scholarly journals The X-ray evolution and geometry of the 2018 outburst of XTE J1810–197

2021 ◽  
Author(s):  
A Borghese ◽  
N Rea ◽  
R Turolla ◽  
M Rigoselli ◽  
J A J Alford ◽  
...  
Keyword(s):  
Phase Shift ◽  
Radio Pulsar ◽  
Spectral Evolution ◽  
Pulse Profile ◽  
X Ray ◽  
Monitoring Campaign ◽  
Surface Emission ◽  
Energy Dependent ◽  
Star Surface

Abstract After 15 years, in late 2018, the magnetar XTE J1810–197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of two change in its spin-down rate from ∼7.2 × 10−12 s s−1 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810–197 is well-modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810–197 has likely evolved relative to that found for the 2003 event.

scholarly journals Discovery of accretion-driven pulsations in the prolonged low X-ray luminosity state of the Be/X-ray transient GX 304–1

2018 ◽  
Vol 620 ◽  
pp. L13 ◽  
Author(s):  
A. Rouco Escorial ◽  
J. van den Eijnden ◽  
R. Wijnands
Keyword(s):  
Neutron Star ◽  
Stable State ◽  
Type I ◽  
X Ray ◽  
Monitoring Campaign ◽  
Spin Period ◽  
One Year ◽  
The Many ◽  
Low X ◽  
Star Surface

We present our Swift monitoring campaign of the slowly rotating neutron star Be/X-ray transient GX 304–1 (spin period of ∼275 s) when the source was not in outburst. We found that between its type I outbursts, the source recurrently exhibits a slowly decaying low-luminosity state (with luminosities of 1034 − 35 erg s−1). This behaviour is very similar to what has been observed for another slowly rotating system, GRO J1008–57. For that source, this low-luminosity state has been explained in terms of accretion from a non-ionised (“cold”) accretion disc. Because of the many similarities between the two systems, we suggest that GX 304–1 enters a similar accretion regime between its outbursts. The outburst activity of GX 304–1 ceased in 2016. Our continued monitoring campaign shows that the source is in a quasi-stable low-luminosity state (with luminosities a few factors lower than previously seen) for at least one year now. Using our NuSTAR observation in this state, we found pulsations at the spin period, demonstrating that the X-ray emission is due to accretion of matter onto the neutron star surface. If the accretion geometry during this quasi-stable state is the same as during the cold-disc state, then matter indeed reaches the surface (as predicted) during this later state. We discuss our results in the context of the cold-disc accretion model.

scholarly journals Long X-ray flares from the central source in RCW 103

2019 ◽  
Vol 626 ◽  
pp. A19 ◽  
Author(s):  
P. Esposito ◽  
A. De Luca ◽  
R. Turolla ◽  
F. Coti Zelati ◽  
W. Hummel ◽  
...  
Keyword(s):  
Near Infrared ◽  
Twist Angle ◽  
Pulse Profile ◽  
Infrared Source ◽  
X Ray ◽  
Very Large Telescope ◽  
Photon Index ◽  
Decay Pattern ◽  
And Behavior ◽  
Star Surface

We observed the slowly revolving pulsar 1E 161348–5055 (1E 1613, spin period of 6.67 h) in the supernova remnant RCW 103 twice with XMM-Newton and once with the Very Large Telescope (VLT). The VLT observation was performed on 2016 June 30, about a week after the detection of a large outburst from 1E 1613. At the position of 1E 1613, we found a near-infrared source with Ks = 20.68 ± 0.12 mag that was not detected (Ks >  21.2 mag) in data collected with the same instruments in 2006, during X-ray quiescence. Its position and behavior are consistent with a counterpart in the literature that was discovered with the Hubble Space Telescope in the following weeks in adjacent near-IR bands. The XMM-Newton pointings were carried out on 2016 August 19 and on 2018 February 14. While the collected spectra are similar in shape between each other and to what is observed in quiescence (a blackbody with kT ∼ 0.5 keV plus a second, harder component, either another hotter blackbody with kT ∼ 1.2 keV or a power law with photon index Γ ∼ 3), the two pointings caught 1E 1613 at different luminosity throughout its decay pattern: about 4.8 × 1034 erg s−1 in 2016 and 1.2 × 1034 erg s−1 in 2018 (0.5–10 keV, for the double-blackbody model and for 3.3 kpc), which is still almost about ten times brighter than the quiescent level. The pulse profile displayed dramatic changes, apparently evolving from the complex multi-peak morphology observed in high-luminosity states to the more sinusoidal form characteristic of latency. The inspection of the X-ray light curves revealed two flares with unusual properties in the 2016 observation: they are long (∼1 ks to be compared with 0.1–1 s of typical magnetar bursts) and faint (≈1034 erg s−1, with respect to 1038 erg s−1 or more in magnetars). Their spectra are comparatively soft and resemble the hotter thermal component of the persistent emission. If the flares and the latter component have a common origin, this may be a spot on the star surface that is heated by back-flowing currents that are induced by a magnetospheric twist. In this hypothesis, since the increase in luminosity of 1E 1613 during the flare is only ∼20%, an irregular variation of the same order in the twist angle could account for it.

