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ROMABZCAT - Roma-BZCAT Multi-Frequency Catalog of Blazars



This table contains the Roma-BZCAT Catalog of blazars based on multifrequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalog is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at

The Roma-BZCAT is structured in two parts. Part 1, at present the only one available on-line, contains the lists of blazars, which are classified in three main groups, according to their spectral properties. Each blazar is identified by a three-letter code, where the first two letters are BZ for blazar and the third one specifies the type, followed by the truncated equatorial coordinates (J2000).

This version of the Roma-BZCAT is Version 4.1.1 (2012 August).

Catalog Bibcode



Roma-BZCAT: a multifrequency catalogue of blazars.
    Massaro E., Giommi P., Leto C., Marchegiani P., Maselli A., Perri M.,
    Piranomonte S., Sclavi S.
   <Astron. Astrophys., 495, 691-696 (2009)>


This table was created by the HEASARC in September 2013 based on CDS Catalog J/A+A/495/691 file bzcat4.dat.


A uniquely identifying source number for each blazar in the catalog, mostly in order of increasing J2000.0 Right Ascension (source numbers 3144-3149 are actually the first 6 blazars in RA, followed by source numbers 1-3143).

The Roma-BZCAT source designation, e.g., '[MGL2009] BZt JHHMM.m+DDMM' where 't' can be 'B', 'Q' or 'U' depending on the blazar sub-type: BL Lacertae object or candidate, flat spectrum radio quasars or a blazar of uncertain/transitional type, respectively, and the numbers are the J2000.0 equatorial coordinates of the blazar.

The Right Ascension of the blazar in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 seconds of time in the original table.

The Declination of the blazar in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table.

The Galactic Longitude of the blazar.

The Galactic Latitude of the blazar.

The redshift of the blazar.

A flag parameter for the redshift indicating uncertainty in the value ('?'), extreme uncertainty ('??') or a lower limit ('>').

The R-band magnitude of the blazar, taken from the USNO-B1 Catalog.

The blazar sub-type classification:

      BZB = BL Lac objects, used for AGNs with a featureless optical
            spectrum or only with absorption lines of galaxian origin and
            weak and narrow emission lines;
      BZ? = BL Lac candidates;
      BZQ = flat-spectrum radio quasars, with an optical spectrum showing
            broad emission lines and dominant blazar characteristics;
      BZU = blazars of uncertain type, adopted for sources with peculiar
            characteristics but also showing blazar activity: for instance,
            occasional presence/absence of broad spectral lines or features,
            transition objects between a radio galaxy and a BL Lac, galaxies
            hosting a low luminosity blazar nucleus, etc.;

The radio flux density of the blazar at 1.4GHz (from NVSS or SUMSS), in mJy: if the 1.4-GHz flux density is unknown, the flux density at another radio frequency is given.

The radio flux density of the blazar at 143 GHz, in mJy.

The X-ray flux of the blazar in the 0.1-2.4 keV band, mostly taken from the ROSAT Archive, in erg cm-2 s-1.

The gamma-ray flux of the blazar in the 1-100 GeV band, taken from Fermi, in photons cm-2 s-1.

Contact Person

Questions regarding the ROMABZCAT database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 20-Sep-2013