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Topic: BL Lac

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BL Lacertae

BL Lac object

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	Blazar
		In astronomy, blazar, also known as BL Lac Objects or BL Lacertaes, are bright, starlike objects that can vary rapidly in their luminosity.
		BL is a progressive ID not unlike car plates, and Lacerta is the constellation where it resides.
		Anyway, it is clear that the BL Lac class is far from understood, and that it will possibly be divided into different classes of similar-appearing, but physically different objects.
	www.ebroadcast.com.au /lookup/encyclopedia/bl/Blazar.html (448 words)

	GTN: BL Lac Objects
		BL Lac objects are named after the protype object which was first believed to be a variable star in our galaxy.
		This amounts to a change in brightness of nearly a factor of 20, and a few BL Lac objects have been reported to undergo changes in brightness of a factor of 100.
		A number of BL Lac objects are known in the vicinity of clusters of galaxies so this provides indirect evidence in support of their extragalactic nature.
	gtn.sonoma.edu /public/resources/active_galaxies/bl_lac_objects.php (290 words)

	THE CFHT IMAGING SURVEY OF BL LACERTAE OBJECTS II:
		Various subsamples of BL Lacs with unique qualities (e.g., presence/absence of weak emission lines, high/low optical core dominance or polarization, Xray vs. radio selected, etc.) have statistically similar clustering properties further arguing that these BL Lacs are all members of the same AGN class.
		Contrary to the expectations of unification schemes for BL Lacs, the clustering environments of BL Lacs, at both high and low redshift, are more similar to those of FR 2 radio galaxies and quasars than to those of FR 1's.
		As a minimum the "parent population" of BL Lacs must be modified to exclude the brightest cluster galaxies (BCGs) in rich clusters at low redshift.
	casa.colorado.edu /Publications/preprints/1996/sepdec/303.shtml (493 words)

	AAVSO: BL Lac, January 2001 Variable Star of the Month
		It is the prototype of the BL Lac class of Active Galactic Nuclei (AGN).
		BL Lac was one of only two known (non-cepheid) extragalactic variable stars at the time.
		BL Lac objects & blazars are highly variable and exhibit a featureless spectrum.
	www.aavso.org /vstar/vsots/0101.shtml (1395 words)

	BL Lac object - Wikipedia, the free encyclopedia
		A BL Lac object, BL Lacertae object, or BL Lac is a type of active galaxy with an active galactic nucleus (AGN).
		In the unified scheme of radio-loud active galactic nuclei, the observed nuclear phenomenology of BL Lacs is interpreted as due to the effects of the relativistic jet that is pointing towards the observer.
		BL Lacs are believed to be intrinsically identical to low power radio galaxies but with the jet closely aligned to the line of sight of the observer.
	en.wikipedia.org /wiki/BL_Lac_object (291 words)

	No Slide Title
		BL Lac objects are radio-loud AGN, with properties similar to quasars except for a lack of any strong emission lines.
		BL Lacs have a similar accretion process to radio-loud and radio-quiet quasars, but with a greater amount of outflow, which reduces the size of the accretion disk.
		BL Lacs have a different accretion process to quasars, in which a disk does not form – for example, an ADAF or ADIOS process with a low accretion rate.
	www.phys.unsw.edu.au /~mwhiting/papers/BLLac_poster_files/slide0001.htm (539 words)

	SAO Observers - AGN - BL Lac (Site not responding. Last check: 2007-10-09)
		BL Lacertae objects (BL Lac for short) exhibit no absorption or emission lines but have a strong continuum stretching from radio through X-ray wavelengths.
		BL Lac is a galaxy that is the prototype of its class.
		BL Lac objects are most likely produced when we view the active core of an elliptical galaxy almost directly through the central opening of the accretion disk.
	astronomy.swin.edu.au /sao/SAO_Observers/BLLac.html (171 words)

