The populations of hard X-ray and<i>γ</i>-ray sources: a correlation study and new possible identifications

Maselli, A.; Cusumano, G.; Massaro, E.; Segreto, A.; Parola, V. La; Tramacere, A.; Donnarumma, I.

doi:10.1051/0004-6361/201116916

Cited by 10 publications

(16 citation statements)

References 33 publications

(53 reference statements)

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“…The number of Fermi-BZCAT blazars with a WISE counterpart within the first region of 2. 4 is 296, corresponding to ∼45% of the Fermi-WISE blazar sample in the WPSC, detected with a chance probability of ∼3% (see Maselli et al 2011;Massaro et al 2011a for more details) We did not find any multiple matches using 2. 4 as search radius.…”

Section: Sample Selectionmentioning

confidence: 71%

Infrared Colors of the Gamma-Ray-Detected Blazars

D’Abrusco

Massaro

Ajello

et al. 2012

ApJ

132

107

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Blazars constitute the most enigmatic class of extragalactic γ-ray sources, and their observational features have been ascribed to a relativistic jet closely aligned to the line of sight. They are generally divided in two main classes: the BL Lac objects (BL Lacs) and the flat-spectrum radio quasars (FSRQs). In the case of BL Lacs the double-bumped spectral energy distribution (SED) is generally described by the synchrotron self-Compton (SSC) emission, while for the FSRQs it is interpreted as due to external Compton (EC) emission. Recently, we showed that in the [3.4]-[4.6]-[12] μm color-color diagram the blazar population covers a distinct region (i.e., the WISE blazar Strip (WBS)) clearly separated from the other extragalactic sources that are dominated by thermal emission. In this paper, we investigate the relation between the infrared and γ-ray emission for a subset of confirmed blazars from the literature, associated with Fermi sources, for which WISE archival observations are available. This sample is a proper subset of the sample of sources used previously, and the availability of Fermi data is critical to constrain the models on the emission mechanisms for the blazars. We found that the selected blazars also lie on the WBS covering a narrower region of the infrared color-color planes than the overall blazar population. We then found an evident correlation between the IR and γ-ray spectral indices expected in the SSC and EC frameworks. Finally, we determined the ratio between their γ-ray and infrared fluxes, a surrogate of the ratio of powers between the inverse Compton and the synchrotron SED components, and used such parameter to test different blazar emitting scenarios.

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Section: Sample Selectionmentioning

confidence: 71%

Infrared Colors of the Gamma-Ray-Detected Blazars

D’Abrusco

Massaro

Ajello

et al. 2012

ApJ

132

107

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“…4 is 1365, corresponding to 92% of the blazars in the WISE first year survey, detected with a chance probability of 2.5%, evaluated applying the same method described in Maselli et al (2011). We did not find any multiple matches adopting the area of 2.…”

Section: Blazar Wise Detectionsmentioning

confidence: 73%

Identification of the Infrared Non-Thermal Emission in Blazars

Massaro

D’Abrusco

Ajello

et al. 2011

ApJ

171

211

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Blazars constitute the most interesting and enigmatic class of extragalactic γ -ray sources dominated by non-thermal emission. In this Letter, we show how the Wide Infrared Survey Explorer (WISE) infrared data make it possible to identify a distinct region of the [3.4]-[4.6]-[12] μm color-color diagram where the sources dominated by the thermal radiation are separated from those dominated by non-thermal emission, in particular the blazar population. This infrared non-thermal region, which we indicate as the WISE blazar strip (WBS), will constitute a new powerful diagnostic tool when the full WISE survey data are released. The WBS can be used to extract new blazar candidates, to identify those of uncertain type and also to search for the counterparts of unidentified γ -ray sources. We show one example of the value of the use of the WBS identifying the TeV source VER J0648+152, recently discovered by VERITAS.

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“…The second problem is the search for possible counterparts in the error boxes of γ‐ray sources. In the LAT catalogues (1FGL; Abdo et al 2010a, and 2FGL, Abdo et al 2011) there are a few hundreds of sources without a reasonable counterpart to associate with. The finding of a source having colours satisfying the above limits, possibly associated with a radio or X‐ray emission, would be useful for selecting interesting candidates as in the case considered by Maselli et al (2011).…”

Section: Discussionmentioning

confidence: 99%

“…In the LAT catalogues (1FGL; Abdo et al 2010a, and 2FGL, Abdo et al 2011) there are a few hundreds of sources without a reasonable counterpart to associate with. The finding of a source having colours satisfying the above limits, possibly associated with a radio or X‐ray emission, would be useful for selecting interesting candidates as in the case considered by Maselli et al (2011). Similar research could be applied to the study of serendipitous sources detected inside the fields of X‐ray imaging telescopes, like Chandra and Swift‐XRT .…”

Section: Discussionmentioning

confidence: 99%

The colours of BL Lac objects: a new approach to their classification

Massaro¹,

Nesci²,

Piranomonte³

2012

Monthly Notices of the Royal Astronomical Society

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We selected a sample of 437 BL Lac objects, taken from the RomaBZCat catalogue, for which spectroscopic information and SDSS photometry is available. We propose a new classification of BL Lacs in which the sources' type is not defined only on the basis of the peak frequency of the synchrotron component in their Spectral Energy Distribution (types L and H), but also on the relevance of this component with respect to the brightness of the host galaxy (types N and G, for nuclear or galaxy dominated sources). We found that the SDSS colour index u-r=1.4 is a good separator between these two types. We used multiband colour-colour plots to study the properties of the BL Lac classes and found that in the X-ray to radio flux ratio vs u-r plot most of the N (blue) sources are located in a rather narrow strip, while the G-sources (red) are spread in a large area, and most of them are located in galaxy clusters or interacting systems, suggesting that their X-ray emission is not from a genuine BL Lac nucleus but it is related to their environment. Of the about 135 sources detected in the gamma-rays by Fermi-GST, nearly all belong to the N-type, indicating that only this type of sources should be considered as genuine BL Lac nuclei. The J-H, H-K plot of sources detected in the 2MASS catalogue is consistent with that of the "bona fide" BL Lac objects, independently of their N or G classification from the optical indices, indicating the existence in G-type sources of a K-band excess possibly due to a steep, low frequency peaked emission which deserves further investigations. We propose to use these colour plots as a further tool for searching candidate counterparts of newly discovered high-energy sources.Comment: 11 pages, 7 figures. Submitted 29/08/2011 to MNRAS, first referee report received 31/10/2011, accepted 21/02/201

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The populations of hard X-ray andγ-ray sources: a correlation study and new possible identifications

Cited by 10 publications

References 33 publications

Infrared Colors of the Gamma-Ray-Detected Blazars

Infrared Colors of the Gamma-Ray-Detected Blazars

Identification of the Infrared Non-Thermal Emission in Blazars

The colours of BL Lac objects: a new approach to their classification

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