X-ray selected BL Lacertae objects: catalogue and statistical properties
The present work focuses on the statistical properties of X-ray selected BL Lacertae objects (XBLs) whose catalogue has been compiled. It consists of 312 sources from different X-ray surveys, unambiguously identified to mid-2010. Results of the statistical research of different observational quantit...
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Головна астрономічна обсерваторія НАН України
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| Цитувати: | X-ray selected BL Lacertae objects: catalogue and statistical properties / B.Z. Kapanadze // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 45-48. — Бібліогр.: 25 назв. — англ. |
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| citation_txt | X-ray selected BL Lacertae objects: catalogue and statistical properties / B.Z. Kapanadze // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 45-48. — Бібліогр.: 25 назв. — англ. |
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| description | The present work focuses on the statistical properties of X-ray selected BL Lacertae objects (XBLs) whose catalogue has been compiled. It consists of 312 sources from different X-ray surveys, unambiguously identified to mid-2010. Results of the statistical research of different observational quantities (redshift, multiwavelength luminosities, host/nucleus absolute magnitudes, central black hole masses, synchrotron peak frequencies, broadband spectral indices) are also provided and existence of the correlation between them is proved. Overall flux variability shows an increasing trend towards larger frequencies. XBLs are found to be much less active in sense of intra-night optical variability as compared to radio-selected BL Lacs (RBLs). A separate list of 106 XBL candidates including the same characteristics for each source as in the case of XBL catalogue was also created.
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X-ray selected BL Lacertae objects:
catalogue and statistical properties
B. Z. Kapanadze∗
Advances in Astronomy and Space Physics, 2, 45-48 (2012)
c© B. Z. Kapanadze, 2012
Abastumani Astrophysical Observatory at the Ilia State University, Cholokashvili Ave. 3/5, 0162 Tbilisi, Georgia
The present work focuses on the statistical properties of X-ray selected BL Lacertae objects (XBLs) whose
catalogue has been compiled. It consists of 312 sources from different X-ray surveys, unambiguously identified
to mid-2010. Results of the statistical research of different observational quantities (redshift, multiwavelength
luminosities, host/nucleus absolute magnitudes, central black hole masses, synchrotron peak frequencies, broadband
spectral indices) are also provided and existence of the correlation between them is proved. Overall flux variability
shows an increasing trend towards larger frequencies. XBLs are found to be much less active in sense of intra-night
optical variability as compared to radio-selected BL Lacs (RBLs). A separate list of 106 XBL candidates including
the same characteristics for each source as in the case of XBL catalogue was also created.
Key words: BL Lacertae objects: general
introduction
BL Lacertae objects form one of the extreme sub-
classes of active galactic nuclei (AGN). The proto-
type of these sources, BL Lacertae, was detected by
[11] who classified it as a short-period variable star
of 13-15 stellar magnitude and named the object
as “363.1929 Lac”. The name “BL Lacertae” was
given by van Schewick in 1941. On the basis of the
photographic plates, taken at the Sonnenberg obser-
vatory during 1927–1933, he deduced that there is
an irregular variable star the apparent magnitude of
which varies between 13.5 mag and 15.1 mag (see
[2]). After almost three decades, it was reported
[21] that BL Lacertae coincides with the radio source
VRO 42.22.01. This was followed by the detection of
high and variable radio/optical polarization [15, 23],
rapid optical variability with 0.1 mag over a few
hours and flicker with the amplitude ∆V = 0.03 mag
per 2 minutes [19], steep optical spectrum following
a single power law similar to quasars but showing no
emission lines [17].
On the basis of the absorption features, detected
in the optical spectra obtained with the 5m Hale
telescope the redshift of BL Lacertae was determined
[18]. The obtained value (z = 0.07) revealed that
it is an extragalactic source hosted by an elliptical
galaxy. During 1970–1978 up to 30 sources with sim-
ilar properties were detected. At the Pitsburgh Con-
ference on BL Lacertae Objects in 1978 it was sug-
gested that the extreme properties of these objects
should be caused by a Doppler-boosted emission
pointed to the observer [3]. During that conference
Ed Speigel introduced a term “blazars” to denote
an independent class of the extragalactic sources,
including BL Lacertae objects (BLLs) and flat spec-
trum radio-quasars (FSRQs, showing the same fea-
tures with additional presence of emission lines). X-
ray satellite Einstein and Energetic Gamma-Ray Ex-
perimental Telescope (EGRET) introduced a new
era in investigation of these sources. It was revealed
that blazars constitute the most observed class of
extragalactic sources through γ−rays up to the TeV
frequencies.
