Samson betrayed by Delilah

Bruyn, J.; Haak, B.; Levie, S. H.; Thiel, P. J. J. Van; Wetering, E. Van De

doi:10.1007/978-94-009-7517-0_55

Cited by 11 publications

(15 citation statements)

References 2 publications

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“…The quiescent SED rises from centimeter to millimeter wavelengths, peaks around 0.8 mm (in flux density units; (Marrone et al 2006;Bower et al 2015), and declines through the IR and X-ray-the only other wavelengths where SgrA * has been clearly detected. The l n -S 0.5 radio spectrum is consistent with optically thick, stratified synchrotron emission (de Bruyn 1976), and the increasing slope ( l n -S 1 ) near the spectral peak, the "submillimeter bump" (Falcke et al 1998), has been interpreted as coming from the innermost regions of the accretion flow (Falcke et al 1998;Doeleman et al 2008;Dexter et al 2010). The transition from optically thick to thin emission appears to occur over a range of wavelengths in the millimeter/submillimeter regime (Marrone et al 2006;Bower et al 2015).…”

Section: Introduction Sagittarius Asupporting

confidence: 55%

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL

Stone

Marrone

Dowell

et al. 2016

ApJ

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Variable emission from SgrA * , the luminous counterpart to the super-massive black hole at the center of our Galaxy, arises from the innermost portions of the accretion flow. Better characterization of the variability is important for constraining models of the low-luminosity accretion mode powering SgrA * , and could further our ability to use variable emission as a probe of the strong gravitational potential in the vicinity of the´ M 4 10 6 black hole. We use the Herschel Spectral and Photometric Imaging Receiver (SPIRE) to monitor SgrA * at wavelengths that are difficult or impossible to observe from the ground. We find highly significant variations at 0.25, 0.35, and 0.5 mm, with temporal structure that is highly correlated across these wavelengths. While the variations correspond to <1% changes in the total intensity in the Herschel beam containing SgrA * , comparison to independent, simultaneous observations at 0.85 mm strongly supports the reality of the variations. The lowest point in the light curves, ∼0.5 Jy below the time-averaged flux density, places a lower bound on the emission of SgrA * at 0.25 mm, the first such constraint on the THz portion of the spectral energy distribution. The variability on few hour timescales in the SPIRE light curves is similar to that seen in historical 1.3 mm data, where the longest time series is available, but the distribution of variations in the sub-mm do not show a tail of large-amplitude variations seen at 1.3 mm. Simultaneous X-ray photometry from XMM-Newton shows no significant variation within our observing period, which may explain the lack of very large submillimeter variations in our data if X-ray and submillimeter flares are correlated.

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Section: Introduction Sagittarius Asupporting

confidence: 55%

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL

Stone

Marrone

Dowell

et al. 2016

ApJ

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“…A plausible simple extension of the homogeneous source model is a spherical source with a radial gradient in both B and in the number density of the relativistic electrons (e.g. de Bruyn 1976; Marscher 1977). In photospheric emission the flux at a given ν comes mostly from the region which is transiting from optically thick to optically thin at that ν.…”

Section: Some Implicationsmentioning

confidence: 99%

On the origin of radio emission in radio-quiet quasars

Laor

Behar

2008

Monthly Notices of the Royal Astronomical Society

204

287

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The radio emission in radio‐loud quasars originates in a jet carrying relativistic electrons. In radio‐quiet quasars (RQQs) the relative radio emission is ∼103 times weaker, and its origin is not established yet. We show here that there is a strong correlation between the radio luminosity (LR) and X‐ray luminosity (LX) with LR∼ 10−5LX, for the radio‐quiet Palomar–Green (PG) quasar sample. The sample is optically selected, with nearly complete radio and X‐ray detections, and thus this correlation cannot be due to direct selection biases. The PG quasars lie on an extension of a similar correlation noted by Panessa et al., for a small sample of nearby low‐luminosity type 1 active galactic nuclei (AGN). A remarkably similar correlation, known as the Güdel–Benz relation, where LR/LX∼ 10−5, holds for coronally active stars. The Güdel–Benz relation, together with correlated stellar X‐ray and radio variability, implies that the coronae are magnetically heated. We therefore raise the possibility that AGN coronae are also magnetically heated, and that the radio emission in RQQ also originates in coronal activity. If correct, then RQQ should generally display compact flat cores at a few GHz due to synchrotron self‐absorption, while at a few hundred GHz we should be able to see directly the X‐ray emitting corona, and relatively rapid and large amplitude variability, correlated with the X‐ray variability, is likely to be seen. We also discuss possible evidence that the radio and X‐ray emission in ultraluminous X‐ray sources and Galactic black holes may be of coronal origin as well.

