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Joint Hα and X-Ray Observations of Massive X-Ray Binaries. III. The Be X-Ray Binaries HDE 245770 = A0535+26 and X Persei
We present results from an Hα monitoring campaign of the Be X-raybinary systems HDE 245770 = A0535+26 and X Per. We use the Hαequivalent widths together with adopted values of the Be star effectivetemperature, disk inclination, and disk outer boundary to determine thehalf-maximum emission radius of the disk as a function of time. Theobservations of HDE 245770 document the rapid spectral variability thatapparently accompanied the regeneration of a new circumstellar disk.This disk grew rapidly during the years 1998-2000, but then slowed ingrowth in subsequent years. The outer disk radius is probably truncatedby resonances between the disk gas and neutron star orbital periods. Tworecent X-ray outbursts appear to coincide with the largest diskhalf-maximum emission radius attained over the last decade. Ourobservations of X Per indicate that its circumstellar disk has recentlygrown to near-record proportions, and concurrently the system hasdramatically increased in X-ray flux, presumably the result of enhancedmass accretion from the disk. We find that the Hα half-maximumemission radius of the disk surrounding X Per reached a size about 6times larger than the stellar radius, a value, however, that is wellbelow the minimum separation between the Be star and neutron star. Wesuggest that spiral arms excited by tidal interaction at periastron mayhelp lift disk gas out to radii where accretion by the neutron starcompanion becomes more effective.
| Discovery of a flux-related change of the cyclotron line energy in Hercules X-1
Aims. We present the results of ten years of repeated measurements ofthe Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of thebinary X-ray pulsar Her X-1 and report the discoveryof a positive correlation of the centroid energy of this absorptionfeature in pulse phase averaged spectra with source luminosity. Methods: . Our results are based on a uniform analysis of observationsby the RXTE satellite from 1996 to 2005, using sufficiently longobservations of 12 individual 35-day Main-On states of the source. Results: . The mean centroid energy Ec of the CRSF inpulse phase averaged spectra of Her X-1 during this time is around 40keV, with significant variations from one Main-On state to the next. Wefind that the centroid energy of the CRSF in Her X-1 changes by ~5% inenergy for a factor of 2 in luminosity. The correlation is positive,contrary to what is observed in some high luminosity transient pulsars. Conclusions: . Our finding is the first significant measurementof a positive correlation between Ec and luminosity in anyX-ray pulsar. We suggest that this behaviour is expected in the case ofsub-Eddington accretion and present a calculation of a quantitativeestimate, which is very consistent with the effect observed in Her X-1.We urge that Her X-1 is regularly monitored further and that other X-raypulsars are investigated for a similar behaviour.
| A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
Aims. In this Letter we present results from INTEGRAL and RXTEobservations of the spectral and timing behavior of the High Mass X-rayBinary A 0535+26 during its August/September 2005 normal (type I)outburst with an average flux F(5-100) keV400 mCrab. The search for cyclotron resonance scattering features(fundamental and harmonic) is one major focus of the paper. Methods: . Our analysis is based on data from INTEGRAL and RXTE Targetof Opportunity Observations performed during the outburst. The pulseperiod is determined. X-ray pulse profiles in different energy rangesare analyzed. The broad band INTEGRAL and RXTE pulse phase averagedX-ray spectra are studied. The evolution of the fundamental cyclotronline at different luminosities is analyzed. Results: .The pulseperiod P is measured to be 103.39315(5) s at MJD 53614.5137. Twoabsorption features are detected in the phase averaged spectra atE1 45 keV and E2 100 keV. These can beinterpreted as the fundamental cyclotron resonance scattering featureand its first harmonic and therefore the magnetic field can be estimatedto be B 4× 1012 G.
