arXiv subjects

R. Della Ceca

Publications and source records attributed to R. Della Ceca.

At least 37 records · Page 2Linked to original sources

arXiv2019

Te-REX: a sample of extragalactic TeV-emitting candidates

The REX (Radio-Emitting X-ray sources) is a catalogue produced by cross-matching X-ray data from the ROSAT-PSPC archive of pointed observations and radio data from the NRAO VLA Sky Survey, aimed at the selection of blazars. From the REX catalogue, we select a well defined and statistically complete sample of high-energy peaked BL Lac (HBL). HBL are expected to be the most numerous class of extragalactic TeV emitting sources. Specifically, we have considered only the REX sources in the currently planned CTA extragalactic survey area satisfying specific criteria and with an optical spectroscopic confirmation. We obtain 46 HBL candidates that we called Te-REX (TeV-emitting REX). We estimate the very high-energy gamma-ray emission, in the TeV domain, using an empirical approach i.e. using specific statistical relations between gamma-rays (at GeV energies) and radio/X-rays properties observed in bright HBL from the literature. We compare the spectral energy distributions (SEDs) with the sensitivities of current and upcoming Cherenkov telescopes and we predict that 14 Te-REX could be detectable with 50 hours of observations of CTA and 7 of them also with current Cherenkov facilities in 50 hours. By extrapolating these numbers on the total extragalactic sky, we predict that about 800 HBL could be visible in pointed CTA observations and about 400 with current Cherenkov telescopes in 50 hours. Interestingly, our predictions show that a non-negligible fraction (about 30%) of the HBL that will be detectable by CTA is composed of relatively weak objects whose optical nuclear emission is swamped by the host-galaxy light and not (yet) detected by Fermi-LAT.

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arXiv2019

X-ray properties of z>4 blazars

We present the X-ray analysis of the largest flux-limited complete sample of blazar candidates at z>4 selected from the Cosmic Lens All Sky Survey (CLASS). After obtaining a nearly complete (24/25) X-ray coverage of the sample (from Swift-XRT, XMM-Newton and Chandra), we analysed the spectra in order to identify the bona-fide blazars. We classified the sources based on the shape of their Spectral Energy Distributions (SEDs) and, in particular, on the flatness of the X-ray emission and its intensity compared to the optical one. We then compared these high-z blazars with a blazar sample selected at lower redshifts (z~1). We found a significant difference in the X-ray-to-radio luminosity ratios, with the CLASS blazars having a mean ratio 2.4+/-0.5 times larger than low-z blazars. We tentatively interpret this evolution as due to the interaction of the electrons of the jet with the Cosmic Microwave Background (CMB) photons, which is expected to boost the observed X-ray emission at high redshifts. Such a dependence has been already observed in highly radio-loud AGNs in the recent literature. This is the first time it is observed using a statistically complete radio flux limited sample of blazars. We have then evaluated whether this effect could explain the differences in the cosmological evolution recently found between radio and X-ray selected samples of blazars. We found that the simple version of this model is not able to solve the tension between the two evolutionary results.

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arXiv2019

Water masers in Compton-thick AGN II. The high detection rate and EVN observations of IRAS 15480-0344

Investigations of H$_2$O maser galaxies at X-ray energies reveal that most AGN associated with water masers are characterized by high levels of absorption. With the aim of finding new maser sources for possible interferometric follow-ups, we have searched for water maser emission in a well-defined sample of heavily absorbed AGN ($N_{\rm H} > 10^{23}$ cm$^{-2}$), including Compton-thick (CT) sources. All the galaxies in the sample were already searched for 22 GHz water maser emission in previous surveys. With the goal of providing a detection or a stringent upper limit on the H$_2$O luminosity, we re-observed some of the non-detected sources with the Green Bank Telescope. A new luminous H$_2$O maser ($L_{\rm H2O} \sim 200\,$L$_\odot$) was detected in the mid-IR-bright Seyfert 2 galaxy IRAS 15480-0344 and then followed-up with the Very Long Baseline Array. In order to shed light on the origin of the maser (jet/outflow vs. disc), we recently observed the radio continuum emission in IRAS 15480-0344 with the European VLBI network (EVN) at 1.7 and 5.0 GHz. With the newly discovered megamaser in IRAS 15480-0344 revealing a narrow ($\sim$0.6 km s$^{-1}$) and a broad ($\sim$90 km s$^{-1}$) component, the maser detection rate of the CT AGN sample is 50% (18/36), which is one of the highest ever found in maser surveys. The EVN maps show two bright sources (labeled SW and NE) in the nuclear region of IRAS 15480-0344, which we interpret as jet knots tracing regions where the radio plasma impacts dense molecular clouds. [abridged]

