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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 ID2004-047AEdit this at Wikidata
SATCATno.28485
Websiteswift.gsfc.nasa.gov
Mission duration2 years (planned)[1]
19 years, 7 months, 25 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]
Power1040watts
Start of mission
Launch date20 November 2004, 17:16:01UTC
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 theSwift Gamma-Ray Burst Explorer,is aNASAthree-telescopespace observatoryfor studyinggamma-ray bursts(GRBs) and monitoring the afterglow in X-ray, and UV/Visible light at the location of a burst.[5]It was launched on 20 November 2004, aboard aDelta IIlaunch vehicle.[4]Headed byprincipal investigatorNeil Gehrelsuntil his death in February 2017, the mission was developed in a joint partnership betweenGoddard Space Flight Center(GSFC) and an international consortium from the United States, United Kingdom, and Italy. The mission is operated byPennsylvania State Universityas part of NASA'sMedium Explorer program(MIDEX).

The burst detection rate is 100 per year, with a sensitivity ~3 times fainter than the BATSE detector aboard theCompton 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, followingIMAGEandWMAP.[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]

Overview[edit]

Swift is a multi-wavelengthspace observatorydedicated to the study ofgamma-ray bursts.Its three instruments work together to observe GRBs and their afterglows in thegamma-ray,X-ray,ultraviolet,andopticalwavebands.

Based on continuous scans of the area of the sky with one of the instrument's monitors, Swift usesmomentum wheelsto 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 rapidslewcapability, and the nimbleswift(bird of the same name).[7]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 inState College, Pennsylvaniaand operated by thePennsylvania State Universityand industry subcontractors. The Swift main ground station is located at theBroglio Space CenternearMalindion the coast of easternKenya,and is operated by theItalian Space Agency(ASI). The Swift Science Data Center (SDC) and archive are located at the Goddard Space Flight Center outsideWashington, D.C.The United Kingdom Swift Science Data Centre is located at theUniversity of Leicester.

The Swiftsatellite buswas built bySpectrum Astro,which was later acquired byGeneral Dynamics Advanced Information Systems,[8]which was in turn acquired byOrbital Sciences Corporation(nowNorthrop Grumman Innovation Systems).

Instruments[edit]

Burst Alert Telescope (BAT)[edit]

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 onesteradianfully coded, three steradians partially coded; by comparison, the full sky solid angle is4πor about 12.6 steradians). It locates the position of each event with an accuracy of 1 to 4arcminuteswithin 15seconds.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 acoded-aperture maskof 52,000 randomly placed 5 mm (0.20 in)leadtiles, 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: 15–150keV.[9]

X-ray Telescope (XRT)[edit]

Swift before launch

The XRT[10]can take images and performspectral analysisof the GRB afterglow. This provides more precise location of the GRB, with a typical error circle of approximately 2arcsecondsradius. 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 aWolter Type I X-ray telescopewith 12 nested mirrors, focused onto a single MOScharge-coupled device(CCD) similar to those used by theXMM-NewtonEPIC 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.[11]

Ultraviolet/Optical Telescope (UVOT)[edit]

UVOT's "first light"image

After Swift has slewed towards a GRB, theUVOTis 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 UVgrisms.The UVOT is also used to provide long-term follow-ups of GRB afterglow lightcurves. The UVOT is based on theXMM-Newton's Optical Monitor (OM) instrument, with improved optics and upgraded onboard processing computers.[12]

On 9 November 2011, UVOT photographed the asteroid2005 YU55as theasteroidmade a close flyby of theEarth.[13]

On 3 June 2013, UVOT unveiled a massive ultraviolet survey of the nearbyMagellanic Clouds.[14]

In August 2017, UVOT imaged UV emissions from gravitational wave eventGW170817detected by LIGO & Virgo detectors.[15][16]

Experiments[edit]

A model of the satellite

Burst Alert Telescope (BAT)[edit]

BAT (Burst Alert Telescope) 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 theLos 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.[17]

Ultraviolet/Optical Telescope (UVOT)[edit]