| The origin of long-period X-ray pulsars
Several relatively bright, persistent X-ray sources display regularpulses, with periods in the range of (0.7-10) × 103 s.These sources are identified with massive close binaries in which aneutron star accretes material on to its surface. The observedpulsations in all of them, but one, are unambiguously associated withthe spin period of the neutron star. Analysing the possible history ofthese pulsars, I conclude that the neutron stars in these systemsundergo spherical accretion, and their evolutionary tracks in a previousepoch contained three instead of two states, namely ejector, supersonicpropeller and subsonic propeller. An assumption about a supercriticalvalue of the initial magnetic field of the neutron stars within thisscenario is not necessary. Furthermore, I show that the scenario inwhich the neutron star in 2S0114+650 is assumed to be a magnetardescendant encounters major difficulties in explaining the evolution ofthe massive companion. An alternative interpretation of the spinevolution of the neutron star in this system is presented and theproblem raised by the association of the 104 s pulsationswith the spin period of the neutron star is briefly discussed.
| Joint Hα and X-Ray Observations of Massive X-Ray Binaries. II. The Be X-Ray Binary and Microquasar LS I +61 303
We present the results of an Hα monitoring campaign on the BeXRBand microquasar system LS I +61 303. We use radial velocity measurementsof He I lines in our spectra to reevaluate the orbital elements and tobetter establish the time of periastron. We list equivalent widths andother parameters for the Hα emission line and discuss the orbitalphase related variations observed. We call attention to a dramaticepisode of emission weakening that occurred in less than 1 day thatprobably resulted from exposure to a transient source of ionizingradiation. We argue that the increase in Hα and X-ray emissionfollowing periastron probably results from the creation of an extendeddensity wave in the disk created by tidal forces. We also discussestimates of the size of the disk from the Hα equivalent widthmeasurements, and we suggest that the disk radius from the averageequivalent width corresponds to a resonant truncation radius of the diskwhile the maximum equivalent width corresponds to a radius limited bythe separation of the stars at periastron. We note that a nearby faintcompanion is probably an unrelated foreground object.
| Joint Hα and X-Ray Observations of Massive X-Ray Binaries. I. The B Supergiant System LS I +65 010 = 2S 0114+650
We report on a 3 yr spectroscopic monitoring program of the Hαemission in the massive X-ray binary LS I +65 010 = 2S 0114+650, whichconsists of a B supergiant and a slowly rotating X-ray pulsar. Wepresent revised orbital elements that yield a period ofP=11.5983+/-0.0006 days and confirm that the orbit has a nonzeroeccentricity e=0.18+/-0.05. The Hα emission profile is formed inthe base of the wind of the B supergiant primary, and we show how thisspectral feature varies on timescales that are probably related to therotational period of the B supergiant. We also examine the X-ray fluxesfrom the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and weshow that the X-ray orbital light curve has a maximum at periastron anda minimum at the inferior conjunction of the B supergiant. We also showthat the wind emission strength and the high-energy X-ray flux appear tovary in tandem on timescales of approximately 1 yr.
| Optical observations of the Be/X-ray transient system KS 1947+300
ROTSE-IIId observations of the Be/X-ray transient system KS 1947+300obtained between September 2004 and December 2005 make it possible tostudy the correlation between optical and X-ray activity. The opticaloutburst of 0.1 mag was accompanied by an increase of the X-ray flux inthe 2004 observations. A strong correlation between the optical andX-ray light curves suggests that the neutron star directly accretes fromthe outflowing material of the Be star. The nearly zero time lag betweenX-ray and optical light curves suggests a heating of the disk of Be starby X-rays. No optical brightening and X-ray enhancement was seen in the2005 observations. There is no indication of an orbital modulation inthe optical light curve.
