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At least 109 records · Page 6
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NASA NTRS2008

Gamma Ray Burst Discoveries with the Swift Mission

Gamma-ray bursts (GRBs) are among the most fascinating occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 3 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from - 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type I1 and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z>5 and one at z=6.3 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy.

Gehrels, Neil↗
NASA NTRS2009

Gamma Ray Burst Discoveries with the Swift Mission

Gamma-ray bursts (GRBs) are among the most fascinating occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 4 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from approximately 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z>5 and one at z=6.7 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy.

Gehrels, Neil↗
NASA NTRS2010

Afterglow Population Studies from Swift Follow-Up Observations of Fermi LAT GRBs

The small population of Fermi LAT detected GRBs discovered over the last year has been providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 5 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into other components of GRB emission structure. We explore the new ability to utilize both of these observatories to study the same GRBs over 10 orders of magnitude in energy, although not always concurrently. Almost all LAT GRBs that have been followed-up by Swift within 1-day have been clearly detected and carefully observed. We will present the context of the lower-energy afterglows of this special subset of GRBs that has > 100 MeV emission compared to the hundreds in the Swift database that may or may not have been observed by LAT, and theorize upon the relationship between these properties and the origin of the high energy gamma-ray emission.

Racusin, Judith L.↗
NASA NTRS2010

Probing the Nature of Short Swift Bursts via Deep INTEGRAL Monitoring of GRB 050925

We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: 1) galactic plane (b=-0.1 deg) localization, 2) 150 msec duration, and 3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than -1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in approximately 5 Ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the H(sub II), regions (W 58) at the galactic longitude of 1=70 deg, we also discuss the source frame properties of GRB 050925.

Sakamoto, T.↗
NASA NTRS2010

Fermi-LAT Gamma-Ray Bursts and Insights from Swift

A new revolution in Gamma-ray Burst (GRB) observations and theory has begun over the last two years since the launch of the Fermi Gamma-ray Space Telescope. The new window into high energy gamma-rays opened by the Fermi-Large Area Telescope (LAT) is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts compared to the large sample detected by Swift over the last 6 years. In this talk, I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by the Swift X-ray Telescope (XRT) and UV/Optical Telescope (UVOT). Through comparisons between the GRBs detected by Swift-BAT, G8M, and LAT, we can learn about the unique characteristics, physical differences, and the relationships between each population. These population characteristics provide insight into the different physical parameters that contribute to the diversity of observational GRB properties.

Racusin, Judith L.↗
NASA NTRS2011

The Swift Era

The study of gamma-ray bursts (GRBs) remains highly dependent on the capabilities of the observatories that carry out the measurements. The large detector size of BATSE produced an impressively large sample of GRBs for duration and sky distribution studies. The burst localization and repointing capabilities of BeppoSAX led to breakthroughs in host and progenitor understanding. The next phase in our understanding of GRBs is being provided by the Swift mission. In this chapter we discuss the capabilities and findings of the Swift mission and their relevance to our understanding of GRBs. We also examine what is being learned about star formation, supernovae and the early Universe from the new results. In each section of the chapter, we close with a discussion of the new questions and issues raised by the Swift findings.

Gehrels, Neil↗
NASA NTRS2006

Gamma Ray Burst Discoveries by the Swift Mission

Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. The NASA swift mission is an innovative new multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Swift is now in orbit since November 20, 2004 and all hardware is performing well. A new-technology wide-field gamma-ray camera is detecting a hundred bursts per year. sensitive narrow-field X-ray and uv/optical telescopes, built in collaboration with UK and Italian partners, are pointed at the burst location in 50-100 sec by an autonomously controlled "swift" spacecraft. For each burst, arcsec positions are determined and optical/UV/X-ray/gamma-ray spectrophotometry performed. Information is also rapidly sent to the ground to a team of more than 50 observers at telescopes around the world. The first year of findings from the mission will be presented. There has been a break-through in the longstanding mystery of short GRBs; they appear to be caused by merging neutron stars. High redshift bursts have been detected leading to a better understanding of star formation rates and distant galaxy environments. GRBs have been found with giant X-ray flares occurring in their afterglow.