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 2048photoncounting CCDpixels.The source location accuracy is better than one arcsecond.[18]

X-Ray Telescope (XRT)[edit]

XRT (X-Ray Telescope) aims at the source more accurately, and monitors the afterglow in X-rays. It was built jointly by thePennsylvania State University(PSU), theBrera Astronomical Observatory,Italy, and theUniversity 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.[19]

Mission goals[edit]

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 ahypernova,creating a gamma-ray beam. More data is needed to explore other explanations
  • To use GRBs to expand understanding of the younguniverse.GRBs seem to take place at "cosmological distances" of many millions or billions oflight-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 assupernova

Mission history[edit]

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

Swift was launched on 20 November 2004, at 17:16:01UTCaboard aDelta II7320-10C fromCape Canaveral Air Force Stationand reached a near-perfect orbit of 585 × 604 km (364 × 375 mi)altitude,with aninclinationof 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.[20]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.[21]

On 1 February 2005, the mission team released thefirst lightpicture of the UVOT instrument and declared Swift operational.

By May 2010, Swift had detected more than 500 GRBs.[22]

By October 2013, Swift had detected more than 800 GRBs.[23]

On 27 October 2015, Swift detected its 1,000th GRB, an event named GRB 151027B and located in the constellationEridanus.[24]

On 10 January 2018, NASA announced that the Swift spacecraft had been renamed the Neil Gehrels Swift Observatory in honor of mission PINeil Gehrels,who died in early 2017.[25][26]

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.[27]

Notable detections[edit]

