arXiv subjects

Javier A. Garcia

Publications and source records attributed to Javier A. Garcia.

At least 109 records · Page 6Linked to original sources

arXiv2020

A variable ionized disk wind in the black-hole candidate EXO 1846-031

After 34 years, the black-hole candidate EXO 1846-031 went into outburst again in 2019. We investigate its spectral properties in the hard intermediate and the soft states with NuSTAR and Insight-HXMT. A reflection component has been detected in the two spectral states but possibly originating from different illumination spectra: in the intermediate state, the illuminating source is attributed to a hard coronal component, which has been commonly observed in other X-ray binaries, whereas in the soft state the reflection is probably produced by the disk self-irradiation. Both cases support EXO 1846-031 as a low inclination system of ~40 degrees. An absorption line is clearly detected at ~7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind (log ξ > 6.1) with a velocity up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the co-existence of disk winds and jets in this system. Additionally, the observed wind in this source is potentially driven by magnetic forces. The absorption line disappeared in the soft state and a narrow emission line appeared at ~6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with the higher spectral resolution are required to examine this.

astro-ph.HE↗

arXiv2020

Testing the Kerr black hole hypothesis using X-ray reflection spectroscopy and a thin disk model with finite thickness

X-ray reflection spectroscopy is a powerful tool for probing the strong gravity region of black holes and can be used for testing general relativity in the strong field regime. Simplifications of the available relativistic reflection models limit the capability of performing accurate measurements of the properties of black holes. In this paper, we present an extension of the model RELXILL_NK in which the accretion disk has a finite thickness rather than being infinitesimally thin. We employ the accretion disk geometry proposed by Taylor & Reynolds (2018) and we construct relativistic reflection models for different values of the mass accretion rate of the black hole. We apply the new model to high quality Suzaku data of the X-ray binary GRS 1915+105 to explore the impact of the thickness of the disk on tests of the Kerr metric.

astro-ph.HE↗

arXiv2020

Testing the Kerr metric using X-ray reflection spectroscopy: spectral analysis of GX 339-4

Signatures of X-ray reprocessing (reflection) out of an accretion disk are commonly observed in the high-energy spectrum of accreting black holes, and can be used to probe the strong gravity region around these objects. In this paper, we extend previous work in the literature and we employ a full emission model for relativistic reflection in non-Kerr spacetime to demonstrate an approach that tests the Kerr black hole hypothesis. We analyze a composite spectrum obtained with the Proportional Counter Array in the Rossi X-ray Timing Explorer (RXTE), of the stellar-mass black hole GX 339-4 in its brightest hard state. With a remarkable sensitivity of ~0.1% and 40 million counts in the 3-45 keV band to capture the faint features in the reflection spectrum, we demonstrate that it is possible with existing data and an adequate model to place constraints on the black hole spin $a_*$ and the deformation parameter that quantifies the departure from the Kerr metric. Our measurement obtained with the best fit model, which should be regarded as principally a proof of concept, is $a_*=0.92^{+0.07}_{-0.12}$ and $α_{13}=-0.76^{+0.78}_{-0.60}$ with a 90% confidence level and is consistent with the hypothesis that the compact object in GX 339-4 is a Kerr black hole. We also discuss how the physical model choice and the emissivity profile adopted could make an impact on the constraints of $α_{13}$ and spin. To enable Kerr metric test using X-ray reflection spectroscopy, it is essential to improve our astrophysical understanding of accreting black holes, e.g., the natures of accretion flow and corona.

gr-qc↗

arXiv2020

Evidence for Returning Disk Radiation in the Black Hole X-ray Binary XTE J1550-564

We explore the accretion properties of the black hole X-ray binary \j1550\ during its outbursts in 1998/99 and 2000. We model the disk, corona, and reflection components of X-ray spectra taken with the {\it Rossi X-ray Timing Explorer} (\rxte), using the {\tt relxill} suite of reflection models. The key result of our modeling is that the reflection spectrum in the very soft state is best explained by disk self-irradiation, i.e., photons from the inner disk are bent by the strong gravity of the black hole, and reflected off the disk surface. This is the first known detection of thermal disk radiation reflecting off the inner disk. There is also an apparent absorption line at $\sim6.9$ keV which may be evidence of an ionized disk wind. The coronal electron temperature ($kT_{\rm e}$) is, as expected, lower in the brighter outburst of 1998/99, explained qualitatively by more efficient coronal cooling due to irradiating disk photons. The disk inner radius is consistent with being within a few times the innermost stable circular orbit (ISCO) throughout the bright-hard-to-soft states (10s of $r_{\rm g}$ in gravitational units). The disk inclination is low during the hard state, disagreeing with the binary inclination value, and very close to $90^{\circ}$ in the soft state, recovering to a lower value when adopting a blackbody spectrum as the irradiating continuum.

