TXS 0506 056
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TXS 0506+056 is a very high energy blazar – a
quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...
with a
relativistic jet An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as extended beams along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets becom ...
pointing directly towards Earth – of BL Lac-type. With a redshift of 0.3365 ± 0.0010, it has a
luminosity distance Luminosity distance ''DL'' is defined in terms of the relationship between the absolute magnitude ''M'' and apparent magnitude ''m'' of an astronomical object. : M = m - 5 \log_\!\, which gives: : D_L = 10^ where ''DL'' is measured in parsecs. ...
of about . Its approximate location on the sky is off the left shoulder of the constellation Orion. Discovered as a radio source in 1983, the blazar has since been observed across the entire
electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
. TXS 0506+056 is the first known source of high energy astrophysical neutrinos, identified following the IceCube-170922A neutrino event in an early example of
multi-messenger astronomy Multi-messenger astronomy is the coordinated observation and interpretation of multiple signals received from the same astronomical event. Many types of cosmological events involve complex interactions between a variety of astrophysical processes, ...
. The only astronomical sources previously observed by
neutrino detector A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neutrinos. Neutrino ...
s were the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
and supernova 1987A, which were detected decades earlier at much lower neutrino energies.


Observational history

The object has been detected by numerous
astronomical survey An astronomical survey is a general celestial cartography, map or astrophotography, image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of image ...
s, so has numerous valid source designations. The most commonly used, TXS 0506+056, comes from its inclusion in the Texas Survey of radio sources (standard abbreviation TXS) and its approximate equatorial coordinates in the B1950 equinox used by that survey. TXS 0506+056 was first discovered as a radio source in 1983. It was identified as an active galaxy in the 1990s, and a possible blazar in the early 2000s. By 2009 it was regarded as a confirmed blazar and catalogued as a BL Lac object. Gamma rays from TXS 0506+056 were detected by the
EGRET Egrets ( ) are herons, generally long-legged wading birds, that have white or buff plumage, developing fine plumes (usually milky white) during the breeding season. Egrets are not a biologically distinct group from herons and have the same build ...
and Fermi Gamma-ray Space Telescope missions. Radio observations using
very-long-baseline interferometry Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. T ...
have shown apparent
superluminal motion In astronomy, superluminal motion is the apparently faster-than-light motion seen in some radio galaxies, BL Lac objects, quasars, blazars and recently also in some galactic sources called microquasars. Bursts of energy moving out along the ...
in the blazar's jet. TXS 0506+056 is one of the blazars regularly monitored by the OVRO 40 meter Telescope, so has an almost-continuous radio
light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...
recorded from 2008 onwards. The gamma-ray flux from TXS 0506+056 is highly variable, by at least a factor of a thousand, but on average it is in the top 4% of brightest gamma-ray sources on the sky. It is also very bright in radio waves, in the top 1% of sources. Given its distance, this makes TXS 0506+056 one of the most intrinsically powerful BL Lac objects known, particularly in high-energy gamma rays.


