J/ApJ/802/69 VLA, ALMA and SMA monitoring of Sgr A* (Bower+, 2015)
Radio and millimeter monitoring of Sgr A*: spectrum, variability, and
constraints on the G2 encounter.
Bower G.C., Markoff S., Dexter J., Gurwell M.A., Moran J.M., Brunthaler A.,
Falcke H., Fragile P.C., Maitra D., Marrone D., Peck A., Rushton A.,
Wright M.C.H.
<Astrophys. J., 802, 69 (2015)>
=2015ApJ...802...69B 2015ApJ...802...69B
ADC_Keywords: Active gal. nuclei ; Accretion ; Milky Way ; Radio continuum ;
Millimetric/submm sources
Keywords: accretion, accretion disks; black hole physics; galaxies: active;
galaxies: jets; Galaxy: center
Abstract:
We report new observations with the Very Large Array, Atacama Large
Millimeter Array, and Submillimeter Array at frequencies from 1.0 to
355GHz of the Galactic Center black hole, Sagittarius A*. These
observations were conducted between 2012 October and 2014 November.
While we see variability over the whole spectrum with an amplitude as
large as a factor of 2 at millimeter wavelengths, we find no evidence
for a change in the mean flux density or spectrum of Sgr A* that can
be attributed to interaction with the G2 source. The absence of a bow
shock at low frequencies is consistent with a cross-sectional area for
G2 that is less than 2x1029cm2. This result fits with several model
predictions including a magnetically arrested cloud, a
pressure-confined stellar wind, and a stellar photosphere of a binary
merger. There is no evidence for enhanced accretion onto the black
hole driving greater jet and/or accretion flow emission. Finally, we
measure the millimeter wavelength spectral index of Sgr A* to be flat;
combined with previous measurements, this suggests that there is no
spectral break between 230 and 690GHz. The emission region is thus
likely in a transition between optically thick and thin at these
frequencies and requires a mix of lepton distributions with varying
temperatures consistent with stratification.
Description:
VLA observations were carried out as part of a service observing
program on the advice of an ad hoc committee (project code TOBS0006;
Sjouwerman & Chandler 2014IAUS..303..327S 2014IAUS..303..327S) between late 2012 and
mid-2014 at frequencies between 1 and 41GHz. See section 2.1.
We carried out ALMA observations between mid-2013 and mid-2014, over
eight epochs, each with band 6 (230GHz) and band 7 (345GHz) receivers.
See section 2.2.
Observations of the flux density of Sgr A* were obtained using the
SMA, an interferometric array of eight 6m diameter radio dishes
located near the summit of Mauna Kea, Hawaii. Data were obtained
during short (∼20 minutes), self-contained observation sets, in which
observations of Sgr A* alternated with those of the relatively nearby
blazar J1733-130. See section 2.3.
Objects:
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RA (ICRS) DE Designation(s)
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17 45 40.04 -29 00 28.2 Sgr A* = NAME Sgr A*
17 45 40.04 -29 00 28.1 G2 = NAME G2 Dust Cloud
17 33 02.71 -13 04 49.5 J1733-130 = IERS B1730-130
14 27 56.300 -42 06 19.54 J1427-421 = IERS B1424-418
17 00 53.154 -26 10 51.73 J1700-261 = IERS B1657-261
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 40 120 VLA results of Sgr A*
table5.dat 72 30 ALMA results of Sgr A*, J1427-421, J1700-261,
J1733-130
table6.dat 47 137 SMA results (Hawaii) of Sgr A*
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "YYYY/MM/DD" Date Date of the observation (2012/2014)
12- 15 F4.1 GHz Freq [1.5/41] Frequency
17- 21 F5.3 Jy S [0.5/2]? Mean flux density
23- 27 F5.3 Jy e_S [0.002/0.3]? Uncertainty in Flux
29- 34 F6.3 Jy DelS [-0.5/0.6] Flux density excess
36- 40 F5.3 Jy e_DelS [0.001/1.1] Uncertainty in DelS
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "YYYY/MM/DD" Date Date of the observation (2013/2014)
12- 20 A9 --- ID Source identifier
22- 26 F5.3 Jy S218.0 [0.7/4.7]? The 218.0GHz flux density
28- 32 F5.3 Jy S220.0 ? The 220.0GHz flux density
34- 38 F5.3 Jy S231.9 ? The 231.9GHz flux density
40- 44 F5.3 Jy S233.8 [0.7/4.8]? The 233.8GHz flux density
46- 51 F6.3 Jy S341.6 ? The 341.6GHz flux density
53- 58 F6.3 Jy S343.6 ? The 343.6GHz flux density
60- 65 F6.3 Jy S351.7 ? The 351.7GHz flux density
67- 72 F6.3 Jy S353.6 [0.5/4.6]? The 353.6GHz flux density
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "YYYY/MM/DD" Obs.date Date of the observation (2013/2014)
12- 16 A5 "h:m" Obs.time UT time of the observation
18- 23 F6.2 GHz Freq [213.2/356.2] Frequency
25- 29 F5.3 Jy SSgrA* [1.9/6.1] Sgr A* flux density
31- 35 F5.3 Jy e_SSgrA* [0.1/0.5] Uncertainty in SSgrA*
37- 41 F5.3 Jy SJ1733 [0.6/1.7] J1733-130 flux density
43- 47 F5.3 Jy e_SJ1733 [0.06/0.4] Uncertainty in SJ1733
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Jul-2015