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arXiv2020

Studying the Reflection Spectra of the New Black Hole X-ray Binary Candidate MAXI J1631-479 Observed by NuSTAR: A Variable Broad Iron Line Profile

We present results from the Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the new black hole X-ray binary candidate MAXI J1631-479 at two epochs during its 2018-2019 outburst, which caught the source in a disk dominant state and a power-law dominant state. Strong relativistic disk reflection features are clearly detected, displaying significant variations in the shape and strength of the broad iron emission line between the two states. Spectral modeling of the reflection spectra reveals that the inner radius of the optically-thick accretion disk evolves from $<1.9$ $r_{\rm g}$ to $12\pm1$ $r_{\rm g}$ (statistical errors at 90% confidence level) from the disk dominant to the power-law dominant state. Assuming in the former case that the inner disk radius is consistent with being at the ISCO, we estimate a black hole spin of $a^*>0.94$. Given that the bolometric luminosity is similar in the two states, our results indicate that the disk truncation observed in MAXI J1631-479 in the power-law dominant state is unlikely to be driven by a global variation in the accretion rate. We propose that it may instead arise from local instabilities in the inner edge of the accretion disk at high accretion rates. In addition, we find an absorption feature in the spectra centered at $7.33\pm0.03$ keV during the disk dominant state, which is evidence for a rare case that an extremely fast disk wind ($v_{\rm out}=0.067^{+0.001}_{-0.004}~c$) is observed in a low-inclination black hole binary, with the viewing angle of $29\pm1^{\circ}$ as determined by the reflection modeling.

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arXiv2020

NuSTAR observations of the Transient Galactic Black Hole Binary Candidate Swift J1858.6-0814: A New Sibling of V404 Cyg and V4641 Sgr?

Swift J1858.6-0814 was discovered by Swift-BAT on October 25, 2018. Here we report on the first follow-up NuSTAR observation of the source, which shows variability spanning two orders of magnitude in count rate on timescales of ~10-100 s. The power-spectrum of the source does not show any quasi-periodic oscillations or periodicity, but has a large fractional rms amplitude of 147%$\pm3$%, exhibiting a number of large flares throughout the observation. The hardness ratio (defined as $R_{10-79 \rm keV}/R_{3-10 \rm keV}$) of the flares tends to be soft, while the source spans a range of hardness ratios during non-flaring periods. The X-ray spectrum of the source shows strong reflection features, which become more narrow and peaked during the non-flaring intervals. We fit an absorbed relativistic reflection model to the source spectra to place physical constraints on the system. Most notably, we find that the source exhibits a large and varying intrinsic absorbing column density ($N_{\rm H}=1.4-4.2\times10^{23}$ cm$^{-2}$). This large intrinsic absorption is further supported by the energy spectra extracted from two flares observed simultaneously by NuSTAR and NICER. We find that the inner accretion disk of the source has a low inclination, $i<29^{\circ}$ ( 3$σ$ upper-limit), while the iron abundance in the disk is close to solar, $A_{\rm Fe}=1.0\pm0.3$. We set a 90% confidence upper limit on the inner radius of the accretion disk of $r_{\rm in}<8 \ r_{\rm ISCO}$, and, by fixing $r_{\rm in}$ to be at $r_{\rm ISCO}$, a 90% confidence lower-limit on the spin of the black hole of $a^{*}>0.0$. Lastly, we compare the properties of Swift J1858.6$-$0814 to those of V404 Cygni and V4641 Sgr, which both show rapid flaring and a strong and variable absorption.

astro-ph.HE↗

arXiv2019

High Density Reflection Spectroscopy: II. the Density of the Inner Black Hole Accretion Disc in AGN

We present a high density disc reflection spectral analysis of a sample of 17 Seyfert 1 galaxies to study the inner disc densities at different black hole mass scales and accretion rates. All the available XMM-Newton observations in the archive are used. OM observations in the optical/UV band are used to estimate their accretion rates. We find that 65% of sources in our sample show a disc density significantly higher than 1e15 cm^{-3}, which was assumed in previous reflection-based spectral analyses. The best-fit disc densities show an anti-correlation with black hole mass and mass accretion rate. High density disc reflection model can successfully explain the soft excess emission and significantly reduce inferred iron abundances. We also compare our black hole spin and disc inclination angle measurements with previous analyses.

