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X-Ray and Optical Observations of A 0535+26
Abstract
We present recent contemporaneous X-ray and optical observations of the
Be/X-ray binary system A\,0535+26 with the \textit{Fermi}/Gamma-ray Burst
Monitor (GBM) and several ground-based observatories. These new observations
are put into the context of the rich historical data (since $\sim$1978) and
discussed in terms of the neutron star Be-disk interaction. The Be
circumstellar disk was exceptionally large just before the 2009 December giant
outburst, which may explain the origin of the unusual recent X-ray activity of
this source. We found a peculiar evolution of the pulse profile during this
giant outburst, with the two main components evolving in opposite ways with
energy. A hard 30-70 mHz X-ray QPO was detected with GBM during this 2009
December giant outburst. It becomes stronger with increasing energy and
disappears at energies below 25\,keV. In the long-term a strong optical/X-ray
correlation was found for this system, however in the medium-term the
H$_\alpha$ EW and the V-band brightness showed an anti-correlation after
$\sim$2002 Agust. Each giant X-ray outburst occurred during a decline phase of
the optical brightness, while the H$_\alpha$ showed a strong emission. In late
2010 and before the 2011 February outburst, rapid V/R variations are observed
in the strength of the two peaks of the H$_\alpha$ line. These had a period of
$\sim$\,25 days and we suggest the presence of a global one-armed oscillation
to explain this scenario. A general pattern might be inferred, where the disk
becomes weaker and shows V/R variability beginning $\sim$\,6 months following a
giant outburst.
... Spectroscopic observations of 1A 0535+262/V725 Tau revealed a strong Hα line variability (Moritani et al., 2011). Before the giant X-ray outburst, the Hα line was observed to evolve from various shapes to a single peak with increasing strength and Full-Width at Zero Intensity (FWZI) (Clark et al., 1998;Coe et al., 2006;Camero-Arranz et al., 2012). This behavior of the Hα line is attributed to the warping of the Be companion's circumstellar disc prior to the giant outburst. ...
... Similar studies were conducted during the 2009 and 2011 giant X-ray outbursts of the 1A 0535+262/HD 245770 system (Camero-Arranz et al., 2012), where the Hα line profiles were found to be marginally asymmetric and single-peaked. The profile during the 2009 outburst had a broader blue wing, while the 2011 outburst showed a broader red wing. ...
... Comparing the Hα line profile before the 2020 outburst to the 2009 outburst, we observed similarities, with the post-outburst profiles being red-shifted with a broader blue wing, while the pre-outburst profiles were blue-shifted with a broader red wing. Higher spectral resolution (R ≃ 30000-60000) by Moritani et al. (2013) around the 2009 outburst indicated that the basic structure of the emission line is consistent with our findings and those from previous studies (Camero-Arranz et al., 2012). Moritani et al. (2013) also reported several absorption features in the Hα line profile suggesting a complex structure of the Be circumstellar disc. ...
We present the findings from our study of the Be/X-ray binary 1A 0535+262/HD 245770 during the giant X-ray outburst in October 2020. We utilized the 1.2-m telescope at Mount Abu Infrared observatory for optical observations of the Be companion star. The outburst reached a peak X-ray flux of approximately 11 Crab in the 15-50 keV range, marking the highest ever recorded X-ray outburst from the pulsar. We conducted optical observations in the 6000-7200 Å range before, during, and after the X-ray outburst, aiming to examine the evolution of the circumstellar disc of the Be star from February 2020 to February 2022. Our optical spectra displayed prominent emission lines at 6563 Å (H I), 6678 Å (He I), and 7065 Å (He I). Notably, the Hα line exhibited significant variability in the spectra. Prior to and during the outburst, the line profiles appeared single-peaked, and asymmetric with broad red and blue wings, respectively. However, post-outburst observations revealed a double-peaked profile with asymmetry in the blue wing. Our pre-outburst observations confirmed a larger Be circumstellar disc that diminished in size as the outburst progressed. Additionally, the observed variations in the Hα line profile and parameters indicate the presence of a highly misaligned, precessing, and warped Be disc.
