arXiv subjects

Thomas J. Maccarone

Publications and source records attributed to Thomas J. Maccarone.

At least 109 records · Page 6Linked to original sources

arXiv2018

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

Nearby galaxy surveys have long classified X-ray binaries (XRBs) by the mass category of their donor stars (high-mass and low-mass). The NuSTAR observatory, which provides imaging data at E $>10$ keV, has enabled the classification of extragalactic XRBs by their compact object type: neutron star (NS) or black hole (BH). We analyzed NuSTAR/Chandra/XMM-Newton observations from a NuSTAR-selected sample of 12 galaxies within 5 Mpc having stellar masses ($M_{\star}$) $10^{7-11}$ $M_{\odot}$ and star formation rates (SFR) $\approx0.01-15$ $M_{\odot}$ yr$^{-1}$. We detect 128 NuSTAR sources to a sensitivity of $\approx10^{38}$ erg s$^{-1}$. Using NuSTAR color-intensity and color-color diagrams we classify 43 of these sources as candidate NS and 47 as candidate BH. We further subdivide BH by accretion states (soft, intermediate, and hard) and NS by weak (Z/Atoll) and strong (accreting pulsar) magnetic field. Using 8 normal (Milky Way-type) galaxies in the sample, we confirm the relation between SFR and galaxy X-ray point source luminosity in the 4-25 and 12-25 keV energy bands. We also constrain galaxy X-ray point source luminosity using the relation $L_{\rm{X}}=αM_{\star}+β\text{SFR}$, finding agreement with previous work. The XLF of all sources in the 4-25 and 12-25 keV energy bands matches with the $α=1.6$ slope for high-mass XRBs. We find that NS XLFs suggest a decline beginning at the Eddington limit for a 1.4 $M_{\odot}$ NS, whereas the BH fraction shows an approximate monotonic increase in the 4-25 and 12-25keV energy bands. We calculate the overall ratio of BH to NS to be $\approx1$ for 4-25 keV and $\approx2$ for 12-25 keV.

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arXiv2018

The Next-Generation Very Large Array: Supermassive Black Hole Pairs and Binaries

The Next-Generation Very Large Array (ngVLA) has the potential to be a workhorse for the discovery and study of paired supermassive black holes either at large separations (dual) or in tightly bound systems (binary). In this chapter, we outline the science case for the study of these supermassive pairs, and summarize discovery methods that can be used at radio wavelengths to discover them: including morphological, spectral, and time-domain identifications. One critical aspect of this work is that multi-messenger binary black hole studies may be possible with the ngVLA when combined with gravitational-wave searches using pulsar timing array techniques. However, long-baseline interferometery (>>1000 km) will make this possibility more likely by expanding the redshift range at which radio emission arising from two separate black holes may be resolved and studied.

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arXiv2018

The MAVERIC survey: A transitional millisecond pulsar candidate in Terzan 5

Transitional millisecond pulsars are accreting millisecond pulsars that switch between accreting X-ray binary and millisecond radio pulsar states. Only a handful of these objects have been identified so far. Terzan 5 CX1 is a variable hard X-ray source in the globular cluster Terzan 5. In this paper, we identify a radio counterpart to CX1 in deep Very Large Array radio continuum data. Chandra observations over the last fourteen years indicate that CX1 shows two brightness states: in 2003 and 2016 the source was the brightest X-ray source in the cluster (at L$_X \sim 10^{33}$ erg s$^{-1}$), while in many intermediate observations, its luminosity was almost an order of magnitude lower. We analyze all available X-ray data of CX1, showing that the two states are consistent with the spectral and variability properties observed for the X-ray active and radio pulsar states of known transitional millisecond pulsars. Finally, we discuss the prospects for the detection of CX1 as a radio pulsar in existing timing data.