scholarly journals X-ray Spectral Evolution of High Energy Peaked Blazars

Galaxies ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 62
Author(s):  
Haritma Gaur
Keyword(s):  
High Energy ◽  
Energy Interval ◽  
Spectral Studies ◽  
Parabolic Model ◽  
Spectral Evolution ◽  
Spectral Variability ◽  
Spectral Parameters ◽  
X Ray ◽  
Wide Energy ◽  
Energy Dependent

The synchrotron hump of the high energy peaked blazars generally lies in the 0.1–10 keV range and such sources show extreme flux and spectral variability in X-ray bands. Various spectral studies showed that the X-ray spectra of high energy peaked blazars are curved and better described by the log-parabolic model. The curvature is attributed to the energy dependent statistical acceleration mechanism. In this work, we review the X-ray spectral studies of high energy peaked blazars. It is found that the log-parabolic model well describes the spectra in a wide energy interval around the peak. The log-parabolic model provides the possibility of investigating the correlation between the spectral parameters derived from it. Therefore, we compiled the studies of correlations between the various parameters derived from the log-parabolic model and their implications to describe the variability mechanism of blazars.

scholarly journals New ASCA Observations of two Anomalous X-ray Pulsars

2000 ◽  
Vol 177 ◽  
pp. 695-698 ◽  
Author(s):  
B. Paul ◽  
M. Kawasaki ◽  
T. Dotani ◽  
F. Nagase
Keyword(s):  
Accretion Rate ◽  
Accretion Disc ◽  
Spectral Shape ◽  
Energy Spectra ◽  
Pulse Profile ◽  
X Ray ◽  
Low Mass ◽  
Low X ◽  
Star Surface ◽  
Made In

AbstractNewASCAobservations of two anomalous X-ray pulsars (AXP) 4U 0142+61 and 1E 1048.1-5937, made in 1998, when compared to earlier observations in 1994 show remarkable stability in the intensity, spectral shape and pulse profile. The energy spectra consist of two components, a power-law and a blackbody emission from the neutron star surface. In IE 1048.1-5937, we have identified three epochs with different spin-down rates and discuss its implications for the magnetar hypothesis of the AXPs. We also note that the spin-down rate and its variations in IE 1048.1-5937 are much larger than what normally can be produced by an accretion disc with very low mass accretion rate corresponding to its low X-ray luminosity.

scholarly journals Timing of the accreting millisecond pulsar IGR J17591–2342: evidence of spin-down during accretion

2020 ◽  
Vol 495 (2) ◽  
pp. 1641-1649
Author(s):  
A Sanna ◽  
L Burderi ◽  
K C Gendreau ◽  
T Di Salvo ◽  
P S Ray ◽  
...  
Keyword(s):  
Neutron Star ◽  
Timing Analysis ◽  
Millisecond Pulsar ◽  
Pulse Profile ◽  
X Ray ◽  
Observed Behaviour ◽  
October 17 ◽  
Refined Estimate ◽  
Star Surface ◽  
Orbital Solution

ABSTRACT We report on the phase-coherent timing analysis of the accreting millisecond X-ray pulsar IGR J17591–2342, using Neutron Star Interior Composition Explorer (NICER) data taken during the outburst of the source between 2018 August 15 and 2018 October 17. We obtain an updated orbital solution of the binary system. We investigate the evolution of the neutron star spin frequency during the outburst, reporting a refined estimate of the spin frequency and the first estimate of the spin frequency derivative ($\dot{\nu }\sim -7\times 10^{-14}$ Hz s−1), confirmed independently from the modelling of the fundamental frequency and its first harmonic. We further investigate the evolution of the X-ray pulse phases adopting a physical model that accounts for the accretion material torque as well as the magnetic threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. From this analysis we estimate the neutron star magnetic field Beq = 2.8(3) × 108 G. Finally, we investigate the pulse profile dependence on energy finding that the observed behaviour of the pulse fractional amplitude and lags as a function of energy is compatible with the down-scattering of hard X-ray photons in the disc or the neutron star surface.

