Neil Gehrels Swift Observatory

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Neil Gehrels Swift Observatory
Neil Gehrels Swift Observatory
NamesExplorer-84
MIDEX-3
Swift Gamma Ray Burst Explorer
Mission typeGamma-ray astronomy
OperatorNASA / Pennsylvania State University
COSPAR ID2004-047A Edit this at Wikidata
SATCAT no.28485
Websiteswift.gsfc.nasa.gov
Mission duration2 years (planned)[1]
19 years, 5 months, 5 days (in progress)
Spacecraft properties
SpacecraftExplorer LXXXIV
Spacecraft typeSwift Gamma Ray Burst Explorer
BusLEOStar-3
ManufacturerSpectrum Astro
Launch mass1,470 kg (3,240 lb)
Dry mass613 kg (1,351 lb)
Payload mass843 kg (1,858 lb)
Dimensions5.6 × 5.4 m (18 × 18 ft)[2]
Power1040 watts
Start of mission
Launch date20 November 2004, 17:16:01 UTC
RocketDelta II 7320-10C (Delta 309)
Launch siteCape Canaveral, SLC-17A
ContractorBoeing Defense, Space & Security[3]
Entered service1 February 2005
Orbital parameters
Reference systemGeocentric orbit[4]
RegimeLow Earth orbit
Perigee altitude585 km (364 mi)
Apogee altitude604 km (375 mi)
Inclination20.60°
Period96.60 minutes
Instruments
Burst Alert Telescope (BAT)
UltraViolet Optical Telescope (UVOT)
X-Ray Telescope (XRT)

Swift Gamma Ray Burst Explorer
Explorer program
← GALEX (Explorer 83)
THEMIS (Explorer 85-89) →
 

Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a

Medium Explorer program
(MIDEX).

The burst detection rate is 100 per year, with a sensitivity ~3 times fainter than the BATSE detector aboard the Compton Gamma Ray Observatory. The Swift mission was launched with a nominal on-orbit lifetime of two years. Swift is a NASA MIDEX (medium-class Explorer) mission. It was the third to be launched, following IMAGE and WMAP.[5]

While originally designed for the study of gamma-ray bursts, Swift now functions as a general-purpose multi-wavelength observatory, particularly for the rapid followup and characterization of astrophysical transients of all types. As of 2020, Swift received 5.5 Target of Opportunity observing proposals per day, and observes ~70 targets per day, on average.[6]

Swift was put into safe mode in March 2024 due to gyroscope noise.[7]

Overview

Swift is a multi-

gamma-ray, X-ray, ultraviolet, and optical
wavebands.

Based on continuous scans of the area of the sky with one of the instrument's monitors, Swift uses

momentum wheels to autonomously slew into the direction of possible GRBs. The name "Swift" is not a mission-related acronym, but rather a reference to the instrument's rapid slew capability, and the nimble swift (bird of the same name).[8]
All of Swift's discoveries are transmitted to the ground and those data are available to other observatories which join Swift in observing the GRBs.

In the time between GRB events, Swift is available for other scientific investigations, and scientists from universities and other organizations can submit proposals for observations.

The Swift Mission Operation Center (MOC), where commanding of the satellite is performed, is located in State College, Pennsylvania and operated by the Pennsylvania State University and industry subcontractors. The Swift main ground station is located at the Broglio Space Center near Malindi on the coast of eastern Kenya, and is operated by the Italian Space Agency (ASI). The Swift Science Data Center (SDC) and archive are located at the Goddard Space Flight Center outside Washington, D.C. The United Kingdom Swift Science Data Centre is located at the University of Leicester.

The Swift satellite bus was built by Spectrum Astro, which was later acquired by General Dynamics Advanced Information Systems,[9] which was in turn acquired by Orbital Sciences Corporation (now Northrop Grumman Innovation Systems).

Instruments

Burst Alert Telescope (BAT)

Diagram of Burst Alert Telescope

The BAT detects GRB events and computes its coordinates in the sky. It covers a large fraction of the sky (over one steradian fully coded, three steradians partially coded; by comparison, the full sky solid angle is 4π or about 12.6 steradians). It locates the position of each event with an accuracy of 1 to 4 arcminutes within 15 seconds. This crude position is immediately relayed to the ground, and some wide-field, rapid-slew ground-based telescopes can catch the GRB with this information. The BAT uses a coded-aperture mask of 52,000 randomly placed 5 mm (0.20 in) lead tiles, 1 m (3 ft 3 in) above a detector plane of 32,768 4 mm (0.16 in) Cadmium zinc telluride (CdZnTe) hard X-ray detector tiles; it is purpose-built for Swift. Energy range: 15–150 keV.[10]

X-ray Telescope (XRT)

Swift before launch

The XRT [11] can take images and perform spectral analysis of the GRB afterglow. This provides more precise location of the GRB, with a typical error circle of approximately 2 arcseconds radius. The XRT is also used to perform long-term monitoring of GRB afterglow light-curves for days to weeks after the event, depending on the brightness of the afterglow. The XRT uses a Wolter Type I X-ray telescope with 12 nested mirrors, focused onto a single MOS charge-coupled device (CCD) similar to those used by the XMM-Newton EPIC MOS cameras. On-board software allows fully automated observations, with the instrument selecting an appropriate observing mode for each object, based on its measured count rate. The telescope has an energy range of 0.2–10 keV.[12]

Ultraviolet/Optical Telescope (UVOT)

