scholarly journals XMM–Newton observations of a gamma-ray pulsar J0633+0632: pulsations, cooling and large-scale emission

2020 ◽  
Vol 493 (2) ◽  
pp. 1874-1887 ◽  
Author(s):  
A Danilenko ◽  
A Karpova ◽  
D Ofengeim ◽  
Yu Shibanov ◽  
D Zyuzin
Keyword(s):  
Neutron Star ◽  
Large Scale ◽  
Gamma Ray ◽  
Thermal Emission ◽  
Absorption Feature ◽  
Model Parameters ◽  
Pulse Profile ◽  
X Ray ◽  
Polar Caps ◽  
Star Surface

ABSTRACT We report results of XMM–Newton observations of a γ-ray pulsar J0633+0632 and its wind nebula. We reveal, for the first time, pulsations of the pulsar X-ray emission with a single sinusoidal pulse profile and a pulsed fraction of 23 ± 6 per cent in the 0.3–2 keV band. We confirm previous Chandra findings that the pulsar X-ray spectrum consists of thermal and non-thermal components. However, we do not find the absorption feature that was previously detected at about 0.8 keV. Thanks to the greater sensitivity of XMM–Newton, we get stronger constraints on spectral model parameters compared to previous studies. The thermal component can be equally well described by either blackbody or neutron star atmosphere models, implying that this emission is coming from either hot pulsar polar caps with a temperature of about 120 eV or from the colder bulk of the neutron star surface with a temperature of about 50 eV. In the latter case, the pulsar appears to be one of the coolest among other neutron stars of similar ages with estimated surface temperatures. We discuss cooling scenarios relevant to this neutron star. Using an interstellar absorption–distance relation, we also constrain the distance to the pulsar to the range of 0.7–2 kpc. Besides the pulsar and its compact nebula, we detect regions of weak large-scale diffuse non-thermal emission in the pulsar field and discuss their possible nature.

scholarly journals PSR B0656+14: the unified outlook from the infrared to X-rays

2021 ◽  
Vol 502 (2) ◽  
pp. 2005-2022
Author(s):  
S Zharikov ◽  
D Zyuzin ◽  
Yu Shibanov ◽  
A Kirichenko ◽  
R E Mennickent ◽  
...  
Keyword(s):  
Neutron Star ◽  
Absorption Line ◽  
Optical Spectrum ◽  
Near Infrared ◽  
Thermal Emission ◽  
Model Parameters ◽  
X Rays ◽  
Polar Cap ◽  
X Ray ◽  
Star Surface

ABSTRACT We report detection of PSR B0656+14 with the Gran Telescopio Canarias in narrow optical F657, F754, F802, and F902 and near-infrared JHKs bands. The pulsar detection in the Ks band extends its spectrum to 2.2 $\mu$m and confirms its flux increase towards the infrared. We also present a thorough analysis of the optical spectrum obtained by us with the VLT. For a consistency check, we revised the pulsar near-infrared and narrow-band photometry obtained with the HST. We find no narrow spectral lines in the optical spectrum. We compile available near-infrared-optical-UV and archival 0.3–20 keV X-ray data and perform a self-consistent analysis of the rotation phase-integrated spectrum of the pulsar using unified spectral models. The spectrum is best fitted by the four-component model including two blackbodies, describing the thermal emission from the neutron star surface and its hot polar cap, the broken power law, originating from the pulsar magnetosphere, and an absorption line near ∼0.5 keV detected previously. The fit provides better constraints on the model parameters than using only a single spectral domain. The derived surface temperature is $T_{NS}^{\infty } = 7.9(3)\times 10^5$ K. The intrinsic radius (7.8–9.9 km) of the emitting region is smaller than a typical neutron star radius (13 km) and suggests a non-uniform temperature distribution over the star surface. In contrast, the derived radius of the hot polar cap is about twice as large as the ‘canonical’ one. The spectrum of the non-thermal emission steepens from the optical to X-rays and has a break near 0.1 keV. The X-ray data suggest the presence of another absorption line near 0.3 keV.