BLLs are thus the extragalactic sources with the
features listed below:
a) quasi-featureless spectra, lack of prominent emis-
sion lines;
b) strong radio sources with a core-dominant mor-
phology;
c) strong and variable optical/radio polarization;
d) violent flux variability through all spectral bands;
e) apparent superluminal motions;
f) broad continuum extending from radio to very
high-energy γ-rays.
Up to now, more than 900 BLLs are unambigu-
ously identified (see the second edition of the Roma-
BZCAT1). Bulk of them are originally detected ei-
ther through radio or X-ray bands. Due to this
reason they were subdivided broadly into the radio-
selected (RBLs) and X-ray selected BLLs (XBLs).
∗bk@genao.org
1http://www.asdc.asi.it/bzcat
45
Advances in Astronomy and Space Physics B. Z. Kapanadze
However, these subclasses differ from each other by
their spectral energy distributions. According to [25]
BLL is assumed to be a XBL if
log Fx/Fr ≥ −5.5,
where the X-ray flux density Fx is measured at 1 keV
(2.42×1017 Hz) and the radio one Fr at 5 GHz (both
in Janskys). Otherwise one deals with an RBL
source.
the catalogue
The XBL catalogue consists of 312 sources [13],
containing their equatorial coordinates, redshifts,
multiwavelength flux values and isotropic luminosi-
ties, X-ray-to-radio flux ratios etc. It was compiled
on the basis of the following X-ray surveys:
1) HEAO-1 Large Area Sky Survey [24] (16 sources);
2) Einstein Observatory Medium Sensitivity Survey
[8, 14] (25 sources);
3) Einstein Observatory Extended Medium Sensitiv-
ity Survey [9] (42 sources);
4) EXOSAT High Galactic Latitude Survey [10] (10
sources);
5) Einstein Slew Survey [6] (61 sources);
6) ROSAT All-Sky Survey [1] (306 sources);
7) XMM-Newton Bright Serendipitous Survey [5] (3
sources).
A great deal of the XBLs belongs to the differ-
ent surveys. A separate list of 106 XBL candidates
including the same characteristics for each source as
in the XBL catalogue was also compiled. We cannot
consider them as BLL sources mainly due to lack
of the optical spectroscopy. Their spectra are either
not published or they are of bad quality and we thus
cannot exclude the existence of the emission lines.
Their observational features are in fact the same as
for confirmed BLLs and we expect that high signal-
to-noise ratio spectroscopy will boost the number of
XBLs.
statistical properties of XBLs
Fig. 1 gives the distributions of different
observational quantities: redshift, 1.4 GHz/V-
band/ROSAT-band luminosities, host and nucleus
R band absolute magnitudes, host V-R indices etc.
Correlations between different quantities are shown
in Fig. 2.
Redshifts. Only 207 XBLs (66.3% of the total
sample) have confirmed redshifts. They range from
z = 0.031 (Mrk 421) to z = 0.702 (H151+660) with
a peak of the distribution at z = 0.23 (Fig. 1a).
About 37% of the sources are concentrated within
z = 0.1− 0.3, and 88% of the sources have z < 0.5.
Redshifts of 105 sources remain still either undeter-
mined or not confirmed due to absence or extremal
weakness of the spectral lines in these sources.
Luminosities. Common logarithms of 1.4 GHz
isotropic luminosities (in erg/s) are distributed from
39.57 to 42.15 peaking at νLr = 40.85 erg/s
(Fig. 1b). The optical V-band luminosities are
distributed from νLo = 43.31 erg/s to νLo =
46.07 erg/s with a peak at νLo = 44.20 erg/s
(Fig. 1c). Finally, νLx = 42.78 − 46.21 erg/s
for ROSAT-band X-ray luminosity that peaks at
νLx = 45.10 erg/s (Fig. 1d). Radio/optical/X-ray
luminosities are found to be correlated with the red-
shift above the 99% confidence level: correlation co-
efficient r is equal to 0.53, 0.47, 0.58, respectively
(Fig. 2a,b,c). In that case, we deal with an evolu-
tion from distant ellipticals with powerful nuclei to
normal elliptical galaxies. However, there is a sig-
nificant scatter in the correlations that are probably
caused by the scatter in jet directions (leading to
the scatter in Doppler boosting of the emission) and
different brightness state.
