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  • 1
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    Swift and NuSTAR observations of GW170817: Detection of a blue kilonova (2017)
    Evans, P. A., Cenko, S. B., Kennea, J. A., Emery, S. W. K., Kuin, N. P. M., Korobkin, O., Wollaeger, R. T., Fryer, C. L., Madsen, K. K., Harrison, F. A., Xu, Y., Nakar, E., Hotokezaka, K., Lien, A., Campana, S., Oates, S. R., Troja, E., Breeveld, A. A., Marshall, F. E., Barthelmy, S. D., Beardmore, A. P., Burrows, D. N., Cusumano, G., DAi, A., DAvanzo, P., DElia, V., de Pasquale, M., Even, W. P., Fontes, C. J., Forster, K., Garcia, J., Giommi, P., Grefenstette, B., Gronwall, C., Hartmann, D. H., Heida, M., Hungerford, A. L., Kasliwal, M. M., Krimm, H. A., Levan, A. J., Malesani, D., Melandri, A., Miyasaka, H., Nousek, J. A., OBrien, P. T., Osborne, J. P., Pagani, C., Page, K. L., Palmer, D. M., Perri, M., Pike, S., Racusin, J. L., Rosswog, S., Siegel, M. H., Sakamoto, T., Sbarufatti, B., Tagliaferri, G., Tanvir, N. R., Tohuvavohu, A.
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-22
    Description: With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counterpart of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (0.03 solar masses) wind-driven outflow with moderate electron fraction ( Y e 0.27). Combined with the x-ray limits, we favor an observer viewing angle of 30° away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a -ray burst afterglow).
    Keywords: Astronomy
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    SWIFT Detects a remarkable Gamma-ray Burst, GRB 060514, that introduces a New Classification Scheme (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Gamma ray bursts (GFU3s) are known to come in two duration classes, separated at approx.2 s. Long bursts originate from star forming regions in galaxies, have accompanying supernovae (SNe) when near enough to observe and are likely caused by massive-star collapsars. Recent observations show that short bursts originate in regions within their host galaxies with lower star formation rates, consistent with binary neutron star (NS) or NS - black hole (BH) mergers. Moreover, although their hosts are predominantly nearby galaxies, no SNe have been so far associated with short GRBs. We report here on the bright, nearby GRB 060614 that does not fit in either class. Its approx.102 s duration groups it with long GRBs, while its temporal lag and peak luminosity fall entirely within the short GRB subclass. Moreover, very deep optical observations exclude an accompanying supernova, similar to short GRBs. This combination of a long duration event without accompanying SN poses a challenge to both a collapsar and merging NS interpretation and opens the door on a new GRB classification scheme that straddles both long and short bursts.
    Keywords: Astronomy
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  • 3
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    Testing the E(sub peak)-E(sub iso) Relation for GRBs Detected by Swift and Suzaku-WAM (2009)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: One of the most prominent, yet controversial associations derived from the ensemble of prompt-phase observations of gamma-ray bursts (GRBs) is the apparent correlation in the source frame between the peak energy (E(sub peak)) of the nuF(nu) spectrum and the isotropic radiated energy, E(sub iso). Since most gamma-ray bursts (GRBs) have E(sub peak) above the energy range (15-150 keV) of the Burst Alert Telescope (BAT) on Swift, determining accurate E(sub peak) values for large numbers of Swift bursts has been difficult. However, by combining data from Swift/BAT and the Suzaku Wide-band All-Sky Monitor (WAM), which covers the energy range from 50-5000 keV, for bursts which are simultaneously detected ; one can accurately fit E(sub peak) and E(sub iso) and test the relationship between them for the Swift sample. Between the launch of Suzaku in July 2005 and the end of March 2009, there were 45 gamma-ray bursts (GRBs) which triggered both Swift/BAT and WAM and an additional 47 bursts which triggered Swift and were detected by WAM, but did not trigger. A BAT-WAM team has cross-calibrated the two instruments using GRBs, and we are now able to perform joint fits on these bursts to determine spectral parameters. For those bursts with spectroscopic redshifts.. we can also calculate the isotropic energy. Here we present the results of joint Swift/BAT-Suzaku/WAM spectral fits for 86 of the bursts detected by the two instruments. We show that the distribution of spectral fit parameters is consistent with distributions from earlier missions and confirm that Swift, bursts are consistent with earlier reported relationships between Epeak and isotropic energy. We show through time-resolved spectroscopy that individual burst pulses are also consistent with this relationship.
