Markarian 501 | |
---|---|
Observation data (J2000 epoch) | |
Constellation | Hercules |
Right ascension | 16h 53m 52.21s [1] |
Declination | 39° 45′ 37.6″ [1] |
Redshift | 9915±25 km/s or 0.033640 Z |
Distance | 456 Mly (140 Mpc; 4.32x1024 m) |
Group or cluster | zw1707.6+4045 |
Characteristics | |
Type | S0 [2] |
Size | ~210,000 ly (64 kpc) (estimated) [3] [2] [lower-alpha 1] |
Apparent size (V) | 94.86" × 71.1" [2] |
Notable features | brightest object in very-high-energy gamma rays |
Other designations | |
4C39.49, PGC 59214, UGC 10599 |
Markarian 501 (or Mrk 501) is a galaxy with a spectrum extending to the highest energy gamma rays. [4] It is a blazar or BL Lac object, which is an active galactic nucleus with a jet that is shooting towards the Earth.
In the very-high-energy gamma ray region of the spectrum, at energies above 1011 eV (100 GeV), it is the brightest object in the sky. [5] The object has a redshift of z = 0.034. [6]
The galaxy hosting the blazar was studied and catalogued by Benjamin Markarian in 1974. [7] It was first determined to be a very high energy gamma ray emitter in 1996 by John Quinn at the Whipple Observatory. [6] [8]
The elliptical galaxy is located in the constellation of Hercules at right ascension 16h 53.9m and declination +39° 45'. Its visible size appears to be 1.2 by 1 minute of arc. [9]
The gamma rays from Mrk 501 are extremely variable, undergoing violent outbursts. [6] The gamma ray spectrum of Mrk 501 shows two humps. One is below 1 keV and can be considered to be X-rays and the other is above 1 TeV. During flares and outbursts the peaks increase in power and frequency. [6] Flares lasting 20 minutes with rise times of 1 minute have been measured by MAGIC. In these flares the higher energy gamma rays (of 1.2 Tev) were delayed 4 minutes over the 0.25 TeV gamma rays. [10] This delay has led to various theories, including that space is bigger at small dimensions with a foamy quantum texture. [11] The foam would create a variation in the speed of light for higher-energy light gamma-rays and the lower-energy radio waves and visible light. Such a variation would contradict Lorentz invariance, but could provide a clue for unification theory. Observations of Dr. Floyd Stecker of NASA's Goddard Space Flight Center of Mrk 501 and Mrk 421 demonstrated that there is no violation of Lorentz invariance. [12] The galaxy is also variable in visible light between magnitude 14.5 and 13.6. [13]
During the discovery observations flashes at the average rate of one in seven minutes were observed. Cosmic rays (that is, fermionic or massive cosmic rays, as opposed to photons) were ruled out by the shape and size of the flashes which are small and elliptical for gamma rays. The flux for photons over 300 GeV at this point in time in 1995 was 8.1±1.5 x 10−12 cm−2s−1 [8]
Blazars are likely to originate from matter falling into a black hole and possibly a binary black hole. The velocity dispersion (which is the maximum difference in the velocity toward or away from Earth) observed in the galaxy is 372 km/s which predicts a black hole mass of (0.9 − 3.4) × 109 M⊙. However, dispersion of velocity was also measured as 291 and 270 km/s so the central mass may be less. [14] A 23-day variability suggested that an object may be orbiting the central black hole with a 23-day period. [14]
With very-long-baseline interferometry, the fine detail of radio waves can be seen down to milliarcsecond (mas) resolution. A central very bright single point called the core is observed. From the core an extremely high-speed blast of plasma emerges in a narrow cone shape as a one-sided jet.
After 30 milliarcseconds, the jet, which is 300 pc long, does a 90° turn and fans out. The inner jet before the kink shows bright edges or a limb-brightened structure less than 10 mas wide. This is probably due to a fast-moving central part to the jet, combined with slower edges. [15]
Normally, there would be jets of gas shooting out in opposite directions. The observed jet is the one that faces the earth and projects plasma towards Earth. There is also a jet heading away from Earth called a counter jet. Close into the core, this counter jet is so much dimmer than the main jet that it is invisible in radio waves.
The brightness of the counter jet is less than the main jet by a factor of 1250. This implies that the jet is relativistic with Γ about 15 (that is, the plasma is moving at 99.8% of the speed of light) and at an angle between 15° and 25° from the line of sight from the Earth. At 408 MHz, the power level is 1.81 Jy, although this is variable. [16]
Beyond 10 kpc from the core, the counter jet becomes visible, showing that the jets have become non-relativistic; that is, plasma is no longer moving close to the speed of light. [16] The symmetrical radio emission extends to 70", which corresponds to 120 to 200 kpc. [16]
In March 2022, scientists led by Ioannis Liodakis studied Markarian 501 during an average state while discerning how blazars make such a bright light using Imaging X-ray Polarimetry Explorer (IXPE.) The researchers were "able to show that the particles in these jets are supercharged by shock fronts, resolving a longstanding 'unanswered question' about the dynamics of these brilliant objects." [17] [18]
We’ve known about these sources from the 60s. They are among the brightest objects in X-rays and for years we did not know how the X-rays are made. We had a few theories, but the radio and optical data we could get are not able to tell us much.
