaxy, over the sky. Using the resulting N(Htot) we show that the dust-to-hydrogen ratio is correlated with the carbon monoxide emission and use this ratio to estimate the fraction of material which forms interstellar dust grains. Our resulting recipe represents a significant revision in Galactic absorption compared to previous standard methods, particularly at low Galactic latitudes.
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TL;DR: In this article, the authors present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands.
Abstract: We present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands. These afterglow observations have uncovered 71 X-ray detections, 30 optical/NIR detections, and 4 radio detections. Employing the standard afterglow synchrotron model, we perform joint probability analyses for a subset of 38 short GRBs with well-sampled light curves to infer the burst isotropic-equivalent energies and circumburst densities. For this subset, we find median isotropic-equivalent gamma-ray and kinetic energies of E_gamma,iso~2x10^51 erg, and E_K,iso~(1-3)x10^51 erg, respectively, depending on the values of the model input parameters. We further find that short GRBs occur in low-density environments, with a median density of n~(3-15)x10^-3 cm^-3, and that ~80-95% of bursts have densities of less than 1 cm^-3. We investigate trends between the circumburst densities and host galaxy properties, and find that events located at large projected offsets of >10 effective radii from their hosts exhibit particularly low densities of n<10^-4 cm^-3, consistent with an IGM-like environment. Using late-time afterglow data for 11 events, we find a median jet opening angle of theta_jet=16+/-10 deg. We also calculate a median beaming factor of f_b~0.04, leading to a beaming-corrected total energy release of E_true~1.6x10^50 erg. Furthermore, we calculate a beaming-corrected event rate of R_true=270 (+1580,-180) Gpc^-3 yr^-1, or ~8 (+47,-5) yr^-1 within a 200 Mpc volume, the Advanced LIGO/Virgo typical detection distance for NS-NS binaries.
498 citations
TL;DR: In this article, the authors present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands.
Abstract: We present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands. These afterglow observations have uncovered 71 X-ray detections, 30 optical/NIR detections, and 4 radio detections. Employing the standard afterglow synchrotron model, we perform joint probability analyses for a subset of 38 short GRBs with well-sampled light curves to infer the burst isotropic-equivalent energies and circumburst densities. For this subset, we find median isotropic-equivalent gamma-ray and kinetic energies of E_gamma,iso~2x10^51 erg, and E_K,iso~(1-3)x10^51 erg, respectively, depending on the values of the model input parameters. We further find that short GRBs occur in low-density environments, with a median density of n~(3-15)x10^-3 cm^-3, and that ~80-95% of bursts have densities of less than 1 cm^-3. We investigate trends between the circumburst densities and host galaxy properties, and find that events located at large projected offsets of >10 effective radii from their hosts exhibit particularly low densities of n<10^-4 cm^-3, consistent with an IGM-like environment. Using late-time afterglow data for 11 events, we find a median jet opening angle of theta_jet=16+/-10 deg. We also calculate a median beaming factor of f_b~0.04, leading to a beaming-corrected total energy release of E_true~1.6x10^50 erg. Furthermore, we calculate a beaming-corrected event rate of R_true=270 (+1580,-180) Gpc^-3 yr^-1, or ~8 (+47,-5) yr^-1 within a 200 Mpc volume, the Advanced LIGO/Virgo typical detection distance for NS-NS binaries.
439 citations
Cites background from "Calibration of X-ray absorption in ..."
...…the X-ray spectrum for each burst to an absorbed power law model characterized by photon index,Γ, and the intrinsic neutral hydrogen absorption column,NH,int, in excess of the Galactic column density in the direction of the burst (Kalberla et al. 2005; Wakker et al. 2011; Willingale et al. 2013)....
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TL;DR: The 1SXPS (Swift-XRT Point Source) catalog of 151,524 X-ray point-sources detected by the Swift XRT in 8 years of operation is presented in this paper.