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arXiv2018

A jet model for the fast IR variability of the black hole X-ray binary GX 339-4

Using the simultaneous Infra-Red (IR) and X-ray light curves obtained by Kalamkar et al. (2016), we perform a Fourier analysis of the IR/X-ray timing correlations of the black hole X-ray binary (BHB) GX 339-4. The resulting IR vs X-ray Fourier coherence and lag spectra are similar to those obtained in previous studies of GX 339-4 using optical light curves. In particular, above 1 Hz, the lag spectrum features an approximately constant IR lag of about 100 ms. We model simultaneously the radio to IR Spectral Energy Distribution (SED), the IR Power Spectral Density (PSD), and the coherence and lag spectra using the jet internal shock model ISHEM assuming that the fluctuations of the jet Lorentz factor are driven by the accretion flow. It turns out that most of the spectral and timing features, including the 100 ms lag, are remarkably well reproduced by this model. The 100 ms time-scale is then associated with the travel time from the accretion flow to the IR emitting zone. Our exploration of the parameter space favours a jet which is at most mildly relativistic ($\barΓ< 3$), and a linear and positive relation between the jet Lorentz factor and X-ray light curve i.e. $Γ(t)-1\propto L_{X}(t)$. The presence of a strong Low Frequency Quasi Periodic Oscillation (LFQPO) in the IR light curve could be caused by jet precession driven by Lense-Thirring precession of the jet-emitting accretion flow. Our simulations confirm that this mechanism can produce an IR LFQPO similar to that observed in GX 339-4.

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arXiv2018

Revealing the Galactic Population of BHs

We discuss the case for using the Next Generation Very Large Array both to discover new black hole X-ray binaries astrometrically, and to characterize them. We anticipate that the ngVLA will be able to find $\sim$100 new black hole X-ray binaries, as well as a host of other interesting radio stars, in a few hundred hour survey. Parallax and astrometric wobble measurements will be achievable in feasible follow-up surveys especially using long baseline capabilities. The ngVLA's high angular resolution, high survey speed, and high frequency sensitivity give it a unique range of parameter space over which it is sensitive.

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arXiv2018

X-ray Variability from the Ultraluminous Black Hole Candidate X-ray Binary in the Globular Cluster RZ 2109

We present the results of long-term monitoring of the X-ray emission from the ultraluminous X-ray source XMMUJ122939.9+075333 in the extragalactic globular cluster RZ2109. The combination of the high X-ray luminosity, short term X-ray variability, X-ray spectrum, and optical emission suggest that this system is likely an accreting black hole in a globular cluster. To study the long-term behavior of the X-ray emission from this source, we analyze both new and archival Chandra and XMM-Newton observations, covering 16 years from 2000 to 2016. For all of these observations, we fit extracted spectra of RZ2109 with xspec models. The spectra are all dominated by a soft component, which is very soft with typical fit temperatures of T $\simeq$ 0.15 keV. The resulting X-ray fluxes show strong variability on short and long timescales. We also find that the X-ray spectrum often shows no significant change even with luminosity changes as large as a factor of five.

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arXiv2018

The MAVERIC Survey: Still No Evidence for Accreting Intermediate-mass Black Holes in Globular Clusters

We present the results of an ultra-deep, comprehensive radio continuum survey for the accretion signatures of intermediate-mass black holes in globular clusters. The sample, imaged with the Karl G.~Jansky Very Large Array and the Australia Telescope Compact Array, comprises 50 Galactic globular clusters. No compelling evidence for an intermediate-mass black hole is found in any cluster in our sample. In order to achieve the highest sensitivity to low-level emission, we also present the results of an overall stack of our sample, as well as various subsamples, also finding non-detections. These results strengthen the idea that intermediate-mass black holes with masses $\gtrsim 1000 M_{\odot}$ are rare or absent in globular clusters.

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arXiv2018

Dust scattering halo of 4U 1630-47 observed with Chandra and Swift: New constraints on the source distance

We have observed the Galactic black hole transient 4U 1630-47 during the decay of its 2016 outburst with Chandra and Swift to investigate the properties of the dust scattering halo created by the source. The scattering halo shows a structure that includes a bright ring between 80" and 240" surrounding the source, and a continuous distribution beyond 250". An analysis of the $^{12}$CO $J=1-0$ map and spectrum in the line of sight to the source indicate that a molecular cloud with a radial velocity of -79 km s$^{-1}$ (denoted MC -79) is the main scattering body that creates the bright ring. We found additional clouds in the line of sight, calculated their kinematic distances and resolved the well known "near" and "far" distance ambiguity for most of the clouds. At the favored far distance estimate of MC -79, the modeling of the surface brightness profile results in a distance to 4U 1630-47 of 11.5 $\pm$ 0.3 kpc. If MC -79 is at the near distance, then 4U 1630-47 is at 4.7 $\pm$ 0.3 kpc. Future Chandra, Swift, and sub-mm radio observations not only can resolve this ambiguity, but also would provide information regarding properties of dust and distribution of all molecular clouds along the line of sight. Using the results of this study we also discuss the nature of this source and the reasons for the anomalously low soft state observation observed during the 2010 decay.

