VLA multifrequency observations of RS CVn binaries

Garcia-Sanchez, J.; Paredes, J. M.; Ribó, M.

doi:10.1051/0004-6361:20030361

Cited by 22 publications

(17 citation statements)

References 38 publications

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“…Such a frequency dependence is consistent with the observed properties of other magnetically active stars such as RS CVn systems: the fractional polarization tends to increase with frequency in the 5-15 GHz range (White & Franciosini 1995;García-Sánchez et al 2003). However, it is not easy to explain this behavior using simple theoretical models of gyrosynchrotron radiation, and inhomogeneous models were suggested (Jones et al 1994;White & Franciosini 1995).…”

Section: Frequency Dependence Of Polarizationsupporting

confidence: 79%

Centimeter Polarimetry of the R Coronae Australis Region

Choi

Tatematsu

Hamaguchi

et al. 2008

ApJ

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Circularly polarized 3.5 cm continuum emission was detected toward three radio sources in the R CrA region using the Very Large Array. The Class I protostar IRS 5b persistently showed polarized radio emission with a constant helicity over 8 yr, which suggests that its magnetosphere has a stable configuration. There is a good correlation between the Stokes I and Stokes V fluxes, and the fractional polarization is about 0.17. During active phases the fractional polarization is a weakly decreasing function of Stokes I flux, which suggests that IRS 5b is phenomenologically similar to other types of flare stars such as RS CVn binaries. The variability timescale of the polarized flux is about a month, and the magnetosphere of IRS 5b must be very large in size. The Class I protostar IRS 7A was detected once in circularly polarized radio emission, even though IRS 7A drives a thermal radio jet. This detection implies that the radio emission from the magnetosphere of a young protostar can escape the absorption by the partially ionized wind at least once in a while. The properties of IRS 7A and IRS 5b suggest that Class I protostars have organized peristellar magnetic fields of a few kilogauss and that the detectability of magnetospheric emission may depend on the evolutionary status of the protostar. Also reported is the detection of circularly polarized radio emission toward the variable radio source B5.

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Section: Frequency Dependence Of Polarizationsupporting

confidence: 79%

Centimeter Polarimetry of the R Coronae Australis Region

Choi

Tatematsu

Hamaguchi

et al. 2008

ApJ

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“…Given that the radio spectra of coronally active stars are approximately flat in the centimetre–decimetre range (e.g. García‐Sánchez, Paredes & Ribó 2003), and using the X‐ray–radio correlation mentioned above, we may estimate the radio luminosity of a GC stellar cusp at ν L ν ≲ 10 28 erg s −1 . For comparison, the measured quiescent luminosity of Sgr A* is much higher, namely ∼4 × 10 32 , ∼5 × 10 31 and ∼6 × 10 30 erg s −1 at 3.6, 26 and 90 cm, respectively (An et al 2005).…”

Section: Discussionmentioning

confidence: 99%

Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*

Sazonov¹,

Sunyaev²,

Revnivtsev³

2011

Monthly Notices of the Royal Astronomical Society

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Chandra has detected optically‐thin, thermal X‐ray emission with a size of ∼1 arcsec and luminosity ∼1033 erg s−1 from the direction of the Galactic supermassive black hole (SMBH), Sgr A*. We suggest that a significant or even dominant fraction of this signal may be produced by several thousand late‐type main‐sequence stars that possibly hide in the central ∼0.1 pc region of the Galaxy. As a result of tidal spin‐ups caused by close encounters with other stars and stellar remnants, these stars should be rapidly rotating and hence have hot coronae, emitting copious amounts of X‐ray emission with temperatures kT≲ a few keV. The Chandra data thus place an interesting upper limit on the space density of (currently unobservable) low‐mass main‐sequence stars near Sgr A*. This bound is close to and consistent with current constraints on the central stellar cusp provided by infrared observations. If coronally active stars do provide a significant fraction of the X‐ray luminosity of Sgr A*, then it should be moderately variable on hourly and daily time‐scales due to giant flares occurring on different stars. Another consequence is that the quiescent X‐ray luminosity and accretion rate of the SMBH are yet lower than believed before.

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“…The hollow markers indicate upper limits. For script and data used to generate the plot, see Bahramian et al (2018). ruled out (as the radio spectral index is reasonable; García-Sánchez et al 2003). The radio luminosity (L R = 6.9 × 10 26 erg s −1 ) can be reached by strong flares in some RS CVn systems (see e.g., García-Sánchez et al 2003), but is far above the steady radio luminosities seen for known lowmass ABs (see e.g., Guedel & Benz 1993).…”

Section: U18: a Hidden Msp?mentioning

confidence: 98%

“…The emission mechanism is generally attributed to gyrosynchrotron radiation of mildly rel-ativistic electrons interacting with photospheric magnetic fields (Hjellming & Gibson 1980;Feldman 1983;Gudel 1992;Kundu & Shevgaonkar 1985). They are generally observed to be non-thermal, highly variable and circularly polarised with flat or negative spectral indices (α 0; García-Sánchez et al 2003). An unusual system, a sub-subgiant 2 in a binary with either a very low-mass star, or else with a more massive compact object (possibly a BH) in an extremely face-on binary, is a radio and X-ray source in the globular cluster M10 (Shishkovsky et al 2018).…”

Section: Radio Sources In Globular Clustersmentioning

confidence: 99%

The MAVERIC survey: a hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397

Zhao

Heinke

Tudor

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Using a 16.2 hr radio observation by the Australia Telescope Compact Array (ATCA) and archival Chandra data, we found > 5σ radio counterparts to 4 known and 3 new X-ray sources within the half-light radius (r h ) of the Galactic globular cluster NGC 6397. The previously suggested millisecond pulsar (MSP) candidate, U18, is a steep-spectrum (S ν ∝ ν α ; α = −2.0 +0.4 −0.5 ) radio source with a 5.5 GHz flux density of 54.7 ± 4.3 µJy. We argue that U18 is most likely a "hidden" MSP that is continuously hidden by plasma shocked at the collision betwen the winds from the pulsar and companion star. The nondetection of radio pulsations so far is probably the result of enhanced scattering in this shocked wind. On the other hand, we observed the 5.5 GHz flux of the known MSP PSR J1740-5340 (U12) to decrease by a factor of >2.8 during epochs of 1.4 GHz eclipse, indicating that the radio flux is absorbed in its shocked wind. If U18 is indeed a pulsar whose pulsations are scattered, we note the contrast with U12's flux decrease in eclipse, which argues for two different eclipse mechanisms at the same radio frequency. In addition to U12 and U18, we also found radio associations for 5 other Chandra X-ray sources, four of which are likely background galaxies. The last, U97, which shows strong Hα variability, is mysterious; it may be either a quiescent black hole low-mass X-ray binary, or something more unusual.

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VLA multifrequency observations of RS CVn binaries

Cited by 22 publications

References 38 publications

Centimeter Polarimetry of the R Coronae Australis Region

Centimeter Polarimetry of the R Coronae Australis Region

Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*

The MAVERIC survey: a hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397

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