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arXiv2018

Evidence for a clumpy disc-wind in the star forming Seyfert\,2 galaxy MCG--03--58--007

We report the results of a detailed analysis of a deep simultaneous $130\,\rm ks$ \textit{XMM-Newton & NuSTAR} observation of the nearby ($z=0.0315$) and bright ($L_{\rm bol}\sim3\times10^{45}\,\rm erg\,s^{-1}$) starburst-AGN Seyfert\,2 system: MCG--03--58--007. From the broadband fitting we show that most of the obscuration needs to be modeled with a toroidal type reprocessor such as \texttt{MYTorus} \citep{MurphyYaqoob09}. Nonetheless the signature of a powerful disc-wind is still apparent at higher energies and the observed rapid short-term X-ray spectral variability is more likely caused by a variable zone of highly ionized fast wind rather than by a neutral clumpy medium. We also detect X-ray emission from larger scale gas as seen from the presence of several soft narrow emission lines in the RGS, originating from a contribution of a weak star forming activity together with a dominant photoionized component from the AGN.

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arXiv2018

A new powerful and highly variable disk wind in an AGN-star forming galaxy, the case of MCG-03-58-007

We present the discovery of a new candidate for a fast disk wind, in the nearby Seyfert 2 galaxy MCG-03-58-007. This wind is discovered in a deep Suzaku observation that was performed in 2010. Overall the X-ray spectrum of MCG-03-58-007 is highly absorbed by a neutral column density of NH~10^23 cm^-2, in agreement with the optical classification as a type 2 AGN. In addition, this observation unveiled the presence of two deep absorption troughs at E = 7.4 +- 0.1 keV and E = 8.5 +- 0.2 keV. If associated with blue-shifted FeXXVI, these features can be explained with the presence of two highly ionised (log ξ/(erg cm/s)~ 5.5) and high column density (NH~5-8 x 10^23cm^-2) outflowing absorbers with v_out1~ -0.1c and v_out2~ -0.2c. The disk wind detected during this observation is most likely launched from within a few hundreds gravitational radii from the central black and has a kinetic output that matches the prescription for significant feedback. The presence of the lower velocity component of the disk wind is independently confirmed by the analysis of a follow-up XMM-Newton & NuSTAR observation. A faster (v_out~ -0.35 c) component of the wind is also seen in this second observation. During this observation we also witnessed an occultation event lasting Δt ~ 120 ksec, which we ascribe to an increase of the opacity of the disk wind (ΔNH~1.4x10^24 cm^-2). Our interpretation is that the slow zone (v_out~ -0.1c) of the wind is the most stable but inhomogeneous component, while the faster zones could be associated with two different inner streamlines of the wind.