	BL Lac's Correlated Gamma-Ray and Optical Flare
		Observations of a Correlated Gamma-Ray and Optical Flare for BL Lacertae
		1997) the CGRO was repointed to observe the BL Lac flare in gamma rays.
		BL Lac is the prototypical object for a class of active galactic nuclei (AGNs) that typically have very weak emission and absorption lines and are characterized by variability in continuum emission and polarization (Peterson 1997).
	ecf.hq.eso.org /~ralbrech/sepdec97apjl/975555.html (2201 words)

	Untitled Document (Site not responding. Last check: 2007-10-09)
		The core of the elliptical galaxy BL Lacertae (BL Lac) is one of the most extreme examples of active galactic nuclei (AGN).
		It is the prototype member of the radio-loud BL Lac class of AGN and displays all the signposts of relativistic beaming from a compact nuclear engine: one-sided superluminal radio components, highly variable radio flux and polarization, and high optical polarization.
		At the University of Iowa we have been monitoring the parsec-scale structure of the radio core of BL Lac since 1980.
	phobos.physics.uiowa.edu /rlm/research/bllac (132 words)

	The HRX-BL Lac sample
		The unification of X-ray and radio selected BL Lacs has been an outstanding problem in the blazar research in the past years.
		Beckmann, 1999, "Evolutionary behaviour of BL Lac objects", in: Takalo L. et al.
		Bade, Beckmann, Engels, Cordis, Nass, Voges, 1998, "On the evolutionary behaviour of BL Lac objects", AandA 334, 459
	www.hs.uni-hamburg.de /DE/For/Exg/Sur/rosat/bllac/index.html (425 words)

	News May 2002: Long XMM-Newton observation of the BL Lac Mkn 421 shows previous studies underestimate jet properties
		Some of them are bright radio sources, and a few of these radio galaxies are BL Lac objects, rare galaxies which look more like stars than galaxies in optical images.
		The X-rays from BL Lacs are thought to come from a jet of particles interacting with a magnetic field, giving rise to synchrotron radiation.
		Recent X-ray observations of the bright BL Lac object Markarian 421 made with XMM-Newton by Steve Sembay, Rick Edelson, Alex Markowitz, Gareth Griffiths, and Martin Turner from the Universities of Leicester and California.
	www.star.le.ac.uk /news/0402.html (793 words)

	Warde_article
		BL Lacs are observed at a low beaming angle, typically less than 10 degrees, Quasars are galaxies that are observed at the same beaming angle as BL Lacs but which are much more energetic.
		Each parameter was tested within a specific range; we tested ro from.05 to.20, lo from 0.1 to 10.0, y from 1.0 to 4.0, x from 175.0 to 183.0 for the object BL Lac and from 265.0 to 273.0 for source 2134 +004, f from 0.0 to 360.0, and q from 4.0 to 10.0.
		The shock that appears in the BL Lac contour maps from August 2001 and January 2002 is called S11.
	www.sbc.edu /honors/HJSpecial_Iss04/Warde.htm (1318 words)

	ROSAT BL Lac Spectra (Site not responding. Last check: 2007-10-09)
		This sample includes all WGA BL Lacs with high-quality data and comprises about 50 per cent of presently known BL Lacs.
		We find that BL Lacs have energy power-law spectral indices between 0 and 3 with a mean value alpha_x ~ 1.4.
		Significant differences, however, are present between high-energy cutoff BL Lacs (HBLs), normally selected in the X-ray band, and low-energy cutoff BL Lacs (LBLs), generally found in radio surveys.
	www.eso.org /~ppadovan/xray_spectra/bllacs.html (201 words)

	I
		BL Lacertae type quasars, or blazars, are known for their violent variability at all observable wavelengths.
		BL Lac objects show neither absorption nor emission lines in their spectra and are believed to be the centers of relatively gas free galaxies.
		Quasars are also thought to be the centers of galaxies, at a distance of many billion light years away, but differ from BL Lac objects in that they do show emission lines.
	www.ifa.hawaii.edu /~mcgrath/0235.html (1550 words)

