BL Lacertae Type Objects Research Articles

Short timescale photometric and polarimetric behavior of two BL Lacertae type objects

Blazars are astrophysical sources whose emission is dominated by non-thermal processes, typically interpreted as synchrotron and inverse Compton emission. Although the general picture is rather robust and consistent with observations, many aspects are still unexplored. Polarimetric monitoring can offer a wealth of information about the physical processes in blazars. Models with largely different physical ingredients can often provide almost indistinguishable predictions for the total flux, but usually are characterized by markedly different polarization properties. We explore, with a pilot study, the possibility to derive structural information about the emitting regions of blazars by means of a joint analysis of rapid variability of the total and polarized flux at optical wavelengths. Short timescale (from tens of seconds to a couple of minutes) optical linear polarimetry and photometry for two blazars, BL Lacertae and PKS 1424+240, was carried out with the PAOLO polarimeter at the 3.6m Telescopio Nazionale Galileo. Several hours of almost continuous observations were obtained for both sources. Our intense monitoring allowed us to draw strongly different scenarios for BL Lacertae and PKS 1424+240, with the former characterized by intense variability on time-scales from hours to a few minutes and the latter practically constant in total flux. Essentially the same behavior is observed for the polarized flux and the position angle. The variability time-scales turned out to be as short as a few minutes, although involving only a few percent variation of the flux. The polarization variability time-scale is generally consistent with the total flux variability. Total and polarized flux appear to be essentially uncorrelated. However, even during our relatively short monitoring, different regimes can be singled out. (abridged)

Radio-optical-gamma-ray properties of MOJAVE AGN detected byFermi/LAT

Aims. We use a sample of 83 core-dominated active galactic nuclei (AGN) selected from the MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) radio-flux-limited sample and detected with the Fermi Large Area Telescope (LAT) to study the relations between non-simultaneous radio, optical, and gamma-ray measurements. Methods. We perform a multi-band statistical analysis to investigate the relations between the emissions in different bands and reproduce these relations by modeling of the spectral energy distributions of blazars. Results. There is a significant correlation between the gamma-ray luminosity and the optical nuclear and radio (15 GHz) luminosities of blazars. We report a well defined positive correlation between the gamma-ray luminosity and the radio-optical loudness for quasars and BL Lacertae type objects (BL Lacs). A strong positive correlation is found between the radio luminosity and the gamma-ray-optical loudness for quasars, while a negative correlation between the optical luminosity and the gamma-ray-radio loudness is present for BL Lacs. Modeling of these correlations with a simple leptonic jet model for blazars indicates that variations of the accretion disk luminosity (and hence the jet power) is able to reproduce the trends observed in most of the correlations. To reproduce all observed correlations, variations of several parameters, such as the accretion power, jet viewing angle, Lorentz factor, and magnetic field of the jet, are required.

THE EFFECT OF BLAZAR SPECTRAL BREAKS ON THE BLAZAR CONTRIBUTION TO THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

The spectral shapes of the contributions of different classes of unresolved gamma-ray emitters can provide insight into their relative contributions to the extragalactic gamma-ray background (EGB) and the natures of their spectra at GeV energies. We calculate the spectral shapes of the contributions to the EGB arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) assuming blazar spectra can be described as broken power laws. We fit the resulting total blazar spectral shape to the Fermi Large Area Telescope measurements of the EGB, finding that the best-fit shape reproduces well the shape of the Fermi EGB for various break scenarios. We conclude that a scenario in which the contribution of blazars is dominant cannot be excluded on spectral grounds alone, even if spectral breaks are shown to be common among Fermi blazars. We also find that while the observation of a featureless (within uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a single class of contributing unresolved sources with featureless individual spectra, such an observation and the collective spectra of the separate contributing populations determine the ratios of their contributions. As such, a comparison with studies including blazar gamma-ray luminosity functions could have profound implications for the blazar contribution to the EGB, blazar evolution, and blazar gamma-ray spectra and emission.

The connection between black hole mass and Doppler boosted emission in BL Lacertae type objects.