scholarly journals 4U 1909+07: a Hidden Pearl

10.14311/1326 ◽  
2011 ◽  
Vol 51 (1) ◽  
Author(s):  
I. Kreykenbohm ◽  
F. Fürst ◽  
L. Barrágan ◽  
J. Wilms ◽  
R. E. Rothschild ◽  
...  
Keyword(s):  
Timing Analysis ◽  
High Mass ◽  
Folding Energy ◽  
Pulse Profile ◽  
Spectral Parameters ◽  
Phase Dependence ◽  
X Ray ◽  
Low Energies ◽  
Fluorescence Line ◽  
Energy Dependent

We present a detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U1909+07 is a persistent accreting X-ray pulsar with a period of approximately 605 s. The period changes erratically consistent with a random walk expected for a wind accreting system. INTEGRAL detects the source with an average of 2.4 cps (corresponding to 15mCrab), but sometimes exhibits flaring activity up to 50 cps (i.e. 300mCrab). The strongly energy dependent pulse profile shows a double peaked structure at low energies and only a single narrow peak at energies above 20 keV. The phase averaged spectrum is well described by a powerlaw modified at higher energies by an exponential cutoff and photoelectric absorption at low energies. In addition at 6.4 keV a strong iron fluorescence line and at lower energies a blackbody component are present. We performed phase resolved spectroscopy to study the pulse phase dependence of the spectral parameters: while most spectral parameters are constant within uncertainties, the blackbody normalization and the cutoff folding energy vary strongly with phase.

scholarly journals Observational appearance of rapidly rotating neutron stars

2020 ◽  
Vol 639 ◽  
pp. A33 ◽  
Author(s):  
Valery F. Suleimanov ◽  
Juri Poutanen ◽  
Klaus Werner
Keyword(s):  
Neutron Stars ◽  
Spectral Evolution ◽  
Rapid Rotation ◽  
X Ray ◽  
Frame Dragging ◽  
Surface Emission ◽  
Inclination Angles ◽  
Analytical Formulae ◽  
Low Mass ◽  
Baryonic Mass

Neutron stars (NSs) in low-mass X-ray binaries rotate at frequencies high enough to significantly deviate from sphericity (ν* ∼ 200–600 Hz). First, we investigate the effects of rapid rotation on the observational appearance of a NS. We propose analytical formulae relating gravitational mass and equatorial radius of the rapidly rotating NS to the mass M and radius R of a non-rotating NS of the same baryonic mass using accurate fully relativistic computations. We assume that the NS surface emission is described by the Planck function with two different emission patterns: the isotropic intensity and that corresponding to the electron-scattering dominated atmosphere. For these two cases we compute spectra from an oblate rotating NS observed at different inclination angles using the modified oblate Schwarzschild approximation, where light bending is computed in Schwarzschild metric, but frame dragging and quadrupole moment of a NS are approximately accounted for in the photon redshift calculations. In particular, we determine the solid angle at which a rotating NS is seen by a distant observer, the observed colour temperature and the blackbody normalization. Then, we investigate how rapid rotation affects the results of NS radius determination using the cooling tail method applied to the X-ray burst spectral evolution. We approximate the local spectra from the NS surface by a diluted blackbody with the luminosity-dependent dilution factor using previously computed NS atmosphere models. We then generalize the cooling tail method to the case of a rapidly rotating NS to obtain the most probable values of M and R of the corresponding non-rotating NS with the same baryonic mass. We show that the NS radius could be overestimated by 3–3.5 km for face-on stars of R ≈ 11 km rotating at ν*= 700 Hz if the version of the cooling tail method for a non-rotating NS is used. We apply the method to an X-ray burst observed from the NS rotating at ν* ≈ 532 Hz in SAX J1810.8−2609. The resulting radius of the non-rotating NS (assuming M = 1.5 M⊙) becomes 11.8 ± 0.5 km if it is viewed at inclination i = 60° and R = 11.2 ± 0.5 km for a face-on view, which are smaller by 0.6 and 1.2 km than the radius obtained using standard cooling tail method ignoring rotation. The corresponding equatorial radii of these rapidly rotating NSs are 12.3 ± 0.6 km (for i = 60°) and 11.6 ± 0.6 km (for i = 0°).

scholarly journals Joint radio and X-ray modelling of PSR J1136+1551

2019 ◽  
Vol 491 (1) ◽  
pp. 80-91 ◽  
Author(s):  
J Pétri ◽  
D Mitra
Keyword(s):  
Magnetic Dipole ◽  
Thermal Emission ◽  
Essential Feature ◽  
Radio Pulse ◽  
Time Lag ◽  
Polar Cap ◽  
Pulse Profile ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Star Surface