	[No title]
		BL Lacs are galaxies which harbour contain a very bright, central source of emission.
		A particular type of AGN, called BL Lacs, were examined by the team.
		Also a dozen optically weak nuclei were found supporting the view that the BL Lac sequence continues to lower luminosities than previously thought.
	www.astro.utu.fi /tuorla/new/agn100.shtml (393 words)

	BL Lac Objects (Site not responding. Last check: 2007-10-09)
		BL Lac objects, like Seyferts, are galaxies without radio lobes but with extremely bright, tiny cores.
		However, BL Lac objects are the active cores of elliptical galaxies.
		BL Lac objects are much less common than Seyferts and therefore have been observed much less often.
	www.astro.umd.edu /education/astro/actgal/bllac.html (150 words)

	[No title]
		Distribution of the apparent magnitudes for the BL Lac objects.
		Contour plot of emission redshift against apparent magnitude for the BL Lac objects.Colour of areas displays amount of objects from red for the largest values, throught yellow and green and on to blue for the smallest values.
		Distribution of the emission redshifts for the BL Lac objects.
	www.ioffe.rssi.ru /astro/QC/notebook.htm (468 words)

	Blazar in the Web - BL Lac, blazar, quasar, agn, variability, monitoring, jet emission, multiwavelenght, X-ray ...
		This radio-loud extragalactic objects are optically violent variable quasars, flat-spectrum quasars, high polarized quasars, and BL Lacertae (BL Lac) type objects, which display extremely intense, broad and rapidly varing electromagnetic emission, from radio to gamma-rays in some case.
		They are called classic BL Lac type objects if the optical continuum emission dominates compared to any line emission.
		It is an electronic newsletter dedicated to research and refereed publications on the BL Lac and blazar phenomena, observationally as well as theoretically.
	astro.fisica.unipg.it /blazarsintheweb.htm (880 words)

	BL LACERTAE OPTICAL CAMPAIGN (JULY-AUGUST 2000)
		Our purpose is to monitor BL Lac in the optical bands from one week before to one week after the high-energy campaign, that is from July 17 to August 11, with particularly dense coverage in the central period.
		A preliminary R-band light curve of BL Lac in the last days is available in postscript format (data from Torino, University of Victoria, Clark and Coyote, and Palomar Observatories).
		You may also have a look at the longer-term behaviour (1996-2000 light curve) of BL Lac as observed from the Torino Observatory.
	www.to.astro.it /blazars/2200.htm (820 words)

	BL Lac Catalogue (Site not responding. Last check: 2007-10-09)
		A smaller fraction consists of miscellaneous (but confirmed) BL Lacs and of objects classified as BL Lac candidates.
		We discuss the selection criteria of the different samples, report the discovery of two previously unnoticed BL Lacs in the Palomar--Green survey, and comment on the possible association of some of the still unidentified high galactic latitude gamma-ray (EGRET) sources with BL Lacs.
		BL Lac catalogue (TeX format) (to be printed in landscape)
	www.eso.org /~ppadovan/catalogue.html (142 words)

	Blazar Times - No. 52 - March 2003
		The delays appear to be correlated to the flares' duration: the shorter the flare, the smaller the delay.
		While BL Lacertae objects are widely believed to be highly beamed, low-luminosity radio galaxies, many radio-selected BL Lacs have extended radio power levels and optical emission lines that are too luminous to be low-luminosity radio galaxies.
		Announcements of general interest to the BL Lac and blazar communities may also be submitted for posting in the newsletter.
	www.aoc.nrao.edu /~trector/blazar/mar03.html (2228 words)

	1993 Abstracts
		No BL Lac objects are found that clearly exhibit quasarlike polarization at milliarcsec resolution.
		This argues against the view that the more luminous BL Lac objects are simply an extension of the quasar/OVV population, or that most BL Lac objects are gravitationally microlensed images of distant quasars.
		Other properties are generally consistent with the view the BL Lac objects are normal radio galaxies whose jets make a small angle to the line of sight.
	www.ras.ucalgary.ca /abstracts/1993/1993.html (1255 words)