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“…A more common mechanism may still be involved in the WR 147 system. De Bruyn (1976) showed that if the relativistic electrons in a synchrotron emitting zone are mixed with thermal ones, different spectral shapes can be achieved. He assumed spherical symmetry and isotropic relativistic particles.…”

Section: Origin Of the Non-thermal Emission In Wr 147mentioning

confidence: 99%

WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

Gunawan¹,

Bruyn²,

Hucht

et al. 2001

A&A

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Abstract. The results of more than 8-yr monitoring (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997) of the Wolf-Rayet binary WR 147 (WN8(h)+OB) with the Westerbork Synthesis Radio Telescope (WSRT) are presented. When the strong winds of the Wolf-Rayet (WR) and OB binary components collide, they produce non-thermal excess radiation in the region where the two winds interact. The binary system, monitored at 1.4 and 5 GHz (21 and 6 cm), is not resolved by the WSRT, thus we observed the total flux density of the system. The time-averaged 5 and 1.4-GHz flux densities are 35.4±0.4 mJy and 26.4 ± 0.3 mJy, respectively. These give a time-averaged spectral index of α5−1.4 GHz ≈ 0.23 ± 0.04, where Sν ∝ ν α . The departure from the value expected for thermal radiation from a spherically symmetric stellar wind, α = 0.6, can be attributed to non-thermal emission from a bow-shaped source to the north of the thermal source associated with the WN8 star. With a possible detection at 350 MHz of 16 ± 4 mJy, in our separate study of the Cygnus region, the spectral energy distribution, after the contribution of the southern thermal source is subtracted, can be fitted by a synchrotron emission model which includes free-free absorption. The nonthermal emission originates in the region where the winds of the binary components collide. This region, therefore, contains a mixture of relativistic particles accelerated by shocks and thermal particles, responsible for the free-free absorption. We show, in a simplified model of the system, that additional free-free absorption may occur when the line of sight to the collision region passes through the radiophotosphere of the WR wind. The 1.4-GHz flux density of WR 147 varied between ∼20 mJy and ∼30 mJy. We attribute the irregular, stochastic variations with a typical timescale of about 60 days to inhomogeneities in the wind, with different mechanisms involved in the flux-density increase than in the flux-density decrease. A flux-density increase results when the inhomogeneities in the wind/clumps enter the wind collision region, fuelling the synchrotron emission. The typical timescale of the flux-density decrease is shorter than the timescale of synchrotron loss (∼10 3 yr) or the Inverse-Compton lifetime (≈4.5 yr), but of the order of the flow time in the colliding-wind region (∼80 d). Therefore, we suggest that the flux-density decrease is due to plasma outflow from the system. Furthermore, variable free-free absorption due to large clumps passing the line of sight may also cause variations in the flux density. We observe a possible long-term flux-density variation on top of the stochastic variation. This variation is fitted with a sinusoid with a ∼7.9-yr period, with a reduced χ 2 of 1.9. However, as the period of the sinusoid is too close to the monitoring time span, further monitoring is needed to confirm this long-term variation.

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Samson betrayed by Delilah

Cited by 11 publications

References 2 publications

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL

On the origin of radio emission in radio-quiet quasars

WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

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Samson betrayed by Delilah

Cited by 11 publications

References 2 publications

FAR INFRARED VARIABILITY OF SAGITTARIUS A*: 25.5 hr OF MONITORING WITH HERSCHEL*

FAR INFRARED VARIABILITY OF SAGITTARIUS A*: 25.5 hr OF MONITORING WITH HERSCHEL*

On the origin of radio emission in radio-quiet quasars

WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

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Product

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About

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL

FAR INFRARED VARIABILITY OF SAGITTARIUS A: 25.5 hr OF MONITORING WITH HERSCHEL