SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF Sgr A* DURING 2007 APRIL 1-11

Journal Article · Fri Nov 20 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/706/1/348· OSTI ID:21378193

Yusef-Zadeh, F ^[1]; Bushouse, H ^[2]; Wardle, M ^[3]; Heinke, C ^[4]; Roberts, D A ^[5]; Dowell, C D ^[6]; Brunthaler, A ^[7]; Reid, M J ^[8]; Martin, C L ^[9]; Marrone, D P ^[10]; Porquet, D; Grosso, N ^[11]; Dodds-Eden, K; Gillessen, S ^[12]; Bower, G C ^[13]; Wiesemeyer, H ^[14]; Miyazaki, A ^[15]; Pal, S ^[16]; Goldwurm, A ^[17]

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1. Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)
2. STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
3. Department of Physics and Engineering, Macquarie University, Sydney NSW 2109 (Australia)
4. Department of Physics, University of Alberta, Room 238 CEB, 11322-89 Avenue, Edmonton AB T6G 2G7 (Canada)
5. Adler Planetarium and Astronomy Museum, 1300 South Lake Shore Drive, Chicago, IL 60605 (United States)
6. Cal Tech, Jet Propulsion Laboratory, Pasadena, CA 91109 (United States)
7. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)
8. Harvard-Smithsonian CfA, 60 Garden Street, Cambridge, MA 02138 (United States)
9. Oberlin College, Department of Physics and Astronomy, Professor 110 N. St., Oberlin, OH 44074 (United States)
10. National Radio Astronomy Observatory, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
11. Observatoire astronomique de Strasbourg, Universite de Strasbourg, NRS, INSU, 11 rue de l'Universite, 67000 Strasbourg (France)
12. Max-Plank-Institut fuer Extraterrestrische Physik 1312, D-85471 Garching (Germany)
13. Radio Astronomy Lab, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)
14. Institut de RadioAstronomie Millimetrique, 300 rue de la Piscine, Domaine Universitaire 38406 Saint Martin d'Heres (France)
15. Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Mizusawa, Oshu, Iwate 023-0861 (Japan)
16. School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)
17. Service d'Astrophysique/IRFU/DSM, CEA Saclay, Bat. 709, 91191 Gif-sur-Yvette Cedex (France)

We report the detection of variable emission from Sgr A* in almost all wavelength bands (i.e., centimeter, millimeter, submillimeter, near-IR, and X-rays) during a multi-wavelength observing campaign. Three new moderate flares are detected simultaneously in both near-IR and X-ray bands. The ratio of X-ray to near-IR flux in the flares is consistent with inverse Compton scattering of near-IR photons by submillimeter emitting relativistic particles which follow scaling relations obtained from size measurements of Sgr A*. We also find that the flare statistics in near-IR wavelengths is consistent with the probability of flare emission being inversely proportional to the flux. At millimeter wavelengths, the presence of flare emission at 43 GHz (7 mm) using the Very Long Baseline Array with milliarcsecond spatial resolution indicates the first direct evidence that hourly timescale flares are localized within the inner 30 x 70 Schwarzschild radii of Sgr A*. We also show several cross-correlation plots between near-IR, millimeter, and submillimeter light curves that collectively demonstrate the presence of time delays between the peaks of emission up to 5 hr. The evidence for time delays at millimeter and submillimeter wavelengths are consistent with the source of emission initially being optically thick followed by a transition to an optically thin regime. In particular, there is an intriguing correlation between the optically thin near-IR and X-ray flare and optically thick radio flare at 43 GHz that occurred on 2007 April 4. This would be the first evidence of a radio flare emission at 43 GHz delayed with respect to the near-IR and X-ray flare emission. The time delay measurements support the expansion of hot self-absorbed synchrotron plasma blob and weaken the hot spot model of flare emission. In addition, a simultaneous fit to 43 and 84 GHz light curves, using an adiabatic expansion model of hot plasma, appears to support a power law rather than a relativistic Maxwellian distribution of particles.

• OSTI ID: 21378193
• Journal Information: Astrophysical Journal, Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/348; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BLACK HOLES
COMPTON EFFECT
CORRELATIONS
EMISSION
GALAXIES
GHZ RANGE 01-100
HOT PLASMA
HOT SPOTS
PHOTONS
PROBABILITY
RELATIVISTIC RANGE
SCHWARZSCHILD RADIUS
SPATIAL RESOLUTION
TIME DELAY
WAVELENGTHS
X RADIATION
BASIC INTERACTIONS
BOSONS
ELASTIC SCATTERING
ELECTROMAGNETIC INTERACTIONS
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY RANGE
FREQUENCY RANGE
GHZ RANGE
INTERACTIONS
IONIZING RADIATIONS
MASSLESS PARTICLES
PLASMA
RADIATIONS
RESOLUTION
SCATTERING