Open Universe for Blazars

Open Universe for blazars is a programme developed as part of the Open Universe Initiative (Giommi et al. 2018) to support multi-frequency/multi-temporal blazar science by creating source catalogues and high-transparency data products that are ready for use or enable anyone interested in astronomy, with or without data analysis expertise, to do the same using innovative analysis methods.

The OU master list of 6077 blazars

Hammer-Aitoff plot in Galactic coordinates of the 6077 blazars included in the latest version of the master list.


Open Universe for Blazars relies on a master list of blazars. The first version of this list was assembled by combining the 5BZCAT, the 3HSP, and the 3LAC catalogs, for a total of 5340 objects.

The first update of this table adds to the previous version over 750 previously uncatalogued gamma-ray detected blazars from the recently released Fermi 4LAC catalogue.

For details on the redshift of many BL Lacs you can visit the

- Scientific publications and papers in preparation

A new generation of astronomical products based on 14 years of Swift-XRT data

Giommi et al. 2019, A&A, 631, A116, arXiv:1904.06043

This paper is dedicated to the analysis of all the Swift-XRT X-ray images including a blazar taken by Swift between November 2004 and November 2018. The analysis was carried out using Swift_deepsky, a data analysis pipeline built on top the official HEASoft-XRTDAS-XIMAGE software packages and encapsulated into a Docker container. The resulting catalog, called 1OUSXB, includes intensity and spectral information of 33,396 sources, 8,896 of which are single or multiple detections of 2,308 distinct blazars. The Swift_deepsky container is the most innovative part of the project as it automatically downloads the low-level data and calibration files, it does not require any expertise in X-ray astronomy, and can be run on Mac, Linux, and Windows operating systems. The Swift_deepsky container is available here .


Plot of the XRT count rate in the 0.3-10.0 keV band versus exposure time for all the sources included in the 1OUSXB catalog. Different type of blazars appear in color, serendipitous sources in light grey.

Data access: the latest release (DR3) of the catalog (15 years, 39,063 X-ray sources, 10,574 detections of 2,831 distinct blazars) in FITS format is available here


The Open Universe VOU-Blazars tool

Chang, Brandt & Giommi

Astronomy and Computing, 2020, 30, 100350

VOU-BLazars is a tool developed within the Open Universe initiative designed to facilitate the discovery of Blazars and build their spectral energy distributions (SED) using multi-wavelength photometric and spectral data that are available from dozens of public archives, or that have been generated as part of the Open Universe initiative and are accessible through VO services. The tool is available as source code, as a Docker container, and as a web-based service accessible within the Open Universe portal.




The Open Universe Survey of Swift-XRT GRB fields (OUSXG)

A flux-limited sample of HBL blazars

Astronomy & Astrophysics 2020, in press. arXiv:2003.05153


We have analysed all the X-ray images centred on Gamma Ray Bursts generated by Swift over the last 15 years using automatic tools that do not require any expertise in X-ray astronomy, producing results in excellent agreement with previous findings. This work, besides presenting the largest medium-deep survey of the X-ray sky and a complete sample of blazars, wishes to be a step in the direction of achieving the ultimate goal of the Open Universe Initiative, that is to enable non expert people to fully benefit of space science data, possibly extending the potential for scientific discovery, currently confined within a small number of highly specialised teams, to a much larger population.
Data access: the catalog of X-ray sources detected in this survey (OUSXG) is available in FITS format here. The sky coverage of the OUSXG survey (ASCII format) can be found at the following links - all Galactic latitudes, - high Galactic latitudes (|b| > 10)


Swift-XRT spectra and light-curves of frequently observed blazars


This paper presents a detailed X-ray spectral and photometric analysis of all the Swift observations (in PC and WT mode) of the 66 blazars that have been observed with XRT more than 50 times during the mission. X-ray light curves have been constructed using both the fluxes from the spectral best fits, when the sources are bright enough for a detailed spectral analysis and for the fainter sources, using the image analysis presented in Paper I. See Giommi (2015) for a description and some preliminary results.

Hammer-Aitoff plot of the sky in Galactic coordinates showing the position of the 28 sources in the sample that have been observed more than 100 times. The names of HBL sources appear in blue color, while those of IBLs and LBLs are green and red respectively. The darker area highlights the part of the sky south of the equator, illustrating how most of the blazars best observed by Swift are in the northern hemisphere.

Fermi-LAT adaptive-bin light-curves of bright blazars

Sahakyan et al., in preparation

The emission from blazars is variable in all parts of the electromagnetic spectrum. The most rapid and the highest amplitude flux changes are observed in the gamma-ray band (> 100 MeV). When the gamma-ray light curves with regular (fixed) time bins are generated, the use of long bins will smooth out the fast variations during bright periods, while using short bins might result in many upper limits during the low- activity periods, which prevents variability studies.

This paper presents detailed gamma-ray light curves of 30 bright blazars generated using the adaptive binning method. In this method, the bin width is adjusted by requiring a constant relative flux uncertainty, which produces longer time intervals during lower flux levels and narrower bins when the source is in a high state.

The figure shows the remarkable improvement in the level of detail that the adaptive bin light-curve (red points) can provide compared to a two-day fixed time bin (blue points) for the case of the bright blazar CTA102.

Fermi Adaptive bin and fixed bin (2 day) light-curve of the blazar CTA 102. For more details see Gasparyan, Sahakyan, V. Baghmanyan and D. Zargaryan, 2018 ApJ ...863..114G

NuSTAR spectra of Blazars from the public archive

Middei et al. in preparation


Blazars play a crucial and rapidly growing role in the field of multi-messenger astrophysics.

We developed the NuSTAR_SPECTRA pipeline, which downloads, reduces low-level data, generates third level scientific products and performs spectral analyses for each source.

We will use this pipeline to produce and release a complete and up-to-date science-ready catalogue of the spectral properties of all the blazars observed by NuSTAR.


- Papers on blazars that make use of Open Universe data and services

  • Extreme & High Synchrotron Peak γ-ray Blazars beyond 4FGL: The 2BIGB γ-ray catalog. Arsioli et al. 2019

  • Dissecting the regions around IceCube high-energy neutrinos: growing evidence for the blazar connection. Giommi et al. 2020. Submitted to A&A, arXiv:2001.09355

  • 3HSP J095507.9+355101: a flaring extreme blazarcoincident in space and time with IceCube-200107, Giommi et al. 2020. Submitted to MNRAS, arXiv:2003.06405









Data access

Source catalogs and spectral/timing high-transparency data products resulting from this program can be accessed in a variety of ways, as described below.

Paper I

The following data products and services are available for paper I (A new generation of astronomical products based on 14 years of Swift-XRT data)

  1. Catalogs in FITS format

  2. Catalogs in CSV format

  3. On-line query interface at the Brazilian Science Data Center, BSDC

  4. Data integrated in the VOU-Blazars, VOU-SED and SSDC-SED tools accesible from the openuniverse.asi.it portal or as standalone tools (VOU-BLazars, Docker container version, VOU-Blazars, source code, SSDC-SED Builder).

  5. Access via Virtual Observatory Simple Conesearch Service (SCS) (e.g. from TOPCAT, Aladin etc...).

Paper II

Products and services for paper II

The FITS formatted file with all the results will be available shortly

Spectral and timing data integrated in the VOU-Blazars, VOU-SED and SSDC-SED tools accesible from the openuniverse.asi.it portal or as standalone tools

Upcoming activities

  • Regular updates (every ~6months) of all catalogs and high-transparency data products

  • Publication of SED movies of bright and densely observed blazar . For an example see the movie below presented in Padovani et al. 2018, MNRAS, 480, 192