| XMM-Newton and ESO observations of the two unidentified γ-ray sources 3EG J0616-3310 and 3EG J1249-8330
The limited angular resolution of γ-ray telescopes prevents adirect identification of the majority of sources detected so far. Thisis particularly true for the low latitude, probably galactic, ones only10% of which has been identified. Most counterparts of the identifiedlow-latitude γ-ray sources are Isolated Neutron Stars (INS), bothradio-loud and radio-quiet (Geminga-like) objects, which arecharacterised by an extremely high value of the X-ray-to-optical fluxratio f_X/f_opt. Therefore, the systematic X-ray and optical coverage oflow-latitude unidentified γ-ray sources aiming at highf_X/fopt sources seems one of the most promising ways to spotINS candidate counterparts. Since low latitude sources are heavilyaffected by the interstellar absorption at both X-ray and opticalwavelengths, we have focussed on two middle-latitude, probably galactic,GRO/EGRET sources: 3EG J0616-3310 and 3EG J1249-8330. These two sources,which could belong to a local galactic population, have been selectedowing to their relatively good positional accuracy, spectral shape andlack of candidate extragalactic radio counterparts. Here we report onX-ray observations of the two γ-ray error boxes performed withXMM-Newton and on their optical follow-up carried on with the Wide FieldImager at the ESO/MPG 2.2 m telescope. Less than half of the ~300sources detected by the X-ray coverage have no optical counterparts.Among those, we have selected few interesting sources withfX/f_opt≥ 100, which we consider promising INScandidates.
| Global optical/infrared-X-ray correlations in X-ray binaries: quantifying disc and jet contributions
The optical/near-infrared (OIR) region of the spectra of low-mass X-raybinaries (XBs) appears to lie at the intersection of a variety ofdifferent emission processes. In this paper we presentquasi-simultaneous OIR-X-ray observations of 33 XBs in an attempt toestimate the contributions of various emission processes in thesesources, as a function of X-ray state and luminosity. A globalcorrelation is found between OIR and X-ray luminosity for low-mass blackhole candidate XBs (BHXBs) in the hard X-ray state, of the formLOIR ~ L0.6X. This correlation holdsover eight orders of magnitude in LX and includes data fromBHXBs in quiescence and at large distances [Large Magellanic Cloud (LMC)and M31]. A similar correlation is found in low-mass neutron star XBs(NSXBs) in the hard state. For BHXBs in the soft state, all thenear-infrared (NIR) and some of the optical emissions are suppressedbelow the correlation, a behaviour indicative of the jet switchingoff/on in transition to/from the soft state. We compare these relationsto theoretical models of a number of emission processes. We find thatX-ray reprocessing in the disc and emission from the jets both predict aslope close to 0.6 for BHXBs, and both contribute to the OIR in BHXBs inthe hard state, the jets producing ~90 per cent of the NIR emission athigh luminosities. X-ray reprocessing dominates the OIR in NSXBs in thehard state, with possible contributions from the jets (only at highluminosity) and the viscously heated disc. We also show that theoptically thick jet spectrum of BHXBs extends to near the K band. OIRspectral energy distributions of 15 BHXBs help us to confirm theseinterpretations. We present a prediction of theLOIR-LX behaviour of a BHXB outburst that entersthe soft state, where the peak LOIR in the hard state rise isgreater than in the hard state decline (the well-known hystereticalbehaviour). In addition, it is possible to estimate the X-ray, OIR andradio luminosity and the mass accretion rate in the hard statequasi-simultaneously, from observations of just one of these wavebands,since they are all linked through correlations. Finally, we havediscovered that the nature of the compact object, the mass of thecompanion and the distance/reddening can be constrained byquasi-simultaneous OIR and X-ray luminosities.
| Cyclotron Resonance Energies at a Low X-Ray Luminosity: A0535+262 Observed with Suzaku
The binary X-ray pulsar A0535+262 was observed with the Suzaku X-rayobservatory on 2005 September 14 for a net exposure of 22 ks. The sourcewas in the declining phase of a minor outburst, exhibiting 3-50 keVluminosity of ~3.7×1035 ergs s-1 at anassumed distance of 2 kpc. In spite of the very low source intensity(about 30 mcrab at 20 keV), its electron cyclotron resonance wasdetected clearly with the Suzaku Hard X-Ray Detector, in absorption atabout 45 keV. The resonance energy is found to be essentially the sameas that measured when the source is almost 2 orders of magnitude moreluminous. These results are compared with the luminosity-dependentchanges in the cyclotron resonance energy, observed from 4U 0115+63 andX0331+53.
