X-ray Selected BL Lac Objects Research Articles

A Statistical Study of XBLs, RBLs and FSRQs at 1.5 GHz

BL Lac objects are similar to theflat spectrumradioquasarsin manyaspects except regarding the emission lines. In order to study their relationship, we selected 56 BL Lacertae objects (33 X-ray-selected, 23 radio-selected) and 45 flat spectrum radio quasars, analyzed their radio luminosities and core-dominanceparameters. We found that the radio luminosities of the radio selected BL Lac objects located in between the X-ray selected BL Lac objects and the flat spectrum radio quasars. However, this intermediate position does not hold for the core-dominance parameter: the RBLs have the largest core-dominanceparameters. This sug- gests that the core-dominance parameter can not be taken as a sequencing criterion. We also investigatedthe correlationbetween the luminosity and the core-dominanceparameterfor the three subclasses. We concluded that, here, the sequence XBL-RBL—FSRQ still exists.

Optical variability of X-ray selected blazars

AbstractWe present optical R band photometry of nine X-ray selected BL Lac objects: 1ES 0229+200, 1ES 0323+022, 1ES 502+675, 1ES 0647+250, 1ES 0806+524, 1ES0927+500, 1ES 1028+511, 1ES 1959+650, 1ES2344+514.Variability on long time scales within one magnitude in R band was found for all of the observed objects, except 1ES 0229+200 and 1ES0927+500. Largest variation was detected for 1ES 0502+675 and equals to 1.07 mag. Only few objects show statistically significant variation on intra-day scale.

On the difference between the X-ray selected and the radio selected BL Lac objects in the near infrared

By using results from the 2MASS observation, the differences between the X-ray selected BL Lac objects (XBLs) and the radio selected ones (RBLs) in the near infrared are discussed in this paper. It is found that, statistically, the RBLs have redder near infrared colors and steeper spectral indices in the near infrared than XBLs, whereas the XBLs have more influences from their host galaxies than the RBLs. It is also seen that the RBLs have much brighter luminosity in the near infrared than the XBLs. In addition, the high polarization characteristics are found in common for RBLs, but not for XBLs.

The HRX-BL Lac sample – Evolution of BL Lac objects

The unification of X-ray and radio selected BL Lacs has been an outstanding problem in the blazar research in the past years. Recent investigations have shown that the gap between the two classes can be filled with intermediate objects and that apparently all differences can be explained by mutual shifts of the peak frequencies of the synchrotron and inverse Compton component of the emission. We study the consequences of this scheme using a new sample of X-ray selected BL Lac objects comprising 104 objects with z<0.9 and a mean redshift z=0.34. 77 BL Lacs, of which the redshift could be determined for 64 (83%) objects, form a complete sample. The new data could not confirm our earlier result, drawn from a subsample, that the negative evolution vanishes below a synchrotron peak frequency log (peak-frequency) = 16.5. The complete sample shows negative evolution at the 2 sigma level (<V_e/V_a> = 0.42 +- 0.04). We conclude that the observed properties of the HRX BL Lac sample show typical behaviour for X-ray selected BL Lacs. They support an evolutionary model, in which flat-spectrum radio quasars (FSRQ) with high energetic jets evolve towards low frequency peaked (mostly radio-selected) BL Lac objects and later on to high frequency peaked (mostly X-ray selected) BL Lacs.

Intraday Variability Statistics in Radio-Selected and X-Ray Selected BL Lac Objects Implications for Unified schemes

BL Lac objects, characterized by their high variability across the electromagnetic spectrum, strong and variable polarization in the radio and optical domain and a (nearly) featureless continuum can in general be divided into the radio-selected (RBL) and X-ray selected BL Lac objects (XBL) according to their αro – αox spectral indices (Stocke et al., 1985). Attempts to unify both classes within a single model have been suggested e.g. by Ghisellini et al. (1993) or Giommi et al. (1994).

BL Lac objects and acceleration model

In this paper, the acceleration model is applied to data from RBLs (Radio Selected BL Lac objects). The corrected data from RBLs are found to be nearly the same as those from XBLs (X-Ray Selected BL Lac objects), the expected result, that points of U - B, B - V of XBLs and RBLs occupy the same region in the (B - V)-(U - B) diagram has been obtained, and the Radio Doppler factors obtained by us are highly consistent with those found by others.

