Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

Vasudevan, R. V.; Mushotzky, R. F.; Gandhi, P.

doi:10.1088/2041-8205/770/2/l37

Cited by 39 publications

(48 citation statements)

References 33 publications

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“…Liu et al 2016; however, see also Vasudevan et al 2013). Although this trend is only seen fixing the photon index, due to the degeneracies in the spectral parameters, this decrease is significant also if we fit the L1 spectrum with a flatter photon index of 1.75 G = to correct for the "artificial" flattening discussed in the previous sections, which yields R 0.93 0.47 0.52…”

Section: G = -+mentioning

confidence: 85%

“…From these spectral fits we obtained R 0.23 < for the NH1 spectrum, R 0.52 0.36 0.39 = -+ for the NH2 spectrum, and R 0.71 < for the NH3 spectrum (see Figure 6; R 0.51 < if we fix 1.75 G = to account for the "artificial" flattening of the composite spectra with high N H ). The contribution from reflection is typically low in unobscured sources (NH1), while it seems to increase in obscured sources (e.g., Ricci et al 2011;Vasudevan et al 2013). The relatively poor fit obtained for the NH3 composite spectrum, however, does not allow us to place tight constraints on R and therefore to securely assess whether there is a clear dependence between the strength of the Compton reflection and N H .…”

Section: Average Spectral Properties For Absorbed and Unabsorbed Agnsmentioning

confidence: 99%

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The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

Moro

Alexander

Aird

et al. 2017

ApJ

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We present a study of the average X-ray spectral properties of the sources detected by the NuSTAR extragalactic survey, comprising observations of the Extended Chandra Deep Field South (E-CDFS), Extended Groth Strip (EGS), and the Cosmic Evolution Survey (COSMOS). The sample includes 182 NuSTAR sources (64 detected at 8-24 keV), with 3-24 keV fluxes ranging between f 10 »´----erg cm −2 s −1 ) and redshifts in the range of z 0.04 3.21 = -. We produce composite spectra from the Chandra + NuSTAR data (E 2 40 keV » -, rest frame) for all the sources with redshift identifications (95%) and investigate the intrinsic, average spectra of the sources, divided into broad-line (BL) and narrow-line (NL) active galactic nuclei (AGNs), and also in different bins of X-ray column density and luminosity. The average power-law photon index for the whole sample is , respectively), likely due to the effect of absorption and to the contribution from the Compton reflection component to the high-energy flux (E 10 > keV). We find that the typical reflection fraction in our spectra is R 0.5 » (for 1.8 G = ), with a tentative indication of an increase of the reflection strength with X-ray column density. While there is no significant evidence for a dependence of the photon index on X-ray luminosity in our sample, we find that R decreases with luminosity, with relatively high levels of reflection (R 1.

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Section: G = -+mentioning

confidence: 85%

Section: Average Spectral Properties For Absorbed and Unabsorbed Agnsmentioning

confidence: 99%

The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

Moro

Alexander

Aird

et al. 2017

ApJ

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“…The extent and strength of reflection in such sources, especially those with L * luminosities and at z 1 that make a large contribution to the CXB flux, is still a matter of debate (e.g. Vasudevan et al 2013;Del Moro et al 2014). Indeed, the CXB can be reproduced with a wide variety of models that assume different X-ray spectral models for the constituent AGNs, as well as different XLFs, NH distributions, and-perhaps most crucially-Comptonthick fractions (e.g.…”

Section: The Nh Distribution the Fraction Of Compton-thick Agns And mentioning

confidence: 99%

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Aird

Coil

Georgakakis

et al. 2015

Monthly Notices of the Royal Astronomical Society

375

559

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We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out to z ∼ 5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately modelling the evolution of the XLFs of unabsorbed (20 < log N H < 22) and absorbed (22 < log N H < 24) AGNs, seeking a model that can reconcile both the hard-and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ∼ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations.

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“…Although quasars are believed to dominate the X-ray background at low redshift 46 , their rapid decline beyond z ∼ 3…”

Section: Other Heating Sourcesmentioning

confidence: 99%

The observable signature of late heating of the Universe during cosmic reionization

Fialkov

Barkana

Visbal

2014

Nature

205

245

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of ionized bubbles. This is based on the assumption 5,6,7 that the cosmic gas was heated by stellar remnants -particularly X-ray binaries -to temperatures well above the cosmic microwave background at that time (∼30 K). Here we show instead that the hard spectra (that is, spectra with more high-energy photons than low-energy photons) of X-ray binaries 8,9 make such heating ineffective, resulting in a delayed and spatially uniform heating 1 that modifies the 21-cm signature of reionization. Rather than looking for a simple rise and fall of the large-scale fluctuations (peaking at several millikelvin), we must expect a more complex signal also featuring a distinct minimum (at less than a millikelvin) that marks the rise of the cosmic mean gas temperature above the microwave background.Observing this signal, possibly with radio telescopes in operation today, will demonstrate the presence of a cosmic background of hard X-rays at that early time.While stellar remnants at high redshift have been previously considered, a more reliable prediction of the radiative feedback from X-ray binaries (XRBs) is now possible due to a recent detailed population synthesis simulation of their evolution across cosmic time 8,9 . This simulation was calibrated to all available observations in the local and low redshift Universe, and it predicts the evolution of the luminosity and X-ray spectrum of XRBs with redshift. In particular, high-mass XRBs (especially black hole binaries) should dominate, with a ratio at high redshift of bolometric X-ray luminosity to star-formation rate (SFR) ofWe have allowed for an uncertainty in the X-ray efficiency with an extra parameter in eq. 1, where f X = 1 indicates our standard value. We focus on XRBs as the most natural heating source, since other observed sources should be sub-dominant at high redshift (see Methods section).Previous calculations of X-ray heating 6,10,11,12,13 have assumed power-law spectra that place most of the X-ray energy at the low-energy end, where the mean free path of the soft X-rays is relatively short. This means that most of the emitted X-rays are absorbed soon after they are emitted, before much energy is lost due to cosmological effects. The absorbed energy is then enough to heat the gas by the time of reionization to ∼ 10 times the temperature of the Cosmic Microwave Background (CMB; see Methods section). Thus, it is generally assumed 2 that reionization occurs when T gas ≫ T CMB , a limit referred to as saturated heating since the 21-cm intensity then becomes independent of T gas and mainly dependent on ionization and density. A different possibility whereby heating is delayed until reionization has only been previously considered as a fringe case of having an unusually low X-ray luminosity to SFR ratio 10,11 .However, the average radiation from XRBs is expected to have a much harder spectrum ( Fig. 1) whose energy content (per logarithmic frequency interval) peaks at ∼ 3 keV. Photons above a (roughly redshift-independent) critical energy of ∼ 1 keV have such a long me...

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Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

Cited by 39 publications

References 33 publications

The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

The observable signature of late heating of the Universe during cosmic reionization

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