Hosts/nuclei. Up to now, the hosts of only 94
XBLS are detected. As a rule, they are elliptical
galaxies with effective radius reff = 3.26−25.40 kpc
and ellipticity ε = 0.04−0.52. R-band absolute mag-
nitude ranges from −21.11 mag to −24.72 (Fig. 1e).
The distribution peaks at MR = −22.80 mag and its
mean is −22.83 mag. The nuclei show much broader
range of R-band absolute magnitudes: they are dis-
tributed from −19.21 mag to −27.24 mag with a
peak at MR = −22.20 mag (Fig. 1f). There is a neg-
ative correlation with a redshift (r = −0.52) above
99% confidence level (Fig. 2e) indicating thus a trend
of increasing luminosities towards greater redshifts.
V-R indices of the hosts. This quantity ranges
from 0.61 to 1.52 and shows three different peaks at
V − R = 0.73, V − R = 1.08, and V − R = 1.50
(Fig. 1g). If confirmed, it might be may related
to the three “waves” in a birth of elliptical galax-
ies. However, it may be caused by poor dataset:
V-R indices are available for only 59 sources. They
show a strong positive correlation with the redshift
(r = 0.97, > 99% confidence level; Fig. 2f) explained
with a redshifted emission of passively evolving el-
liptical galaxies with an old stellar population [22].
This correlation, fitted well with a third-order poly-
nomial [13] may be used to evaluate the redshifts of
that XBLs whose V-R indices are derived photomet-
rically but their z values remain either unknown or
controversial.
Masses of central BHs. According to the widely
accepted scenario, BLL contain in their nuclei super-
massive BHs whose masses are estimated mainly via
the velocity dispersions in their hosts. log MBH/M¯
values are currently estimated for 47 XBLs and
range from 7.39 to 9.30 (Fig. 1h). A peak of the
distribution is found to be at log MBH/M¯ = 8.30.
These values do not show a correlation with a red-
shift. However, there are weak but statistically
significant correlations between logMBH/M¯ and
1.4 GHZ/V-band luminosities (Fig. 2g,h).
46
Advances in Astronomy and Space Physics B. Z. Kapanadze
Synchrotron peak frequencies. Peak frequencies
of synchrotron SEDs (radio to UV/X-ray frequen-
cies) are currently determined for 187 XBLs. They
range from log νpeak = 14.56 Hz to log νpeak =
21.46 Hz with a peak of the distribution at
log νpeak = 16.60 Hz (Fig. 1i). It seems that a
subclass of ultra-high peaked BLLs (UHBLs) with
log νpeak > 19.00 should be an artefact of the poor
datasets of multi-frequency flux values used for con-
structing the SEDs of these sources. Among 22
UHBLs, provided in [16], 13 sources are proven to
have much lower peak frequencies [13]. ROSAT
band X-ray luminosity shows a positive correlation
(r = 0.40) with synchrotron peak frequencies while
those for 1.4 GHz and V-band do not reveal any
trend (Fig. 2j,k,m, respectively). This means a trend
of increasing bolometric luminosity towards greater
log νpeak values. This result is in contradiction with
[7] about the decreasing power along the sequence
LBLs → IBLs → HBLs that is explained in [4] as a
cosmological result of gradual depletion of circumnu-
clear material causing a decreasing jet power along
this sequence.
Broadband spectral indices. Radio-to-optical in-
dices are distributed from 0.17 to 0.59, peaking at
αro = 0.40. The range of optical-to-X-ray indices is
much broader: αox = 0.56− 1.48 with a peak of the
distribution at αox = 0.98. As for radio-to-X-ray in-
dices, they span from αrx = 0.41 to αrx = 0.75 and
peak at αrx = 0.56. The corresponding plots are in
Fig. 1j, Fig. 1k, and Fig. 1m, respectively.