We investigate the relationship between black hole mass (MBH) and Doppler boosted emission for BL Lacertae type objects (BL Lacs) detected in the SDSS and FIRST surveys. The synthesis of stellar population and bidimensional decomposition methods allows us to disentangle the components of the host galaxy from that of the nuclear black hole in their optical spectra and images, respectively. We derive estimates of black hole masses via stellar velocity dispersion and bulge luminosity. We find that masses delivered by both methods are consistent within errors. There is no difference between the black hole mass ranges for high-synchrotron peaked BL Lacs (HBL) and low-synchrotron peaked BL Lacs (LBL). A correlation between the black-hole mass and radio, optical and X-ray luminosity has been found at a high significance level. The optical-continuum emission correlates with the jet luminosity as well. Besides, X-ray and radio emission are correlated when HBLs and LBLs are considered separately. Results presented in this work: (i) show that the black hole mass does not decide the SED shapes of BL Lacs, (ii) confirm that X-ray and optical emission is associated to the relativistic jet, and (iii) present evidence of a relation between MBH and Doppler boosted emission, which among BL Lacs may be understood as a close relation between faster jets and more massive black holes.

Observations of the rapid variability of the two BL Lac type objects J2005+77 and J2022+76 with the RATAN-600

We report here the results of observations of two BL Lacertae-type objects, J2005+77 and J2022+76, using the RATAN-600 at frequencies 11.2, 7.7, and 4.8 GHz. We found variations of radio emission on timescales of one day and we are the first to discover a variability of this type for J2022+76.We compare our observations with long-term multifrequency radio observations of the same sources performed on RATAN-600 within the framework of other observational programs. We analyze the behaviour of variability of the two sources and provide arguments in favour of the preferred emission generation mechanisms for the objects studied.

VHE observations of BL Lacertae objects: 1995–2000

Over the past eight years, observations of BL Lacertae type objects have been an important part of the observing program at the Whipple Observatory 10 m γ-ray telescope. During this time, TeV emission was detected from five such objects: Markarian 421, Markarian 501, 1ES2344+514, H1426+428 and 1ES1959+650. Upper limits were placed on the TeV emission from 29 other BL Lacertae objects. Among these objects are two unconfirmed TeV sources, 3C66A and BL Lacertae. An overview of the results of these observations of BL Lacertae objects, between 1995 and 2000, at the Whipple Observatory is presented here.

A possibility to reveal parent populations for objects with active nuclei comparing their spatial correlation functions

Abstract The possibility to derive conclusions about parent population comparing two-point spatial correlation functions of single objects and/or of systems of different types, including AGN, is demonstrated. Similarity of correlation function for groups of galaxies, radio-quiet QSGs, and Seyfert galaxies testify to their evolutionary connection. This method can be used for choosing FR-I-type radiogalaxies or radi-quiet QSGs as parent population of BL Lacertae-type objects.

Cm-Wavelength Flux Variability: Constraints on AGN Modeling

To study whether the radio properties of BL Lacertae type objects and QSOs differ, we initiated a program in 1979 to monitor the total flux density and linear polarization at 14.5, 8.0 and 4.8 GHz of the strongest then known BL Lac objects which met the Hewitt-Burbidge criteria (Ledden, private communications) plus 3 subsequently identified high declination BL Lacs (Biermann et al. 1981). Results based on the behavior of the 45 brightest sample members are compared here with the properties of the QSOs in the flux-limited Pearson-Readhead sample (Pearson and Readhead 1988).

A study of BL Lacertae-type objects with Exosat. I - Flux correlations, luminosity variability, and spectral variability