... In our pulse-to-pulse analysis, we extract the net light curve from LE (1-10 keV), ME (10-30 keV), and HE (30-120 keV), respecti vely. The arri v al times of photons are corrected to the Solar system barycentre with the HXMTDAS tool hxbary , and the effects of binary orbital modulation are corrected using the ephemerides provided by Camero-Arranz et al. ( 2012 ). Based on the binary-and barycentre-corrected data, we measure the pulse periods and produce pulse profiles (see Wang et al. 2022 ;Hou et al. 2023 , for details about the timing analysis). ...
We present a detailed analysis of the X-ray luminosity (LX) dependence of the cyclotron absorption line energy (Ecyc) for the X-ray binary pulsar 1A 0535+262 during its 2020 giant outburst based on pulse-to-pulse analysis. By applying this technique to high cadence observations of Insight-HXMT, we reveal the most comprehensive Ecyc-LX correlation across a broad luminosity range of ∼(0.03–1.3) × 1038 erg s−1. Apart from the positive and negative correlations between cyclotron line energy and luminosity at LX ∼ (1–3) × 1037 erg s−1 and ∼(7–13) × 1037 erg s−1, which are expected from the typical subcritical and supercritical accretion regimes, respectively, a plateau in the correlation is also detected at ∼(3–7) × 1037 erg s−1. Moreover, at the lowest luminosity level (LX ≲ 1037 erg s−1), the positive Ecyc-LX correlation seems to be broken, and the pulse profile also occurs a significant transition. These discoveries provide the first complete view on the correlation between luminosity and the centriod energy of the cyclotron line, and therefore are relevant for understanding how accretion onto magnetized neutron stars depends on luminosity.
... Re vni vtse v & Mereghetti 2015 ). During the 1994 and 1999 giant outbursts, A0535 + 26 showed broad quasi-periodic oscillations which are considered good indicators of the presence of an accretion disc (see Finger , W ilson & Harmon 1996 ;Camero-Arranz et al. 2012 and references therein) during the outbursts. ...
The detection of γ −ray emission from accreting pulsars in X-ray binaries (XRBs) has long been sought after. For some high-mass X-ray binaries (HMXBs), marginal detections have recently been reported. Regardless of whether these will be confirmed or not, future telescopes operating in the γ −ray band could offer the sensitivity needed to achieve solid detections and possibly spectra. In view of future observational advances, we explored the expected emission above 10 GeV from XRBs, based on the Cheng & Ruderman model, where γ −ray photons are produced by the decay of π0 originated by protons accelerated in the magnetosphere of an accreting pulsar fed by an accretion disc. We improved this model by considering, through Monte Carlo simulations, the development of cascades inside of and outside the accretion disc, taking into account pair and photon production processes that involve interaction with nuclei, X-ray photons from the accretion disc, and the magnetic field. We produced grids of solutions for different input parameter values of the X-ray luminosity (Lx), magnetic field strength (B), and for different properties of the region where acceleration occurs. We found that the γ −ray luminosity spans more than five orders of magnitude, with a maximum of ∼1035 erg s−1. The γ −ray spectra show a large variety of shapes: some have most of the emission below ∼100 GeV, others are harder (emission up to 10−100 TeV). We compared our results with Fermi/LAT and VERITAS detections and upper-limits of two HMXBs: A0535+26 and GRO J1008−57. More consequential comparisons will be possible when more sensitive instruments will be operational in the coming years.
... This energy corresponds to a magnetic field of about 4 × 10 12 G (see, e.g., Revnivtsev & Mereghetti 2015). During the 1994 and 1999 giant outbursts, A0535+26 showed broad quasi-periodic oscillations which are considered good indicators of the presence of an accretion disc (see Finger et al. 1996;Camero-Arranz et al. 2012 and references therein) during the outbursts. Transient γ−ray radiation from a region spatially coincident with A0535+26, on a timescale of months, was detected by EGRET (source name: 3EG J0542+2610; energy band: 30 MeV−10 GeV; Romero et al. 2001;Torres et al. 2001). ...