    Keywords: Astronomy
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  • 4
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    Correlative Analysis of GRBs detected by Swift, Konus and HETE (2005)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Swift has now detected a large enough sample of gamma-ray bursts (GRBs) to allow correlation studies of burst parameters. Such studies of earlier data sets have yielded important results leading to further understanding of burst parameters and classifications. This work focuses on seventeen Swift bursts that have also been detected either by Konus-Wind or HETE-II, providing high energy spectra and fits to E(sub peak). Eight of these bursts have spectroscopic redshifts and for others we can estimate redshifts using the variability/luminosity relationship. We can also compare E(sub peak) with E(sub iso), and for those bursts for which a jet break was observed in the afterglow we can derive E(sub g) and test the relationship between E(peak) and E(sub gamma). For all bursts we can derive durations and hardness ratios from the prompt emission.
    Keywords: Astronomy
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  • 5
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    Correlations of Prompt and Afterglow Emission in Swift Long and Short Gamma Ray Bursts (2008)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Correlation studies of prompt and afterglow emissions from gamma-ray bursts (GRBs) between different spectral bands has been difficult to do in the past because few bursts had comprehensive and intercomparable afterglow measurements. In this paper we present a large and uniform data set for correlation analysis based on bursts detected by the Swift mission. For the first time, short and long bursts can be analyzed and compared. It is found for both classes that the optical, X-ray and gamma-ray emissions are linearly correlated, but with a large spread about the correlation line; stronger bursts tend to have brighter afterglows, and bursts with brighter X-ray afterglow tend to have brighter optical afterglow. Short bursts are, on average, weaker in both prompt and afterglow emissions. No short bursts are seen with extremely low optical to X-ray ratio as occurs for 'dark' long bursts. Although statistics are still poor for short bursts, there is no evidence yet for a subgroup of short bursts with high extinction as there is for long bursts. Long bursts are detected in the dark category at the same fraction as for pre-Swift bursts. Interesting cases are discovered of long bursts that are detected in the optical, and yet have low enough optical to X-ray ratio to be classified as dark. For the prompt emission, short and long bursts have different average tracks on flux vs fluence plots. In Swift, GRB detections tend to be fluence limited for short bursts and flux limited for long events.
    Keywords: Astronomy
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  • 6
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    POET: POlarimeters for Energetic Transients (2008)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: POET (Polarimeters for Energetic Transients) is a Small Explorer mission concept proposed to NASA in January 2008. The principal scientific goal of POET is to measure GRB polarization between 2 and 500 keV. The payload consists of two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2-15 keV and a high energy polarimeter (Gamma-Ray Polarimeter Experiment - GRAPE) that will measure polarization in the 60-500 keV energy range. Spectra will be measured from 2 keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for maximizing the exposure to deep space. Spacecraft rotation will provide a means of effectively dealing with systematics in the polarization response. POET will provide sufficient sensitivity and sky coverage to measure statistically significant polarization for up to 100 GRBs in a two-year mission. Polarization data will also be obtained for solar flares, pulsars and other sources of astronomical interest.
    Keywords: Astronomy
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  • 7
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    Studying Galaxy Formation with the Hubble, Spitzer and James Webb Space Telescopes (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The deepest optical to infrared observations of the universe include the Hubble Deep Fields, the Great Observatories Origins Deep Survey and the recent Hubble Ultra-Deep Field. Galaxies are seen in these surveys at redshifts 2-6, less than 1 Gyr after the Big Bang, at the end of a period when light from the galaxies has reionized Hydrogen in the inter-galactic medium. These observations, combined with theoretical understanding, indicate that the first stars and galaxies formed at z〉10, beyond the reach of the Hubble and Spitzer Space Telescopes. To observe the first galaxies, NASA is planning the James Webb Space Telescope (JWST), a large (6.5m), cold (50K), infrared-optimized observatory to be launched early in the next decade into orbit around the second Earth- Sun Lagrange point. JWST will have four instruments: The Near-Infrared Camera, the Near-Infrared multi-object Spectrograph, and the Tunable Filter Imager will cover the wavelength range 0.6 to 5 microns, while the Mid-Infrared Instrument will do both imaging and spectroscopy from 5 to 27 microns. In addition to JWST s ability to study the formation and evolution of galaxies, I will also briefly review its expected contributions to studies of the formation of stars and planetary systems.