	Iowa Robotic Telescope Facilities
		We observed a large optical outburst in the blazar BL Lac in 1997.
		The observations consist of 50-second exposures in each of the two filters (photometric R and I) during the observing period for August 5 and 7, 1997 UT. In the light curves found below, BL Lac is plotted along with the check star C, with star B used as the calibrator (see finding chart).
		A Serendipitous Multi-wavelength study of BL Lac in the Summer of 1997
	www-astro.physics.uiowa.edu /research/projects.html (1092 words)

	[65.07] The BL Lac Classification (Site not responding. Last check: 2007-10-09)
		In the optical wavelength range the distinction between a radio galaxy and a BL Lac object is mainly based on the Ca II H and K break observed in the optical spectrum.
		We present new evidence that there is a smooth transition between BL Lac objects and Fanaroff-Riley type I radio galaxies.
		This suggests that the only difference between BL Lac objects and their parent population lies in orientation.
	www.aas.org /publications/baas/v31n5/aas195/238.htm (186 words)

	Decijansky Radio Flux BL Lac Objects
		This challenges the unification of BL Lac objects, because any moderate unified model calls for a smooth distribution of objects on diagrams.
		According to this observational discrepancy, we wonder if a sample composed of BL Lac objects with a radio flux in the range of [1, 10) dJy (called dJy sample) could be an observational class in the medium of RBLs and XBLs, and connecting the two classes.
		In order to have a more reliable study, we suggest that 1 dJy radio surveys of BL Lac objects be made.
	ecf.hq.eso.org /~ralbrech/sepdec97apjl/5203.html (2391 words)

	BL Lac campaign 2000 (Site not responding. Last check: 2007-10-09)
		The optical campaign was organized by Aimo Sillanpää and Massimo Villata, involving the WEBT collaboration.
		In mid-September, BL Lacertae had entered a rather long-lasting, very active optical state, which seems to be rather long-lasting.
		In May / June 2001, BL Lacertae returned to a very bright optical state, and a new campaign is currently being carried out by the WEBT collaboration.
	www.phy.ohiou.edu /~mboett/bllac2000.html (227 words)

	BL Lacertae concept from the Astronomy knowledge base (Site not responding. Last check: 2007-10-09)
		BL Lacertae concept from the Astronomy knowledge base
		High energy peaked BL Lac object (2 facts) (HBL)
		X-ray selected BL Lac object (2 facts) (SBL)
	www.site.uottawa.ca:4321 /astronomy/BLLacertae.html (158 words)

	BL Lac Objects (Site not responding. Last check: 2007-10-09)
		BL Lacertae objects (BL Lac for short) exhibit no emission lines but have a strong continuum stretching from rf through X-ray frequencies.
		Here are spectra of BL Lac and other active galaxies - see the following description.
		Here are some light curves at different wavelengths illustrating the variability in intensity of BL Lac and some other active galaxies.
	csep10.phys.utk.edu /astr162/lect/active/BLlac.html (143 words)

	The SCAE group Blazar database - BL Lac, quasar & blazar list, optical observation, variability, finding chart, ... (Site not responding. Last check: 2007-10-09)
		These instruments are now dedicated to the monitoring of a sample of about 20 blazars, quasars, and BL Lac objects with the principal aims of searching for possible typical time scales and spectral variability.
		From 1996 to 2000 the observations were performed also with the Cassegrain Telescope of Monte Porzio Catone (RM): this telescope has collected also some data in the Arizona filters F72, F80, F86 and F99.
		BL= BL Lac object (HBL or LBL), HPQ= High Polarized Quasar, LPQ=Low Polarized Quasar, OVV=Optically Violent Variable quasar, UG=unusual galaxy.
	astro1.phys.uniroma1.it /nesci/paginahtml/pagwebarc.html (372 words)

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