A polarized infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots

In this article we summarize and discuss the infrared, radio and X-ray emission from the supermassive black hole in the Galactic Centre, SgrA*. We include new results from near-infrared polarimetric imaging observations obtained on 2006 May 31. In that night, a strong flare in K s band (2.08 μm) reaching top fluxes of ∼16 mJy could be observed. This flare was highly polarized (up to ∼40 per cent) and showed clear substructure on a time-scale of 15 min, including a swing in the polarization angle of about 70°. For the first time we were able to observe both polarized flux and short-time variability, with high significance in the same flare event. This result adds decisive information to the puzzle of the SgrA* activity. The observed polarization angle during the flare peak is the same as observed in two events in 2004 and 2005. Our observations strongly support the dynamical emission model of a decaying plasma hotspot orbiting SgrA* on a relativistic orbit. The observed polarization parameters and their variability with time might allow to constrain the orientation of accretion disc and spin axis with respect to the Galaxy.

[1]  T. Paumard,et al.  Variations in the spectral slope of Sgr A* during a NIR flare , 2006 .

[2]  S. Trippe,et al.  Polarimetry of near-infrared flares from Sagittarius A* , 2006, astro-ph/0610103.

[3]  J. Krolik,et al.  Light Curves from an MHD Simulation of a Black Hole Accretion Disk , 2006, astro-ph/0606615.

[4]  H. Falcke,et al.  The Rotation Measure and 3.5 Millimeter Polarization of Sagittarius A* , 2006, astro-ph/0606381.

[5]  Los Angeles,et al.  Diffraction-limited Imaging Spectroscopy of the Sagittarius A* Region Using OSIRIS, a New Keck Instrument , 2006, astro-ph/0605253.

[6]  J. M. Moran,et al.  Interferometric Measurements of Variable 340 GHz Linear Polarization in Sagittarius A* , 2005, astro-ph/0511653.

[7]  T. Paumard,et al.  Variations in the Spectral Slope of Sagittarius A* during a Near-Infrared Flare , 2005, astro-ph/0511302.

[8]  S. Shapiro,et al.  A Multiwavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-Ray, Soft γ-Ray, and Submillimeter Emission , 2005, astro-ph/0510787.

[9]  J. Pétri,et al.  Forced oscillations in a hydrodynamical accretion disk and QPOs , 2005, astro-ph/0509668.

[10]  Harvard University,et al.  Imaging optically-thin hotspots near the black hole horizon of Sgr A* at radio and near-infrared wavelengths , 2005, astro-ph/0509237.

[11]  H. Falcke,et al.  The Rotation Measure and 3.5 Mm Polarization of Sgr A , 2006 .

[12]  W. Brandt,et al.  The flare activity of Sagittarius A : New coordinated mm to X-ray observations , 2005, astro-ph/0512440.

[13]  Andrea Goldwurm,et al.  Repeated X-Ray Flaring Activity in Sagittarius A* , 2005, astro-ph/0508412.

[14]  Norbert Hubin,et al.  SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month , 2005 .

[15]  D. Rouan,et al.  A dual emission mechanism in Sgr A*/L ' ? ⋆ , 2005, astro-ph/0507088.

[16]  C.Dumas,et al.  SINFONI in the Galactic Center: young stars and IR flares in the central light month , 2005, astro-ph/0502129.

[17]  Jessica R. Lu,et al.  The First Laser Guide Star Adaptive Optics Observations of the Galactic Center: Sgr A*’s Infrared Color and the Extended Red Emission in its Vicinity , 2005, astro-ph/0508664.

[18]  H. Falcke,et al.  Variable Linear Polarization from Sagittarius A*: Evidence of a Hot Turbulent Accretion Flow , 2004, astro-ph/0411551.

[19]  Bernard Delabre,et al.  First light of SINFONI at the VLT , 2004 .