UVOT's "first light" image

After Swift has slewed towards a GRB, the UVOT is used to detect an optical afterglow. The UVOT provides a sub-arcsecond position and provides optical and ultra-violet photometry through lenticular filters and low resolution spectra (170–650 nm) through the use of its optical and UV grisms. The UVOT is also used to provide long-term follow-ups of GRB afterglow lightcurves. The UVOT is based on the XMM-Newton's Optical Monitor (OM) instrument, with improved optics and upgraded onboard processing computers.[13]

On 9 November 2011, UVOT photographed the asteroid 2005 YU55 as the asteroid made a close flyby of the Earth.[14]

On 3 June 2013, UVOT unveiled a massive ultraviolet survey of the nearby Magellanic Clouds.[15]

In August 2017, UVOT imaged UV emissions from gravitational wave event GW170817 detected by LIGO & Virgo detectors.[16][17]

Experiments

A model of the satellite

Burst Alert Telescope (BAT)

BAT (Burst Alert Telesope) is a gamma ray telescope, built by NASA's Goddard Space Flight Center, uses a coded aperture to locate the source. The software to locate the source is provided by the Los Alamos National Laboratory (LANL). The CdZnTe detector of 5,200 cm2 (810 sq in) area, consisting of 32,500 units of 4 × 4 × 2 mm (0.157 × 0.157 × 0.079 in), can pin-point the location of sources within 1.4 arcminutes. The energy range is 15-150 keV.[18]

Ultraviolet/Optical Telescope (UVOT)

UVOT (Ultraviolet/Optical Telescope) monitors the afterglow in ultraviolet and visible light, and locates the source at an accuracy of one arcsecond. Its aperture is 30 cm (12 in), with an f-number equal to 12.7, and is backed by 2048 x 2048 photon counting CCD pixels. The source location accuracy is better than one arcsecond.[19]

X-Ray Telescope (XRT)

XRT (X-Ray Telescope) aims at the source more accurately, and monitors the afterglow in X-rays. It was built jointly by the Pennsylvania State University (PSU), the Brera Astronomical Observatory, Italy, and the University of Leicester, United Kingdom. It has a detector of area 135 cm2 (20.9 sq in) consisting of 600 x 600 pixels, and covers the energy range of 0.2-10 keV. It can locate the afterglow source at an accuracy of four arcseconds.[20]

Mission goals

The Swift mission has four key scientific objectives:

  • To determine the origin of GRBs. There seem to be at least two types of GRBs, only one of which can be explained with a hypernova, creating a gamma-ray beam. More data is needed to explore other explanations
  • To use GRBs to expand understanding of the young
    light-years
    , which means they can be used to probe the distant, and therefore young, cosmos
  • To conduct an all-sky survey which will be more sensitive than any previous one, and will add significantly to scientific knowledge of astronomical X-ray sources. Thus, it could also yield unexpected results
  • To serve as a general purpose gamma-ray/X-ray/optical observatory platform, performing rapid "target of opportunity" observations of many transient astrophysical phenomena, such as supernova

Mission history

Animation of Swift Observatory's orbit around Earth, Earth is not shown.

Swift was launched on 20 November 2004, at 17:16:01 UTC aboard a Delta II 7320-10C from Cape Canaveral Air Force Station and reached a near-perfect orbit of 585 × 604 km (364 × 375 mi) altitude, with an inclination of 20.60°.[4]

On 4 December 2004, an anomaly occurred during instrument activation when the Thermo-Electric Cooler (TEC) Power Supply for the X-Ray Telescope did not turn on as expected. The XRT Team at University of Leicester and Pennsylvania State University were able to determine on 8 December 2004 that the XRT would be usable even without the TEC being operational. Additional testing on 16 December 2004 did not yield any further information as to the cause of the anomaly.

On 17 December 2004 at 07:28:30 UTC, the Swift Burst Alert Telescope (BAT) triggered and located on board an apparent gamma-ray burst during launch and early operations.[21] The spacecraft did not autonomously slew to the burst since normal operation had not yet begun, and autonomous slewing was not yet enabled. Swift had its first GRB trigger during a period when the autonomous slewing was enabled on 17 January 2005, at about 12:55 UTC. It pointed the XRT telescope to the on-board computed coordinates and observed a bright X-ray source in the field of view.[22]

On 1 February 2005, the mission team released the first light picture of the UVOT instrument and declared Swift operational.

By May 2010, Swift had detected more than 500 GRBs.[23]

By October 2013, Swift had detected more than 800 GRBs.[24]

On 27 October 2015, Swift detected its 1,000th GRB, an event named GRB 151027B and located in the constellation Eridanus.[25]

On 10 January 2018, NASA announced that the Swift spacecraft had been renamed the Neil Gehrels Swift Observatory in honor of mission PI Neil Gehrels, who died in early 2017.[26][27]

Swift entered safe mode on March 15, 2024 and was not conducting science. A software patch for two-gyroscope mode was developed, uplinked and tested in April 2024, and Swift returned to nominal operations at that point.[28]

Notable detections

GRB 080319B, one of the brightest astronomical events ever detected, seen in X-ray and visible/UV light.
GRB 151027B, the 1000th GRB detected by Swift.
All-sky map of GRBs detected by Swift between 2004 and 2015.
Illustration of a brown dwarf combined with a graph of light curves from OGLE-2015-BLG-1319: Ground-based data (grey), Swift (blue), and Spitzer (red)

See also

References

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  5. ^ a b "Display: SWIFT (Explorer 84) 2004-047A". NASA. 28 October 2021. Retrieved 4 December 2021. Public Domain This article incorporates text from this source, which is in the public domain.
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Further reading

External links

Wikimedia Commons has media related to Swift Gamma-Ray Burst Mission.
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