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arXiv2018

Swift data hint at a binary Super Massive Black Hole candidate at sub-parsec separation

Dual/binary Supermassive Black Hole (SMBH) systems are the inevitable consequence of the current Lambda Cold Dark Matter cosmological paradigm. In this context, we discuss here the properties of MCG+11-11-032, a local (z=0.0362) Seyfert 2 galaxy. This source was proposed as a dual AGN candidate on the basis of the presence of double-peaked [OIII] emission lines in its optical spectrum. MCG+11-11-032 is also an X-ray variable source and was observed several times by the Swift X-ray Telescope (XRT) on time scales from days to years. In this work, we analyze the SDSS-DR13 spectrum and find evidence for double-peaked profiles in all the strongest narrow emission lines. We also study the XRT light curve and unveil the presence of an alternating behavior of the intrinsic 0.3-10 keV flux, while the 123-month Swift BAT light curve supports the presence of almost regular peaks and dips almost every 25 months. In addition, the XRT spectrum suggests for the presence of two narrow emission lines with rest-frame energies of E~6.16 keV and E~6.56 keV. Although by considering only the optical emission lines, different physical mechanisms may be invoked to explain the kinematical properties, the X-ray results are most naturally explained by the presence of a binary SMBH in the center of this source. In particular, we evidence a remarkable agreement between the putative SMBH pair orbital velocity derived from the BAT light curve and the velocity offset derived by the rest-frame Delta_E between the two X-ray line peaks in the XRT spectrum (i.e. Delta_v~0.06c).

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arXiv2017

XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties

We report on the X-ray monitoring programme (covering slightly more than 11 days) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert galaxy Mrk 915. The light curves extracted in different energy ranges show a variation in intensity but not a significant change in spectral shape. The X-ray spectra reveal the presence of a two-phase warm absorber: a fully covering mildly ionized structure [log xi/(erg cm/s)~2.3, NH~1.3x10^21 cm-2] and a partial covering (~90 per cent) lower ionized one [log xi/(erg cm/s)~0.6, NH~2x10^22 cm-2]. A reflection component from distant matter is also present. Finally, a high-column density (NH~1.5x10^23 cm-2) distribution of neutral matter covering a small fraction of the central region is observed, almost constant, in all observations. Main driver of the variations observed between the datasets is a decrease in the intrinsic emission by a factor of ~1.5. Slight variations in the partial covering ionized absorber are detected, while the data are consistent with no variation of the total covering absorber. The most likely interpretation of the present data locates this complex absorber closer to the central source than the narrow line region, possibly in the broad line region, in the innermost part of the torus, or in between. The neutral obscurer may either be part of this same stratified structure or associated with the walls of the torus, grazed by (and partially intercepting) the line of sight.

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arXiv2017

AGN with discordant optical and X-ray classification are not a physical family: Diverse origin in two AGN

Approximately 3-17 percent of Active Galactic Nuclei (AGN) without detected rest-frame UV/optical broad emission lines (type-2 AGN) do not show absorption in X-rays. The physical origin behind the apparently discordant optical/X-ray properties is not fully understood. Our study aims at providing insight into this issue by conducting a detailed analysis of the nuclear dust extinction and X-ray absorption properties of two AGN with low X-ray absorption and with high optical extinction, for which a rich set of high quality spectroscopic data is available from XMM-Newton archive data in X-rays and XSHOOTER proprietary data at UV-to-NIR wavelengths. In order to unveil the apparent mismatch, we have determined the A$_{\rm V}$/N$_{\rm H}$ and both the Super Massive Black Hole (SMBH) and the host galaxy masses. We find that the mismatch is caused in one case by an abnormally high dust-to-gas ratio that makes the UV/optical emission to appear more obscured than in the X-rays. For the other object we find that the dust-to-gas ratio is similar to the Galactic one but the AGN is hosted by a very massive galaxy so that the broad emission lines and the nuclear continuum are swamped by the star-light and difficult to detect.

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arXiv2016

A deep Chandra observation of the interacting star-forming galaxy Arp 299

We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above 4.0x10^38 erg s^-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metalicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72+-0.03 keV, contributing 20% of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.