[20]  H Germany,et al.  Detection of the Sgr A* activity at 3.8 and 4.8 $\mathsf{\mu}$m with NACO , 2004, astro-ph/0407527.

[21]  Francois Lacombe,et al.  Detection of the Sgr A activity at 3.8 and 4.8 µm with NACO , 2004 .

[22]  A. Miyazaki,et al.  Intraday Variation of Sagittarius A* at Short Millimeter Wavelengths , 2004, astro-ph/0407252.

[23]  Garching,et al.  X-ray flares reveal mass and angular momentum of the Galactic Center black hole , 2004, astro-ph/0401589.

[24]  Ramesh Narayan,et al.  On the Nature of the Variable Infrared Emission from Sagittarius A* , 2004, astro-ph/0401429.

[25]  Caltech,et al.  Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way , 2003, astro-ph/0309076.

[26]  D. Rouan,et al.  Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre , 2003, Nature.

[27]  Ralf Bender,et al.  The universe in 3D : First observations with SPIFFI, the infrared integral field spectrometer for the VLT , 2003 .

[28]  J. Krolik,et al.  Magnetically Driven Accretion Flows in the Kerr Metric. I. Models and Overall Structure , 2003, astro-ph/0307260.

[29]  Rashid Sunyaev,et al.  X-ray flares from Sgr A$^*$: Star-disk interactions? , 2003 .

[30]  Anne-Marie Lagrange,et al.  NAOS-CONICA first on sky results in a variety of observing modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[31]  Norbert N. Hubin,et al.  SINFONI - Integral field spectroscopy at 50 milli-arcsecond resolution with the ESO VLT , 2003, SPIE Astronomical Telescopes + Instrumentation.

[32]  G. Bower.  Linear and Circular Polarization from Sagittarius A* and M81* , 2003, astro-ph/0302228.

[33]  Geoffrey C. Bower,et al.  Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHz , 2003, astro-ph/0302227.

[34]  David Mouillet,et al.  NAOS, the first AO system of the VLT: on-sky performance , 2003, SPIE Astronomical Telescopes + Instrumentation.

[35]  Norbert N. Hubin,et al.  Implementation of MACAO for SINFONI at the VLT, in NGS and LGS modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[36]  United Kingdom,et al.  A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton Photon Imaging Cameras , 2002, astro-ph/0207620.

[37]  Caltech,et al.  Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre , 2001, Nature.

[38]  H. Falcke,et al.  The Nature of the 10 kilosecond X-ray flare in Sgr A* , 2001, astro-ph/0109081.

[39]  Fulvio Melia,et al.  Electron Acceleration around the Supermassive Black Hole at the Galactic Center , 2001, astro-ph/0106162.

[40]  S. Kato.  Basic Properties of Thin-Disk Oscillations , 2001 .

[41]  UCLA,et al.  Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy , 2001, astro-ph/0102151.

[42]  K. Kjär,et al.  About The ESO Messenger , 2000 .

[43]  Holland,et al.  Detection of Polarized Millimeter and Submillimeter Emission from Sagittarius A* , 2000, The Astrophysical journal.

[44]  Reinhard Genzel,et al.  Variable and Embedded Stars in the Galactic Center , 1999 .

[45]  H. Falcke,et al.  Detection of Circular Polarization in the Galactic Center Black Hole Candidate Sagittarius A* , 1999, astro-ph/9907215.

[46]  H. Falcke,et al.  The Linear Polarization of Sagittarius A*. I. VLA Spectropolarimetry at 4.8 and 8.4 GHz , 1999, astro-ph/9904091.

[47]  Reinhard Genzel,et al.  High Angular Resolution Spectroscopic and Polarimetric Imaging of the Galactic Center in the Near-Infrared , 1995 .

[48]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[49]  R. L. Brown,et al.  Intense sub-arcsecond structure in the galactic center , 1974 .

[50]  R. Daves.  Radio Astrophysics , 1970, Nature.