The detection of gamma-ray emission from accreting pulsars in X-ray binaries (XRBs) has long been sought after. For some high-mass X-ray binaries (HMXBs), marginal detections have recently been reported. Regardless of whether these will be confirmed or not, future telescopes operating in the gamma-ray band could offer the sensitivity needed to achieve solid detections and possibly spectra. In view of future observational advances, we explored the expected emission above 10 GeV from XRBs, based on the Cheng & Ruderman model, where gamma-ray photons are produced by the decay of pion-0 originated by protons accelerated in the magnetosphere of an accreting pulsar fed by an accretion disc. We improved this model by considering, through Monte Carlo simulations, the development of cascades inside of and outside the accretion disc, taking into account pair and photon production processes that involve interaction with nuclei, X-ray photons from the accretion disc, and the magnetic field. We produced grids of solutions for different input parameter values of the X-ray luminosity (L_x), magnetic field strength (B), and for different properties of the region where acceleration occurs. We found that the gamma-ray luminosity spans more than five orders of magnitude, with a maximum of ~1E35 erg/s. The gamma-ray spectra show a large variety of shapes: some have most of the emission below ~100 GeV, others are harder (emission up to 10-100 TeV). We compared our results with Fermi/LAT and VERITAS detections and upper-limits of two HMXBs: A0535+26 and GROJ1008-57. More consequential comparisons will be possible when more sensitive instruments will be operational in the coming years.
... The H line can have either a symmetric profile (pointing to quasi-Keplerian disks) or an asymmetric one (caused by distortions of the quasi-Keplerian disk, associated with one-armed global disk oscillations), and it can change from one profile type to the other on timescales of Periodic type I outbursts at periastron are observed, as well as a couple of bright Type II outbursts (also near periastron for this source) which coincide with sharp increases of the spin frequency as the NS is spun-up. Credit: Figure 5 in [19], reproduced with permission ©AAS. months to years. ...
Binary systems in which a neutron star or black hole accretes material from a high-mass star are known as high-mass X-ray binaries (HMXBs). This chapter provides a brief introduction to the physics of wind accretion and an observational view of HMXBs, including their classification, X-ray spectra, X-ray variability, orbital and compact object properties, as well as studies of Galactic and Magellanic HMXB populations. Two classes of X-ray sources whose possible connections to HMXBs have been debated, ultraluminous X-ray sources and gamma-ray binaries, are also discussed. Approximately 300 HMXBs residing either in the Milky Way or the Magellanic Clouds have been discovered. The majority of these HMXBs host wind-accreting neutron stars. Their X-ray properties depend both on the interaction of the accreting material with the neutron star's strong magnetic field and the properties of the donor star's wind. Most HMXBs are classified as either supergiant XBs or Be XBs based on the spectral type of the donor star; these classes exhibit different patterns of X-ray variability and occupy different phase space in diagrams of neutron star spin versus orbital period. While studies of HMXBs in the Milky Way and Magellanic Clouds find that their luminosity functions have similar shapes, an overabundance of Be XBs in the Small Magellanic Cloud points to important variations of the HMXB population with metallicity and age.
... It has been reported that, in some BeXRBs, e.g. 4U 0115+63 19 , and 1A 0535+262 20,21 , the giant outbursts occur after the loss of circumstellar disk, implying that a large amount of material is transferred from a warped (and potentially eccentric) Be disk onto a NS near the periastron 11,19,22 . However, there are several issues in this preliminary scenario, including (1) until now, the association between giant outbursts and warping episodes of Be disk has only been confirmed in a few sources; (2) the large changes in the Be disk do not ignite giant outburst immediately, i.e. the catastrophic perturbation of the Be disk and the onset of outburst are not strictly simultaneous; (3) the occurrence of giant outbursts is not correlated with any orbital parameters. ...
