Multifrequency observations of blazars. III - The spectral shape of the radio to X-ray continuum

Brown, L. M. J.; Robson, E. I.; Gear, W. K.; Hughes, D. H.; Griffin, Matthew Joseph; Geldzahler, B. J.; Schwartz, P. R.; Smith, M. G.; Smith, Alex; Shepherd, David W.; Webb, J. R.; Valtaoja, E.; Teräsranta, H.; Salonen, E.

doi:10.1086/167380

Cited by 64 publications

(21 citation statements)

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“…The scale on our detector is 2.29 arcsec/pixel and we used typically for our aperture photometry a radius of 3 pixels (12 Kpc at z = 0.07), so the host galaxy of BL Lac is substantially within our aperture. The apparent magnitude of this galaxy has been estimated B ∼ 18.3, V ∼ 16.8 (Brown et al 1989), one magnitude fainter than the lowest value recorded by us in this period (V = 15.9). Data reduction was performed with the APPHOT tasks within the IRAF package, using the comparison stars given by Smith et al (1985), which were all within our instrument field of view.…”

Section: Optical Photometrycontrasting

confidence: 53%

“…The fainter value in the last 15 years was reported by Carini et al (1992) on 1980-May-13 when BL Lac was observed at V = 16.73, but two days after it has already raised to V = 15.17. Such a faint level corresponds to the estimated value for the host galaxy (Brown et al 1989) so that in this case the central engine of BL Lac should have switched off for a while. We conclude therefore that BL Lac attained similarly low levels also in the past, but there is no evidence that it remained for long times at a level substantially fainter than that recorded by us.…”

Section: Discussionmentioning

confidence: 56%

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BVRI photometry of BL Lacertae in 1993-1995

Maesano

Montagni

Massaro

et al. 1997

Astron. Astrophys. Suppl. Ser.

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Abstract. The results of optical photometry of BL Lac over a time interval of two years in the B, V, R, I filters are presented. The source is found for most of the time in a low state. The mean colour indexes are similar to those observed in higher luminosity states, however a flattening of the spectral slope was present during three small amplitude outbursts. A brief comparison with the observations available in the literature and some considerations on the physical conditions driving the appearance of emission lines are made.

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Section: Optical Photometrycontrasting

confidence: 53%

Section: Discussionmentioning

confidence: 56%

BVRI photometry of BL Lacertae in 1993-1995

Maesano

Montagni

Massaro

et al. 1997

Astron. Astrophys. Suppl. Ser.

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“…Detailed modelling, however, shows that this simple criterion has to be used with care. For example, the strongly inverted "edges" often seen in the radio-millimetre spectra of variable blazars (Valtaoja et al 1988;Brown et al 1989;Krichbaum et al 2008; Planck Collaboration 2011d,e) can be explained both by synchrotron self-absorbed emission from a compact, shocked region with temporarily enhanced emission compared to the surrounding jet (e.g., Valtaoja et al 1988;Brown et al 1989;Türler et al 2000;Rachen et al 2010), and by decreasing inclination angle in a steady but rotating helical jet (Ostorero et al 2004). The same ambiguity affects the interpretation of helically moving VLBI components (Savolainen et al 2002;Bach et al 2006;Rastorgueva et al 2009;Jorstad et al 2010).…”

Section: Physics Of Blazars and Models For Variabilitymentioning

confidence: 99%

Long-term variability of extragalactic radio sources in thePlanckEarly Release Compact Source Catalogue

Chen

Rachen

López‐Caniego

et al. 2013

A&A

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Combining measurements taken using the Wilkinson Microwave Anisotropy Probe (WMAP) from 2001 to 2008 with measurements taken using Planck from 2009 to 2010, we investigate the long-term flux density variability of extragalactic radio sources selected from the Planck Early Release Compact Source Catalogue. The single-year, single-frequency WMAP maps are used to estimate yearly-averaged flux densities of the sources in the four WMAP bands: Ka (33 GHz), Q (41 GHz), V (61 GHz), and W (94 GHz). We identify 82, 67, 32, and 15 sources respectively as variable at greater than 99% confidence level in these four bands. The amplitudes of variation are comparable between bands, and are not correlated with either the flux densities or the spectral indices of the sources. The number counts of WMAP Ka-band sources are stable from year to year despite the fluctuation caused by individual source variability. Most of our sources show strong correlation in variability between bands. Almost all the sources that show variability are blazars. We have attempted to fit two simple, four-parameter models to the time-series of 32 sources showing correlated variability at multiple frequencies -a long-term flaring model and a rotating-jet model. We find that 19 sources (60%) can be fit with the simple rotating-jet model, and ten of these also fit the simple long-term flaring model. The remaining 13 sources (40%) show more complex variability behaviour that is not consistent with either model. Extended radio galaxies in our sample show no sign of variability, as expected, with the exception of Pictor A for which we report evidence for a millimetre flare lasting between 2002 and 2010.

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“…PKS 0736+01 (z ¼ 0:191, 1 00 ' 3:14 kpc) was classified as a blazar by Angel & Stockman (1980), as a compact flat-spectrum radio quasar by Wall & Peacock (1985), and as optically violently variable by Brown et al (1989). The host galaxy was described as an elliptical by Wright et al (1998), McLure et al (1999), Falomo & Ulrich (2000), and Hamilton et al (2002).…”

Section: A2 Pks 0736+01mentioning

confidence: 99%

Evidence for Merger Remnants in Early‐Type Host Galaxies of Low‐Redshift QSOs1

Bennert

Canalizo

Jungwiert

et al. 2008

ApJ

167

206

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We present results from a pilot HST ACS deep imaging study in broadband Vof five low-redshift QSO host galaxies classified in the literature as ellipticals. The aim of our study is to determine whether these early-type hosts formed at high redshift and have since evolved passively, or whether they have undergone relatively recent mergers that may be related to the triggering of the nuclear activity. We perform two-dimensional modeling of the light distributions to analyze the host galaxies' morphology. We find that, while each host galaxy is reasonably well fitted by a de Vaucouleurs profile, the majority of them (4/5) reveal significant fine structure such as shells and tidal tails. These structures contribute between $5% and 10% to the total V-band luminosity of each host galaxy within a region of r $ 3r eA and are indicative of merger events that occurred between a few hundred Myr and a Gyr ago. These timescales are comparable to starburst ages in the QSO hosts previously inferred from Keck spectroscopy. Our results thus support a consistent scenario in which most of the QSO host galaxies suffered mergers with accompanying starbursts that likely also triggered the QSO activity in some way, but we are also left with considerable uncertainty on physical mechanisms that might have delayed this triggering for several hundred Myr after the merger.

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Multifrequency observations of blazars. III - The spectral shape of the radio to X-ray continuum

Cited by 64 publications

References 0 publications

BVRI photometry of BL Lacertae in 1993-1995

BVRI photometry of BL Lacertae in 1993-1995

Long-term variability of extragalactic radio sources in thePlanckEarly Release Compact Source Catalogue

Evidence for Merger Remnants in Early‐Type Host Galaxies of Low‐Redshift QSOs1

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