X-Ray Spectra of BL Lacertae Objects from the ROSAT Archive

1996 ◽  
Vol 175 ◽  
pp. 265-266 ◽  
Author(s):  
G. Lamer ◽  
H. Brunner ◽  
R. Staubert
Keyword(s):  
Broad Band ◽  
Spectral Indices ◽  
Photoelectric Absorption ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
V Band ◽  
Bl Lac ◽  
5 Ghz ◽  
Single Power

Our sample comprises all BL Lac objects listed in the catalogue of Véron-Cetty & Véron (1993) and which are detected in a ROSAT PSPC observation with at least 50 source counts: 74 objects in total. We reduced the data from the ROSAT archives at MPE and GSFC and fitted single power-law models with photoelectric absorption to the spectra. We calculated the broad band spectral indices αrx, αro, and αox from the ROSAT 1 keV fluxes, 5 GHz radio, and optical V band fluxes (Véron-Cetty & Véron 1993).

scholarly journals A Comparison of the X-ray Spectra of Quasars and BL Lac Objects

1989 ◽  
Vol 134 ◽  
pp. 197-198
Author(s):  
D. M. Worrall ◽  
B. J. Wilkes
Keyword(s):  
Power Law ◽  
Radio Spectrum ◽  
Spectral Indices ◽  
Mean Power ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Infrared Frequencies

Quasars with similar core-compact radio properties can be classified by their differences at optical and infrared frequencies. Their X-ray properties might be expected to be similar if the synchrotron self-Compton mechanism relates their radio and X-ray emission. We have compared the 0.2–3.5 keV mean power-law energy spectral indices, , for 4 quasar classes: 12 Highly Polarized QSOs (HPQs), 19 Flat Radio Spectrum, core-compact, low-polarization, QSOs (FRS QSOs), 24 radio-selected BL Lac objects, and 7 X-ray-selected BL Lac objects.

scholarly journals Discovery of Five New X-ray–Selected BL Lacertae Objects and Three New Quasars

1997 ◽  
Vol 159 ◽  
pp. 423-424
Author(s):  
G.Z. Xie ◽  
W. Brinkmann ◽  
G.W. Cha ◽  
S. Laurent-Muehleisen ◽  
Y.H. Zhang ◽  
...  
Keyword(s):  
Astronomical Observatory ◽  
Bl Lacertae Objects ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
Bl Lac

Through combined ROSAT and VLA observations, we have identified 19 BL Lac/quasar candidates. In 1994 December, 1995 January and October, and 1996 January 1996, we obtained spectra of all 19 candidates using the 2.16-m telescope of Beijing Astronomical Observatory. The dispersion used is 195 Å mm−1, which yields a dispersion of about 4.65 Å pixel−1, and the wavelength coverage is 3500–7800 Å. Five of these objects are uniformly featureless, and we identify them as BL Lac objects. Three new quasars are also identified. Table 1 presents VLA positions and redshifts for the 5 new BL Lac objects and three new quasars. By checking them in the NASA/IPAC Extragalactic Database (NED) and Véron-Cetty & Véron’s (1993) Catalogue of Quasars and AGNs, and other recent reports about discovery of new BL Lac objects and quasars, we find that these sources are previously unreported.

scholarly journals Frequency Dependence of the Parsec-scale Polarization Structures of BL Lac Objects

2001 ◽  
Vol 205 ◽  
pp. 140-141
Author(s):  
A.B. Pushkarev ◽  
D.C. Gabuzda ◽  
T.V. Cawthorne
Keyword(s):  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Sky Survey ◽  
Radiation Sources ◽  
Wide Wavelength Range ◽  
Bl Lac ◽  
5 Ghz

BL Lacertae objects are active galactic nuclei with weak or undetectable line emission and strong variability in total intensity and linear polarization over a wide wavelength range from optical to radio. The radio emission and much of the optical emission is believed to be synchrotron radiation. Sources in the complete sample of BL Lac objects defined by Kühr and Schmidt (1990) have: 5 GHz fluxes of at least 1 Jy, radio spectral index α ≥ −0.5 (Sv ˜ v+α), rest frame equivalent width of the strongest emission lines less than 5 Å, and optical counterparts on the Sky Survey plates with brightness greater than 20m.

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

1996 ◽  
Vol 175 ◽  
pp. 246-247
Author(s):  
J. Heidt
Keyword(s):  
High Variability ◽  
Electromagnetic Spectrum ◽  
Spectral Indices ◽  
Single Model ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Optical Domain ◽  
Intraday Variability

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).

scholarly journals The broad band X-ray spectra of intermediate BL Lac objects

2000 ◽  
Vol 25 (3-4) ◽  
pp. 729-732
Author(s):  
J. Siebert ◽  
W. Brinkmann ◽  
S.A. Laurent-Muehleisen ◽  
M. Matsuoka
Keyword(s):  
Broad Band ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

scholarly journals A new hard X-ray-selected sample of extreme high-energy peaked BL Lac objects and their TeV gamma-ray properties

2019 ◽  
Vol 486 (2) ◽  
pp. 1741-1762 ◽  
Author(s):  
L Foffano ◽  
E Prandini ◽  
A Franceschini ◽  
S Paiano
Keyword(s):  
Spectral Properties ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
High Energy ◽  
Spectral Energy ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