Flux variability. Almost 60% of the XBLs are
not investigated for multiwavelength flux variabil-
ity. The best studied are only brightest XBLs
1ES 2155-304 (since 1890) and Mrk 421 (since 1900).
Only several sources have a history of observations
greater than three decades. XBLs show basically
erratic variability — changing duration, amplitude
and base flux level from flare to flare. Periodical
changes are reported very rarely, e.g. flares with
420 d period in 1ES 2321+419 through 1.5-12 keV
band was reported in [20]; quasi-periodical flares
with 3.2 yr duration in 1ES 1028+511 through op-
tical R- band, reported in [12] etc. There is a trend
of increasing overall range of optical variability to-
wards shorter wavelengths [13]: 〈4mR〉 = 1.22 mag
(18 sources), 〈4mV 〉 = 1.52 mag (66 sources),
〈4mB〉 = 1.65 mag (28 sources). On the intra-
night time-scales XBLs are less active compared
to RBLs in the optical domain: flickerings with
4m ∼ 0.1 mag/night were recorded for several times
while there are much more occasions and higher am-
plitudes in the case of RBLs. The reason is still
unclear and cannot be simply related to the differ-
ent jet orientation to the observer of these two BLL
subclasses that could lead to the different boosting
in the observed flux.
summary and conclusions
In the present paper a catalogue of 312 XBLs,
updated to mid-2010, is presented. In the fu-
ture, we may expect the number of XBLs to grow
on the expense of XBL candidates (106 sources)
which may not be assumed as BLL sources mainly
due to the lack of high signal-to-noise ratio optical
spectra. XBLs are the extragalactic sources with
0.031 < z < 0.702 and with the common loga-
rithms of radio/optical/X-ray luminosities of 39−42,
43−45, and 42−46 erg/s order, respectively. These
sources show a trend of increasing luminosity to-
wards distant objects that has a deep cosmological
implication: there is an evolution from distant el-
liptical galaxies with powerful nuclei into the ellip-
ticals without active nuclei. However, this correla-
tion may be related simply to the selection effect
— great number of distant BLLs, whose apparent
fluxes are below the detection threshold of current
observing technique, may exist. XBL hosts are ellip-
tical galaxies with effective radii of 3.26− 25.40 kpc
and MR = −21.11.. − 24.86 while the nuclei reveal
much broader range of optical absolute magnitude
of (−19.93.. − 27.24). V − R indices of the hosts
reveal a third order polynomial relationship with
z. log MBH/M¯ values range with almost two or-
der of masses up to maximum value of 9.30 and
do not show any correlation with redshift. But
they show positive correlations with radio and op-
tical luminosities that may serve as an argument of
the Blandford-Znajek mechanism of jet production.
Bolometric luminosities do not show an decreasing
trend towards higher synchrotron peak frequencies,
as it was shown in some previous works, and the
blazar sequence may not be simply explained by
the hypothesis of depleting circumnuclear material
along this sequence. As for Synchrotron peak fre-
quencies, log νpeak ∼ 15− 21 Hz with a mean value
of 16.76. We are also far from perfect understand-
ing both of the character of multiwavelength flux
variability and the nature of unstable processes, re-
sponsible for these variations.
acknowledgement
My participation in the conference was supported
by the Shota Rustaveli Science Foundation grant
N3/15.
references
[1] Bade N., Engels D., Fink H. et al. 1992, A&A, 254, L21
[2] Beckmann V. 2000, PhD Thesis, University of Hamburg
Press
[3] Blandford R.D. & Rees M. J. 1978, in Pittsburgh Con-
ference on BL Lac Objects, Pittsburgh, Pa., April 24-26,
47
Advances in Astronomy and Space Physics B. Z. Kapanadze
Fig. 1: Distribution of the observational quantities of XbLs.
Fig. 2: Correlation between the different observational quantities of XBLs.