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)
  • 9 May 2005: Swift detectedGRB 050509B,a burst of gamma rays that lasted one-twentieth of a second. The detection marked the first time that the accurate location of a short-duration gamma-ray burst had been identified and the first detection of X-ray afterglow in an individual short burst.[28][29]
  • 4 September 2005: Swift detectedGRB 050904with aredshiftvalue of 6.29 and a duration of 200 seconds (most of the detected bursts last about 10 seconds). It was also found to be the most distant yet detected, at approximately 12.6 billionlight-years.
  • 18 February 2006: Swift detectedGRB 060218,an unusually long (about 2000 seconds) and nearby (about 440 million light-years) burst, which was unusually dim despite its close distance, and may be an indication of an imminentsupernova.
  • 14 June 2006: Swift detectedGRB 060614,a burst of gamma rays that lasted 102 seconds in a distant galaxy (about 1.6 billion light-years). No supernova was seen following this event (andGRB 060505to deep limits) leading some to speculate that it represented a new class of progenitors. Others suggested that these events could have been massive star deaths, but ones which produced too little radioactive56Nito power a supernova explosion.
  • 9 January 2008: Swift was observing a supernova inNGC 2770when it witnessed an X-ray burst coming from the same galaxy. The source of this burst was found to be the beginning of another supernova, later calledSN 2008D.Never before had a supernova been seen at such an early stage in its evolution. Following this stroke of luck (position, time, most appropriate instruments), astronomers were able to study in detail thisType Ibc supernovawith theHubble Space Telescope,theChandra X-ray Observatory,theVery Large ArrayinNew Mexico,theGemini Northtelescope inHawaii,Gemini Southin Chile, theKeck Itelescope in Hawaii, the 1.3 m (4 ft 3 in) PAIRITEL telescope atMount Hopkins,the200-inchand 60 in (1,500 mm) telescopes at thePalomar ObservatoryinCalifornia,and the 3.5 m (11 ft) telescope at theApache Point Observatoryin New Mexico. The significance of this supernova was likened by discovery team leaderAlicia Soderbergto that of theRosetta Stonefor egyptology.[30]
  • 8 and 13 February 2008: Swift provided critical information about the nature ofHanny's Voorwerp,mainly the absence of an ionizing source within the Voorwerp or in the neighboringIC 2497.
  • 19 March 2008: Swift detectedGRB 080319B,a burst of gamma rays amongst the brightest celestial objects ever witnessed. At 7.5 billionlight-years,Swiftestablished a new record for the farthest object (briefly) visible to the naked eye. It was also said to be 2.5 million times intrinsically brighter than the previousbrightest accepted supernova (SN 2005ap).Swiftobserved a record four GRBs that day, which also coincided with the death of noted science-fiction writerArthur C. Clarke.[31]
  • 13 September 2008: Swift detectedGRB 080913,at the time the most distant GRB observed (12.8 billion light-years) until the observation ofGRB 090423a few months later.[32][33]
  • 23 April 2009: Swift detectedGRB 090423,the most distant cosmic explosion ever seen at that time, at 13.035 billion light-years. In other words, the universe was only 630 million years old when this burst occurred.[34]
  • 29 April 2009: Swift detectedGRB 090429B,which was found by later analysis published in 2011 to be 13.14 billion light-years distant (approximately equivalent to 520 million years after the Big Bang), even farther than GRB 090423.[35]
  • 16 March 2010: Swift tied its record by again detecting and localizing four bursts in a single day.
  • 13 April 2010: Swift detected its 500th GRB.[36]
  • 28 March 2011: Swift detected Swift J1644+57 which subsequent analysis showed to possibly be the signature of a star being disrupted by a black hole or the ignition of an active galactic nucleus.[37]"This is truly different from any explosive event we have seen before", saidJoshua Bloomof theUniversity of California, Berkeley,the lead author of the study published in the June issue ofScience.[38]
  • 16 and 17 September 2012: BAT triggered two times on a previously unknown hard X-ray source, namedSw J1745-26,a few degrees from theGalactic Center.The outburst, produced by a rare X-ray nova, announced the presence of a previously unknown stellar-mass black hole undergoing a dramatic transition from the low/hard to the high/soft state.[39][40][41]
  • 2013: Discovery of ultra-long class of gamma-ray bursts
  • 24 April 2013: Swift detected an X-ray flare from the Galactic Center. This proved not to be related toSgr A*but to a previously unsuspectedmagnetar.Later observations by theNuSTARand theChandra X-ray Observatoryconfirmed the detection.[42]
  • 27 April 2013: Swift detected the "shockingly bright" Gamma-ray burstGRB 130427A.Observed simultaneously by theFermi Gamma-ray Space Telescope,it is one of the five closest GRBs detected and one of the brightest seen by either space telescope.[43]
  • 3 June 2013: Evidence for kilonova emission in short GRB
  • 23 April 2014: Swift detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from anearby red dwarf star.The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded.[44]
  • 3 May 2014: Detection of a UV Pulse from an iPTF discovered young Type Ia SN
  • June–July 2015: Thebrown dwarfOGLE-2015-BLG-1319 was discovered using thegravitational microlensingdetection method in a joint effort between Swift,Spitzer Space Telescope,and the ground-basedOptical Gravitational Lensing Experiment,the first time two space telescopes have observed the same microlensing event. This method was possible because of the large separation between the two spacecraft: Swift is inlow Earth orbitwhile Spitzer is more than oneAUdistant in an Earth-trailingheliocentric orbit.This separation provided significantly different perspectives of the brown dwarf, allowing for constraints to be placed on some of the object's physical characteristics.[45]
  • 27 October 2015: Swift detected its 1000th gamma-ray burst, GRB 151027B.[24]
  • 18 August 2017: Swift discovers UV emission from thekilonovaAT 2017gfo,the electromagnetic counterpart toGW170817.[16]
  • 23 September 2017: Swift is the first to identifyTXS 0506+056as the possible source of the IceCube-170922A extremely high energy (EHE)neutrinos.[46]
  • 14 January 2019: Swift discovers the most powerful observed gamma-ray burst,GRB 190114C,reachingteraelectronvoltenergies.[47]
  • 09 October 2022: Swift discovers, simultaneously with Fermi,GRB 221009A,one of the closest GRBs ever detected and the brightest ever detected.

See also[edit]

References[edit]

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Further reading[edit]

External links[edit]

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