Abstract: We present the 1SXPS (Swift-XRT Point Source) catalog of 151,524 X-ray point-sources detected by the Swift-XRT in 8 years of operation. The catalog covers 1905 square degrees distributed approximately uniformly on the sky. We analyze the data in two ways. First we consider all observations individually, for which we have a typical sensitivity of 3 10 13 erg cm 2 s 1 (0.3{10 keV). Then we co-add all data covering the same location on the sky: these images have a typical sensitivity of 9 10 14 erg cm 2 s 1 (0.3{10 keV). Our sky coverage is nearly 2.5 times that of 3XMM-DR4, although the catalog is a factor of 1.5 less sensitive. The median position error is 5.5 00 (90% condence), including systematics. Our source detection method improves on that used in previous XRT catalogs and we report > 68; 000 new X-ray sources. The goals and observing strategy of the Swift satellite allow us to probe source variability on multiple timescales, and we nd 30; 000 variable objects in our catalog. For every source we give positions, uxes, time series (in four energy bands and two hardness ratios), estimates of the spectral properties, spectra and spectral ts for the brightest sources, and variability probabilities in multiple energy bands and timescales. Subject headings: Catalogs { Surveys { X-rays: general { Methods: data analysis
182 citations
Northwestern University1, Columbia University2, Ohio University3, University of Tartu4, University of Maryland, College Park5, California Institute of Technology6, University of Geneva7, Massachusetts Institute of Technology8, University of California, Berkeley9, INAF10, Purdue University11, York University12, Harvard University13, Moscow State University14, University of Tübingen15, University of Ferrara16, European Space Research and Technology Centre17, University of Edinburgh18, National Radio Astronomy Observatory19, Carnegie Institution for Science20, University of Toronto21, New York University22
TL;DR: In this paper, the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ~100 days were presented.
Abstract: We present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ~100 days. AT 2018cow rose over a few days to a peak luminosity L_(pk) ~ 4 × 10^(44) erg s^(−1), exceeding that of superluminous supernovae (SNe), before declining as L ∝ t^(−2). Initial spectra at δt ≾ 15 days were mostly featureless and indicated large expansion velocities v ~ 0.1c and temperatures reaching T ~ 3 × 10^4 K. Later spectra revealed a persistent optically thick photosphere and the emergence of H and He emission features with v ~ 4000 km s^(−1) with no evidence for ejecta cooling. Our broadband monitoring revealed a hard X-ray spectral component at E ≥ 10 keV, in addition to luminous and highly variable soft X-rays, with properties unprecedented among astronomical transients. An abrupt change in the X-ray decay rate and variability appears to accompany the change in optical spectral properties. AT 2018cow showed bright radio emission consistent with the interaction of a blast wave with v_(sh) ~ 0.1c with a dense environment (M ~ 10^(-3) – 10^(-4) M⊙
Yr^(-1) for v w = 1000 km s−1). While these properties exclude ^(56)Ni-powered transients, our multiwavelength analysis instead indicates that AT 2018cow harbored a "central engine," either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. The engine released ~10^(50)–10^(51.5) erg over ~10^3–10^5 s and resides within low-mass fast-moving material with equatorial–polar density asymmetry (M_(ej,fast) ≾ 0.3 M ☉). Successful SNe from low-mass H-rich stars (like electron-capture SNe) or failed explosions from blue supergiants satisfy these constraints. Intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations.
175 citations
Cites methods from "Calibration of X-ray absorption in ..."
...The shortest allowed variability time ∆t if the ejecta covers a large frac- 14 Further Coulomb heating of the electrons by ions downstream of the shock (e.g., Katz et al. 2011) is inefficient given the low densities of the forward shock. tion of the solid angle is the light crossing time, which for shock of radius rsh = vsht with vsh ≈ 0.1 − 0.2c (§3.2.1) is constrained to obey ∆t t & rsh ct ∼ vsh c ≈ 0.1 − 0.2 (20) We measure the properties of the X-ray flares in AT 2018cow following the same procedure as is used for long GRBs, adopting a Norris et al. (2005) profile....
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...We use p = 2.5 and explore the parameter space for two jets of θ j = 5◦ and θ j = 30◦, representative of strongly collimated and less collimated outflows, respectively (as found for normal GRBs and low-energy GRBs, (e.g., Racusin et al. 2009; Ryan et al. 2015; Margutti et al. 2013b)....
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...Margalit et al. (2018) show that the central engine jet can escape homologously expanding ejecta if the energy of the jet exceeds a critical value Ej & 0.195(γj/2)−4Ek,0 ∼ 1049 − 1050erg (26) where Ek,0 & 1051 erg is the initial kinetic energy of the explosion and γj is the jet Lorentz factor while propagating through the star (values γj ∼ 2 − 3 are required to produce jet opening angles similar to GRBs, Mizuta & Ioka 2013)....
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...With a different method based on X-ray afterglows of GRBs, Willingale et al. (2013) estimate NH,MW = 0.07× 1022 cm−2....
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TL;DR: In this article, the authors quantify the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements.
