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, followingIMAGE andWMAP.[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 follow-up 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]
Based on continuous scans of the area of the sky with one of the instrument's monitors, Swift usesmomentum 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 rapidslew capability, 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 BAT detects GRB events and computes its coordinates in the sky. It covers a large fraction of the sky (over onesteradian fully coded, three steradians partially coded; by comparison, the full sky solid angle is4π or about 12.6 steradians). It locates the position of each event with an accuracy of 1 to 4arcminutes within 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 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: 15–150keV.[9]
The XRT[10] can take images and performspectral analysis of the GRB afterglow. This provides more precise location of the GRB, with a typical error circle of approximately 2arcseconds 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 aWolter Type I X-ray telescope with 12 nested mirrors, focused onto a single MOScharge-coupled device (CCD) similar to those used by theXMM-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.[11]
After Swift has slewed towards a GRB, theUVOT 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 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 YU55 as theasteroid made 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 eventGW170817 detected byLIGO & Virgo detectors.[15][16]
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]
UVOT (Ultraviolet/Optical Telescope) monitors the afterglow inultraviolet and visible light, and locates the source at an accuracy of onearcsecond. Its aperture is 30 cm (12 in), with anf-number equal to 12.7, and is backed by 2048 x 2048photon counting CCDpixels. The source location accuracy is better than one arcsecond.[18]
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]
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 assupernovae
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 light picture 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 (after the 2nd of 4 gyroscopes failed) 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]
NASA announced in September 2025 that due to natural orbital decay exacerbated by increased solar activity, Swift needed to be boosted to a higher orbit. NASA issued a contract to a private U.S. firm to perform the boost in 2026.[28]
GRB 080319B, one of the brightest astronomical events ever detected, seen in X-ray and visible/UV lightGRB 151027B, the 1000th GRB detected by SwiftAll-sky map of GRBs detected by Swift between 2004 and 2015Illustration 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.[29][30]
4 September 2005: Swift detectedGRB 050904 with aredshift value 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 060505 to 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 radioactive56Ni to power a supernova explosion.
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,Swift established 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).Swift observed a record four GRBs that day, which also coincided with the death of noted science-fiction writerArthur C. Clarke.[32]
13 September 2008: Swift detectedGRB 080913, at the time the most distant GRB observed (12.8 billion light-years) until the observation ofGRB 090423 a few months later.[33][34]
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.[35]
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.[36]
16 March 2010: Swift tied its record by again detecting and localizing four bursts in a single day.
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.[38] "This is truly different from any explosive event we have seen before", saidJoshua Bloom of theUniversity of California, Berkeley, the lead author of the study published in the June issue ofScience.[39]
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.[40][41][42]
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 theNuSTAR and theChandra X-ray Observatory confirmed the detection.[43]
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.[44]
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.[45]
3 May 2014: Detection of a UV Pulse from an iPTF discovered young Type Ia SN
June–July 2015: Thebrown dwarf OGLE-2015-BLG-1319 was discovered using thegravitational microlensing detection 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 orbit while Spitzer is more than oneAU distant 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.[46]
27 October 2015: Swift detected its 1000th gamma-ray burst, GRB 151027B.[24]
^"Swift Explorer"(PDF). NASA. 1 November 2004. Retrieved18 December 2016. This article incorporates text from this source, which is in thepublic domain.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
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