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arXiv2018

The Maveric Survey: a Red Straggler Binary with an Invisible Companion in the Galactic Globular Cluster M10

We present the discovery and characterization of a radio-bright binary in the Galactic globular cluster M10. First identified in deep radio continuum data from the Karl G. Jansky Very Large Array, M10-VLA1 has a flux density of $27\pm4$ $μ$Jy at 7.4 GHz and a flat to inverted radio spectrum. Chandra imaging shows an X-ray source with $L_X \approx 10^{31}$ erg s$^{-1}$ matching the location of the radio source. This places M10-VLA1 within the scatter of the radio--X-ray luminosity correlation for quiescent stellar-mass black holes, and a black hole X-ray binary is a viable explanation for this system. The radio and X-ray properties of the source disfavor, though do not rule out, identification as an accreting neutron star or white dwarf system. Optical imaging from the Hubble Space Telescope and spectroscopy from the SOAR telescope show the system has an orbital period of 3.339 d and an unusual "red straggler" component: an evolved star found redward of M10's red giant branch. These data also show UV/optical variability and double-peaked H$α$ emission characteristic of an accretion disk. However, SOAR spectroscopic monitoring reveals that the velocity semi-amplitude of the red straggler is low. We conclude that M10-VLA1 is most likely either a quiescent black hole X-ray binary with a rather face-on ($ i < $ 4$^{\circ}$) orientation or an unusual flaring RS CVn-type active binary, and discuss future observations that could distinguish between these possibilities.

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arXiv2017

Simultaneous multiwavelength observations of V404 Cygni during its 2015 June outburst decay strengthen the case for an extremely energetic jet-base

We present results of multiband optical photometry of the black hole X-ray binary system V404 Cygni obtained using Wheaton College Observatory's 0.3m telescope, along with strictly simultaneous INTEGRAL and Swift observations during 2015 June 25.15--26.33 UT, and 2015 June 27.10--27.34 UT. These observations were made during the 2015 June outburst of the source when it was going through an epoch of violent activity in all wavelengths ranging from radio to $γ$-rays. The multiwavelength variability timescale favors a compact emission region, most likely originating in a jet outflow, for both observing epochs presented in this work. The simultaneous INTEGRAL/Imager on Board the Integral Satellite (IBIS) 20--40 keV light curve obtained during the June 27 observing run correlates very strongly with the optical light curve, with no detectable delay between the optical bands as well as between the optical and hard X-rays. The average slope of the dereddened spectral energy distribution was roughly flat between the $I_C$- and $V$-bands during the June 27 run, even though the optical and X-ray flux varied by $>$25$\times$ during the run, ruling out an irradiation origin for the optical and suggesting that the optically thick to optically thin jet synchrotron break during the observations was at a frequency larger than that of $V$-band, which is quite extreme for X-ray binaries. These observations suggest that the optical emission originated very close to the base of the jet. A strong H$α$ emission line, probably originating in a quasi-spherical nebula around the source, also contributes significantly in the $R_C$-band. Our data, in conjunction with contemporaneous data at other wavelengths presented by other groups, strongly suggest that the jet-base was extremely compact and energetic during this phase of the outburst.

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arXiv2017

Key Science Goals for the Next Generation Very Large Array (ngVLA): Report from the ngVLA Science Advisory Council

This document describes some of the fundamental astrophysical problems that require observing capabilities at millimeter- and centimeter wavelengths well beyond those of existing, or already planned, telescopes. The results summarized in this report follow a solicitation from the National Radio Astronomy Observatory to develop key science cases for a future U. S.-led radio telescope, the "next generation Very Large Array" (ngVLA). The ngVLA will have roughly 10 times the collecting area of the Jansky VLA, operate at frequencies from 1 GHz to 116 GHz with up to 20 GHz of bandwidth, possess a compact core for high surface-brightness sensitivity, and extended baselines of at least hundreds of kilometers and ultimately across the continent to provide high-resolution imaging. The ngVLA builds on the scientific and technical legacy of the Jansky VLA and ALMA, and will be designed to provide the next leap forward in our understanding of planets, galaxies, and black holes.

