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Register a new userEnhanced X-ray Emission from the Most Radio-Powerful Quasar in the Universes First Billion Years
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We present deep (265 ks) Chandra X-ray observations of PSO J352.4034$-$15.3373, a quasar at z=5.831 that, with a radio-to-optical flux ratio of R>1000, is one of the radio-loudest quasars in the early universe and is the only quasar with observed extended radio jets of kpc-scale at $z gtrsim 6$. Modeling the X-ray spectrum of the quasar with a power law, we find a best fit of $Gamma = 1.99^{+0.29}_{-0.28}$, leading to an X-ray luminosity of $L_{2-10} = 1.26^{+0.45}_{-0.33} times 10^{45} {rm erg} {rm s}^{-1}$ and an X-ray to UV brightness ratio of $alpha_{rm OX} = -1.36 pm 0.11$. We identify a diffuse structure 50 kpc (${sim}8^{primeprime}$) to the NW of the quasar along the jet axis that corresponds to a $3sigma$ enhancement in the angular density of emission and can be ruled out as a background fluctuation with a probability of P=0.9985. While with few detected photons the spectral fit of the structure is uncertain, we find that it has a luminosity of $L_{2-10}sim10^{44} {rm erg} {rm s}^{-1}$. These observations therefore potentially represent the most distant quasar jet yet seen in X-rays. We find no evidence for excess X-ray emission where the previously-reported radio jets are seen (which have an overall linear extent of $0.^{primeprime}28$), and a bright X-ray point source located along the jet axis to the SE is revealed by optical and NIR imaging to not be associated with the quasar.
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Variations in scaling behavior in the flux and emissions of distant astronomical sources with respect to their cosmic time are important l phenomena that can provide valuable information about the dynamics within the sources and their cosmological evolution with time. Different studies have been applying linear analysis to understand and model quasars light curves. Here, we study the multifractal behavior of selected quasars radio emissions in their observed frame (at 22 and 37 GHz bands) and and their rest frame. To this end, we apply the wavelet transform-based multifractal analysis formalism called wavelet transform modulus maxima. In addition, we verify whether the autoregressive integrated moving average (ARIMA) models fit our data or not. In our work, we observe strong multifractal behavior for all the sources. Additionally, we find that the degree of multifractality is strongly similar for each source and significantly different between sources at 22 and 37 GHz. This similarity implies that the two frequencies have the same radiation region and mechanism, whereas the difference indicates that the sources have intrinsically different dynamics. Furthermore, we show that the degree of multifractality is the same in the observed and rest frames of the quasars, i.e., multifractality is an intrinsic property of radio quasars. Finally, we show that the ARIMA models fit the 3C 345 quasar at 22 GHz and partially fit most of the time series with the exception of the 3C 273 and 3C 279 quasars at 37 GHz, for which the models are found to be inadequate.
We searched for high-z quasars within the X-ray source population detected in the contiguous $sim 140^2$ eFEDS field observed by eROSITA during the performance verification phase. We collected the available spectroscopic information in the field, including the sample of all currently known optically selected z>5.5 quasars and cross-matched secure Legacy DR8 counterparts of eROSITA-detected X-ray point-like sources with this spectroscopic sample. We report the X-ray detection of an eROSITA source securely matched to the well-known quasar SDSS J083643.85+005453.3 (z=5.81). The soft X-ray flux of the source derived from eROSITA is consistent with previous Chandra observations. In addition, we report the detection of the quasar with LOFAR at 145 MHz and ASKAP at 888 MHz. The reported flux densities confirm a spectral flattening at lower frequencies in the emission of the radio core, indicating that the quasar could be a (sub-) gigahertz peaked spectrum source. The inferred spectral shape and the parsec-scale radio morphology of SDSS J083643.85+005453.3 suggest that it is in an early stage of its evolution into a large-scale radio source or confined in a dense environment. We find no indications for a strong jet contribution to the X-ray emission of the quasar, which is therefore likely to be linked to accretion processes. The detection of this source allows us to place the first constraints on the XLF at z>5.5 based on a secure spectroscopic redshift. Compared to extrapolations from lower-redshift observations, this favours a relatively flat slope for the XLF at $zsim 6$ beyond $L_*$. The population of X-ray luminous AGNs at high redshift may be larger than previously thought. From our XLF constraints, we make the conservative prediction that eROSITA will detect $sim 90$ X-ray luminous AGNs at redshifts 5.7<z<6.4 in the full-sky survey (De+RU).
This paper studied the faint, diffuse extended X-ray emission associated with the radio lobes and the hot gas in the intracluster medium (ICM) environment for a sample of radio galaxies. We used shallow ($sim 10$ ks) archival Chandra observations for 60 radio galaxies (7 FR I and 53 FR II) with $0.0222 le z le 1.785$ selected from the 298 extragalactic radio sources identified in the 3CR catalog. We used Bayesian statistics to look for any asymmetry in the extended X-ray emission between regions that contain the radio lobes and regions that contain the hot gas in the ICM. In the Chandra broadband ($0.5 - 7.0$ keV), which has the highest detected X-ray flux and the highest signal-to-noise ratio, we found that the non-thermal X-ray emission from the radio lobes dominates the thermal X-ray emission from the environment for $sim 77%$ of the sources in our sample. We also found that the relative amount of on-jet axis non-thermal emission from the radio lobes tends to increase with redshift compared to the off-jet axis thermal emission from the environment. This suggests that the dominant X-ray mechanism for the non-thermal X-ray emission in the radio lobes is due to the inverse Compton upscattering of cosmic microwave background (CMB) seed photons by relativistic electrons in the radio lobes, a process for which the observed flux is roughly redshift independent due to the increasing CMB energy density with increasing redshift.
The high-redshift quasar PMN J0909+0354 ($z=3.288$) is known to have a pc-scale compact jet structure, based on global 5-GHz very long baseline interferometry (VLBI) observations performed in 1992. Its kpc-scale structure was studied with the Karl G. Jansky Very Large Array (VLA) in the radio and the Chandra space telescope in X-rays. Apart from the north-northwestern jet component seen in both the VLA and Chandra images at $2.3$ separation from the core, there is another X-ray feature at $6.48$ in the northeastern (NE) direction. To uncover more details and possibly structural changes in the inner jet, we conducted new observations at 5 GHz using the European VLBI Network (EVN) in 2019. These data confirm the northward direction of the one-sided inner jet already suspected from the 1992 observations. A compact core and multiple jet components were identified that can be traced up to $sim0.25$ kpc projected distance towards the north, while the structure becomes more and more diffuse. A comparison with arcsec-resolution imaging with the VLA shows that the radio jet bends by $sim30^circ$ between the two scales. The direction of the pc-scale jet as well as the faint optical counterpart found for the newly-detected X-ray point source (NE) favors the nature of the latter as a background or foreground object in the field of view. However, the extended ($sim160$ kpc) emission around the positions of the quasar core and NE detected by the Wide-field Infrared Survey Explorer (WISE) in the mid-infrared might suggest physical interaction of the two objects.
Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the sub-parsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near-IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new, deep Chandra and HST observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR, HST, and Chandra will allow us to further constrain the emission mechanisms.
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