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 Emission of particles and photons in the pulsar polar cap

2000 ◽  
Vol 177 ◽  
pp. 473-478
Author(s):  
A. I. Tsygan
Keyword(s):  
Gamma Ray ◽  
Radio Pulsars ◽  
Polar Cap ◽  
X Ray ◽  
Polar Caps ◽  
Electron Positron ◽  
Inertial Frames ◽  
General Relativistic ◽  
Star Surface ◽  
General Relativistic Effect

AbstractWe study emission of particles and photons from a pulsar polar cap. The Goldreich-Julian model for the regime of free emission of charged particles from the neutron star surface is used. In this case the electric field is generated due to the general relativistic effect of dragging of inertial frames. The spectra and shapes of gamma-ray pulses, the parameters of the electron-positron plasma and the intensity of X-ray emission from hot spots in the polar region of radio pulsars are discussed. The effect of non-dipole magnetic field on X-ray emission of polar caps is considered. It is shown that the increase of magnetic line curvature leads to much smaller temperatures and X-ray luminosities of the polar caps as compared with the purely dipole field.

scholarly journals NICER Study of Pulsed Thermal X-Rays from Calvera: A Neutron Star Born in the Galactic Halo?

2021 ◽  
Vol 922 (2) ◽  
pp. 253
Author(s):  
S. Mereghetti ◽  
M. Rigoselli ◽  
R. Taverna ◽  
L. Baldeschi ◽  
S. Crestan ◽  
...  
Keyword(s):  
Neutron Star ◽  
Galactic Halo ◽  
Galactic Disk ◽  
Good Description ◽  
Hydrogen Atmosphere ◽  
Galactic Latitude ◽  
X Rays ◽  
X Ray ◽  
Polar Caps ◽  
Star Surface

Abstract Calvera (1RXS J141256.0+792204) is an isolated neutron star detected only through its thermal X-ray emission. Its location at high Galactic latitude (b = +37°) is unusual if Calvera is a relatively young pulsar, as suggested by its spin period (59 ms) and period derivative (3.2 × 10−15 s s−1). Using the Neutron Star Interior Composition Explorer, we obtained a phase-connected timing solution spanning four years, which allowed us to measure the second derivative of the frequency ν ̈ = − 2.5 × 10 − 23 Hz s−2 and to reveal timing noise consistent with that of normal radio pulsars. A magnetized hydrogen atmosphere model, covering the entire star surface, provides a good description of the phase-resolved spectra and energy-dependent pulsed fraction. However, we found that a temperature map more anisotropic than that produced by a dipole field is required, with a hotter zone concentrated toward the poles. By adding two small polar caps, we found that the surface effective temperature and that of the caps are ∼0.1 and ∼0.36 keV, respectively. The inferred distance is ∼3.3 kpc. We confirmed the presence of an absorption line at 0.7 keV associated with the emission from the whole star surface, difficult to interpret as a cyclotron feature and more likely originating from atomic transitions. We searched for pulsed γ-ray emission by folding seven years of Fermi-LAT data using the X-ray ephemeris, but no evidence for pulsations was found. Our results favor the hypothesis that Calvera is a normal rotation-powered pulsar, with the only peculiarity of being born at a large height above the Galactic disk.

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 Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437−4715

2019 ◽  
Vol 490 (4) ◽  
pp. 5848-5859 ◽  
Author(s):  
Denis González-Caniulef ◽  
Sebastien Guillot ◽  
Andreas Reisenegger
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Hydrogen Atmosphere ◽  
Large Radius ◽  
X Ray ◽  
Dust Extinction ◽  
Polar Caps ◽  
Bulk Surface ◽  
Neutron Star Radius ◽  
Rule Out