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arXiv2017

An excess of low-mass X-ray binaries in the outer halo of NGC 4472

We present new Chandra observations of the outer halo of the giant elliptical galaxy NGC 4472 (M49) in the Virgo Cluster. The data extend to 130 kpc (28'), and have a combined exposure time of 150 ks. After identifying optical counterparts using the Next Generation Virgo Cluster Survey to remove background active galactic nuclei and globular cluster (GC) sources, and correcting for completeness, we find that the number of field low-mass X-ray binaries (LMXBs) per unit stellar V-band light increases significantly with galactocentric radius. Because the flux limit of the complete sample corresponds to the Eddington limit for neutron stars in NGC 4472, many of the ~90 field LMXBs in this sample could host black holes. The excess of field LMXBs at large galactocentric radii may be partially caused by natal kicks on black holes and neutron stars in binary systems in the inner part of the galaxy. Furthermore, since the metallicity in the halo of NGC 4472 strongly decreases towards larger galactocentric radii, the number of field LMXBs per unit stellar mass is anti-correlated with metallicity, opposite to what is observed in GCs. Another way to explain the spatial distribution of field LMXBs is therefore a reversed metallicity effect, although we have not identified a mechanism to explain this in terms of stellar and binary evolution.

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arXiv2017

Gemini/GNIRS infrared spectroscopy of the Wolf-Rayet stellar wind in Cygnus X-3

The microquasar Cygnus X-3 was observed several times with the Gemini North Infrared Spectrograph while the source was in the hard X-ray state. We describe the observed 1.0-2.4 $μ$m spectra as arising from the stellar wind of the companion star and suggest its classification as a WN 4-6 Wolf-Rayet star. We attribute the orbital variations of the emission line profiles to the variations in the ionization structure of the stellar wind caused by the intense X-ray emission from the compact object. The strong variability observed in the line profiles will affect the mass function determination. We are unable to reproduce earlier results, from which the mass function for the Wolf-Rayet star was derived. Instead, we suggest that the system parameters are difficult to obtain from the infrared spectra. We find that the near-infrared continuum and the line spectra can be represented with non-LTE Wolf-Rayet atmosphere models if taking into account the effects arising from the peculiar ionization structure of the stellar wind in an approximative manner. From the representative models, we infer the properties of the Wolf-Rayet star and discuss possible mass ranges for the binary components.

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arXiv2017

Further constraints on variations in the IMF from LMXB populations

We present constraints on variations in the initial mass function (IMF) of nine local early-type galaxies based on their low mass X-ray binary (LMXB) populations. Comprised of accreting black holes and neutron stars, these LMXBs can be used to constrain the important high mass end of the IMF. We consider the LMXB populations beyond the cores of the galaxies ($>0.2R_{e}$; covering $75-90\%$ of their stellar light) and find no evidence for systematic variations of the IMF with velocity dispersion ($σ$). We reject IMFs which become increasingly bottom heavy with $σ$, up to steep power-laws (exponent, $α>2.8$) in massive galaxies ($σ>300$km/s), for galactocentric radii $>1/4\ R_{e}$. Previously proposed IMFs that become increasingly bottom heavy with $σ$ are consistent with these data if only the number of low mass stars $(<0.5M_{\odot}$) varies. We note that our results are consistent with some recent work which proposes that extreme IMFs are only present in the central regions of these galaxies. We also consider IMFs that become increasingly top-heavy with $σ$, resulting in significantly more LMXBs. Such a model is consistent with these observations, but additional data are required to significantly distinguish between this and an invariant IMF. For six of these galaxies, we directly compare with published IMF mismatch parameters from the Atlas3D survey, $α_{dyn}$. We find good agreement with the LMXB population if galaxies with higher $α_{dyn}$ have more top-heavy IMFs -- although we caution that our sample is quite small. Future LMXB observations can provide further insights into the origin of $α_{dyn}$ variations.