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arXiv2016

The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue

Thanks to the large collecting area (3 x ~1500 cm$^2$ at 1.5 keV) and wide field of view (30' across in full field mode) of the X-ray cameras on board the European Space Agency X-ray observatory XMM-Newton, each individual pointing can result in the detection of hundreds of X-ray sources, most of which are newly discovered. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision, greater net sensitivity and the extraction of spectra and time series for fainter sources, with better signal-to-noise. Further, almost 50\% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre (XMM-SSC) to produce a much larger and better quality X-ray source catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data automatically and using improved calibration a new catalogue version has been produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data). Manual screening ensures the highest data quality. This catalogue is known as 3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections comprising 396910 unique X-ray sources. For the 133000 brightest sources, spectra and lightcurves are provided. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To identify the detections, a cross correlation with 228 catalogues is also provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products, it is an excellent resource in which to find new and extreme objects.

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arXiv2016

Water masers in Compton-thick AGN I. Detailed study of the new water megamaser in IRAS15480-0344

A relationship between the water maser detection rate and large nuclear column densities in AGN has often been cited in the literature. Indeed, detailed studies of luminous water masers, typically associated with the nuclear activity, allow us to investigate the innermost regions of AGN, with an impact on the still debated Unified Model for this class of objects.We have recently entertained a search for maser emission in a well-defined sample of Compton-thick AGN aimed at investigating, on firm statistical bases, the aforementioned relationship. While the survey is still ongoing, and is matter of a forthcoming publication, a new luminous water maser has been detected in the lenticular (field) S0 galaxy IRAS15480-0344, whose origin, associated with an accretion disc or a nuclear outflow/jet, needs to be assessed. Multi-epoch single-dish observations and VLBI measurements were performed to investigate the distribution, spatial extension, and variability of the maser emission in order to infer the main characteristics of the water megamaser. The new detection in IRAS15480-0344 is reported: a megamaser with a total single-dish isotropic luminosity of ~200 Lsun and a profile composed of two main features, a broad line with a full width to half maximum (FWHM) linewidth of ~90 km/s and a narrow (FWHM<1 km/s) one. We performed a follow-up to the detection with the Very Long Baseline Array (VLBA) and confidently detected only the narrow component, which is coincident with the nuclear radio continuum emission detected with the Very Large Array at 8.4 GHz. A weak narrow feature has also been detected in the velocity range of the broad feature and is located 15 pc to the north-west with respect to the stronger component. Neither maser spot is associated with the compact radio continuum sources derived from the same VLBA dataset. [Abridged]

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arXiv2015

The structure of the X-ray absorber in Mrk 915 revealed by Swift

In this paper we present the results obtained with a monitoring programme (23 days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The light-curve analysis shows a significant count rate variation (about a factor of 2-3) on a time-scale of a few days, while the X-ray colours show a change in the spectral curvature below 2 keV and the presence of two main spectral states. From the spectral analysis we find that the observed variations can be explained by the change of the intrinsic nuclear power (about a factor of 1.5) coupled with a change of the properties of an ionized absorber. The quality of the data prevents us from firmly establishing if the spectral variation is due to a change in the ionization state and/or in the covering factor of the absorbing medium. The latter scenario would imply a clumpy structure of the ionized medium. By combining the information provided by the light curve and the spectral analyses, we can derive some constraints on the location of the absorber under the hypotheses of either homogeneous or clumpy medium. In both cases, we find that the absorber should be located inside the outer edge of an extended torus and, in particular, under the clumpy hypothesis, it should be located near, or just outside, to the broad emission line region.

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arXiv2015

AGN feedback in action: a new powerful wind in 1SXPSJ050819.8+172149?

