ABSTRACT We report the detection of coherent pulsations from the ultraluminous X-ray source (ULX) NGC 7793 P13. The 0.42 s nearly sinusoidal pulsations were initially discovered in broadband X-ray ...observations using XMM-Newton and NuSTAR taken in 2016. We subsequently also found pulsations in archival XMM-Newton data taken in 2013 and 2014. The significant (>5 ) detection of coherent pulsations demonstrates that the compact object in P13 is a neutron star, and given the observed peak luminosity of 1040 erg s − 1 (assuming isotropy), it is well above the Eddington limit for a 1.4 M accretor. This makes P13 the second ULX known to be powered by an accreting neutron star. The pulse period varies between epochs, with a slow but persistent spin-up over the 2013-2016 period. This spin-up indicates a magnetic field of B 1.5 × 1012 G, typical of many Galactic accreting pulsars. The most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile.
We present broadband X-ray analyses of a sample of bright ultraluminous X-ray sources (ULX) with the goal of investigating the spectral similarity of this population to the known ULX pulsars, M82 ...X-2, NGC 7793 P13, and NGC 5907 ULX. We perform a phase-resolved analysis of the broadband XMM-Newton+NuSTAR data set of NGC 5907 ULX, finding that the pulsed emission from the accretion column in this source exhibits a similar spectral shape to that seen in both M82 X-2 and NGC 7793 P13, and that this is responsible for the excess emission observed at the highest energies when the spectra are fit with accretion disk models. We then demonstrate that similar "hard" excesses are seen in all ULXs in the broadband sample. Finally, for ULXs where the nature of the accretor is currently unknown, we test whether the hard excesses are all consistent with being produced by an accretion column similar to those present in M82 X-2, NGC 7793 P13, and NGC 5907 ULX. Based on the average shape of the pulsed emission, we find that in all cases a similar accretion column can successfully reproduce the observed data, consistent with the hypothesis that this ULX sample may be dominated by neutron star accretors. Compared to the known pulsar ULXs, our spectral fits for the remaining ULXs suggest that the non-pulsed emission from the accretion flow beyond the magnetosphere makes a stronger relative contribution than the component associated with the accretion column. If these sources do also contain neutron star accretors, this may help to explain the lack of detected pulsations.
ABSTRACT
MAXI J1820+070 (optical counterpart ASASSN-18ey) is a black hole candidate discovered through its recent very bright outburst. The low extinction column and long duration at high flux allow ...detailed measurements of the accretion process to be made. In this work, we compare the evolution of X-ray spectral and timing properties through the initial hard state of the outburst. We show that the inner accretion disc, as measured by relativistic reflection, remains steady throughout this period of the outburst. Nevertheless, subtle spectral variability is observed, which is well explained by a change in coronal geometry. However, characteristic features of the temporal variability – low-frequency roll-over and quasi-periodic oscillation frequency – increase drastically in frequency, as the outburst proceeds. This suggests that the variability time-scales are governed by coronal conditions rather than solely by the inner disc radius. We also find a strong correlation between X-ray luminosity and coronal temperature. This can be explained by electron pair production with a changing effective radius and a non-thermal electron fraction of $\sim 20$ per cent.
The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as ...XMM–Newton and Chandra, but was well observed by photon counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array (NuSTAR). We report here on the discovery of an excess emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is 8Msun). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.
Abstract
Ultrafast outflows (UFOs) are the most extreme winds launched by active galactic nuclei (AGN) due to their mildly relativistic speeds (∼0.1–0.3c) and are thought to significantly contribute ...to galactic evolution via AGN feedback. Their nature and launching mechanism are however not well understood. Recently, we have discovered the presence of a variable UFO in the narrow-line Seyfert 1 IRAS 13224−3809. The UFO varies in response to the brightness of the source. In this work we perform flux-resolved X-ray spectroscopy to study the variability of the UFO and found that the ionization parameter is correlated with the luminosity. In the brightest states the gas is almost completely ionized by the powerful radiation field and the UFO is hardly detected. This agrees with our recent results obtained with principal component analysis. We might have found the tip of the iceberg: the high ionization of the outflowing gas may explain why it is commonly difficult to detect UFOs in AGN and possibly suggest that we may underestimate their actual feedback. We have also found a tentative correlation between the outflow velocity and the luminosity, which is expected from theoretical predictions of radiation-pressure-driven winds. This trend is rather marginal due to the Fe xxv–xxvi degeneracy. Further work is needed to break such degeneracy through time-resolved spectroscopy.