Neutrino emission

On September 22, 2017, the
IceCube Neutrino Observatory The IceCube Neutrino Observatory (or simply IceCube) is a neutrino observatory developed by the University of Wisconsin–Madison and constructed at the Amundsen–Scott South Pole Station in Antarctica. The project is a recognized CERN experime ...
detected a high energy
muon neutrino The muon neutrino is an elementary particle which has the symbol and zero electric charge. Together with the muon it forms the second generation of leptons, hence the name muon neutrino. It was discovered in 1962 by Leon Lederman, Melvin Schwa ...
, dubbed IceCube-170922A. The neutrino carried an energy of ~290 tera–electronvolts (TeV); for comparison, the
Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...
can generate a maximum energy of 13 TeV. Within one minute of the neutrino detection, IceCube sent an automated alert to astronomers around the world with coordinates to search for a possible source. A search of this region in the sky, 1.33 degrees across, yielded only one likely source: TXS 0506+056, a previously-known blazar, which was found to be in a flaring state of high
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
emission. It was subsequently observed at other wavelengths of light across the
electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
, including radio, infrared, optical, X-rays and gamma-rays. The detection of both neutrinos and light from the same object was an early example of
multi-messenger astronomy Multi-messenger astronomy is the coordinated observation and interpretation of multiple signals received from the same astronomical event. Many types of cosmological events involve complex interactions between a variety of astrophysical processes, ...
. A search of archived neutrino data from IceCube found evidence for an earlier flare of lower-energy neutrinos in 2014-2015 (a form of precovery), which supports identification of the blazar as a source of neutrinos. An independent analysis found no gamma-ray flare during this earlier period of neutrino emission, but supported its association with the blazar. The neutrinos emitted by TXS 0506+056 are six
orders of magnitude In a ratio scale based on powers of ten, the order of magnitude is a measure of the nearness of two figures. Two numbers are "within an order of magnitude" of each other if their ratio is between 1/10 and 10. In other words, the two numbers are wi ...
higher in energy than those from any previously-identified astrophysical neutrino source. The observations of high energy neutrinos and gamma-rays from this source imply that it is also a source of
cosmic rays Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar ...
, because all three should be produced by the same physical processes, though no cosmic rays from TXS 0506+056 have been directly observed. In the blazar, a charged
pion In particle physics, a pion (, ) or pi meson, denoted with the Greek alphabet, Greek letter pi (letter), pi (), is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the ...
was produced by the interaction of a high-energy proton or nucleus (i.e. a cosmic ray) with the radiation field or with matter. The pion then decayed into a
lepton In particle physics, a lepton is an elementary particle of half-integer spin (Spin (physics), spin ) that does not undergo strong interactions. Two main classes of leptons exist: electric charge, charged leptons (also known as the electron-li ...
and the neutrino. The neutrino interacts only weakly with matter, so it escaped the blazar. Upon reaching Earth, the neutrino interacted with the Antarctic ice to produce a
muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of  ''ħ'', but with a much greater mass. It is classified as a ...
, which was observed by the
Cherenkov radiation Cherenkov radiation () is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium (such as distilled water) at a speed greater than the phase velocity (speed of propagation of a wavefro ...
it generated as it moved through the IceCube detector. Analysis of 16 very long baseline radio array 15-GHz observations between 2009 and 2018 of TXS 0506+056 revealed the presence of a curved jet or potentially a collision of two jets, which could explain the 2014-2015 neutrino generation at the time of a low gamma-ray flux and indicate that TXS 0506+056 might be an atypical blazar. In 2020, a study using MASTER global telescope network found that TXS 0506+056 was in an 'off' state in the optical spectrum 1 minute after the alert for IceCube-170922A event and switched back on 2 hours later. This would indicate that the blazar was in a state of neutrino efficiency.


See also

* Messier 77 – a second neutrino source reported by IceCube in November 2022 * SN 1987A#Neutrino emissions – a burst of neutrinos observed to come from a supernova *
Neutrino astronomy Neutrino astronomy is a branch of astronomy that gathers information about astronomical objects by observing and studying neutrinos emitted by them with the help of neutrino detectors in special Earth observatories. It is an emerging field in as ...
*
GW170817 GW170817 was a gravitational wave (GW) observed by the LIGO and Virgo detectors on 17 August 2017, originating within the shell elliptical galaxy NGC 4993, about 144 million light years away. The wave was produced by the last moments of the in ...
– the first multi-messenger event involving gravitational waves; occurred five weeks before IceCube-170922A


References


External links


Frankfurt Quasar Monitoring: MG 0509+0541
with finding chart.
Aladin Lite view of Fermi data centered on TXS 0506+056
* {{Sky, 05, 09, 25.96370, +, 05, 41, 35.3279, 3700000000 Astronomical X-ray sources BL Lacertae objects Orion (constellation) Neutrino astronomy Radio galaxies