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arXiv2017

The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9

47 Tuc X9 is a low mass X-ray binary (LMXB) in the globular cluster 47 Tucanae, and was previously thought to be a cataclysmic variable. However, Miller-Jones et al. (2015) recently identified a radio counterpart to X9 (inferring a radio/X-ray luminosity ratio consistent with black hole LMXBs), and suggested that the donor star might be a white dwarf. We report simultaneous observations of X9 performed by Chandra, Nustar and Australia Telescope Compact Array. We find a clear 28.18$\pm$0.02 min periodic modulation in the Chandra data, which we identify as the orbital period, confirming this system as an ultracompact X-ray binary. Our X-ray spectral fitting provides evidence for photoionized gas having a high oxygen abundance in this system, which indicates a C/O white dwarf donor. We also identify reflection features in the hard X-ray spectrum, making X9 the faintest LMXB to show X-ray reflection. We detect a $\sim$ 6.8 day modulation in the X-ray brightness by a factor of 10, in archival Chandra, Swift, and Rosat data. The simultaneous radio/X-ray flux ratio is consistent with either a black hole primary or a neutron star primary, if the neutron star is a transitional millisecond pulsar. Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy.

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arXiv2017

Deep Chandra observations of NGC~7457, the X-ray point source populations of a low mass early-type galaxy

We present the X-ray point source population of NGC 7457 based on 124 ks of Chandra observations. Previous deep Chandra observations of low mass X-ray binaries (LMXBs) in early-type galaxies have typically targeted the large populations of massive galaxies. NGC 7457 is a nearby, early-type galaxy with a stellar luminosity of $1.7\times10^{10} L_{K\odot}$, allowing us to investigate the populations in a relatively low mass galaxy. We classify the detected X-ray sources into field LMXBs, globular cluster LMXBs, and background AGN based on identifying optical counterparts in new HST/ACS images. We detect 10 field LMXBs within the $r_{ext}$ ellipse of NGC 7457 (with semi-major axis $\sim$ 9.1 kpc, ellipticity = 0.55). The corresponding number of LMXBs with $L_{x}>2\times10^{37}erg/s$ per stellar luminosity is consistent with that observed in more massive galaxies, $\sim 7$ per $10^{10} L_{K\odot}$. We detect a small globular cluster population in these HST data and show that its colour distribution is likely bimodal and that its specific frequency is similar to that of other early type galaxies. However, no X-ray emission is detected from any of these clusters. Using published data for other galaxies, we show that this non-detection is consistent with the small stellar mass of these clusters. We estimate that 0.11 (and 0.03) LMXBs are expected per $10^{6}M_{\odot}$ in metal-rich (and metal-poor) globular clusters. This corresponds to 1100 (and 330) LMXBs per $10^{10} L_{K\odot}$, highlighting the enhanced formation efficiency of LMXBs in globular clusters. A nuclear X-ray source is detected with $L_{x}$ varying from $2.8-6.8\times10^{38}erg/s$. Combining this $L_{x}$ with a published dynamical mass estimate for the central SMBH in NGC 7457, we find that $L_{x}/L_{Edd}$ varies from $0.5-1.3\times10^{-6}$.

astro-ph.HE↗

arXiv2016

A comprehensive long term study of the radio and X-ray Variability of NGC 4051 Paper II

The origin of the low luminosity radio emission in radio-quiet AGN, is unknown. The detection of a positive correlation between the radio and X-ray emission would imply a jet-like origin, similar to that seen in `hard state' X-ray binary systems. In our previous work, we found no believable radio variability in the well known X-ray bright Seyfert 1 galaxy NGC 4051, despite large amplitude X-ray variability. In this study we have carefully re-analysed radio and X-ray observations using the same methods as our previous work, we again find no evidence for core radio variability. In direct contrast to our findings, another study claim significant radio variability and a distinctive anti-correlation between radio and X-ray data for the same source. The other study report only integral flux values and do not consider the effect of the changing array on the synthesised beam. In both our studies of NGC 4051 we have taken great care to account for the effect that the changing beam size has on the measured radio flux and as a result we are confident that our method gives more accurate values for the intrinsic core radio flux. However, the lack of radio variability we find is hard to reconcile because radio images of NGC 4051 do show jet-like structure. We suggest that the radio structures observed are likely the result of a previous period of higher radio activity and that the current level of radio emission from a compact nuclear jet is low.

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arXiv2016

Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy

We present the results of a joint Swift-NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6-8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM-Newton. We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it should already have been realized that it was unlikely that these objects were black holes on the basis of their being persistent sources, and we re-examine past work which suggested that tidal capture products would be persistently bright X-ray emitters. We discuss how this problem is likely due to neglecting disk winds in older work that predict which systems will be persistent and which will be transient.

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