We present 3–50 keV NuSTAR observations of the active galactic nuclei Mrk 335 in a very low flux state. The spectrum is dominated by very strong features at the energies of the iron line at 5–7 keV ...and Compton hump from 10–30 keV. The source is variable during the observation, with the variability concentrated at low energies, which suggesting either a relativistic reflection or a variable absorption scenario. In this work, we focus on the reflection interpretation, making use of new relativistic reflection models that self consistently calculate the reflection fraction, relativistic blurring and angle-dependent reflection spectrum for different coronal heights to model the spectra. We find that the spectra can be well fitted with relativistic reflection, and that the lowest flux state spectrum is described by reflection alone, suggesting the effects of extreme light-bending occurring within ∼2 gravitational radii (R
G) of the event horizon. The reflection fraction decreases sharply with increasing flux, consistent with a point source moving up to above 10 R
G as the source brightens. We constrain the spin parameter to greater than 0.9 at the 3σ confidence level. By adding a spin-dependent upper limit on the reflection fraction to our models, we demonstrate that this can be a powerful way of constraining the spin parameter, particularly in reflection dominated states. We also calculate a detailed emissivity profile for the iron line, and find that it closely matches theoretical predictions for a compact source within a few R
G of the black hole.
Black hole feedback in the luminous quasar PDS 456 Nardini, E.; Reeves, J. N.; Gofford, J. ...
Science (American Association for the Advancement of Science),
02/2015, Letnik:
347, Številka:
6224
Journal Article
Recenzirano
Odprti dostop
The evolution of galaxies is connected to the growth of supermassive black holes in their centers. During the quasar phase, a huge luminosity is released as matter falls onto the black hole, and ...radiation-driven winds can transfer most of this energy back to the host galaxy. Over five different epochs, we detected the signatures of a nearly spherical stream of highly ionized gas in the broadband x-ray spectra of the luminous quasar PDS 456. This persistent wind is expelled at relativistic speeds from the inner accretion disk, and its wide aperture suggests an effective coupling with the ambient gas. The outflow's kinetic power larger than 1046 ergs per second is enough to provide the feedback required by models of black hole and host galaxy coevolution.
Based on phase-resolved broadband spectroscopy using XMM-Newton and NuSTAR, we report on a potential cyclotron resonant scattering feature (CRSF) at E ∼ 13 keV in the pulsed spectrum of the recently ...discovered ultraluminous X-ray source (ULX) pulsar NGC 300 ULX1. If this interpretation is correct, the implied magnetic field of the central neutron star is B ∼ 1012 G (assuming scattering by electrons), similar to that estimated from the observed spin-up of the star, and also similar to known Galactic X-ray pulsars. We discuss the implications of this result for the connection between NGC 300 ULX1 and the other known ULX pulsars, particularly in light of the recent discovery of a likely proton cyclotron line in another ULX, M51 ULX-8.
ABSTRACT We present broadband, multi-epoch X-ray spectroscopy of the pulsating ultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton and NuSTAR data from 2014 are best described by a ...multicolor blackbody model with a temperature gradient as a function of accretion disk radius significantly flatter than expected for a standard thin accretion disk ( , with ). Additionally, we detect a hard power-law tail at energies above 10 keV, which we interpret as being due to Comptonization. We compare this observation to archival XMM-Newton, Chandra, and NuSTAR data from 2003, 2012, and 2013, and investigate possible spectral changes as a function of phase over the 78-day super-orbital period of this source. We find that observations taken around phases 0.3-0.4 show very similar temperature profiles, even though the observed flux varies significantly, while one observation taken around phase 0 has a significantly steeper profile. We discuss these findings in light of the recent discovery that the compact object is a neutron star and show that precession of the accretion disk or the neutron star can self-consistently explain most observed phenomena.
ABSTRACT We present the detection of an absorption feature at E = 8.77 − 0.06 + 0.05 keV in the combined X-ray spectrum of the ultraluminous X-ray source NGC 1313 X-1 observed with XMM-Newton and ...NuSTAR, significant at the 3 level. If associated with blueshifted ionized iron, the implied outflow velocity is ∼0.2c for Fe xxvi, or ∼0.25c for Fe xxv. These velocities are similar to the ultrafast outflow seen in absorption recently discovered in this source at lower energies by XMM-Newton, and we therefore conclude that this is an iron component to the same outflow. Photoionization modeling marginally prefers the Fe xxv solution, but in either case the outflow properties appear to be extreme, potentially supporting a super-Eddington hypothesis for NGC 1313 X-1.
PDF
