We report on the
Swift
/XRT observation and classification of eleven blazar candidates at
z
> 4. These sources were selected as part of a sample of extremely radio-loud quasars, with a focus on ...quasars with jets oriented roughly close to our line of sight. Deriving their viewing angles and their jets’ bulk Lorentz factors was crucial for a strict blazar classification, which was made possible only thanks to X-ray observations. Out of eleven sources, five show strong and hard X-ray fluxes that set the foundation for their blazar classification, while two are uncertain and three host relativistic jets that we observe just outside their beaming cone (i.e. are not strictly blazars), while one went undetected by
Swift
/XRT. Following this approach, we were able to trace the > 10
9
M
⊙
active super-massive black hole (SMBH) population hosted in jetted active galactic nuclei (AGN). At
z
≥ 4, the massive jetted sources are likely predominant in the overall quasar population: this calls for a deep review of our understanding of the first SMBH formations and evolution. Jets are indeed key actors in fast accretion and must be searched for across the whole high-redshift quasar population. A note of caution must be added: radio-loudness and, in general, radio features at high redshifts seem do not seem to perfectly reflect high-energy properties. A strong effect attributed to the interaction with cosmic microwave background (CMB) radiation is surely at work, which quenches the radio emission with respect to the X-rays; however, in addition, more frequent occasions for the jet to be bent seem to play a relevant role in this regard. Thus, classifications and population studies must be carefully performed, so as to avoid interference resulting from these inconsistencies.
We observed three blazars at z > 2 with the NuSTAR satellite. These were detected in the γ-rays by Fermi/LAT and in the soft X-rays, but have not yet been observed above 10 keV. The flux and slope ...of their X-ray continuum, together with Fermi/LAT data allows us to estimate their total electromagnetic output and peak frequency. For some of them we were able to study the source in different states, and investigate the main cause of the different observed spectral energy distribution. We then collected all blazars at redshifts greater than 2 observed by NuSTAR, and confirm that these hard and luminous X-ray blazars are among the most powerful persistent sources in the Universe. We confirm the relation between the jet power and the disk luminosity, extending it at the high-energy end.
We present BeppoSAX LECS, MECS, and PDS spectra of eleven X-ray selected BL Lacertae objects. Combining these sources with the ones presented elsewhere we have a sample of 21 BL Lacs from the ...Einstein Medium Sensitivity and Einstein Slew Survey. The sample shows strong correlations of several physical parameters with the peak frequency of the synchrotron branch of the spectral energy distribution. In particular the peak frequency is correlated with the X-ray spectral shape: objects with the peak near to the X-ray band show harder and straighter X-ray spectra than those of the low energy peaked sources. This work shows that the recently proposed unification scenario for different types of blazars can hold also within the class of high frequency peaked BL Lac objects.
Blazars are highly variable sources over timescales that can be as low as minutes. This is the case of the High Energy Peaked BL Lac (HBL) objects showing strong variability in X-rays, which highly ...correlates with that of the TeV emission. The degree of this correlation is still debated, particularly when the flaring activity is followed down to very short time scales. This correlation could challenge the synchrotron-self-Compton scenario in which one relativistic electron population dominates the entire radiative output. Constraints to the location of the high energy emission will be provided by: a) temporal investigation on second timescale; b) spectral trend investigation on minute timescales. This represents a further link with CTA because of the rapid (unexpected) TeV emission recently detected in some FSRQs.
The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 ...Delta *g-ray sources located at high Galactic latitudes (|b| > 10?) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency <1014 Hz, about half of the BL Lac objects have a synchrotron-peak frequency >1015 Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as Delta *g-ray fluxes and photon power-law spectral indices, redshifts, Delta *g-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.
Multiwavelength observations with TeV photons are an essential diagnostic tool to study the physics of TeV sources. The X-ray and optical bands are especially valuable, since give information on the ...same energy electrons and most effective seed photons for the TeV emission. The complex variability of blazars, however (with timescales from years down to minutes, with different patterns and SED behaviours), requires a great effort on simultaneous campaigns, which should be performed possibly over several days. Most important is the possibility to have spectra in all the three bands: with the new instruments, both in TeV and X-ray bands, this has become now feasable on timescales less than one hour. The insights from such observations can be tremendous, since recent results have shown that the X-ray and TeV emissions do not always follow the same behaviour, and flares can have different rise and decay times. Unfortunately, the strong pointing constraints of XMM do not allow the full use of this satellite simultaneously with ground telescopes.
We present new BeppoSAX LECS and MECS observations, covering the energy range 0.1–10 keV (observer's frame), of four BL Lacertae objects selected from the 1-Jy sample. All sources display a flat (αx∼ ...0.7) X-ray spectrum, which we interpret as inverse Compton emission. One object shows evidence for a low-energy steepening (Δαx∼ 0.9), which is probably due to the synchrotron component merging into the inverse Compton one around ∼2 keV. A variable synchrotron tail would explain why the ROSAT spectra of our sources are typically steeper than the BeppoSAX ones (Δαx∼ 0.7). The broad-band spectral energy distributions fully confirm this picture, and model fits using a synchrotron inverse Compton model allow us to derive the physical parameters (intrinsic power, magnetic field, etc.) of our sources. By combining the results of this paper with those previously obtained on other sources, we present a detailed study of the BeppoSAX properties of a well-defined subsample of 14 X-ray bright ƒx(0.1–10) keV > 3 × 10−12 erg cm−2 s−1 1-Jy BL Lacs. We find a very tight proportionality between nearly simultaneous radio and X-ray powers for the 1-Jy sources in which the X-ray band is dominated by inverse Compton emission, which points to a strong link between X-ray and radio emission components in these objects.
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