Galaxy merging is widely accepted to be a key driving factor in galaxy formation and evolution, while the feedback from AGN is thought to regulate the BH-bulge coevolution and the star formation process. In this context, we focused on 1SXPSJ050819.8+172149, a local (z=0.0175) Seyfert 1.9 galaxy (L_bol~4x10^43 ergs/s). The source belongs to an IR-luminous interacting pair of galaxies, characterized by a luminosity for the whole system (due to the combination of star formation and accretion) of log(L_IR/L_sun)=11.2. We present the first detailed description of the 0.3-10keV spectrum of 1SXPSJ050819.8+172149, monitored by Swift with 9 pointings performed in less than 1 month. The X-ray emission of 1SXPSJ050819.8+172149 is analysed by combining all the Swift pointings, for a total of ~72ks XRT net exposure. The averaged Swift-BAT spectrum from the 70-month survey is also analysed. The slope of the continuum is ~1.8, with an intrinsic column density NH~2.4x10^22 cm-2, and a deabsorbed luminosity L(2-10keV)~4x10^42 ergs/s. Our observations provide a tentative (2.1sigma) detection of a blue-shifted FeXXVI absorption line (rest-frame E~7.8 keV), suggesting the discovery for a new candidate powerful wind in this source. The physical properties of the outflow cannot be firmly assessed, due to the low statistics of the spectrum and to the observed energy of the line, too close to the higher boundary of the Swift-XRT bandpass. However, our analysis suggests that, if the detection is confirmed, the line could be associated with a high-velocity (vout~0.1c) outflow most likely launched within 80r_S. To our knowledge this is the first detection of a previously unknown ultrafast wind with Swift. The high NH suggested by the observed equivalent width of the line (EW~ -230eV, although with large uncertainties), would imply a kinetic output strong enough to be comparable to the AGN bolometric luminosity.

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arXiv2015

Mining the XRT archive to probe the X-ray absorber structure in the AGN population

One of the key ingredients of the Unified Model of Active Galactic Nuclei (AGN) is the presence of a torus-like optically thick medium composed by dust and gas around the putative supermassive black hole. However, the structure, size and composition of this circumnuclear medium are still matter of debate. To this end, the search for column density variations through X-ray monitoring on different timescales (months, weeks and few days) is fundamental to constrain size, kinematics and location of the X-ray absorber(s). Here we describe our project of mining the Swift-XRT archive to assemble a sample of AGN with extreme column density variability and determining the physical properties of the X-ray absorber(s). We also present the results obtained from a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the most interesting new candidates for variability discovered so far, Mrk 915.

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arXiv2015

WISE colours and star-formation in the host galaxies of radio-loud narrow-line Seyfert 1

We investigate the mid-infrared properties of the largest (42 objects) sample of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data from the Wide-field Infrared Survey Explorer (WISE). We analyse the mid-IR colours of these objects and compare them to what is expected from different combinations of AGN and galaxy templates. We find that, in general, the host-galaxy emission gives an importan contribution to the observed mid-IR flux in particular at the longest wavelengths (W3, at 12micron, and W4, at 22micron). In about half of the sources (22 objects) we observe a very red mid-IR colour (W4-W3>2.5) that can be explained only using a starburst galaxy template (M82). Using the 22micron luminosities, corrected for the AGN contribution, we have then estimated the star-formation rate for 20 of these "red" RL NLS1, finding values ranging from 10 to 500 Msun/y. For the RL NLS1 showing bluer colours, instead, we cannot exclude the presence of a star-forming host galaxy although, on average, we expect a lower star-formation rate. Studying the radio (1.4GHz) to mid-IR (22micron) flux ratios of the RL NLS1 in the sample we found that in ~10 objects the star-forming activity could represent the most important component also at radio frequencies, in addition (or in alternative) to the relativistic jet. We conclude that both the mid-IR and the radio emission of RL NLS1 are a mixture of different components, including the relativistic jet, the dusty torus and an intense star-forming activity.