astro-ph.HE↗

arXiv2019

Testing the Kerr metric with X-ray Reflection Spectroscopy of Mrk 335 Suzaku data

Einstein's gravity has undergone extensive tests in the weak field gravitational limit, with results in agreement with theoretical predictions. There exist theories beyond general relativity (GR) which modify gravity in the strong field regime but agree with GR in the weak field. Astrophysical black holes are believed to be described by the Kerr metric and serve as suitable candidates to test strong gravity with electromagnetic radiation. We perform such a test by fitting one Suzaku dataset of the narrow-line Seyfert 1 (NLS1) galaxy Mrk 335 with X-ray reflection spectroscopy, using the Johannsen metric to model the black hole spacetime and test for deviations from Kerr. We find the data is best modeled with a hybrid model that includes both partial covering absorption and a reflection component. This is the first time such a model has been proposed for a high-flux (low reflection) Mrk 335 dataset. We constrain the Johannsen deformation parameter $α_{13}$ to $-1.5<α_{13}<0.6$ with spin parameter $a_{*}>0.8$, and the $α_{22}$ parameter to $-0.4<α_{22}<2.1$ with $a_{*}>0.7$, both at the 99% confidence level. Although additional solutions at large deviations from the Kerr metric show statistical similarity with the ones above, further analysis suggests these solutions may be manifestations of uncertainties beyond our control and do not represent the data. Hence, our results are in agreement with the idea that the supermassive compact object at the center of Mrk 335 is described by the Kerr metric.

gr-qc↗

arXiv2019

Public Release of RELXILL_NK: A Relativistic Reflection Model for Testing Einstein's Gravity

We present the public release version of relxill_nk, an X-ray reflection model for testing the Kerr hypothesis and general relativity. This model extends the relxill model that assumes the black hole spacetime is described by the Kerr metric. We also present relxilllp_nk, the first non-Kerr X-ray reflection model with a lamppost corona configuration, as well as all other models available in the full relxill_nk package. In all models the relevant relativistic effects are calculated through a general relativistic ray-tracing code that can be applied to any well-behaved, stationary, axisymmetric, and asymptotically flat black hole spacetime. We show that the numerical error introduced by using a ray-tracing code is not significant as compared with the observational error present in current X-ray reflection spectrum observations. In addition, we present the reflection spectrum for the Johannsen metric as calculated by relxill_nk.

gr-qc↗

arXiv2019

Testing the Kerr hypothesis using X-ray reflection spectroscopy with NuSTAR data of Cygnus X-1 in the soft state

We continue exploring the constraining capabilities of X-ray reflection spectroscopy to test the Kerr-nature of astrophysical black holes and we present the results of our analysis of two NuSTAR observations of Cygnus X-1 in the soft state. We find that the final measurement can strongly depend on the assumption of the intensity profile. We conclude that Cygnus X-1 is not suitable for tests of general relativity using X-ray reflection spectroscopy and we discuss the desired properties of a source to be a good candidate for our studies.

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arXiv2019

Re-awakening of GRS 1716--249 after 23 years, observed by {\it Swift}/XRT and {\it NuSTAR}

In this work, we present a spectral and temporal analysis of {\it Swift}/XRT and {\it NuSTAR} observations of GRS 1716--249 during its recent 2016--2017 outburst. This low mass X-ray binary underwent an extraordinary outburst after a long quiescence of 23 years, since its last major outburst in 1993. The source was observed over two different epochs during 2017 April, 07 and 10. The best fit joint spectral fitting in the energy range 0.5 $-$ 79.0 keV indicates that the spectrum is best described by relatively cold, weak disk blackbody emission, dominant thermal Comptonization emission, and a relativistically broadened fluorescent iron K$α$ emission line. We observed a clear indication of a Compton hump around 30 keV. We also detected an excess feature of $\sim1.3$ keV. Assuming a lamp-post geometry of the corona, we constrained the inner disk radius for both observations to 11.92$^{+8.62}_{-11.92}$ R$_{ISCO}$ (i.e., an upper limit) and 10.39$^{+9.51}_{-3.02}$ R$_{ISCO}$ (where R$_{ISCO}\equiv$ radius of the innermost stable circular orbit) for the first epoch (E1) and second epoch (E2), respectively. A significant ($\sim5σ$) type$-$C quasi-periodic oscillation (QPO) at $1.20\pm0.04$ Hz is detected for the first time for GRS 1716--249, which drifts to $1.55\pm0.04$ Hz ($\sim6σ$) at the end of the second observation. The derived spectral and temporal properties show a positive correlation between the QPO frequency and the photon index.

