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 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 The γ-ray sky seen at X-ray energies

2020 ◽  
Vol 638 ◽  
pp. A128 ◽  
Author(s):  
E. J. Marchesini ◽  
A. Paggi ◽  
F. Massaro ◽  
N. Masetti ◽  
R. D’Abrusco ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Large Fraction ◽  
Large Area ◽  
Bl Lac Objects ◽  
X Ray ◽  
Positional Uncertainty ◽  
Bl Lac ◽  
Frequency Behavior ◽  
Bl Lacs ◽  
Selection Of

Context. Nearly 50% of all sources detected by the Fermi Large Area Telescope are classified as blazars or blazar candidates, one of the most elusive classes of active galaxies. Additional blazars can also be hidden within the sample of unidentified or unassociated γ-ray sources (UGSs) that constitute about one-third of all gamma-ray sources detected to date. We recently confirmed that the large majority of Fermi blazars of the BL Lac subclass have an X-ray counterpart. Aims. Using the X-ray properties of a BL Lac training set and combining these with archival multifrequency information, we aim to search for UGSs that could have a BL Lac source within their γ-ray positional uncertainty regions. Methods. We reduced and analyzed the Swift X-ray observations of a selected sample of 327 UGSs. We then compared the X-ray fluxes and hardness ratios of all sources detected in the pointed fields with those of known Fermi BL Lacs. Results. We find at least one X-ray source, lying within the γ-ray positional uncertainty at 95% confidence level, for 223 UGSs and a total of 464 X-ray sources in all fields analyzed. The X-ray properties of a large fraction of them, eventually combined with radio, infrared, and optical information, exhibit BL Lac multi-frequency behavior, thus allowing us to select high-confidence BL Lac candidates; some of them were recently observed during our optical spectroscopic campaign which confirmed their nature. Conclusions. We find that out of 50 X-ray sources that were confirmed as BL Lacs through optical spectroscopy, 12 do not show canonical mid-infrared or radio BL Lac properties. This indicates that the selection of X-ray BL Lac candidates is a strong method to find new counterparts within Fermi UGSs. Finally, we pinpoint a sample of 32 Swift/XRT candidate counterparts to Fermi UGSs that are most likely BL Lac objects.

scholarly journals BL Lacertae objects as an evolutionary population

1986 ◽  
Vol 119 ◽  
pp. 491-492
Author(s):  
A. Cavaliere ◽  
E. Giallongo ◽  
F. Vagnetti
Keyword(s):  
Luminosity Function ◽  
Bl Lacertae Objects ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs

If the BL Lac Objects are active nuclei with a beamed component that is dominant when directed at us, their observed luminosity function must comprise a flat faint branch: N(L)dL ∝ L1+1/pdL with p=4.5 (Urry and Shafer 1984). If this is flatter than the LF NP(L) of the parent objects at equal observed L, then we expect the counts of BL Lacs to flatten out in turn at fluxes quite higher than the counts of the parents, even when both populations evolve strongly and uniformly with comparable timescales (Cavaliere, Giallongo and Vagnetti 1985).

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.

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.

VERITAS OBSERVATIONS OF RELATIVISTIC OUTFLOWS IN LOW- AND INTERMEDIATE-FREQUENCY-PEAKED BL LAC OBJECTS

2014 ◽  
Vol 28 ◽  
pp. 1460178
Author(s):  
◽  
HEIKE PROKOPH
Keyword(s):  
Gamma Ray ◽  
Intermediate Frequency ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Gamma Ray Telescopes ◽  
Very High

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

scholarly journals The intraday variability in the radio-selected and X-ray-selected BL Lacertae objects

1998 ◽  
Vol 132 (1) ◽  
pp. 83-92 ◽  
Author(s):  
J. M. Bai ◽  
G. Z. Xie ◽  
K. H. Li ◽  
X. Zhang ◽  
W. W. Liu
Keyword(s):  
Bl Lacertae Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
Intraday Variability

scholarly journals The variability and periods in the BL Lac AO 0235+164

2014 ◽  
Vol 10 (S313) ◽  
pp. 81-82
Author(s):  
J. H. Fan ◽  
O. Kurtanidze ◽  
X. Liu ◽  
Y. Liu ◽  
H. T. Wang ◽  
...  
Keyword(s):  
Ccd Camera ◽  
Monitoring Programme ◽  
Bl Lacertae Objects ◽  
Monitoring Period ◽  
Bl Lacertae ◽  
Periodicity Analysis ◽  
Photometric Observations ◽  
Bl Lac ◽  
Primary Focus ◽  
Electro Magnetic

AbstractVariability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands, it is violently variable in the optical bands. In the present work, we show its optical R band photometric observations carried out during the period of Nov. 2006 to Dec. 2012 using the Ap6E CCD camera attached to the primary focus of the 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of ΔR = 4.88 mag (14.20 - 19.08 mag) during our monitoring period. When periodicity analysis methods are adopted to its R observations from our Abastumani monitoring programme and those in the literature, the signs of some periods, P1 = 8.26 yr, P2 = 0.55 yr, P3 = 0.85 yr, P4 = 1.99 yr are found.

Two new BL Lacertae objects discovered in the error boxes of hard X-ray sources

2005 ◽  
pp. 257-260
Author(s):  
G. Tagliaferri ◽  
P. Giommi ◽  
K. Beuermann ◽  
G. Branduardi-Raymont ◽  
R. Brissenden ◽  
...  
Keyword(s):  
Bl Lacertae Objects ◽  
X Ray ◽  
Bl Lacertae
Sign in / Sign up

Export Citation Format

Share Document