ABSTRACT Multiwavelength observations of pulsar emission properties are powerful means to constrain their magnetospheric activity and magnetic topology. Usually a star centred magnetic dipole model is invoked to explain the main characteristics of this radiation. However, in some particular pulsars where observational constraints exist, such simplified models are unable to predict salient features of their multiwavelength emission. This paper aims to carefully model the radio and X-ray emission of PSR J1136+1551 with an off-centred magnetic dipole to reconcile both wavelength measurements. We simultaneously fit the radio pulse profile with its polarization and the thermal X-ray emission from the polar cap hotspots of PSR J1136+1551. We are able to pin down the parameters of the non-dipolar geometry (which we have assumed to be an offset dipole) and the viewing angle, meanwhile accounting for the time lag between X-ray and radio emission. Our model fits the data if the off-centred magnetic dipole lies about 20 per cent below the neutron star surface. We also expect very asymmetric polar cap shapes and sizes, implying non-antipodal and non-identical thermal emission from the hotspots. We conclude that a non-dipolar surface magnetic field is an essential feature to explain the multiwavelength aspects of PSR J1136+1551 and other similar pulsars.

scholarly journals Constraining pulsar birth properties with supernova X-ray observations

2017 ◽  
Vol 12 (S331) ◽  
pp. 63-68
Author(s):  
Y. A. Gallant ◽  
R. Bandiera ◽  
N. Bucciantini ◽  
E. Amato
Keyword(s):  
Magnetic Fields ◽  
Large Fraction ◽  
Spectral Component ◽  
Rotation Period ◽  
High Energy ◽  
Radio Pulsar ◽  
X Rays ◽  
Spectral Evolution ◽  
X Ray ◽  
Pulsar Wind

AbstractA large fraction of core-collapse supernovae are thought to result in the birth of a rotation-powered pulsar, which is later observable as a radio pulsar up to great ages. The birth properties of these pulsars, and in particular the distribution of their initial rotation periods, are however difficult to infer from studies of the radio pulsar population in our Galaxy. Yet the distributions of their birth properties is an important assumption for scenarios in which ultra-high-energy cosmic rays (UHECRs) originate in very young, extragalactic pulsars with short birth periods and/or high magnetic fields.Using a model of the very young pulsar wind nebula’s dynamical and spectral evolution, with pulsar wind and accelerated particle parameters assumed similar to those inferred from modeling young pulsar wind nebulae (PWNe) in our Galaxy, we show that X-ray observations of supernovae, a few years to decades after the explosion, constitute a favored window to obtain meaningful constraints on the initial spin-down luminosity of the newly-formed pulsar. We examine the expected emerging PWN spectral component, taking into account the X-ray opacity of the expanding supernova ejecta, and find that it is typically best detectable in < 10 keV X-rays some years after the explosion. We use this framework to assess available X-ray observations and flux upper limits on supernovae, building on the work of Pernaet al.(2008). We note that a resulting limit on spin-down luminosity corresponds univocally to a limit on the maximum magnetospheric acceleration potential, irrespective of the specific combination of magnetic field and rotation period that achieves it. We use available X-ray observations of supernovae to place constraints on the birth spin-down luminosity and period distribution of classical pulsars. We also examine the case of magnetars, born with much higher magnetic fields, and show that their much shorter initial spin-down time implies that any plausible signature of young magnetar wind nebulae can only be observed in harder X-ray or gamma-rays.

scholarly journals Switches between accretion structures during flares in 4U 1901+03

2020 ◽  
Vol 493 (4) ◽  
pp. 5680-5692
Author(s):  
L Ji ◽  
L Ducci ◽  
A Santangelo ◽  
S Zhang ◽  
V Suleimanov ◽  
...  
Keyword(s):  
Neutron Star ◽  
Phase Shift ◽  
Direct Evidence ◽  
Accretion Rate ◽  
Short Time Scale ◽  
Polar Cap ◽  
Pulse Profile ◽  
X Ray ◽  
Supercritical Accretion ◽  
Short Time

ABSTRACT We report on our analysis of the 2019 outburst of the X-ray accreting pulsar 4U 1901+03 observed with Insight-HXMT and NICER. Both spectra and pulse profiles evolve significantly in the decaying phase of the outburst. Dozens of flares are observed throughout the outburst. They are more frequent and brighter at the outburst peak. We find that the flares, which have a duration from tens to hundreds of seconds, are generally brighter than the persistent emission by a factor of ∼1.5. The pulse-profile shape during the flares can be significantly different from that of the persistent emission. In particular, a phase shift is clearly observed in many cases. We interpret these findings as direct evidence of changes of the pulsed beam pattern, due to transitions between the sub- and supercritical accretion regimes on a short time-scale. We also observe that at comparable luminosities the flares’ pulse profiles are rather similar to those of the persistent emission. This indicates that the accretion on the polar cap of the neutron star is mainly determined by the luminosity, i.e. the mass accretion rate.

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