Gehrels, Neil↗
NASA NTRS2011

Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare

We report the discovery by the Swift hard X-ray monitor of the transient source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up campaign uncovered a long-lived (duration approximately greater than months), luminous X-ray (L(sub x.iso) approximates 3 X 10(exp47) erg/s) and radio (vL(sub v.iso) approximates 10(exp 42) erg/s) counterpart. The associated optical emission, however, from which we measure a redshift of 1.1853, is relatively faint, and this is not due to a large amount of dust extinction in the host galaxy. Based on numerous similarities with the recently discovered GRB 110328A / Swift 1164449.3+573451 (Sw 11644+57), we suggest that Sw J2058+05 may be the second member of a new class of relativistic outbursts resulting from the tidal disruption of a star by a supermassive black hole. If so, the relative rarity of these sources implies that either these outflows are extremely narrowly collimated (theta < 1 deg), or only a small fraction of tidal disruptions generate relativistic ejecta. Analogous to the case of long duration gamma-ray bursts and core-collapse supernovae, we speculate that the spin of the black hole may be a necessary condition to generate the relativistic component. Alternatively, if powered by gas accretion (i.e., an active galactic nucleus), this would imply that some galaxies can transition from apparent quiescence to a radiatively efficient state of accretion on quite short time scales.

Cenko, S. Bradely↗
NASA NTRS2009

The Nature of the X-Ray Binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift Observations

We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+ 1816. The Swift/XRT data allow us to refine the position of the source to R.A. (J2000) = 19h 29m 55.9s, Decl. (J2000) = +18 deg 18 feet 38 inches . 4 (+/- 3 inches .5), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma approx 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic absorption in this source. We detected a strong (P = 40%) pulsations at 12.43781 (+/- 0.00003) s that we interpret as the spin period of a pulsar. All these results, coupled with the possible 117 day orbital period, point to IGR J19294+ 1816 being an high-mass X-ray binary (HMXB) with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI 18-40 keV light curve shows that the source spends most of its time in an undetectable state, we detect occurrences of short (2000-3000 s) and intense flares that are more typical of supergiant fast X-ray transients. We therefore cannot make firm conclusions on the type of system, and we discuss the possible implication of IGR J19294+1816 being an Supergiant Fast X-ray Transient (SFXT).

Rodriquez, J.↗
NASA NTRS2012

Recent Progress on GRBs with Swift

Gamma-ray bursts (GRBs) are powerful explosions, visible to high red shift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 7 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from ~ 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type. II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z>S and one at z=9.4 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy .

Gehrels, Neil↗
NASA NTRS2013

1SXPS: A Deep Swift X-Ray Telescope Point Source Catalog with Light Curves and Spectra

We present the 1SXPS (Swift-XRT point source) catalog of 151,524 X-ray point sources detected by the Swift-XRT in 8 yr of operation. The catalog covers 1905 sq deg 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 approximately 3 × 10(exp −13) erg cm(exp −2) s(exp −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 approximately 9 × 10(exp −14) erg cm(exp −2) s(exp −1) (0.3-10 keV). Our sky coverage is nearly 2.5 times that of 3XMM-DR4, although the catalog is a factor of approximately 1.5 less sensitive. The median position error is 5.5 (90% confidence), including systematics. Our source detection method improves on that used in previous X-ray Telescope (XRT) catalogs and we report greater than 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 find approximately 30,000 variable objects in our catalog. For every source we give positions, fluxes, time series (in four energy bands and two hardness ratios), estimates of the spectral properties, spectra and spectral fits for the brightest sources, and variability probabilities in multiple energy bands and timescales.

telescope↗
NASA NTRS2020

Observations of a GX 301–2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM

The accretion-powered X-ray pulsar GX 301−2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late 2018 December, with contiguous observations by the Neutron star Interior Composition Explorer Mission (NICER) X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin up of the pulsar discovered with the Fermi Gamma-ray Burst Monitor. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15–35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of (27 ((sup +38),(sub -27)) % (90% confidence limit) averaged over all pulse phases. We discuss the spin up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.

Q. Abarr↗
NASA NTRS2020

Discovery of Thermonuclear (Type 1) X-ray Bursts in the X-ray Binary Swift J1858.6-0814 Observed with NICER and NuSTAR

Swift J1858.6–0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors of >100 in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6–0814, implying that the compact object in the system is a neutron star (NS). Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, D = 12.8+0.8−0.6 kpc, although systematic effects allow a conservative range of 9–18 kpc. Before one burst, we detect a QPO at 9.6 ± 0.5 mHz with a fractional rms amplitude of 2.2 ± 0.2 per cent (0.5–10 keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15 per cent fractional amplitude (over 1–8 keV). Finally, we discuss the implications of the NS accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6–0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst.