X-ray pulsars (XRPs) consist of a magnetized neutron star (NS) and an optical donor star. The NS accretes matter from the donor star, producing pulsed X-ray emission. In most cases the donor stars are Be stars, and accretion is episodic, that is, the NSs are generally X-ray dim, but occasionally experience outbursts. The triggering mechanism of giant outbursts remains mysterious. Here, we carry out a statistical study with the X-ray monitoring data, and obtain strong correlations between the spin periods of the NSs and the outburst parameters for the first time. We show that XRPs containing faster rotating NSs tend to display more violent eruptions. These results provide clear evidence of ``magnetic gates", that is, larger accretion rates are required to penetrate into a faster rotating magnetosphere.
... The distance to the source is estimated at about 2 kpc measured by Gaia (Bailer-Jones et al. 2018). 1A 0535+262 is an active Be X-ray binary that has shown frequent outbursts in its history (see Camero-Arranz et al. 2012, and references therein). Caballero et al. (2011) applied the decomposition method to the pulse profiles observed during the outburst in 2005 with the RXTE mission at a luminosity level of about 0.8 × 10 37 erg s −1 . ...
We report on pulse profile decomposition analysis of bright transient X-ray pulsar 1A 0535+262 using broadband Insight-HXMT observations during a giant outburst of the source in 2020. We show that the observed pulse profile shape can be described in terms of a combination of two symmetric single-pole contributions for a wide range of energies and luminosities for a fixed geometry defining the basic geometry of the pulsar. This corresponds to a slightly distorted dipole magnetic field, i.e., one pole has to be offset by ∼12° from the antipodal position of the other pole. We reconstruct the intrinsic beam patterns of the pulsar assuming that the geometry is recovered from the decomposition analysis, and we find evidence for a transition between “pencil” and “fan” beams in energy ranges above the cyclotron line energy, which can be interpreted as a transition from sub- to supercritical accretion regimes associated with the onset of an accretion column. At lower energies, however, the beam pattern appears to be more complex and contains a substantial “fan” beam and an additional “pencil” beam component at all luminosities. The latter is not related to the accretion rate and is stronger in the fading phase of the outburst. We finally discuss the results in the context of other observational and theoretical findings earlier reported for the source in the literature.
Context. 1A 0535+262 is a high-mass X-ray binary that went into a giant X-ray outburst in 2020. During this event, the X-ray luminosity reached the highest value measured over the last 30 years.
Aims. Our aim is to study the long-term variability of 1A 0535+262 before and after the 2020 major X-ray outburst and to uncover the mechanism that led to the X-ray outburst.
Methods. We used the long-term photometric light curve and the equivalent widths of the H α and He I λ 6678 lines to monitor the state of the Be star’s circumstellar disk. The H α line profiles show evidence for V / R variability, which we revealed by fitting the H α spectral line profiles with two Gaussian functions. In addition, we divided our data into four periods according to the intensity of the X-ray, optical, and infrared emission.
Results. The H α line profiles show single-peaked profiles in most cases. This is consistent with the previously reported orbital inclination of i = 37° ±2°. Unlike the H α lines, the He I λ 6678 lines show a maximal intensity in October 2020, which is one month before the giant X-ray outburst in 2020. Based on the behavior of the equivalent widths of the H α and He I λ 6678 lines, and the V -band magnitude, we find two mass ejection processes from the Be star to the Be disk on MJD 55820 and MJD 56600. The V / R quasi-period is about two years during 2011–2015, which is different from 1994 to 1995. Furthermore, the periods I → II → III → IV in the ( B − V ) color index versus V -band magnitude diagram constitute a cycle. From the behavior of the V / R ratio of H α lines, and the variability of the V band, we believe that the precession of the density perturbation inside the disk is retrograde.