ABSTRACT Extreme high-energy peaked BL Lac objects (EHBLs) are an emerging class of blazars with exceptional spectral properties. The non-thermal emission of the relativistic jet peaks in the spectral energy distribution (SED) plot with the synchrotron emission in X-rays and with the gamma-ray emission in the TeV range or above. These high photon energies may represent a challenge for the standard modelling of these sources. They are important for the implications on the indirect measurements of the extragalactic background light, the intergalactic magnetic field estimate, and the possible origin of extragalactic high-energy neutrinos. In this paper, we perform a comparative study of the multiwavelength spectra of 32 EHBL objects detected by the Swift-BAT telescope in the hard X-ray band and by the Fermi-LAT telescope in the high-energy gamma-ray band. The source sample presents uniform spectral properties in the broad-band SEDs, except for the TeV gamma-ray band where an interesting bimodality seems to emerge. This suggests that the EHBL class is not homogeneous, and a possible subclassification of the EHBLs may be unveiled. Furthermore, in order to increase the number of EHBLs and settle their statistics, we discuss the potential detectability of the 14 currently TeV gamma-ray undetected sources in our sample by the Cherenkov telescopes.

scholarly journals X-Ray Properties of Compact Extragalactic Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 109-110 ◽  
Author(s):  
D. M. Worrall
Keyword(s):  
Radio Emission ◽  
Gaussian Distribution ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Bl Lac Objects ◽  
X Ray ◽  
Logarithmic Plot ◽  
Bl Lac ◽  
5 Ghz ◽  
Bl Lacs

A good correlation is known to exist between the X-ray and radio luminosity of flat-spectrum, core-dominated radio sources (e.g., Owen, Helfand and Spangler 1981). Worrall (1987) presents a logarithmic plot of spectral luminosity in the source frame at 2 keV versus that at 5 GHz for a variety of QSOs, Highly Polarized QSOs (HPQs), and BL Lac Objects. Friedmann cosmology with Ho = 100h km s−1 Mpc−1, qo = 0 is assumed. Exclusion of objects which are optically or X-ray selected, or in which the radio emission is not dominated by a flat-spectrum compact core, gives a sub-sample consisting of 50 QSOs, 20 HPQs, and 10 BL Lacs, of which 5,4,3, respectively, are known superluminals. The dispersion of these data about the log-log correlation (assuming a Gaussian distribution), is σobs = 0.44 ± 0.06 (90% confidence errors for one interesting parameter).

scholarly journals The Rosat X-Ray Spectra of BL Lacertae Objects

1996 ◽  
Vol 175 ◽  
pp. 267-268
Author(s):  
Paolo Padovani ◽  
Paolo Giommi
Keyword(s):  
Spectral Information ◽  
Spectral Indices ◽  
Bl Lacertae Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Selection Of

We have analyzed the X-ray spectra of all BL Lacs observed (as pointed or serendipitous sources) by ROSAT. Spectral indices were obtained from the hardness ratios given in the WGA catalogue, a large list of X-ray sources generated from all the ROSAT PSPC pointed observations. The selection of the objects was done by cross-correlating the first revision of the WGA catalogue with our recent catalogue of BL Lacs. This resulted in 163 observations of 85 distinct BL Lacs, which correspond to about half the confirmed BL Lacs presently known. This represents the largest number of BL Lacs for which homogeneous X-ray spectral information is available and the largest BL Lac sample ever studied at X-ray frequencies.

scholarly journals ROSAT Observations of Bright BL Lacertae Objects

1994 ◽  
Vol 159 ◽  
pp. 377-377
Author(s):  
G. Lamer ◽  
H. Brunner ◽  
R. Staubert
Keyword(s):  
Power Laws ◽  
Spectral Indices ◽  
Bl Lacertae Objects ◽  
Mean Values ◽  
X Ray ◽  
Bl Lacertae ◽  
Spectrum Radio ◽  
Significant Difference ◽  
The Mean ◽  
5 Ghz

We have compiled a sample of 23 X-ray and radio selected BL Lacertae objects which have been observed with the Position Sensitive Proportional Counter (PSPC) on board of the ROSAT Satellite. The sample consists of three parts:In Table I results from 4 objects observed for their known rapid X-ray variability are presented. 5 objects are the BL Lac subset of a complete sample of flat spectrum radio sources with 5 GHz flux densities > 1 Jy. Detailed results from this sample will be published in Brunner et al. 1993. The data of the 14 remainig objects were collected from the ROSAT data archive to supplement the sample. The whole sample contains 7 X-ray selected objects (XBLs,αOX < 1.2) and 16 radio selected objects (RBLs).The X-ray spectra of the sources are well described by single power laws with galactic absorption. The X-ray energy indices αX are widely dispersed around a mean of 1.34. Significant X-ray flux variability and correlated spectral variability was detected on timescales down to hours. The object H 1218+304 was found to be rapidly variable within each of three observations. Its spectral hardness is correlated with the flux level (see Table I).We calculated the intrinsic distributions of the spectral indices αX for the XBL and RBL samples and of the differences between ROSAT and EXOSAT ME spectral indices αPSPC – αME (only XBL sample) using a maximum likelihood fit. There is no significant difference in the mean spectral indices between the X-ray and radio selected subsamples. The mean values < αX > are 1.34 for XBLs and 1.33 for RBLs. The spectra of the X-ray selected objects slightly steepen at higher X-ray energies (< αPSPC – αME > = −0.11). This supports the view that the X-ray emission of XBLs is supplied by synchrotron radiation. The steepening of the X-ray spectrum is then due to a cutoff in the energy distribution of the electrons.

Sign in / Sign up

Export Citation Format

Share Document