D J K Buisson↗
NASA NTRS2019

Polarimetry of relativistic tidal disruption event Swift J2058+0516

A small fraction of candidate tidal disruption events (TDEs) show evidence of powerful relativistic jets, which are particularly pronounced at radio wavelengths, and likely contribute non-thermal emission at a wide range of wavelengths. A non-thermal emission component can be diagnosed using linear polarimetry, even when the total received light is dominated by emission from an accretion disc or disc outflow. In this paper, we present Very Large Telescope (VLT) measurements of the linear polarization of the optical light of jetted TDE Swift J2058+0516. This is the second jetted TDE studied in this manner, after Swift J1644+57. We find evidence of non-zero optical linear polarization, PV ∼ 8 per cent, a level very similar to the near-infrared polarimetry of Swift J1644+57. These detections provide an independent test of the emission mechanisms of the multiwavelength emission of jetted TDEs.

K Wiersema↗
NASA NTRS2019

Swift-XRT Follow-up of Gravitational-wave Triggers in the Second Advanced LIGO/Virgo Observing Run

The Neil Gehrels Swift Observatory carried out prompt searches for gravitational-wave (GW) events detected by the LIGO/Virgo Collaboration (LVC) during the second observing run ("O2"). Swift performed extensive tiling of eight LVC triggers, two of which had very low false-alarm rates (GW170814 and the epochal GW170817), indicating a high confidence of being astrophysical in origin; the latter was the first GW event to have an electromagnetic counterpart detected. In this paper we describe the follow-up performed during O2 and the results of our searches. No GW electromagnetic counterparts were detected; this result is expected, as GW170817 remained the only astrophysical event containing at least one neutron star after LVC's later retraction of some events. A number of X-ray sources were detected, with the majority of identified sources being active galactic nuclei. We discuss the detection rate of transient X-ray sources and their implications in the O2 tiling searches. Finally, we describe the lessons learned during O2 and how these are being used to improve the Swift follow-up of GW events. In particular, we simulate a population of gamma-ray burst afterglows to evaluate our source ranking system's ability to differentiate them from unrelated and uncataloged X-ray sources. We find that ≈60%–70% of afterglows whose jets are oriented toward Earth will be given high rank (i.e., "interesting" designation) by the completion of our second follow-up phase (assuming that their location in the sky was observed), but that this fraction can be increased to nearly 100% by performing a third follow-up observation of sources exhibiting fading behavior.

N. J. Klingler↗
NASA NTRS2021

Swift Multiwavelength Follow-up of LVC S200224ca and the Implications for Binary Black Hole Mergers

On 2020 February 24, during their third observing run (“O3”), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, qˆ < 1.4 x 10-4, and an upper limit on the isotropic-equivalent energy of a blast wave E<4.1×1051 erg (assuming typical GRB parameters).

N J Klinger↗
NASA NTRSDate not supplied

Searching for GRB Counterparts to GW Events from the Third Gravitational Wave Observing Run with Fermi-GBM and Swift-BAT

We present Fermi Gamma-ray Burst Monitor (Fermi-GBM) and Swift Burst Alert Telescope (Swift-BAT) observations of gravitational-wave (GW) events detected during the third LIGO/Virgo/KAGRA Collaboration observing run (O3). Using Fermi-GBM on-board triggers as well as sub-threshold searches in both Fermi-GBM and Swift-BAT ground data, we search for coincident gamma-ray transients associated with the GW events. No new joint events beyond GRB 170817A and GW170817 were found. We therefore calculate flux upper limits for the associated gamma-ray luminosity of each GW event. Using the lack of electromagnetic (EM) emission from binary black hole (BBH) mergers, we begin to constrain theoretical models of any such emission.

Joshua Wood↗
NASA NTRSDate not supplied

Searching for GRB Counterparts to GW Events from the Third Gravitational Wave Observing Run with Fermi-GBM and Swift-BAT

We present Fermi Gamma-ray Burst Monitor (Fermi-GBM) and Swift Burst Alert Telescope (Swift-BAT) observations of gravitational-wave (GW) events detected during the third LIGO/Virgo/KAGRA Collaboration observing run (O3). Using Fermi-GBM on-board triggers as well as sub-threshold searches in both Fermi-GBM and Swift-BAT ground data, we search for coincident gamma-ray transients associated with the GW events. No new joint events were found. We therefore calculate flux upper limits for the associated gamma-ray luminosity of each GW event. Using the lack of electromagnetic (EM) emission from binary black hole (BBH) mergers, we begin to constrain theoretical models of any such emission.

GRB↗