Aims. We introduce a method for extracting spectral information from energy-resolved light curves folded at the neutron star spin period (known as pulse profiles) in accreting X-ray binaries. Spectra of these sources are sometimes characterized by features superimposed on a smooth continuum, such as iron emission lines and cyclotron resonant scattering features. We address here the question on how to derive quantitative constraints on such features from energy-dependent changes in the pulse profiles.
Methods. We developed a robust method for determining in each energy-selected bin the value of the pulsed fraction using the fast Fourier transform opportunely truncated at the number of harmonics needed to satisfactorily describe the actual profile. We determined the uncertainty on this value by sampling through Monte Carlo simulations a total of 1000 faked profiles. We rebinned the energy-resolved pulse profiles to have a constant minimum signal-to-noise ratio throughout the whole energy band. Finally we characterize the dependence of the energy-resolved pulsed fraction using a phenomenological polynomial model and search for features corresponding to spectral signatures of iron emission or cyclotron lines using Gaussian line profiles.
Results. We apply our method to a representative sample of NuSTAR observations of well-known accreting X-ray pulsars. We show that, with this method, it is possible to characterize the pulsed fraction spectra, and to constrain the position and widths of such features with a precision comparable with the spectral results. We also explore how harmonic decomposition, correlation, and lag spectra might be used as additional probes for detection and characterization of such features.
Accretion Power in Astrophysics examines accretion as a source of energy in both binary star systems containing compact objects, and in active galactic nuclei. Assuming a basic knowledge of physics, the authors describe the physical processes at work in accretion discs and other accretion flows. The first three chapters explain why accretion is a source of energy, and then present the gas dynamics and plasma concepts necessary for astrophysical applications. The next three chapters then develop accretion in stellar systems, including accretion onto compact objects. Further chapters give extensive treatment of accretion in active galactic nuclei, and describe thick accretion discs. A new chapter discusses recently discovered accretion flow solutions. The third edition is greatly expanded and thoroughly updated. New material includes a detailed treatment of disc instabilities, irradiated discs, disc warping, and general accretion flows. The treatment is suitable for advanced undergraduates, graduate students and researchers.
In 1985 May - October, EXOSAT observed two outbursts from the previously unknown accreting X-ray pulsar EXO 2030+375. Using the orbital solution derived by the BATSE experiment on CGRO, the behavior of the pulse period variations can now be studied with much less ambiguity than was possible based on the EXOSAT observations alone. There is little evidence for spin-down allow luminosity during the first outburst. Three different accretion torque models are applied to the intrinsic pulse-period data, but none give formally acceptable fits. However models for the pulse period variations which allow the possibility of spin-down (magnetically-threaded disk models) provide a better description of the observed variations than the simplest accretion torque model. We confirm that the dependence of pulse period with observed X-ray luminosity is significantly steeper than that predicted by simple accretion torque theory, with -Ṗpulse ∝ LX1.2 rather than -Ṗpulse ∝ LX6/7 as expected. Distance estimates using the Wang and Ghosh & Lamb models range from 4.2 - 5.2 kpc respectively, while the magnetic dipole moment is 10 - 11 1030 G cm3. The distance is consistent with that derived from photometric studies of the companion star, and the magnetic moment is consistent with both the luminosity at which centrifugal inhibition of accretion would terminate the outburst, and the non-detection of a cyclotron feature in the X-ray spectrum.
Three outbursts of the x‐ray binary system A 0535+262 have been detected in the 20–120 keV energy range by the BATSE instrument onboard the Compton Gamma Ray Observatory. The system orbital parameters have been determined by a pulse timing analysis during data from these outbursts.
Chevalier & Ilovaisky use Hipparcos data to show that the X-ray binary systems LSI+61° 303 and A0535+262 are a factor of 10 closer (i.e. d ∼ few hundred pc) than previously thought (d ∼ kpc). We present high-quality CCD spectra of the systems, and conclude that the spectral types, reddening and absolute magnitudes of these objects are strongly inconsistent with the closer distances. We propose that the Hipparcos distances to these two systems are incorrect owing to their relatively faint optical magnitudes.
