Open Universe for Blazars: a new generation of astronomical products based on 14 years ofSwift-XRT data

Abstract

Aims. Open Universe for blazars is a set of high-transparency multi-frequency data products for blazar science, and the tools designed to generate them. Blazars are drawing growing interest following the consolidation of their position as the most abundant type of source in the extragalactic very-high energy γ-ray sky, and because of their status as prime candidate sources in the nascent field of multi-messenger astrophysics. As such, blazar astrophysics is becoming increasingly data driven, depending on the integration and combined analysis of large quantities of data from the entire span of observational astrophysics techniques. The project was therefore chosen as one of the pilot activities within the United Nations Open Universe Initiative. Methods. We aim to deliver innovative data science tools for multi-messenger astrophysics. In this work we developed a data analysis pipeline called Swift-DeepSky based on the Swift XRTDAS software and the XIMAGE package, encapsulated into a Docker container. Swift-DeepSky downloads and reads low-level data, generates higher-level products, detects X-ray sources and estimates several intensity and spectral parameters for each detection, thus facilitating the generation of complete and up-to-date science-ready catalogues from an entire space-mission dataset. The Docker version of the pipeline -whose concept can be reproduced with other missions -and its derived products is publicly available from the Open Universe Website at openuniverse.asi.it Results. We present the results of a detailed X-ray image analysis based on Swift-DeepSky that was run on all Swift XRT observations including a known blazar, carried out during the first 14 years of operations of the Neil Gehrels Swift Observatory. Short exposures executed within one week of each other have been added to increase sensitivity, which ranges between ∼ 1 × 10 −12 and ∼ 1 × 10 −14 erg cm −2 s −1 (0.3-10.0 keV). After cleaning for problematic fields, the resulting database includes over 27,000 images integrated in different X-ray bands, and a catalogue, called 1OUSXB, that provides intensity and spectral information for 33,396 X-ray sources, 8,896 of which are single or multiple detections of 2,308 distinct blazars. All the results can be accessed on-line in a variety of ways: e.g., from the Open Universe portal at openuniverse.asi.it, through Virtual Observatory services, via the VOU-Blazar tool and the SSDC SED builder. One of the most innovative aspects of this work is that the results can be safely reproduced and extended by anyone.

The first blazar observed at z > 6

“…The reported errors on the flux and luminosity take into account both the uncertainty on the photon index and the Poissonian error associated with the photon counts. Although the value of the measured photon index is consistent with a flat index that is typical of blazars sources (Γ X ∼ 1.5; e.g., Giommi et al 2019), it is also consistent, within 1σ, with that of radio-quiet (RQ) or misaligned RL AGNs (Γ X ∼ 2; e.g., Ishibashi et al 2010 and references therein). Therefore, with the current X-ray data, we cannot distinguish between a flat or a steep X-ray spectrum.…”

3HSP J095507.9+355101: A flaring extreme blazar coincident in space and time with IceCube-200107A

“…The remaining pointings were carried out either as a Target of Opportunity (ToO) after the IceCube200107A event, which revealed the source to be in a flaring and very hard state (Giommi et al 2020b;Krauss et al 2020) or as part of a subsequent monitoring programme. We analysed all the X-Ray Telescope (XRT; Burrows et al 2005) imaging data using Swift-DeepSky, a Docker container 4 encapsulated pipeline software developed in the context of the Open Universe initiative (Giommi et al 2018(Giommi et al , 2019. Spectral analysis was also performed on all exposures with a sufficiently strong signal using the XSPEC-12 software embedded in a dedicated processing pipeline, called Swift-xrtproc, that was first presented in Giommi (2015).…”

Open Universe survey of Swift-XRT GRB fields: Flux-limited sample of HBL blazars

“…Following the approach adopted in Paper I, we used the Docker container 2 version of the Swift_deepsky pipeline to analyse all the Swift-XRT observations pointing at GRBs and carried out in photon counting (PC) readout mode (Burrows et al 2005;Giommi et al 2019). The Swift_deepsky software, built on top of the official HEASoft data reduction package 3 , automatically performs the following tasks:…”

“…-estimation of spectral parameters based on the count rates in the three energy bands considered and on the amount of Galactic absorption in the direction of each source. At the end of the processing the software checks the quality of the results and flags fields affected by excessive background or other potential problems (for more details see Giommi et al 2019).…”

“…These are traditional catalogues that reflect the sequence of observations performed by the satellite but do not provide accurate information about the area of sky covered as a function of sensitivity nor the many details that are essential to control the observational biases resulting from the complex scientific and guest observer programs that determine the composition of the archive. Thematic catalogues concentrate on a specific type of sources, like for example blazars, as in Giommi et al (2019), or GRBs, while survey catalogues (e.g. Puccetti et al 2011;Dai et al 2015, and this work) are designed for the purpose of statistical use and therefore pay attention to the need to control observational biases and provide details about the sky coverage as a function of sensitivity.…”