1978, Proceedings, Pittsburgh, Pa., University of Pitts-
burgh, 341
[4] Cavaliere A. & D’Elia V. 2002, ApJ, 571, 226
[5] Della Ceca R., Maccacaro T., Caccianiga A. et al. 2004,
A&A, 428, 383
[6] Elvis M., Plummer D., Schachter J. & Fabbiano G.,
1992, ApJS, 80, 257
[7] Fossati G., Maraschi L., Celotti A., Comastri A. & Ghis-
ellini G. 1998, MNRAS, 299, 433
[8] Gioia I. M., Maccacaro T., Schild R.E. et al. 1984, ApJ,
283, 495
[9] Gioia I. M., Maccacaro T., Schild R. E. et al. 1990, ApJS,
72, 567
[10] Giommi P., Tagliaferri G., Beuermann K. et al. 1991,
ApJ, 378, 77
[11] Hoffmeister K. 1929, Astron. Nachr., 236, 233
[12] Kapanadze B. Z. 2009, MNRAS, 398, 832
[13] Kapanadze B. Z. 2012 (to appear in AJ)
[14] Maccacaro T., Gioia I.M., Zamorani G. et al. 1982, ApJ,
253, 504
[15] MacLeod J.M. & Andrew B.H. 1968, Astrophys. Lett.,
1, 243
[16] Nieppola E., Tornikoski M. & Valtaoja E. 2006, A&A,
445, 441
[17] Oke J. B., Neugebauer G. & Becklin E. E. 1969, ApJ,
156, 41
[18] Oke J. B. & Gunn J. E. 1974, ApJ, 189, L5
[19] Racine R. 1970, ApJ, 159, L99
[20] Rani B., Wiita P. J. & Gupta A. C. 2009, ApJ, 696, 2170
[21] Schmitt J. 1968, Nature, 218, 663
[22] Urry C. M., Scarpa R., O’Dowd M. et al. 2000, ApJ, 532,
816
[23] Visvanathan N. 1969, ApJ, 155, L133
[24] Wood K. S., Meekins J. F., Yentis D. J. et al. 1984, ApJS,
56, 507
[25] Wurtz R.E. 1994, PhD Thesis, University of Colorado
Press
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|
| id | nasplib_isofts_kiev_ua-123456789-119151 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 2227-1481 |
| language | English |
| last_indexed | 2025-12-02T04:16:57Z |
| publishDate | 2012 |
| publisher | Головна астрономічна обсерваторія НАН України |
| record_format | dspace |
| spelling | Kapanadze, B.Z. 2017-06-04T17:59:43Z 2017-06-04T17:59:43Z 2012 X-ray selected BL Lacertae objects: catalogue and statistical properties / B.Z. Kapanadze // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 45-48. — Бібліогр.: 25 назв. — англ. 2227-1481 https://nasplib.isofts.kiev.ua/handle/123456789/119151 The present work focuses on the statistical properties of X-ray selected BL Lacertae objects (XBLs) whose catalogue has been compiled. It consists of 312 sources from different X-ray surveys, unambiguously identified to mid-2010. Results of the statistical research of different observational quantities (redshift, multiwavelength luminosities, host/nucleus absolute magnitudes, central black hole masses, synchrotron peak frequencies, broadband spectral indices) are also provided and existence of the correlation between them is proved. Overall flux variability shows an increasing trend towards larger frequencies. XBLs are found to be much less active in sense of intra-night optical variability as compared to radio-selected BL Lacs (RBLs). A separate list of 106 XBL candidates including the same characteristics for each source as in the case of XBL catalogue was also created. My participation in the conference was supported by the Shota Rustaveli Science Foundation grant N3/15. en Головна астрономічна обсерваторія НАН України Advances in Astronomy and Space Physics X-ray selected BL Lacertae objects: catalogue and statistical properties Article published earlier |
| spellingShingle | X-ray selected BL Lacertae objects: catalogue and statistical properties Kapanadze, B.Z. |
| title | X-ray selected BL Lacertae objects: catalogue and statistical properties |
| title_full | X-ray selected BL Lacertae objects: catalogue and statistical properties |
| title_fullStr | X-ray selected BL Lacertae objects: catalogue and statistical properties |
| title_full_unstemmed | X-ray selected BL Lacertae objects: catalogue and statistical properties |
| title_short | X-ray selected BL Lacertae objects: catalogue and statistical properties |
| title_sort | x-ray selected bl lacertae objects: catalogue and statistical properties |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/119151 |
| work_keys_str_mv | AT kapanadzebz xrayselectedbllacertaeobjectscatalogueandstatisticalproperties |