— Ioannis Liodakis, Postdoctoral Researcher, Finnish Centre for Astronomy with ESO
Early designations were 4C 39.49 and B2 1652+39. [19] The Uppsala General Catalogue of Galaxies lists this as UGC 10599. [20]
Other designations: B1652+39 or 1H1652+398 or TeV J1653+397. [21]
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milliseconds to several hours. After an initial flash of gamma rays, a longer-lived "afterglow" is usually emitted at longer wavelengths.
3C 273 is a quasar located at the center of a giant elliptical galaxy in the constellation of Virgo. It was the first quasar ever to be identified and is the visually brightest quasar in the sky as seen from Earth, with an apparent visual magnitude of 12.9. The derived distance to this object is 749 megaparsecs. The mass of its central supermassive black hole is approximately 886 million times the mass of the Sun.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.
A blazar is an active galactic nucleus (AGN) with a relativistic jet directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth. Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales. Some blazar jets exhibit apparent superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.
A BL Lacertae object or BL Lac object is a type of active galactic nucleus (AGN) or a galaxy with such an AGN, named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical polarization. Because of these properties, the prototype of the class was originally thought to be a variable star. When compared to the more luminous active nuclei (quasars) with strong emission lines, BL Lac objects have spectra dominated by a relatively featureless non-thermal emission continuum over the entire electromagnetic range. This lack of spectral lines historically hindered identification of the nature and distance of such objects.
MAGIC is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, at about 2200 m above sea level. MAGIC detects particle showers released by gamma rays, using the Cherenkov radiation, i.e., faint light radiated by the charged particles in the showers. With a diameter of 17 meters for the reflecting surface, it was the largest in the world before the construction of H.E.S.S. II.
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 become relativistic jets as they show effects from special relativity.
VERITAS is a major ground-based gamma-ray observatory with an array of four 12 meter optical reflectors for gamma-ray astronomy in the GeV – TeV photon energy range. VERITAS uses the Imaging Atmospheric Cherenkov Telescope technique to observe gamma rays that cause particle showers in Earth's atmosphere that are known as extensive air showers. The VERITAS array is located at the Fred Lawrence Whipple Observatory, in southern Arizona, United States. The VERITAS reflector design is similar to the earlier Whipple 10-meter gamma-ray telescope, located at the same site, but is larger in size and has a longer focal length for better control of optical aberrations. VERITAS consists of an array of imaging telescopes deployed to view atmospheric Cherenkov showers from multiple locations to give the highest sensitivity in the 100 GeV – 10 TeV band. This very high energy observatory, completed in 2007, effectively complements the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope due to its larger collection area as well as coverage in a higher energy band.
Markarian 421 is a blazar located in the constellation Ursa Major. The object is an active galaxy and a BL Lacertae object, and is a strong source of gamma rays. It is about 397 million light-years to 434 million light-years (133Mpc) from the Earth. It is one of the closest blazars to Earth, making it one of the brightest quasars in the night sky. It is suspected to have a supermassive black hole (SMBH) at its center due to its active nature. An early-type high inclination spiral galaxy is located 14 arc-seconds northeast of Markarian 421.
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3C 66B is an elliptical Fanaroff and Riley class 1 radio galaxy located in the constellation Andromeda. With an estimated redshift of 0.021258, the galaxy is about 300 million light-years away.
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Markarian 231 is a Type-1 Seyfert galaxy that was discovered in 1969 as part of a search of galaxies with strong ultraviolet radiation. It contains the nearest known quasar. Markarian 231 is located about 581 million light years away from Earth, in the constellation of Ursa Major.
Very-high-energy gamma ray (VHEGR) denotes gamma radiation with photon energies of 100 GeV (gigaelectronvolt) to 100 TeV (teraelectronvolt), i.e., 1011 to 1014 electronvolts. This is approximately equal to wavelengths between 10−17 and 10−20 meters, or frequencies of 2 × 1025 to 2 × 1028 Hz. Such energy levels have been detected from emissions from astronomical sources such as some binary star systems containing a compact object. For example, radiation emitted from Cygnus X-3 has been measured at ranges from GeV to exaelectronvolt-levels. Other astronomical sources include BL Lacertae, 3C 66A Markarian 421 and Markarian 501. Various other sources exist that are not associated with known bodies. For example, the H.E.S.S. catalog contained 64 sources in November 2011.
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