astro-ph.HE↗

arXiv2019

Broadband X-ray Spectral and Timing Analyses of the Black Hole Binary Candidate Swift J1658.2-4242: Rapid Flux Variation and the Turn-on of a Transient QPO

We report results from joint NuSTAR, Swift and XMM-Newton observations of the newly discovered black hole X-ray binary candidate Swift J1658.2-4242 in the intermediate state. We observe a peculiar event in this source, with its X-ray flux rapidly decreasing by $\sim$45\% in $\sim$40~s, accompanied by only subtle changes in the shape of the broadband X-ray spectrum. In addition, we find a sudden turn-on of a transient QPO with a frequency of $6-7$~Hz around the time of the flux change, and the total fractional rms amplitude of the power spectrum increases from $\sim$2\% to $\sim$10\%. X-ray spectral and timing analyses indicate that the flux decrease is driven by intrinsic changes in the accretion flow around the black hole, rather than intervening material along the line of sight. In addition, we do not significantly detect any relativistic disk reflection component, indicating it is much weaker than previously observed while the source was in the bright hard state. We propose accretion disk instabilities triggered at a large disk radius as the origin of the fast transition in spectral and timing properties, and discuss possible causes of the unusual properties observed in Swift J1658.2-4242. The prompt flux variation detected along with the emergence of a QPO makes the event an interesting case for investigating QPO mechanisms in black hole X-ray binaries.

astro-ph.HE↗

arXiv2019

Towards precision tests of general relativity with black hole X-ray reflection spectroscopy

Astrophysical black hole systems are the ideal laboratories for testing Einstein's theory of gravity in the strong field regime. We have recently developed a framework which uses the reflection spectrum of black hole systems to perform precision tests of general relativity by testing the Kerr black hole hypothesis. In this paper, we analyze XMM-Newton and NuSTAR observations of the supermassive black hole in the Seyfert 1 galaxy MCG-06-30-15 with our disk reflection model. We consider the Johannsen metric with the deformation parameters $α_{13}$ and $α_{22}$, which quantify deviations from the Kerr metric. For $α_{22} = 0$, we obtain the black hole spin $0.928 < a_* < 0.983$ and $-0.44 < α_{13} < 0.15$. For $α_{13} = 0$, we obtain $0.885 < a_* < 0.987$ and $-0.12 < α_{22} < 1.05$. The Kerr solution is recovered for $α_{13} = α_{22} = 0$. Thus, our results include the Kerr solution within statistical uncertainties. Systematic uncertainties are difficult to account for, and we discuss some issues in this regard.

gr-qc↗

arXiv2019

About the Kerr nature of the stellar-mass black hole in GRS 1915+105

We employ the accretion disk reflection model RELXILL_NK to test the spacetime geometry around the stellar-mass black hole in GRS 1915+105. We adopt the Johannsen metric with the deformation parameters $α_{13}$ and $α_{22}$, for which the Kerr solution is recovered when $α_{13} = α_{22} = 0$. We analyze a NuSTAR observation of 2012, obtaining vanishing and non-vanishing values of the deformation parameters depending on the astrophysical model adopted. Similar difficulties were not found in our previous tests with other sources. The results of this work can shed light on the choice of sources suitable for testing the Kerr metric using X-ray reflection spectroscopy and on the parts of our reflection models that more urgently require improvement.

gr-qc↗

arXiv2019

Constraints on the spacetime metric around seven "bare" AGNs using X-ray reflection spectroscopy

We present the study of a sample of seven "bare" active galactic nuclei (AGN) observed with Suzaku. We interpret the spectrum of these sources with a relativistic reflection component and we employ our model RELXILL_NK to test the Kerr nature of their supermassive black holes. We constrain the Johannsen deformation parameters $α_{13}$ and $α_{22}$, in which the Kerr metric is recovered when $α_{13} = α_{22} = 0$. All our measurements are consistent with the hypothesis that the spacetime geometry around these supermassive objects is described by the Kerr solution. For some sources, we obtain quite strong constraints on $α_{13}$ and $α_{22}$ when compared to those found in our previous studies. We discuss the systematic uncertainties in our tests and the implications of our results.

gr-qc↗

arXiv2018

The Soft-Excess in Mrk 509: Warm Corona or Relativistic Reflection?