| XMM-Newton observation of the Be/neutron star system RX J0146.9+6121: a soft X-ray excess in a low luminosity accreting pulsar
We report on the XMM-Newton observation of the Be/neutron star X-raybinary system RX J0146.9+6121, a long period (~23 m) pulsar in the NGC663 open cluster. The X-ray luminosity decreased by a factor of twocompared to the last observation carried out in 1998, reaching a levelof 1×1034 erg s-1, the lowest everobserved in this source. The spectral analysis reveals the presence of asignificant excess at low energies over the main power-law spectralcomponent. The soft excess can be described by a black-body spectrumwith a temperature of about 1 keV and an emitting region with a radiusof ~140 m. Although the current data do not permit us to ascertainwhether the soft excess is pulsed or not, its properties are consistentwith emission from the neutron star polar cap. This is the thirddetection of a soft excess in a low luminosity(1×1034 erg s-1) pulsar, the othersbeing X Per and 3A 0535+262, suggesting that such a spectral component,observed to date in higher luminosity systems, is a common feature ofaccreting X-ray pulsars. The results of these three sources indicatethat, in low luminosity systems, the soft excess tends to have a highertemperature and a smaller surface area than in the high luminosity ones.
| New γ Cassiopeiae-like objects: X-ray and optical observations of SAO 49725 and HD 161103
A growing number of early Be stars exhibit X-ray luminosities that areintermediate between those typical of early type stars and those emittedby most Be/X-ray binaries in quiescence. We report on XMM-Newtonobservations of two such Be stars, SAO 49725 andHD 161103, which were originally discovered in asystematic cross-correlation between the ROSAT all-sky survey andSIMBAD. The new observations confirm the X-ray luminosity excess(LX ~ 1032-33 erg s-1) and the hardnessof their X-ray spectra, which are both unusual for normal early typestars. An iron Kα complex is clearly detected in HD161103 in which the H-like, He-like, and fluorescentcomponents are resolved, while strong evidences also exist for thepresence of similar features in SAO 49725. X-rayspectra can be equally well-fitted by a thermal plasma (mekal) with T ~108 K and solar abundances or by a power law + iron linemodel with photon index ~1.5-1.8, both with a soft thermal componentwith T ~ 107 K. The intensity of the fluorescence 6.4 keVline reflects the presence of large amounts of cold material close tothe X-ray sources and strongly argues against accretion onto a companionneutron star in a large orbit. On the other hand, the probable thermalorigin of the X-ray emission, as supported by the ionised iron lines,disagrees with those observed in all known Be/X-ray binaries, in which anon-thermal component is always required. Remarkably, the X-ray featuresare similar to those of white dwarves in several cataclysmic variables.There is no evidence of high frequency pulsations in neither of the twosystems. However, a large oscillation in the light curve of HD161103 with P ~ 3200 s is readily detected. The X-ray lightcurve of SAO 49725 exhibits clear variability by ~80%on time scales as short as ~1000 s. New optical observations provideupdated spectral types (B0.5 III-Ve) and disclose a dense, large, andapparently stable circumstellar disc for both stars. The nature of theexcess X-ray emission is discussed in light of the models proposed forγ Cas, magnetic disc-star interaction, oraccretion onto a compact companion object - whether neutron star orwhite dwarf. These two new objects, added to similar cases discovered inXMM-Newton surveys, point to the emergence of a new class ofγ Cas analogs.
| A 0535+26: back in business
In 2005 May/June, after 10 yr of inactivity, the Be/X-ray binary systemA 0535+26 underwent a major X-ray outburst. In this paper, data arepresented from 10 yr of optical, infrared and X-ray monitoring showingthe behaviour of the system during the quiescent epoch and the lead upto the new outburst. The results show the system going through a periodwhen the Be star in the system had a minimal circumstellar disc and thena dramatic disc recovery leading, presumably, to the latest flare up ofX-ray emission. The data are interpreted in terms of the state of thedisc and its interaction with the neutron star companion.
