# Markarian 501

Markarian 501
Sloan Digital Sky Survey image of Mrk 501
Observation data (J2000 epoch)
ConstellationHercules
Right ascension 16h 53m 52.21s[1]
Declination39° 45′ 37.6″[1]
Redshift9915±25 km/s or 0.033640 Z
Distance456 Mly (140 Mpc; 4.32x1024 m)
Group or clusterzw1707.6+4045
Characteristics
TypeS0 [2]
Size~159,000–12,581,000 ly (48.8–3,857.4 kpc) (estimated)[2][a]
Apparent size (V)94.86" × 71.1" [2]
Notable featuresbrightest object in very-high-energy gamma rays
Other designations
4C39.49

Markarian 501 (or Mrk 501) is a galaxy with a spectrum extending to the highest energy gamma rays.[3] 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 (0.1 TeV), it is the brightest object in the sky.[4] The object has a redshift of z = 0.034.[5]

The galaxy hosting the blazar was studied and catalogued by Benjamin Markarian in 1974.[6] It was first determined to be a very high energy gamma ray emitter in 1996 by J. Quinn at the Whipple Observatory.[5][7]

## Galaxy

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.[8]

## Gamma rays

The gamma rays from Mrk 501 are extremely variable, undergoing violent outbursts.[5] 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.[5] Flares lasting 20 minutes long 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.[9] This delay has led to various theories, including that space is bigger at small dimensions with a foamy quantum texture.[10] 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. However, 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.[11] The galaxy is also variable in visible light between magnitude 14.5 and 13.6.[12]

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[7]

## Black hole

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.[13] A 23-day variability suggested that an object may be orbiting the central black hole with a 23-day period.[13]

## Jet

With Very Long Baseline Interferometry radio waves fine detail 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 comes out in a narrow cone shape as a one sided jet. After 30 milliarcseconds the jet does a 90° turn and fans out. The jet is 300 pc long. 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, and slower edges.[14] Normally there would be jets of gas shooting out in opposite directions. The observed jet is the one that faces the earth and project plasma towards the earth. There is also a jet heading away from the 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.[15] Beyond 10 kpc from the core the counter jet becomes visible, showing that the jets have become non-relativistic (plasma is no longer moving close to the speed of light).[15] The symmetrical radio emission extends to 70" which corresponds to 120 to 200 kpc.[15]

## Catalog entries

Early designations were 4C 39.49 and B2 1652+39.[16] The Uppsala General Catalogue of Galaxies lists this as UGC 10599.[17]

Other designations: B1652+39 or 1H1652+398 or TeV J1653+397.[18]

## Notes

1. ^ Calculated from apparent size and distance:${\displaystyle 456Mly*sin(1.2-94.86arcmin)=159,000-12,581,000ly}$

## References

1. ^ a b Ochsenbein, F.; Bauer, P.; Marcout, J. (10 April 2000). "The VizieR database of astronomical catalogues". Astronomy & Astrophysics Supplement Series. 143: 23–32. arXiv:astro-ph/0002122. Bibcode:2000A&AS..143...23O. doi:10.1051/aas:2000169.
2. ^ a b c "Results for Mrk 501". MARKARIAN2 – Markarian Galaxies Optical Database. Retrieved 2011-12-06. Data base query page is at http://heasarc.nasa.gov/db-perl/W3Browse/w3table.pl?tablehead=name%3Dmarkarian2&Action=More+Options. Fill in Mrk 501 for name and click start search at bottom of page.
3. ^ Aharonian, F. A. (1999). "The time averaged TeV energy spectrum of Mkn 501 of the extraordinary 1997 outburst as measured with the stereoscopic Cherenkov telescope system of HEGRA" (PDF). Astronomy and Astrophysics. 349: 11–28. arXiv:astro-ph/9903386. Bibcode:1999A&A...349...11A.
4. ^ Protheroe, Ray J.; C.L. Bhat; P. Fleury; E. Lorenz; M. Teshima; T.C. Weekes (12 October 1997). "Very high energy gamma rays from Markarian 501" (PDF). arXiv:astro-pn/9710118v1.
5. ^ a b c d Acciari, V. A.; et al. (VERITAS Collaboration and MAGIC Collaboration) (2011). "Spectral Energy Distribution of Markarian 501: Quiescent State vs. Extreme Outburst". Astrophysical Journal. 729 (2): 2. arXiv:1012.2200. Bibcode:2011ApJ...729....2A. doi:10.1088/0004-637X/729/1/2.
6. ^ Markaryan, B. E.; V. A. Lipovetskii (1974). "Galaxies with ultraviolet continuum V". Astrophysics. 8 (2): 89–99. Bibcode:1972Ap......8...89M. doi:10.1007/BF01002156. ISSN 0571-7256.
7. ^ a b Quinn J, Akerlof CW, Biller S, Buckley J, Carter-Lewis DA, Cawley MF, Catanese M, Connaughton V, et al. (10 January 1996). "Detection of Gamma Rays with E > 300 GeV from Markarian 501". The Astrophysical Journal Letters. 465 (2): L83–L86. Bibcode:1996ApJ...456L..83Q. doi:10.1086/309878.
8. ^
9. ^ Albert, J; et al. (MAGIC Collaboration) (5 December 2007). "Variable VHE gamma-ray emission from Markarian 501" (PDF). The Astrophysical Journal. 669 (2): 862–883. arXiv:astro-ph/0702008. Bibcode:2007ApJ...669..862A. doi:10.1086/521382.
10. ^ Albert J, Ellis J, Mavromatos NE, Nanopoulos DV, Sakharov AS, Sarkisyan EKG (2008). "Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope". Physics Letters B. 668 (4): 253–257. arXiv:0708.2889. Bibcode:2008PhLB..668..253M. doi:10.1016/j.physletb.2008.08.053.
11. ^ "Einstein Makes Extra Dimensions Toe The Line". NASA. Retrieved 19 December 2011.
12. ^ Barbieri, G; G. Romano (1977). "The optical variability of the galaxy Markarian 501". Acta Astronomica. 27 (2): 195–197. Bibcode:1977AcA....27..195B.
13. ^ a b Rieger, F. M.; Mannheim, K. (2003). "On the central black hole mass in Mkn 501". Astronomy and Astrophysics. 397: 121–125. arXiv:astro-ph/0210326v1. Bibcode:2003A&A...397..121R. doi:10.1051/0004-6361:20021482.
14. ^ Bondi, M.; L. Feretti; M. Giroletti; K.-H. Mack; F. Mantovani; C. Stanghellini; T. Venturi; D. Dallacasa; et al. "Very Long Baseline Interferometry Research". Instituto di Radioastronomia. Archived from the original on 3 February 2010. Retrieved 6 December 2011. with further detail at arXiv:astro-ph/0309285
15. ^ a b c Giroletti, M.; G. Giovannini; L. Feretti; W.D. Cotton; P.G. Edwards; L. Lara; A.P. Marscher; J.R. Mattox; et al. (11 September 2003). "Parsec Scale Properties of Markarian 501" (PDF). Retrieved 6 December 2011.
16. ^ Ulrich, Marie Helene; Shakeshaft, John R. (1974). "Optical Observations of Nuclei of Galaxies". The Formation and Dynamics of Galaxies. Dordrecht, Holland: Kluwer Academic Publishers. p. 292. ISBN 978-90-277-0461-0.
17. ^ "UGC 10599". VII/26D/catalog Uppsala General Catalogue of Galaxies (UGC) (Nilson 1973). Retrieved 9 December 2011.
18. ^ "Markarian 501". TeVCat. Retrieved 10 December 2011.