Abstract: Context. Robust X-ray temperature measurements of the intracluster medium (ICM) of galaxy clusters require an accurate energy-dependent effective area calibration. Since the hot gas X-ray emission of galaxy clusters does not vary on relevant timescales, they are excellent cross-calibration targets. Moreover, cosmological constraints from clusters rely on accurate gravitational mass estimates, which in X-rays strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological constraints. This is of special interest in light of the tension between the Planck results of the primary temperature anisotropies of the cosmic microwave background (CMB) and Sunyaev-Zel’dovich-plus-X-ray cluster-count analyses.Aims. We quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra , and the influence on temperature measurements. Furthermore, we assess the impact of the cross-calibration uncertainties on cosmology.Methods. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM temperatures through spectral fitting in the same, mostly isothermal regions and compare the different instruments. We use the stacked residual ratio method to evaluate the cross-calibration uncertainties between the instruments as a function of energy. Our work is an extension to a previous one using X-ray clusters by the International Astronomical Consortium for High Energy Calibration (IACHEC) and is carried out in the context of IACHEC.Results. Performing spectral fitting in the full energy band, (0.7−7) keV, as is typical of the analysis of cluster spectra, we find that best-fit temperatures determined with XMM-Newton /EPIC are significantly lower than Chandra /ACIS temperatures. This confirms the previous IACHEC results obtained with older calibrations with high precision. The difference increases with temperature, and we quantify this dependence with a fitting formula. For instance, at a cluster temperature of 10 keV, EPIC temperatures are on average 23% lower than ACIS temperatures. We also find systematic differences between the three XMM-Newton /EPIC instruments, with the PN detector typically estimating the lowest temperatures. Testing the cross-calibration of the energy-dependence of the effective areas in the soft and hard energy bands, (0.7−2) keV and (2−7) keV, respectively, we confirm the previously indicated relatively good agreement between all instruments in the hard and the systematic differences in the soft band. We provide scaling relations to convert between the different instruments based on the effective area, gas temperature, and hydrostatic mass. We demonstrate that effects like multitemperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. We conclude that using XMM-Newton /EPIC instead of Chandra /ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift toward lower ΩM values and 8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift alone is insufficient to significantly alleviate the tension between Planck CMB primary anisotropies and Sunyaev-Zel’dovich-plus-XMM-Newton cosmological constraints.
155 citations
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TL;DR: In this article, a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed, is presented.
Abstract: We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 μm data, we have constructed a map of the dust temperature so that the 100 μm map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected. To generate the full-sky dust maps, we must first remove zodiacal light contamination, as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 μm DIRBE map against the Leiden-Dwingeloo map of H I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 μm flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 μm map no significant CIB is detected. At longer wavelengths, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 ± 13 nW m-2 sr-1 at 140 μm and of 17 ± 4 nW m-2 sr-1 at 240 μm (95% confidence). This integrated flux ~2 times that extrapolated from optical galaxies in the Hubble Deep Field. The primary use of these maps is likely to be as a new estimator of Galactic extinction. To calibrate our maps, we assume a standard reddening law and use the colors of elliptical galaxies to measure the reddening per unit flux density of 100 μm emission. We find consistent calibration using the B-R color distribution of a sample of the 106 brightest cluster ellipticals, as well as a sample of 384 ellipticals with B-V and Mg line strength measurements. For the latter sample, we use the correlation of intrinsic B-V versus Mg2 index to tighten the power of the test greatly. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles reddening estimates in regions of low and moderate reddening. The maps are expected to be significantly more accurate in regions of high reddening. These dust maps will also be useful for estimating millimeter emission that contaminates cosmic microwave background radiation experiments and for estimating soft X-ray absorption. We describe how to access our maps readily for general use.
15,988 citations
"Calibration of X-ray absorption in ..." refers methods in this paper
...We can calculate the molecular hydrogen fraction using all the pixels in the FTOOLS version of the LAB survey all-sky image and the rebinned version of the E(B-V) data from Schlegel et al. (1998)....
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...We modified the functionality of the NH2 profile so that it includes the extinction measure E(B − V ), using the allsky maps of E(B − V ) produced by Schlegel et al. (1998) from IRAS and COBE/DIRBE infra-red 100 µm and 240 µm data....
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TL;DR: In this paper, the authors presented a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed.
Abstract: We present a full sky 100 micron map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 micron and 240 micron data, we have constructed a map of the dust temperature, so that the 100 micron map can be converted to a map proportional to dust column density. The result of these manipulations is a map with DIRBE-quality calibration and IRAS resolution.