| Accretion torque on magnetized neutron stars
The conventional picture of disk accretion onto magnetized neutron starshas been challenged by the spin changes observed in a few X-ray pulsars,and by theoretical results from numerical simulations of disk-magnetizedstar interactions. These indicate possible accretion during thepropeller regime and the spin-down torque increasing with the accretionrate. Here we present a model for the accretion torque exerted by thedisk on a magnetized neutron star, assuming accretion continues even forrapid rotators. The accretion torque is shown to have some differentcharacteristics from that in the conventional model, but in accord withobservations and numerical calculations of accretion-powered magnetizedneutron stars. We also discuss its possible applications to the spinevolution in X-ray pulsars.
| Correlated X-ray spectral and timing variability of the Be/X-ray binary V0332+53/BQ Camelopardalis during a type II outburst
Context: .After more than 15 years of quiescence the Be/X-ray binaryV0332+53 underwent a giant outburst in December 2004.Aims.We haveinvestigated the timing properties of the source in correlation with itsspectral states as defined by different positions in the colour-colourdiagram. Methods.We have used RXTE and INTEGRAL light curves to obtaincolour-colour diagrams, power spectra and phase-lag spectra. The powerspectra were fitted with a multi-Lorentzian function.Results. The sourceshows two distinct branches in the colour-colour diagram that resemblethose of the Z sources. The hard branch (similar to the horizontalbranch of Z sources) is characterised by a low-amplitude change of thehard colour compared to the change in the soft colour. In the softbranch (analogue to the normal branch) the amplitude of variability ofthe hard colour is about three times larger than that of the softcolour. As the count rate decreases the source moves up graduallythrough the soft to the hard branch. The aperiodic variability(excluding the pulse noise) consists of band-limited noise (representedby three broad Lorentzian components) and two QPOs at 0.05 Hz and 0.22Hz. The strength of the lower frequency QPO increases as the sourceapproaches the hard branch (similar to HBOs in Z sources). The higherfrequency QPO reaches maximum significance when the source is in themiddle of the branch (like NBOs). We have performed the firstmeasurements of phase lags in the band limited noise below 8 Hz in anaccreting X-ray pulsar and found that soft lags dominate at highfrequencies. Above the pulse frequency (0.23 Hz), the amplitude of thelag increases as the X-ray flux increases. Conclusions.The Z topologyappears to be a signature of the neutron star binaries as it is presentin all types of neutron-star binaries (Z, atoll and, as we show here, inaccreting pulsars as well). However, the motion along this track, thetime scales through the different branches of the diagram and theaperiodic variability associated with portions of the Z track differ foreach subclass of neutron-star binary.
| Variable Quasi Periodic Oscillations during an Outburst of the Transient X-ray Pulsar XTE J1858+034
We have investigated the Quasi Periodic Oscillation (QPO) properties ofthe transient accreting X-ray pulsar XTE J1858 +034 dur-ing the secondoutburst of this source in April-May 2004. We have used observationsmade with the Proportional Counter Array (PCA) of the Rossi X-ray TimingExplorer (RXTE) during May 14-18, 2004, in the declining phase of theoutburst. We detected the presence of low frequency QPOs in thefrequency range of 140-185 mHz in all the RXTE-PCA observations. Wereport evolution of the QPO parameters with the time, X-ray flux, andX-ray photon energy. Though a correlation between the QPO centroidfre-quency and the instantaneous X-ray flux is not very clear from thedata, we point out that the QPO frequency and the one day averaged X-rayflux decreased with time during these observations. We have obtained aclear energy dependence of the RMS variation in the QPOs, increasingfrom about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is asingle peaked sinusoidal, with pulse fraction increasing from 20% at 3keV to 45% at 30 keV. We found that, similar to the previous outburst,the energy spectrum is well fitted with a model consisting of a cut-offpower law along with an iron emission line.