view Abstract Citations (161) References (83) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of BL Lacertae--Type Objects with EXOSAT. I. Flux Correlations, Luminosity, Variability, and Spectral Variability Giommi, P. ; Barr, P. ; Garilli, B. ; Maccagni, D. ; Pollock, A. M. T. Abstract Results are presented from a uniform and systematic analysis of more than 200 X-ray observations of 36 BL Lacertae objects obtained from the EXOSAT archive. All but two objects were detected at least once. Strong luminosity variability, which reached a factor of 30 in one case, was a common property of these objects. Variability was usually more pronounced in the hard (0.7-8 keV) X-ray energy band than in soft X-rays, implying hardening of the spectrum as the sources brightened. This behavior is opposite to that observed in some Seyfert galaxies. Four objects (ON 325, 1E 1402.3+0416, PKS 2005-489, PKS 2155-304) showed large-amplitude flux variations on time scales of a few hours. In addition, 1H 0414+009, PKS 0548-322, Mrk 421, and Mrk 501 changed their intensity by ~ 20%-40% on the same time scale. There were no long-term trends in the X-ray emission of any of the objects that were well monitored over a long period of time. The commonest form of variability in the soft X-ray band can be represented by small- amplitude variations about a quiescent level that remains approximately constant for years. A statistical analysis shows that, on average, BL Lacs spend less than 10% of the time in flares that involve luminosity variations of factors of 2 or more. The α_ox_-α_ro_ diagram of the objects in the sample allows the identification of two subclasses of BL Lacs characterized by different intrinsic properties, namely, the Q-BL Lacs, which include most of the classical radio-selected objects and show energy distributions similar to those of other radio-loud active galactic nuclei, and the X-BL Lacs, which include all the optically and X-ray discovered objects. X-BL Lacs probably constitute the predominant population. There were no obvious differences in the X-ray variability properties of the two subclasses. Analysis of the soft X-ray emission reveals no evidence for intrinsic absorption in excess of a few times 10^20^ atoms cm^-2^ in any of the objects for which data of sufficiently good quality were available. Publication: The Astrophysical Journal Pub Date: June 1990 DOI: 10.1086/168851 Bibcode: 1990ApJ...356..432G Keywords: Astronomical Spectroscopy; Bl Lacertae Objects; Exosat Satellite; Luminosity; X Ray Sources; Absorption Spectra; Active Galactic Nuclei; Light Curve; Spectral Energy Distribution; Synchrotron Radiation; Astrophysics; BL LACERTAE OBJECTS; GALAXIES: X-RAYS; X-RAYS: SOURCES full text sources ADS | data products NED (36) SIMBAD (35)

Soft X-ray observations of two BL Lacertae objects - Markarian 421 and 501

view Abstract Citations (8) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Soft X-ray observations of two BL Lacertae objects : Markarian 421 and 501. Singh, K. P. ; Garmire, G. P. Abstract This paper reports on the soft X-ray (0.15-2.8 keV) observations of two BL Lacertae-type objects, viz., Mrk 421 and Mrk 501. The observations were made with the low-energy detectors on the HEAO 1 satellite during the period 1977 August-1978 December. Steep, soft X-ray power-law spectra with photon index Gamma = 3 are found for both Mrk 421 and Mrk 501. The power-law models are found to give a significantly better fit than the thermal models to the observed pulse-height spectra of Mrk 421 and Mrk 501. Day-to-day soft X-ray (0.25 keV band) intensity variations are observed only in Mrk 501. No significant change is found in Gamma from both the BL Lac objects during the period of observations. However, the sum of all the X-ray observations from 1976 until 1980 can be understood in terms of two spectral components of variable intensity to account for the X-ray emission observed between 0.15 and 20 keV from Mrk 421 and Mrk 501. Publication: The Astrophysical Journal Pub Date: October 1985 DOI: 10.1086/163516 Bibcode: 1985ApJ...297..199S Keywords: Bl Lacertae Objects; Emission Spectra; X Ray Sources; Bremsstrahlung; Synchrotron Radiation; Astrophysics full text sources ADS | data products SIMBAD (2) NED (2)

A SEARCH FOR RAPID VARIABILITY IN EIGHT QUASARS AND BL LACERTAE OBJECTS.

ABSTRACT Observations of eight quasar- and BL Lacertae-type objects (3C 120, PKS 0735+178, PKS 0736+017, OJ 287, ON 325, W Com=ON 321, 3C 273 and OQ 208) with rapid and large-amplitude light variations are considered. The source of the comparison sequence for each of the eight objects is presented as well as observed blue magnitudes. The BL Lacertae-type object PKS 0735+178 was found to vary significantly in brightness on a time scale of weeks.

The radio spectra of Markarian galaxies

view Abstract Citations (67) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The radio spectra of Markarian galaxies. Kojoian, G. ; Sramek, R. A. ; Dickinson, D. F. ; Tovmassian, H. ; Purton, C. R. Abstract Radio flux densities between 2.7 and 15.5 GHz are given for 16 Markarian galaxies. Spectra for these objects are obtained from these and previously published data. The Seyfert-type galaxies show power-law spectra with an average index of -0.82, except for MRK 348, which is an active galaxy with a complex spectrum. The Markarian galaxies with featureless optical spectra have rather flat radio spectra, similar to the BL Lacertae-type objects. Publication: The Astrophysical Journal Pub Date: January 1976 DOI: 10.1086/154082 Bibcode: 1976ApJ...203..323K Keywords: Astronomical Spectroscopy; Markarian Galaxies; Radio Galaxies; Radio Spectra; Seyfert Galaxies; Active Galaxies; Emission Spectra; Power Spectra; Radiant Flux Density; Spectrum Analysis; Astronomy full text sources ADS | data products NED (22)