It is proposed that the quasi-periodic behavior of the bright galactic
bulge source GX5 - 1 results from fluctuations in accretion rate onto a
millisecond pulsar which has been spun up by accretion to its
steady-state spin rate. According to models that use spin-up by
accretion to bring the neutron stars to steady-state fast short periods,
galactic bulge sources are likely progenitors of millisecond pulsars.
After steady state is achieved in these systems, accretion may continue
without further spin-up, so that for a substantial fraction of the
lifetime of a galactic bulge X-ray source, the neutron star may already
be spinning rapidly at the equilibrium spin. The behavior of GX5 - 1 can
be explained in terms of deviations from this equilibrium state
resulting from changes in the accretion rate.
We report a preliminary solution for the accreting millisecond pulsar
based on RXTE PCA observations performed between 2011 Nov 4.9 and Nov
9.2, during its ongoing outburst (ATel #3733, #3736), with a total
exposure of 66.5 ks.
The Be/X-ray binary 1A 0535+262 is known as the accreting X-ray pulsar with the highest observed magnetic field. Usually the field strength is quoted as approx. 1O^13 G, based on the strong cyclotron line feature at ~110 keV observed by CGRO/OSSE during a giant outburst in 1994 (Grove et al., 1995, ApJ 438, L25). Observations by HEXE and TTM on Mir/Kvant of another giant outburst in 1989 had indicated cyclotron line features at ~50 and ~100 keV but the lower energy feature was of low significance (Kendziorra et al., 1994, A&A 291, L31).
The High Energy X-ray Timing Experiment (HEXTE) is one of three science instruments of NASA's X-ray Timing Explorer (XTE) mission, which was launched into low earth orbit in late 1995. Its energy range of 15-250keV overlaps with the OSSE and BATSE detectors of the Compton Gamma Ray Observatory (CGRO). The HEXTE consists of eight NaI scintillation detectors grouped into two independent clusters, each with its own data processing electronics. State-of-the art detector resolution is achieved with the help of an automatic gain control system. Like OSSE, the HEXTE permits on-the-fly correction of internal background by beamswitching to blank fields adjacent to the source on the sky. We present here a description of the HEXTE, and demonstrate some aspects of its performance by a spectral simulation of a bright Galactic source with cyclotron absorption. While the HEXTE's large collecting area yields the high event rates essential for temporal studies, the sensitivity to faint sources (such as active galaxies) is limited by systematic effects in the residual background, which we discuss in some detail.
MEASUREMENTS of high energy X rays in the region of the Crab Nebula were made with the Imperial College detector on Ariel V between April 13 and April 29, 1975. During that time the X-ray nova A0535+26 was first detected and observed to rise to its maximum intensity1,2. At 30 keV this nova reached an intensity considerably brighter than the Crab Nebula, making it the brightest known source in the sky.
The proportional counter array (PCA) is designed to perform microsecond timing of bright galactic sources and broad band, confusion limited, studies of faint extragalactic sources in the 2 - 60 keV x-ray band. The PCA was launched as part of the Rossi X-ray Timing Explorer (RXTE) satellite into a circular orbit of altitude 580 km and 23 degrees inclination on December 30, 1995. The mission contains three experiments: a set of large area xenon proportional counters sensitive from 2 - 60 keV (proportional counter array: PCA), a set of large area sodium iodide scintillators sensitive from 15 - 200 keV (high energy x-ray timing experiment: HEXTE), and three wide field of view scanning detectors which monitor most of the sky each orbit (all sky monitor: ASM). The goals of the mission are summarized by Swank et al. We present performance and calibration data on the measured and predicted in-orbit background, energy response, relative and absolute timing performance, and the operational possibilities made available with the high performance experiment data system (EDS) designed and built by MIT.