The X-ray ribs within the cocoon shock of Cygnus A

We use new and archival Chandra observations of Cygnus A, totalling ∼1.9 Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon shock and exhibiting a rib-like structure. We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly 2 × 1010M⊙. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity.

[1]  M. Hardcastle,et al.  Numerical modelling of the lobes of radio galaxies in cluster environments – IV. Remnant radio galaxies , 2013, Monthly Notices of the Royal Astronomical Society.

[2]  C. Carilli,et al.  The Cocoon Shocks of Cygnus A: Pressures and Their Implications for the Jets and Lobes , 2018, 1802.10106.

[3]  Erdal Yiğit,et al.  Introduction to Plasma , 2018 .

[4]  A. Hillier,et al.  The non-linear growth of the magnetic Rayleigh-Taylor instability , 2017, 1707.07987.

[5]  D. Perley,et al.  Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A , 2017, 1705.07901.

[6]  M. C. Toribio,et al.  LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra , 2016, 2103.16961.

[7]  A. Edge,et al.  Mass Distribution in Galaxy Cluster Cores , 2016, 1610.04617.

[8]  M. Donahue,et al.  MOLECULAR GAS ALONG A BRIGHT Hα FILAMENT IN 2A 0335+096 REVEALED BY ALMA , 2016, 1610.00716.

[9]  R. Kraft,et al.  Buoyancy-driven inflow to a relic cold core: the gas belt in radio galaxy 3C 386 , 2016, 1604.05946.

[10]  A. Edge,et al.  A MECHANISM FOR STIMULATING AGN FEEDBACK BY LIFTING GAS IN MASSIVE GALAXIES , 2016, 1604.04629.

[11]  NuSTAR observations of the powerful radio-galaxy Cygnus A , 2015, 1506.07175.

[12]  P. Gibbon,et al.  Introduction to Plasma Physics , 2017, 2007.04783.

[13]  H. Martel,et al.  MAJOR CLUSTER MERGERS AND THE LOCATION OF THE BRIGHTEST CLUSTER GALAXY , 2014, 1403.3063.

[14]  A. Fabian,et al.  A volume-limited sample of X-ray galaxy groups and clusters – I. Radial entropy and cooling time profiles , 2013, 1312.0798.

[15]  E. Mannering,et al.  Galaxy gas ejection in radio galaxies: the case of 3C 35 , 2013, 1302.1585.

[16]  H. Böhringer,et al.  Discovery of an X-ray cavity near the radio lobes of Cygnus A indicating previous AGN activity , 2012, 1207.0699.

[17]  F. Guo,et al.  DYNAMICS INSIDE THE RADIO AND X-RAY CLUSTER CAVITIES OF CYGNUS A AND SIMILAR FRII SOURCES , 2012, 1206.4997.

[18]  R. Morganti,et al.  The jet-cloud interacting radio galaxy PKS B2152-699. I. Structures revealed in new deep radio and X-ray observations , 2012, 1205.4726.

[19]  W. Mathews,et al.  SELF-CONSISTENT EVOLUTION OF GAS AND COSMIC RAYS IN CYGNUS A AND SIMILAR FR II CLASSICAL DOUBLE RADIO SOURCES , 2010, 1010.4899.

[20]  M. Kino,et al.  EVIDENCE OF NON-THERMAL X-RAY EMISSION FROM RADIO LOBES OF CYGNUS A , 2010, 1003.3104.

[21]  M. J. Hardcastle,et al.  Searching for the inverse-Compton emission from bright cluster-centre radio galaxies , 2010, 1001.4742.

[22]  K. Blundell,et al.  Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma , 2009, 0909.1073.

[23]  Megan Donahue,et al.  INTRACLUSTER MEDIUM ENTROPY PROFILES FOR A CHANDRA ARCHIVAL SAMPLE OF GALAXY CLUSTERS , 2009, 0902.1802.

[24]  P. S. Bunclark,et al.  Astronomical Data Analysis Software and Systems , 2008 .

[25]  K. Blundell,et al.  Multiwavelength study of Cygnus A – II. X-ray inverse-Compton emission from a relic counterjet and implications for jet duty cycles , 2008, 0805.2172.

[26]  R. Sutherland,et al.  Interactions of a Light Hypersonic Jet with a Nonuniform Interstellar Medium , 2007, 0707.3668.

[27]  R. Kraft,et al.  The Interaction between Radio Lobes and Hot Gas in the Nearby Radio Galaxies 3C 285 and 3C 442A , 2007, astro-ph/0703080.

[28]  M. Birkinshaw,et al.  The Effect of a Chandra-measured Merger-related Gas Component on the Lobes of a Dead Radio Galaxy , 2007, astro-ph/0702411.

[29]  S. Borgani,et al.  Temperature profiles of a representative sample of nearby X-ray galaxy clusters , 2006, astro-ph/0609480.

[30]  J. Sanders.  Contour binning: a new technique for spatially-resolved X-ray spectroscopy applied to Cassiopeia A , 2006, astro-ph/0606528.

[31]  W. C. Erickson,et al.  Cygnus A: A Long-Wavelength Resolution of the Hot Spots , 2006, astro-ph/0603717.

[32]  A. Wilson,et al.  The Cavity of Cygnus A , 2006, astro-ph/0603435.

[33]  M. Birkinshaw,et al.  Multiwavelength Evidence of the Physical Processes in Radio Jets , 2004, astro-ph/0410297.

[34]  Danielle Alloin,et al.  Physics of active galactic nuclei at all scales , 2006 .

[35]  C. Jones,et al.  ERRATUM: “CHANDRA SAMPLE OF NEARBY RELAXED GALAXY CLUSTERS: MASS, GAS FRACTION, AND MASS–TEMPERATURE RELATION” (2006, ApJ, 640, 691) , 2005, astro-ph/0507092.

[36]  W. B. Burton,et al.  The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI - Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections , 2005, astro-ph/0504140.

[37]  R. Antonucci,et al.  Adaptive Optics Imaging and Spectroscopy of Cygnus A. I. Evidence for a Minor Merger , 2003, astro-ph/0307376.

[38]  K. Arnaud,et al.  A Chandra X-Ray Study of Cygnus A. II. The Nucleus , 2001, astro-ph/0109527.

[39]  K. Arnaud,et al.  A Chandra X-Ray Study of Cygnus A. III. The Cluster of Galaxies , 2001, astro-ph/0109488.

[40]  D. Liedahl,et al.  Collisional Plasma Models with APEC/APED: Emission-Line Diagnostics of Hydrogen-like and Helium-like Ions , 2001, astro-ph/0106478.

[41]  C. Crawford,et al.  Chandra imaging of the X-ray core of Abell 1795 , 2000, astro-ph/0011547.

[42]  A. Edge,et al.  Molecular hydrogen emission in Cygnus A , 2000, astro-ph/0007223.

[43]  The Cluster of Galaxies Surrounding Cygnus A , 1997, astro-ph/9708150.

[44]  C. Carilli,et al.  Multifrequency radio observations of Cygnus A - Spectral aging in powerful radio galaxies , 1991 .

[45]  J. Dickey,et al.  H I in the Galaxy , 1990 .

[46]  N. Grevesse,et al.  Abundances of the elements: Meteoritic and solar , 1989 .

[47]  C. Carilli,et al.  Faraday rotation of Cygnus A - magnetic fields in cluster gas , 1987 .

[48]  W. Forman,et al.  The intracluster gas around Cygnus-A , 1984 .

[49]  A. W. Trivelpiece,et al.  Introduction to Plasma Physics , 1976 .