The redshift of the X-ray selected BL Lacertae object H0414 + 009

view Abstract Citations (26) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Redshift of the X-ray Selected BL Lacertae Object H0414+009 Halpern, Jules P. ; Chen, Vera S. ; Madejski, Greg M. ; Chanan, Gary A. Abstract The x-ray selected BL Lac object H0414+004 has a redshift of 0.287, measured from the starlight of its host galaxy. The optical spectrum is well described by the sum of a standard elliptical galaxy plus a relatively flat power law (α~0.3). The galaxy contributes ~40% of the light in the spectrum in the rest-frame V band, and is one of the most luminous galaxies known (My - - 24). The properties of H0414 + 009 are similar in all respects to a previously studied object, 1E 1415+259 at ζ=0.237. If x- ray selected BL Lacs continue to be found in such bright galaxies, then the prospects of studying their luminosity function and evolution are considerably enhanced. There is also possible evidence for intrinsic x-ray absorption by a warm medium, as has been found in several other BL Lacs. Publication: The Astronomical Journal Pub Date: March 1991 DOI: 10.1086/115725 Bibcode: 1991AJ....101..818H Keywords: Bl Lacertae Objects; Red Shift; Spectrum Analysis; X Ray Spectra; Elliptical Galaxies; Interstellar Extinction; Stellar Luminosity; Visible Spectrum; Astrophysics; BL LACERTAE OBJECTS full text sources ADS | data products SIMBAD (2) NED (1) MAST (1)

On the galaxy surrounding the BL Lac object H2356 - 309

view Abstract Citations (23) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Galaxy Surrounding the BL Lac Object H2356-309 Falomo, Renato Abstract Imaging, optical spectrophotometry, and simultaneous near IR photometry of the x-ray selected BL Lac object H2356-309 are presented. The surrounding nebulosity is found well represented by a de Vaucouleurs r^1/4^ law with a small disk contribution suggested by pointed isophotes. The detection of stellar absorption features Ca II, G band, and Mg I allows to derive the redshift z = 0.165 for the underlying galaxy whose absolute magnitude is M_v_=-22.3. Decomposition of the observed spectral flux distribution into a standard elliptical galaxy plus a power law is obtained with α_v_=0.75 and a galaxy contribution of 40% at 5500 A. Publication: The Astronomical Journal Pub Date: March 1991 DOI: 10.1086/115726 Bibcode: 1991AJ....101..821F Keywords: Astronomical Spectroscopy; Bl Lacertae Objects; Elliptical Galaxies; Infrared Photometry; Absorption Spectra; Red Shift; X Ray Sources; Astrophysics; BL LACERTAE OBJECTS full text sources ADS | data products SIMBAD (2) NED (1)

Two X-ray-selected BL Lacertae objects observed with the HEAO 1 scanning modulation collimator

Two 16th magnitude BL Lac objects, H1101 - 232 and H1426 + 428, have been discovered. Each is a persistent and relatively bright X-ray source. A 2.7 percent linear polarization is measured in the optical emission or H101 - 232. The X-ray identification of H1426 + 428 is confirmed in an Exosat observation. The X-ray spectrum is well-modeled by a power law with an energy index of 1.19. Both BL Lac objects exhibit high f(x)/f(opt) ratios and they show a distinct resemblance to other X-ray selected BL Lac objects. The host galaxies are about 18th mag with angular diameters of about 20 arcsec and each may be the dominant member of a cluster of galaxies. Additional wide-slit spectroscopy reveals faint absorption features with redshifts of 0.129 for H1426 + 428 and 0.186 for H1101 - 232. The implied X-ray and optical luminosities exceed 10 to the 45th ergs/s for both BL Lac nuclei, assuming isotropic emission.

4U1722 + 11: the discovery of an X-ray selected BL Lac object

The Uhuru X-ray source 4U1722 + 11 was observed using the microchannel-plate detector (High Resolution Imager) on the Einstein Observatory, and its coordinates measured to a precision of about 5 arcsec. A 16th-magnitude stellar object within the error circle was observed spectroscopically at CTIO, and at the AAT, and found to have a featureless continuum. Subsequent radio observations at the VLA have established that the object is a radio source at the level of 60 mJy, and optical polarization measurements have determined that the source exhibits variable polarization at the level of 10 percent. On the basis of these observations, it is concluded that 4U1722 + 11 is a member of the class of objects known as X-ray selected blazars of BL Lac objects.