    Keywords: Astronomy
    Type: JPL Colloquium for the Astrophysics Group: Studying Galaxy Formation with Hubble, Spitzer, and James Webb Space Telescope; Jan 29, 2006 - Feb 03, 2006; Pasadena, CA; United States
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  • 8
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    A Jet Break in the X-ray Light Curve of Short GRB 111020A: Implications for Energetics and Rates (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present broadband observations of the afterglow and environment of the short GRB 111020A. An extensive X-ray light curve from Swift/XRT, XMM-Newton, and Chandra, spanning approx.100 s to 10 days after the burst, reveals a significant break at (delta)t approx. = 2 days with pre- and post-break decline rates of (alpha)X,1 approx. = -0.78 and (alpha)X,2 〈 or approx. 1.7, respectively. Interpreted as a jet break, we infer a collimated outflow with an opening angle of (theta)j approx. = 3deg - 8deg. The resulting beaming-corrected gamma-ray (10-1000 keV band) and blast-wave kinetic energies are (2-3) x 10(exp 48) erg and (0.3-2) x 10(exp 49) erg, respectively, with the range depending on the unknown redshift of the burst. We report a radio afterglow limit of 〈39 micro-Jy (3(sigma)) from Expanded Very Large Array observations that, along with our finding that v(sub c) 〈 v(sub X), constrains the circumburst density to n(sub 0) approx.0.01 0.1/cu cm. Optical observations provide an afterglow limit of i 〉 or approx.24.4 mag at 18 hr after the burst and reveal a potential host galaxy with i approx. = 24.3 mag. The subarcsecond localization from Chandra provides a precise offset of 0".80+/-0".11 (1(sigma))from this galaxy corresponding to an offset of 5.7 kpc for z = 0.5-1.5. We find a high excess neutral hydrogen column density of (7.5+/-2.0) x 10(exp 21)/sq cm (z = 0). Our observations demonstrate that a growing fraction of short gamma-ray bursts (GRBs) are collimated, which may lead to a true event rate of 〉 or approx.100-1000 Gpc(sup -3)/yr, in good agreement with the NS-NS merger rate of approx. = 200-3000 Gpc(sup -3)/ yr. This consistency is promising for coincident short GRB-gravitational wave searches in the forthcoming era of Advanced LIGO/VIRGO.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN6804 , The Astrophysical Journal; 756; 2
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  • 9
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    Global Properties of X-Ray Flashes and X-Ray-Rich GRBs Observed by Swift (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: We describe and discuss the spectral and temporal characteristics of the prompt emission and X-ray afterglow emission of X-ray flashes (XRFs) detected and observed by Swift between December 2005 and September 2006. We compare these characteristics to a sample of X-ray rich gamma-ray bursts (XRRs) and conventional classical gamma-ray bursts (C-GRBs)observed during the same period. We confirm the correlation between Epeak and fluence noted by others and find further evidence that XRFs and C-GRBs form a continuum. We also confirmed that our known redshift samples are consistent with the correlation between the peak energy (Epeak) and the isotropic radiated energy (Eiso), so called the Epeak-Eiso relation. The spectral properties of X-ray afterglows are similar to those of gamma-ray burst afterglows, but the temporal properties of the two classes are quite different. We found that the light curves of C-GRBs afterglow show a break to steeper indices (shallow-to-steep break) at much earlier times than do XRF afterglows. Moreover, the overall luminosity of X-ray afterglows of XRFs are systematically smaller by a factor of two or more compared with that of C-GRBs. These distinct differences in the X-ray afterglow between XRFs and C-GRBs are key to understanding not only a mysterious shallow-to-steep phase in the X-ray afterglow but also the unique nature of XRFs.
    Keywords: Astronomy
    Type: American Astronomical Society 210th Hawaii Meeting; May 27, 2007 - May 31, 2007; Honolulu, HI; United States
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  • 10
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    Reviewing Epeak Relations with Swift and Suzaku Data (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: in recent years several authors have derived correlations between gamma-ray burst (GRB) spectral peak energy (Epeak) and either isotropic-equivalent radiated energy (Eiso) or peak luminosity (Liso) . Since these relationships are controversial, but could provide redshift estimators, it is important to determine whether bursts detected by Swift exhibit the same correlations. Swift has greatly added to the number of GRBs for which redshifts are known and hence Eiso and Lisc could be calculated. However, for most bursts it is not possible to adequately constrain Epeak with Swift data alone since most GRBs have Epeak above the energy range (15-50 keV) of the Swift Burst Alert Telescope (BAT). Therefore we have analyzed the spectra of 78 bursts (31 with redshift) which were detected by both Swift/BAT and the Suzaku Wide-band All-sky Monitor (WAM), which covers the energy range 50-50C0 keV. For most bursts in this sample we can precisely determine Epeak and for bursts with known redshift we can compare how the Epeak relations for the Swift/Suzaku sample compare to earlier published results.
    Keywords: Astronomy
    Type: 6th Huntsville Symposium on Gamma-Ray Bursts; Oct 20, 2008 - Oct 23, 2008; Huntsville, AL; United States
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