| Neutron Star Kicks in Isolated and Binary Pulsars: Observational Constraints and Implications for Kick Mechanisms
We study observational constraints on neutron star (NS) kicks forisolated pulsars and for NSs in binary systems. We are particularlyinterested in the evidence of kick-spin alignment/misalignment and itsdependence on the NS initial spin period. For several young pulsars,X-ray observations of compact nebulae showed that pulsar proper motionis aligned with the spin direction as defined by the symmetry axis ofthe nebula. We also critically examine the measurements of the propermotion and the projected spin axis from a large sample of pulsars withwell-calibrated polarization data. We find that among the two dozenpulsars for which reliable measurements are available, there is asignificant correlation between the spin axis and the proper motion. Forvarious NS binaries, including double NS systems, binaries with massivemain-sequence star companions, and binaries with massive white-dwarfcompanions, we obtain constraints on the kick magnitudes and directionsfrom the observed orbital characteristics of the system. We find thatthe kick velocity is misaligned with the NS spin axis in a number ofsystems, and the NS spin period (when available) in these systems isgenerally longer than several hundred milliseconds. These constraints,together with the spin-kick alignment observed in many isolated pulsars,suggest that the kick timescale is hundreds of milliseconds to 1 s, sothat spin-kick alignment or misalignment can be obtained depending onthe initial spin period of the NS. We discuss the implication of ourresult for various NS kick mechanisms.
| Isolated, Massive Supergiants near the Galactic Center
We have carried out a pilot project to assess the feasibility of usingradio, infrared, and X-ray emission to identify young, massive starslocated between 1 and 25 pc from the Galactic center. We first comparedcatalogs compiled from the VLA, Chandra, and 2MASS. We identified twomassive, young stars: the previously identified star that is associatedwith the radio H II region H2 and a newly identified star that we referto as CXOGC J174516.1-290315. The infrared spectra of both stars exhibitvery strong Brγ and He I lines and resemble those of massivesupergiants that have evolved off of the main sequence but not yetreached the Wolf-Rayet phase. We estimate that each star has abolometric luminosity >~106 Lsolar. These twostars are also associated with bright mid-infrared sources from the MSXsurvey, although the origin of this emission is uncertain. Likewise, thedetection of these two sources in X-rays is surprising because stars atsimilar evolutionary states are not uniformly bright X-ray sources.Therefore, we suggest that both stars are in binary systems that containeither OB stars whose winds collide with those of the luminoussupergiants or compact objects that are accreting from the winds of thesupergiants. We also identify X-ray emission from a nitrogen-typeWolf-Rayet star and place upper limits on the X-ray luminosities ofthree more evolved, massive stars that previously have been identifiedbetween 1 and 25 pc from Sgr A*. Finally, we briefly discuss theimplications that future searches for young stars will have for ourunderstanding of the recent history of star formation near the Galacticcenter.
| Search for Neutron-Capture Gamma-Ray Lines from A0535+26 in Outburst
In 2005 May-June, the Reuven Ramaty High Energy Solar SpectroscopicImager (RHESSI) observed the Be/X-ray binary system A0535+26 during agiant outburst, during which time its hard X-ray intensity reachedseveral crab. This bright source presented a unique opportunity tosearch for redshifted neutron-capture lines from the surface of theneutron star. Such lines, if discovered, would strongly constrain theneutron star equation of state, motivating this search. An upper limiton the narrow, unredshifted line has been set at6.5×10-4 photons cm-2 s-1, whilewidth-dependent limits on a broadened, redshifted line are set in therange of (4.0-10.5)×10-4 photons cm-2s-1. To our knowledge, these are the first measured upperlimits on redshifted 2.2 MeV emission from an accreting neutron star.