Energy distribution and variability of BL Lac objects: Recent observations and a theoretical scheme

Spectral properties of X-ray selected and radio-selected BL Lacs are discussed. The results provide a direct indication that the X-ray emission is more isotropic than the radio emission. Recent results of multifrequency observations of the brightest X-ray selected BL Lac object, PKS 2155-304, are reviewed, showing how the fast X-ray variability is smeared out at low frequencies. A theoretical jet model is presented which can quantitatively account for the different spectral properties of X-ray selected and radio selected BL Lacs in terms of different line-of-sight angles to the jet.

Spectral properties of blazars. I - Objects observed in the far-ultraviolet. II - an X-ray observed sample

All blazars observed with the IUE are studied and shown to form a well-defined subgroup according to their spectral properties. These properties are discussed with respect to theoretical models and are compared with those of quasars. Radio, ultraviolet, and X-ray fluxes are used to construct composite spectral indices, and systematic differences between X-ray selected and otherwise selected objects are discussed. It is confirmed that X-ray selected objects have flatter overall spectra, and are therefore weaker radio emitters relative to their X-ray emission than objects selected otherwise. It is found that X-ray selected blazars have the same average X-ray luminosity as blazars selected otherwise and are underluminous at UV and radio frequencies. This finding is used to argue that the radio-weak, X-ray selected BL Lac objects are, in terms of space density, the dominant members of the blazar population. The results are interpreted in the framework of synchrotron emission models involving relativistic plasma jets. 134 references.

X-ray selected BL Lac objects: time variability and X-ray spectrum

The Einstein Observatory Medium Sensitivity Survey contains four sources identified with BL Lac objects. The radio and optical properties of these objects have been described in Stocke et al. (1985).

Optical and radio properties of X-ray selected BL Lacertae objects

view Abstract Citations (147) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical and radio properties of X-ray selected BL Lacertae objects. Stocke, J. T. ; Liebert, J. ; Schmidt, G. ; Gioia, I. M. ; Maccacaro, T. ; Schild, R. E. ; Maccagni, D. ; Arp, H. C. Abstract The eight BL Lac objects from the HEAO 1 A-2 all-sky survey and from the Einstein medium-sensitivity survey (MSS) form a flux-limited complete X-ray selected sample. The optical and radio properties of the MSS BL Lac objects are presented and compared with those of the HEAO 1 A-2 sample and with those of radio-selected BL Lac objects. The X-ray selected BL Lac objects possess smaller polarized fractions and less violent optical variability than radio-selected BL Lac objects. These properties are consistent with the substantial starlight fraction seen in the optical spectra of a majority of these objects. This starlight allows a determination of definite redshifts for two of four MSS BL Lac objects and a probable redshift for a third. These redshifts are 0.2, 0.3, and 0.6. Despite the differences in characteristics between the X-ray selected and radio-selected samples, it is concluded that these eight objects possess most of the basic qualities of BL Lac objects and should be considered members of that class. Moreover, as a class, these X-ray selected objects have the largest ratio of X-ray to optical flux of any active galactic nuclei yet discovered. Publication: The Astrophysical Journal Pub Date: November 1985 DOI: 10.1086/163646 Bibcode: 1985ApJ...298..619S Keywords: Bl Lacertae Objects; Galactic Nuclei; X Ray Sources; Active Galactic Nuclei; Astronomical Photometry; Galactic Clusters; Heao 1; Polarimetry; Radio Astronomy; Sky Surveys (Astronomy); Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (20) NED (8)

The extragalactic nature of H0323 + 022

H 0323 + 22, if galactic, is unprecedented in its radio and X-ray properties. A deep R-band image of the source shows it to be spatially extended, with significant light detectable 10 arcsec from the bright nucleus, thereby implying, in the event that it represents an underlying galaxy, that its distance is in the 0.5-1.5 Gpc range and that its radio, optical, and X-ray luminosities are typical of other BL Lac objects. The G star-like absorption spectrum, however, then remains to be explained. Because the two closest bright optical objects also exhibit G star spectra, it is suggested that the Doxsey et al. (1983) G spectra are due to misidentification of the object. H 0323 + 22 is both extragalactic and probably similar to other X-ray selected BL Lac objects.