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arXiv2015

Revisiting the relationship between 6 μm and 2-10 keV continuum luminosities of AGN

We have determined the relation between the AGN luminosities at rest-frame 6 μm associated to the dusty torus emission and at 2-10 keV energies using a complete, X-ray flux limited sample of 232 AGN drawn from the Bright Ultra-hard XMM-Newton Survey. The objects have intrinsic X-ray luminosities between 10^42 and 10^46 erg/s and redshifts from 0.05 to 2.8. The rest-frame 6 μm luminosities were computed using data from the Wide-Field Infrared Survey Explorer and are based on a spectral energy distribution decomposition into AGN and galaxy emission. The best-fit relationship for the full sample is consistent with being linear, L_6 μm $\propto$ L_2-10 keV^0.99$\pm$0.032, with intrinsic scatter, ~0.35 dex in log L_6 μm. The L_6 μm/L_2-10 keV luminosity ratio is largely independent on the line-of-sight X-ray absorption. Assuming a constant X-ray bolometric correction, the fraction of AGN bolometric luminosity reprocessed in the mid-IR decreases weakly, if at all, with the AGN luminosity, a finding at odds with simple receding torus models. Type 2 AGN have redder mid-IR continua at rest-frame wavelengths <12 μm and are overall ~1.3-2 times fainter at 6 μm than type 1 AGN at a given X-ray luminosity. Regardless of whether type 1 and type 2 AGN have the same or different nuclear dusty toroidal structures, our results imply that the AGN emission at rest-frame 6 μm is not isotropic due to self-absorption in the dusty torus, as predicted by AGN torus models. Thus, AGN surveys at rest-frame 6 μm are subject to modest dust obscuration biases.

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arXiv2015

Exploring the Active Galactic Nuclei population with extreme X-ray to optical flux ratios (Fx/Fo >50)

The cosmic history of the growth of supermassive black holes in galactic centers parallels that of star-formation in the Universe. However, an important fraction of this growth occurs inconspicuously in obscured objects, where ultraviolet/optical/near-infrared emission is heavily obscured by dust. Since the X-ray flux is less attenuated, a high X-ray-to-optical flux ratio (Fx/Fo) is expected to be an efficient tool to find out these obscured accreting sources. We explore here via optical spectroscopy, X-ray spectroscopy and infrared photometry the most extreme cases of this population (those with Fx/Fo >50, EXO50 sources hereafter), using a well defined sample of seven X-ray sources extracted from the 2XMM catalogue. Five EXO50 sources (about 70 percent of the sample) in the bright flux regime explored by our survey (f(2-10 keV) > 1.5E-13 cgs) are associated with obscured AGN (Nh > 1.0E22 cm-2), spanning a redshift range between 0.75 and 1 and characterised by 2-10 keV intrinsic luminosities in the QSO regime (e.g. well in excess to 1.0E44 cgs). We did not find compelling evidence of Compton Thick AGN. Overall the EXO50 Type 2 QSOs do not seem to be different from standard X-ray selected Type 2 QSOs in terms of nuclear absorption; a very high AGN/host galaxy ratio seems to play a major role in explaining their extreme properties. Interestingly three out of five EXO50 Type 2 QSO objects can be classified as Extreme Dust Obscured Galaxies (EDOGs), suggesting that a very high AGN/host ratios (along with the large amount of dust absorption) could be the natural explanation also for a part of the EDOG population. The remaining two EXO50 sources are classified as BL Lac objects, having rather extreme properties, and which are good candidates for TeV emission.

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arXiv2014

A Focused, Hard X-ray Look at Arp 299 with NuSTAR

We report on simultaneous observations of the local starburst system Arp 299 with NuSTAR and Chandra, which provides the first resolved images of this galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a column density of $N_{\rm H}$ ~ 4 x10^{24} cm^{-2}, characteristic of a Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The hard X-rays detected by NuSTAR above 10 keV are centered on the western nucleus, Arp 299-B, which previous X-ray observations have shown to be the primary source of neutral Fe-K emission. Other X-ray sources, including Arp 299-A, the eastern nucleus which is also thought to harbor an AGN, as well as X-ray binaries, contribute $\lesssim 10%$ to the 10-20 keV emission from the Arp 299 system. The lack of significant emission above 10 keV other than that attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily obscured ($N_{\rm H}$ > 10^{24} cm^{-2}) or have a much lower luminosity than Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray (ULX) sources observed to date by NuSTAR.

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