J/A+A/682/A97 The internal Faraday screen of Sagittarius A* (Wielgus+, 2024)
The internal Faraday screen of Sagittarius A*.
Wielgus M., Issaoun S., Marti-Vidal I., Emami R., Moscibrodzka M.,
Brinkerink Ch.D., Goddi C., Fomalont E.
<Astron. Astrophys. 682, A97 (2024)>
=2024A&A...682A..97W 2024A&A...682A..97W (SIMBAD/NED BibCode)
ADC_Keywords: Galactic center ; Black holes ; Millimetric/submm sources ;
Polarization
Keywords: black hole physics - magnetic fields - polarization -
techniques: interferometric - techniques: polarimetric -
Galaxy: center
Abstract:
We report on 85-101 GHz light curves of the Galactic Center
supermassive black hole, Sagittarius A* (Sgr A*), observed in April
2017 with the Atacama Large Millimeter/submillimeter Array (ALMA).
This study of high-cadence full-Stokes data provides new measurements
of the fractional linear polarization at a 1-2% level resolved in 4 s
time segments, and stringent upper limits on the fractional circular
polarization at 0.3%. We compare these findings to ALMA light curves
of Sgr A* at 212-230GHz observed three days later, characterizing a
steep depolarization of the source at frequencies below about 150GHz.
We obtain time-dependent rotation measure (RM) values, with the mean
RM at 85-101GHz being a factor of two lower than that at 212-230GHz.
Together with the rapid temporal variability of the RM and its
different statistical characteristics in both frequency bands, these
results indicate that the Faraday screen in Sgr A* is largely
internal, with about half of the Faraday rotation taking place inside
the inner 10 gravitational radii, contrary to the common external
Faraday screen assumption. We then demonstrate how this observation
can be reconciled with theoretical models of radiatively inefficient
accretion flows for a reasonable set of physical parameters.
Comparisons with numerical general relativistic magnetohydrodynamic
simulations suggest that the innermost part of the accretion flow in
Sgr A* is much less variable than these models predict; in particular,
the observed magnetic field structure appears to be coherent and
persistent.
Description:
Full Stokes light curves of Sagittarius A* observed in ALMA band 3 on
2017 April 3. Fully calibrated, averaged in 2GHz wide bands, as
presented in the paper.
Objects:
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RA (2000) DE Designation(s)
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17 45 40.03 -29 00 28.1 Sgr A* = SWIFT J1746.3-2850A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb0.dat 38 1353 Light curve observed at 86.3GHz
tableb1.dat 38 1353 Light curve observed at 88.3GHz
tableb2.dat 38 1353 Light curve observed at 98.3GHz
tableb3.dat 38 1353 Light curve observed at 100.3GHz
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See also:
J/A+A/549/A57 : Young, massive star candidates in Sgr A* (Nishiyama+, 2013)
J/ApJ/793/120 : Spitzer/IRAC Sgr A* light curve data (Hora+, 2014)
J/MNRAS/454/1525 : XMM-Newton and Chandra monitoring of Sgr A* (Ponti+, 2015)
J/A+A/589/A116 : Multiwavelength study of Sgr A* (Mossoux+, 2016)
J/A+A/601/A80 : LABOCA 345GHz observations of Sgr A* (Subroweit+, 2017)
J/A+A/603/A68 : Images of molecular and ionized gas around Sgr A*
(Moser+, 2017)
J/ApJ/859/60 : Sgr A* 1.3mm VLBI observations with the EHT in 2013
(Lu+, 2018)
J/ApJ/931/7 : Variability of Sgr A* in 2019 July (Boyce+, 2022)
Byte-by-byte Description of file: tableb0.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 h Time UTC time on 2017 April 3 in hours
9- 14 F6.4 Jy I Stokes I flux density in the 86.3GHz band
16- 22 F7.4 Jy Q Stokes Q flux density in the 86.3GHz band
24- 30 F7.4 Jy U Stokes U flux density in the 86.3GHz band
32- 38 F7.4 Jy V Stokes V flux density in the 86.3GHz band
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 h Time UTC time on 2017 April 3 in hours
9- 14 F6.4 Jy I Stokes I flux density in the 88.3GHz band
16- 22 F7.4 Jy Q Stokes Q flux density in the 88.3GHz band
24- 30 F7.4 Jy U Stokes U flux density in the 88.3GHz band
32- 38 F7.4 Jy V Stokes V flux density in the 88.3GHz band
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 h Time UTC time on 2017 April 3 in hours
9- 14 F6.4 Jy I Stokes I flux density in the 98.3GHz band
16- 22 F7.4 Jy Q Stokes Q flux density in the 98.3GHz band
24- 30 F7.4 Jy U Stokes U flux density in the 98.3GHz band
32- 38 F7.4 Jy V Stokes V flux density in the 98.3GHz band
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 h Time UTC time on 2017 April 3 in hours
9- 14 F6.4 Jy I Stokes I flux density in the 100.3GHz band
16- 22 F7.4 Jy Q Stokes Q flux density in the 100.3GHz band
24- 30 F7.4 Jy U Stokes U flux density in the 100.3GHz band
32- 38 F7.4 Jy V Stokes V flux density in the 100.3GHz band
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Acknowledgements:
Maciek Wielgus, maciek.wielgus(at)gmail.com
(End) Patricia Vannier [CDS] 19-Jan-2024