We present the analysis of the first NuSTAR observations ($\sim 220$ ks), simultaneous with the last SUZAKU observations ($\sim 50$ ks), of the active galactic nucleus of the bright Seyfert 1 galaxy Mrk 509. The time-averaged spectrum in the $1-79$ keV X-ray band is dominated by a power-law continuum ($Γ\sim 1.8-1.9$), a strong soft excess around 1 keV, and signatures of X-ray reflection in the form of Fe K emission ($\sim 6.4$ keV), an Fe K absorption edge ($\sim 7.1$ keV), and a Compton hump due to electron scattering ($\sim 20-30$ keV). We show that these data can be described by two very different prescriptions for the soft excess: a warm ($kT\sim 0.5-1$ keV) and optically thick ($τ\sim10-20$) Comptonizing corona, or a relativistically blurred ionized reflection spectrum from the inner regions of the accretion disk. While these two scenarios cannot be distinguished based on their fit statistics, we argue that the parameters required by the warm corona model are physically incompatible with the conditions of standard coronae. Detailed photoionization calculations show that even in the most favorable conditions, the warm corona should produce strong absorption in the observed spectrum. On the other hand, while the relativistic reflection model provides a satisfactory description of the data, it also requires extreme parameters, such as maximum black hole spin, a very low and compact hot corona, and a very high density for the inner accretion disk. Deeper observations of this source are thus necessary to confirm the presence of relativistic reflection, and to further understand the nature of its soft excess.

astro-ph.HE↗

arXiv2018

A study of the strong gravity region of the black hole in GS 1354-645

It is thought that the spacetime metric around astrophysical black holes is well described by the Kerr solution of Einstein's gravity. However, a robust observational evidence of the Kerr nature of these objects is still lacking. Here we fit the X-ray spectrum of the stellar-mass black hole in GS 1354-645 with a disk reflection model beyond Einstein's gravity in order test the Kerr black hole hypothesis. We consider the Johannsen metric with the deformation parameters $α_{13}$ and $α_{22}$. The Kerr metric is recovered for $α_{13} = α_{22} = 0$. For $α_{22} = 0$, our measurements of the black hole spin and of the deformation parameter $α_{13}$ are $a_* > 0.975$ and $-0.34 < α_{13} < 0.16$, respectively. For $α_{13} = 0$, we find $a_* > 0.975$ and $-0.09 < α_{22} < 0.42$. All the reported uncertainties are at 99% of confidence level for two relevant parameters.

gr-qc↗

arXiv2018

The Hard State of the Highly Absorbed High Inclination Black Hole Binary Candidate Swift J1658.2-4242 Observed by NuSTAR and Swift

We present a spectral and timing analysis of the newly reported Galactic X-ray transient Swift J1658.2-4242 observed by NuSTAR and Swift. The broad-band X-ray continuum is typical of a black hole binary in the bright hard state, with a photon index of $Γ=1.63\pm0.02$ and a low coronal temperature of $kT_{\rm e}=22\pm1$ keV, corresponding to a low spectral cutoff well constrained by NuSTAR. Spectral modeling of the relativistic disk reflection features, consisting of a broad Fe K$α$ line and the Compton reflection hump, reveals that the black hole is rapidly spinning with the spin parameter of $a^{*}>0.96$, and the inner accretion disk is viewed at a high inclination angle of $i=64^{+2}_{-3}{^\circ}$ (statistical errors, 90% confidence). The high inclination is independently confirmed by dips in the light curves, which can be explained by absorbing material located near the disk plane temporarily obscuring the central region. In addition, we detect an absorption line in the NuSTAR spectra centered at $7.03^{+0.04}_{-0.03}$ keV. If associated with ionized Fe K absorption lines, this provides evidence for the presence of outflowing material in the low/hard state of a black hole binary candidate. A timing analysis shows the presence of a type-C QPO in the power spectrum, with the frequency increasing from $\sim0.14$ Hz to $\sim0.21$ Hz during the single NuSTAR exposure. Our analysis reveals that Swift J1658.2-4242 displays characteristics typical for a black hole binary that is viewed at a high inclination angle, making it a good system for studying the accretion geometry in black hole binaries.

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