J/A+A/625/A99 WR11 field at decimeter wavelengths (Benaglia+, 2019)
Investigation of the WR11 field at decimeter wavelengths.
Benaglia P., del Palacio S., Ishwara-Chandra C.H., De Becker M.,
Isequilla N.L., Saponara J.
<Astron. Astrophys. 625, A99 (2019)>
=2019A&A...625A..99B 2019A&A...625A..99B (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Stars, radio ; Stars, Wolf-Rayet
Keywords: radio continuum: general - radio continuum: stars -
radiation mechanisms: non-thermal - stars: individual: WR11
Abstract:
The massive binary system WR 11 (γ2-Velorum) has recently been
proposed as the counterpart of a Fermi source. If this association is
correct, this system would be the second colliding wind binary detected
in GeV γ-rays. However, the reported flux measurements from
1.4 to 8.64 GHz fail to establish the presence of nonthermal (synchrotron)
emission from this source. Moreover, WR 11 is not the only radio source
within the Fermi detection box. Other possible counterparts have been
identified in archival data, some of which present strong nonthermal
radio emission. We conducted arcsec-resolution observations toward WR 11
at very low frequencies (150-1400 MHz) where the nonthermal emission
- if existent and not absorbed - is expected to dominate. We present
a catalog of more than 400 radio emitters, among which a significant
portion are detected at more than one frequency, including limited
spectral index information. Twenty-one of these radio emitters are
located within the Fermi significant emission. A search for counterparts
for this last group pointed at MOST 0808-471; this source is 2' away
from WR 11 and is a promising candidate for high-energy emission, having
a resolved structure along 325-1390 MHz. For this source, we reprocessed
archive interferometric data up to 22.3 GHz and obtained a nonthermal
radio spectral index of -0.97±0.09. However, multiwavelength
observations of this source are required to establish its nature and
to assess whether it can produce (part of) the observed γ-rays.
WR 11 spectrum follows a spectral index of 0.74±0.03 from 150 to 230 GHz,
consistent with thermal emission. We interpret that any putative
synchrotron radiation from the colliding-wind region of this relatively
short-period system is absorbed in the photospheres of the individual
components. Notwithstanding, the new radio data allowed us to derive a
mass-loss rate of 2.5x10-5 M☉/yr, which, according to the latest
models for γ-ray emission in WR 11, would suffice to provide the
required kinetic power to feed nonthermal radiation processes.
Description:
Position, sizes and radio fluxes of 700 sources detected in the field
of the colliding-wind binary WR11, at images built from Giant
Metrewave Radio Telescope continuum data; observing bands centered at
150, 325, and 610MHz. The system WR11 (gamma2-Velorum) is
positionally coincident with a Fermi excess.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 144 700 Sources detected at 150, 325 and 610MHz
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- MACS MACS designation (GNNN-NNN), where GNNN
indicates the observed band
10- 11 I2 h RAh Right Ascension (J2000, Epoch 2000)
13- 14 I2 min RAm Right Ascension (J2000, Epoch 2000)
16- 19 F4.1 s RAs [] Right Ascension (J2000, Epoch 2000)
21- 24 F4.2 s e_RAs Mean error on RAs
26 A1 --- DE- Declination sign (J2000, Epoch 2000)
28- 29 I2 deg DEd Declination (J2000, Epoch 2000)
31- 32 I2 arcmin DEm Declination (J2000, Epoch 2000)
34- 37 F4.1 arcsec DEs [] Declination (J2000, Epoch 2000)
39- 41 F3.1 arcsec e_DEs Mean error on DEs
45- 52 F8.1 mJy S Integrated flux density of radio source
54- 58 F5.2 mJy e_S Mean error on S
60- 67 F8.1 mJy BS Peak flux density of radio source
69- 73 F5.2 mJy e_BS Mean error on BS
75- 76 I2 h RABh RAh maxima value
78- 79 I2 min RABm RAm maxima value
81- 84 F4.1 s RABs RAs maxima value
86- 89 F4.2 s e_RABs Mean error on BRAs
91 A1 --- DEB- Declination J2000 (sign)
93- 94 I2 deg DEBd DEd maxima value
96- 97 I2 arcmin DEBm DEm maxima value
99-102 F4.1 arcsec DEBs DEs maxima value
104-106 F3.1 arcsec e_DEBs Mean error on B_DEs
108-112 F5.1 arcsec Bmaj Beam major axis
114-117 F4.1 arcsec e_Bmaj Mean error on major axis
119-123 F5.1 arcsec Bmin Beam minor axis
125-128 F4.1 arcsec e_Bmin Mean error on minor axis
130-134 F5.1 deg bPA Beam position angle
136-140 F5.1 deg e_bPA Mean error on beam position angle
142-144 I3 MHz Band Radio band for the flux (150, 325 or 610)
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Acknowledgements:
Paula Benaglia, paula(at)iar-conicet.gov.ar
(End) Paula Benaglia [IAR, Argentina], Patricia Vannier [CDS] 23-Apr-2019