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

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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An Emission Line in the Hard X-Ray Spectrum of Hercules X-1: Quantized Cyclotron Emission from the Neutron Star

International Astronomical Union Colloquium ◽

10.1017/s0252921100120329 ◽

1977 ◽

Vol 43 ◽

pp. 34-34

Author(s):

W. Pietsch ◽

C. Reppin ◽

R. Staubert ◽

J. Truemper ◽

W. Voges ◽

...

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Field Strength ◽

Second Harmonic ◽

Narrow Line ◽

Electron Cyclotron Emission ◽

Polar Cap ◽

Astrophysical Application ◽

X Ray ◽

Cyclotron Emission

A four hour balloon observation of HERC X-l during the 'On-state' in the 35 day cycle was performed on May 3rd, 1976. The 1.24 second pulsations show a pulsed fraction of 58 ± 8% in the 18-31 KeV interval. A pulsed flux (1.24 sec) was discovered in the 31-88 KeV interval with a pulsed fraction of 51 ± 14%. The spectrum of the pulsed flux can be represented up to 50 KeV by an exponential distribution with KT approximately 8 KeV. At approximately 58 KeV a strong and narrow line feature occurs which we interpret as electron cyclotron emission (ΔN = 1 Landau transition) from the polar cap plasma of the rotating neutron star. The corresponding magnetic field strength is approximately 5 x 1012 Gauss, neglecting gravitational red shift. There is evidence for a second harmonic at approximately 110 KeV (ΔN = 2 ).The astrophysical application of this discovery will be discussed in some detail.

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Torque Reversals in Disk Accreting Pulsars

Publications of the Astronomical Society of Australia ◽

10.1071/as98250 ◽

1998 ◽

Vol 15 (2) ◽

pp. 250-253

Author(s):

Jianke Li ◽

Dayal T. Wickramasinghe

Keyword(s):

Neutron Star ◽

Binary System ◽

Recent Work ◽

Time Scale ◽

Accretion Rate ◽

Future Studies ◽

X Ray ◽

The Past ◽

X Ray Binaries ◽

Coherent Picture

AbstractX-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10−13 Hz s−1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque–mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.

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Thick-target bremsstrahlung interpretation of short time-scale solar hard X-ray features

The Astrophysical Journal ◽

10.1086/161202 ◽

1983 ◽

Vol 271 ◽

pp. 367 ◽

Cited By ~ 16

Author(s):

A. G. Emslie

Keyword(s):

Time Scale ◽

Thick Target ◽

Short Time Scale ◽

X Ray ◽

Short Time

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New ASCA Observations of two Anomalous X-ray Pulsars

International Astronomical Union Colloquium ◽

10.1017/s0252921100061005 ◽

2000 ◽

Vol 177 ◽

pp. 695-698 ◽

Cited By ~ 1

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.

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Accretion onto Magnetized Neutron Stars: Polar Cap Flow and Centrifugally Driven Winds

Symposium - International Astronomical Union ◽

10.1017/s0074180900160784 ◽

1987 ◽

Vol 125 ◽

pp. 207-225

Author(s):

Jonathan Arons

Keyword(s):

Angular Momentum ◽

Neutron Star ◽

Neutron Stars ◽

Orbital Evolution ◽

Time Dependent ◽

Polar Cap ◽

Periodic Oscillations ◽

X Ray ◽

Polar Caps ◽

Basic Concepts

Some basic concepts of accretion onto the polar caps of magnetized neutron stars are reviewed. Preliminary results of new, multidimensional, time–dependent calculations of polar cap flow are outlined, and are used to suggest the possible observability of fluctuations in the X–ray intensity of accretion powered pulsars on time scales of 10–100 msec. The possible relevance of such fluctuations to Quasi–Periodic oscillations is suggested. Basic concepts of the interaction between a disk and the magnetosphere of a neutron star are also discussed. Some recent work on the disk–magnetosphere interaction is outlined, leading to the suggestion that a neutron star can lose angular momentum by driving some or all of the mass in the disk off as a centrifugally driven wind. The relevance of such mass loss to the orbital evolution of the binary is pointed out.

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IPS Observations of Short-Time Scale Interplanetary Activity

International Astronomical Union Colloquium ◽

10.1017/s0252921100030232 ◽

1996 ◽

Vol 154 ◽

pp. 225-228

Author(s):

Pradeep Gothoskar ◽

A. Pramesh Rao

Keyword(s):

Time Scale ◽

Solar Maximum ◽

Component Model ◽

Scintillation Index ◽

Short Time Scale ◽

High Time Resolution ◽

The Sun ◽

X Ray ◽

Average Mass ◽

Short Time

AbstractWe have carried out a program of continuous Interplanetary Scintillation (IPS) monitoring of the interplanetary activity using Ooty Radio Telescope (ORT). From May 1990 to March 1991, during the 22nd solar maximum, a few radio sources were monitored to provide long stretches of IPS data with a high-time resolution of few minutes. These observations covered 0.3 to 0.8 AU region (12° to 70° elongations) around the sun at several heliographic latitudes. During the observation, we detected 33 short-time scale IPS events which had significant variation in the scintillation index and solar wind velocity. These were considered to be due to travelling interplanetary disturbances.A multi-component model of plasma density enhancement was developed to estimate the geometry and physical properties of these IPS events. Detailed analysis of 20 of these events suggests, 1. fast IPS events were interplanetary signatures of Coronal Mass Ejections (CMEs), 2. the average mass and energy of these events was ~ 1016 gm and 1033 erg respectively, 3. 80% of IPS events were associated with X-ray flares on the sun and 50% were associated with geomagnetic activity at earth. Detailed study of the multi-component model suggests IPS observations at smaller elongations (hence at higher radio frequencies) are more suited to detect fast-moving interplanetary disturbances such as produced by CMEs.

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Thermal state of transiently accreting neutron stars with additional heating beyond deep crustal heating

Progress of Theoretical and Experimental Physics ◽

10.1093/ptep/ptaa029 ◽

2020 ◽

Vol 2020 (4) ◽

Author(s):

Helei Liu ◽

Masa-aki Hashimoto ◽

Guoliang Lü ◽

Yasuhide Matsuo ◽

Dehua Wen ◽

...

Keyword(s):

Neutron Star ◽

Heat Source ◽

Neutron Stars ◽

High Temperatures ◽

Accretion Rate ◽

Thermal State ◽

X Ray ◽

Mass Accretion Rate ◽

Accretion Rates ◽

Theoretical Predictions

Abstract As some neutron star transients require an additional unknown heat source (referred to as “shallow heating”) to explain their high temperatures at the beginning of quiescence, we investigate the effect of shallow heating as well as compressional heating on the thermal state of transiently accreting neutron stars with the use of evolutionary calculations in the present work. Through comparing our theoretical predictions of the equilibrium redshifted luminosities $(L_{\gamma}^{\infty})$ produced by both deep crustal heating and shallow heating/compressional heating for different time-averaged mass-accretion rates $\langle\dot{M}\rangle$ with 35 updated observations of soft X-ray transients, the results show that both shallow heating and compressional heating make significant contributions to the equilibrium redshifted luminosity. The hotter sources (XTE J1701, MAXI J0556, EXO 0748, Aql X-1 etc.) with higher accretion rates are more likely to be explained with the effect of shallow heating or compressional heating. In addition, for a proper shallow heat $q_\mathrm{sh}$ and mass-accretion rate $\dot{M}$, the effect of shallow heating could be simulated by compressional heating.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1253 ◽

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.

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