To generate the full sky dust maps, we must first remove zodiacal light contamination as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 micron DIRBE map against the Leiden- Dwingeloo map of H_I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 micron flux. For the 100 micron map, no significant CIB is detected. In the 140 micron and 240 micron maps, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 \pm 13 nW/m^2/sr at 140 micron, and 17 \pm 4 nW/m^2/sr at 240 micron (95% confidence). This integrated flux is ~2 times that extrapolated from optical galaxies in the Hubble Deep Field.
The primary use of these maps is likely to be as a new estimator of Galactic extinction. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles estimates in regions of low and moderate reddening. These dust maps will also be useful for estimating millimeter emission that contaminates CMBR experiments and for estimating soft X-ray absorption.
14,295 citations
TL;DR: In this article, new abundance tables have been compiled for C1 chondrites and the solar photosphere and corona, based on a critical review of the literature to mid-1988.
10,322 citations
"Calibration of X-ray absorption in ..." refers methods in this paper
...To test the effect of this change we re-ran the group fitting using the Anders & Grevesse (1989) abundances for the NH,g component....
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...We also tried varying the global percentage of molecular hydrogen from 0 to 30% and varying the elemental abundances between values consistent with Wilms et al. (2000) and Anders & Grevesse (1989) but no combination improved the situation....
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...The Wilms et al. (2000) model includes updated abundances which are approximately 70% of the previously widely used values from Anders & Grevesse (1989)....
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TL;DR: The final data release of observations of 21 cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey (LDS: Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen) with the Instituto Argentino de Radioastronomia Survey (IAR: Arnal et al. 2000, AA and Bajaja et al., 2005, A&A, 440, 767) of the sky south of? =?25?, is presented in this article.
Abstract: We present the final data release of observations of ?21-cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey (LDS: Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen) of the sky north of ? = ?30? with the Instituto Argentino de Radioastronomia Survey (IAR: Arnal et al. 2000, AA and Bajaja et al. 2005, A&A, 440, 767) of the sky south of ? = ?25?. The angular resolution of the combined material is HPBW ? 0. ?6. The LSR velocity coverage spans the interval ?450 km s?1 to +400 km s?1, at a resolution of 1.3 kms?1. The data were corrected for stray radiation at the Institute for Radioastronomy of the University of Bonn, refining the original correction applied to the LDS. The rms brightness-temperature noise of the merged database is 0.07?0.09 K. Residual errors in the profile wings due to defects in the correction for stray radiation are for most of the data below a level of 20?40 mK. It would be necessary to construct a telescope with a main beam efficiency of ?MB >? 99% to achieve the same accuracy. The merged and refined material entering the LAB Survey of Galactic HI is intended to be a general resource useful to a wide range of studies of the physical and structural characteristices of the Galactic interstellar environment. The LAB Survey is the most sensitive Milky Way HI survey to date, with the most extensive coverage both spatially and kinematically.
4,228 citations
Goddard Space Flight Center1, University of Milan2, Brera Astronomical Observatory3, University College London4, Pennsylvania State University5, University of Leicester6, Sonoma State University7, University of California, Berkeley8, Universities Space Research Association9, National Research Council10, University of Southampton11, Los Alamos National Laboratory12, National Radio Astronomy Observatory13, Space Telescope Science Institute14, Max Planck Society15, California Institute of Technology16, University of Texas at Austin17, French Alternative Energies and Atomic Energy Commission18, University of Toronto19, University of Maryland, College Park20, Princeton University21, Lawrence Livermore National Laboratory22, University of Cambridge23, University of California, Santa Barbara24, Rice University25, University of Tokyo26, Saitama University27, University of Florence28
TL;DR: The Swift mission as discussed by the authors is a multi-wavelength observatory for gamma-ray burst (GRB) astronomy, which is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions.
Abstract: The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr � 1 and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to (1) determine the origin of GRBs, (2) classify GRBs and search for new types, (3) study the interaction of the ultrarelativistic outflows of GRBs with their surrounding medium, and (4) use GRBs to study the early universe out to z >10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a newgeneration wide-field gamma-ray (15‐150 keV) detector that will detect bursts, calculate 1 0 ‐4 0 positions, and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5 00 positions and perform spectroscopy in the 0.2‐10 keV band; and a narrow-field UV/optical telescope that will operate in the 170‐ 600 nm band and provide 0B3 positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of � 1m crab (� 2;10 � 11 ergs cm � 2 s � 1 in the 15‐150 keV band), more than an order of magnitude better than HEAO 1 A-4. A flexible data and operations system will allow rapid follow-up observations of all types of
3,753 citations