ABSTRACT We analysed the thermal emission from the entire surface of the millisecond pulsar PSR J0437−4715 observed in the ultraviolet and soft X-ray bands. For this, we calculated non-magnetized, partially ionized atmosphere models of hydrogen, helium, and iron compositions and included plasma frequency effects that may affect the emergent spectrum. This is particularly true for the coldest atmospheres composed of iron (up to a few per cent changes in the soft X-ray flux). Employing a Markov chain Monte Carlo method, we found that the spectral fits favour a hydrogen atmosphere, disfavour a helium composition, and rule out iron atmosphere and blackbody models. By using a Gaussian prior on the dust extinction, based on the latest 3D map of Galactic dust, and accounting for the presence of hot polar caps found in the previous work, we found that the hydrogen atmosphere model results in a well-constrained neutron star radius ${R_{\rm NS}}= 13.6^{+0.9}_{-0.8}{\, {\rm km}}$ and bulk surface temperature ${T_{\rm eff}^{\infty }}=\left(2.3\pm 0.1\right){\times 10^{5}}{\, {\rm K}}$. This relatively large radius favours a stiff equation of state and disfavours a strange quark composition inside neutron stars.

scholarly journals Aperiodic Flux Variability in A 0535+262

1996 ◽  
Vol 165 ◽  
pp. 313-319
Author(s):  
Mark H. Finger ◽  
Robert B. Wilson ◽  
B. Alan Harmon ◽  
William S. Paciesas
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Beat Frequency ◽  
Power Spectra ◽  
Center Frequency ◽  
X Ray ◽  
Binary Pulsar ◽  
Transient Source ◽  
Flux Variability ◽  
Burst And Transient Source

A “giant” outburst of A 0535+262, a transient X-ray binary pulsar, was observed in 1994 February and March with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory. During the outburst power spectra of the hard X-ray flux contained a QPO-like component with a FWHM of approximately 50% of its center frequency. Over the course of the outburst the center frequency rose smoothly from 35 mHz to 70 mHz and then fell to below 40 mHz. We compare this QPO frequency with the neutron star spin-up rate, and discuss the observed correlation in terms of the beat frequency and Keplerian frequency QPO models in conjunction with the Ghosh-Lamb accretion torque model.

scholarly journals UV and X-ray observations of the neutron star LMXB EXO 0748–676 in its quiescent state

2020 ◽  
Vol 501 (1) ◽  
pp. 1453-1462
Author(s):  
A S Parikh ◽  
N Degenaar ◽  
J V Hernández Santisteban ◽  
R Wijnands ◽  
I Psaradaki ◽  
...  
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Hubble Space Telescope ◽  
Dense Matter ◽  
Continuum Emission ◽  
Quiescent State ◽  
X Ray ◽  
Low Level ◽  
Low Mass ◽  
Different Origins

ABSTRACT The accretion behaviour in low-mass X-ray binaries (LMXBs) at low luminosities, especially at <1034 erg s−1, is not well known. This is an important regime to study to obtain a complete understanding of the accretion process in LMXBs, and to determine if systems that host neutron stars with accretion-heated crusts can be used probe the physics of dense matter (which requires their quiescent thermal emission to be uncontaminated by residual accretion). Here, we examine ultraviolet (UV) and X-ray data obtained when EXO 0748–676, a crust-cooling source, was in quiescence. Our Hubble Space Telescope spectroscopy observations do not detect the far-UV continuum emission, but do reveal one strong emission line, C iv. The line is relatively broad (≳3500 km s−1), which could indicate that it results from an outflow such as a pulsar wind. By studying several epochs of X-ray and near-UV data obtained with XMM–Newton, we find no clear indication that the emission in the two wavebands is connected. Moreover, the luminosity ratio of LX/LUV ≳ 100 is much higher than that observed from neutron star LMXBs that exhibit low-level accretion in quiescence. Taken together, this suggests that the UV and X-ray emission of EXO 0748–676 may have different origins, and that thermal emission from crust-cooling of the neutron star, rather than ongoing low-level accretion, may be dominating the observed quiescent X-ray flux evolution of this LMXB.

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.

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