| A Neutron Star with a Massive Progenitor in Westerlund 1
We report the discovery of an X-ray pulsar in the young, massiveGalactic star cluster Westerlund 1. We detected a coherent signal fromthe brightest X-ray source in the cluster, CXO J164710.2-455216, duringtwo Chandra observations on 2005 May 22 and June 18. The period of thepulsar is 10.6107(1) s. We place an upper limit to the period derivativeof P˙<2×10-10 s s-1, which impliesthat the spin-down luminosity is E˙<=3×1033 ergss-1. The X-ray luminosity of the pulsar isLX~3+10-2×1033(D/5kpc)2 ergs s-1, and the spectrum can be describedby a kT=0.61+0.02-0.02 keV blackbody with a radiusof Rbb=0.27+/-0.03(D/5 kpc) km. Deep infrared observationsreveal no counterpart with K<18.5, which rules out a binary companionwith M>1 Msolar. Taken together, the properties of thepulsar indicate that it is a magnetar. The rarity of slow X-ray pulsarsand the position of CXO J164710.2-455216 only 1.6 arcmin from the core ofWesterlund 1 indicates that it is a member of the cluster with>99.97% confidence. Westerlund 1 contains 07 V stars with initialmasses Mi~35 Msolar and >50 post-main-sequencestars that indicate the cluster is 4+/-1 Myr old. Therefore, theprogenitor to this pulsar had an initial mass Mi>40Msolar. This is the most secure result among a handful ofobservational limits to the masses of the progenitors to neutron stars.
| Physics of strongly magnetized neutron stars.
There has recently been growing evidence for the existence of neutronstars possessing magnetic fields with strengths that exceed the quantumcritical field strength of $4.4 \times 10^{13}$ G, at which thecyclotron energy equals the electron rest mass. Such evidence has beenprovided by new discoveries of radio pulsars having very high spin-downrates and by observations of bursting gamma-ray sources termedmagnetars. This article will discuss the exotic physics of thishigh-field regime, where a new array of processes becomes possible andeven dominant, and where familiar processes acquire unusual properties.We review the physical processes that are important in neutron starinteriors and magnetospheres, including the behavior of free particles,atoms, molecules, plasma and condensed matter in strong magnetic fields,photon propagation in magnetized plasmas, free-particle radiativeprocesses, the physics of neutron star interiors, and field evolutionand decay mechanisms. Application of such processes in astrophysicalsource models, including rotation-powered pulsars, soft gamma-rayrepeaters, anomalous X-ray pulsars and accreting X-ray pulsars will alsobe discussed. Throughout this review, we will highlight theobservational signatures of high magnetic field processes, as well asthe theoretical issues that remain to be understood.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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| Suzaku observations of iron lines and reflection in AGN
Initial results on the iron K-shell line and reflection component inseveral AGN observed as part of the Suzaku Guaranteed Time program arereviewed. This paper discusses a small sample of Compton-thin Seyfertsobserved to date with Suzaku; namely MCG -5-23-16, MCG -6-30-15, NGC4051, NGC 3516, NGC 2110, 3C 120 and NGC 2992. The broad iron K\alphaemission line appears to be present in all but one of these Seyfertgalaxies, while the narrow core of the line from distant matter isubiquitous in all the observations. The iron line in MCG -6-30-15 showsthe most extreme relativistic blurring of all the objects, the red-wingof the line requires the inner accretion disk to extend inwards towithin 2.2R_g of the black hole, in agreement with the XMM-Newtonobservations. Strong excess emission in the Hard X-ray Detector (HXD)above 10 keV is observed in many of these Seyfert galaxies, consistentwith the presence of a reflection component from reprocessing inCompton-thick matter (e.g. the accretion disk). Only one Seyfert galaxy(NGC 2110) shows neither a broad iron line nor a reflection component.The spectral variability of MCG -6-30-15, MCG -5-23-16 and NGC 4051 isalso discussed. In all 3 cases, the spectra appear harder when thesource is fainter, while there is little variability of the iron line orreflection component with source flux. This agrees with a simple twocomponent spectral model, whereby the variable emission is the primarypower-law, while the iron line and reflection component remainrelatively constant.
| A 0535+26 Begins Outburst
The Be/X-ray transient pulsar A 0535+26 is beginning another outburst.Observations with RXTE/PCA on December 15.4 and 17.3 show fluxes of 4and 28 mCrab respectively. These fluxes, which are based on the standard1 PCA rates (2.5-60 keV), are lower than at the same phase in theprevious 111 day orbit cycle (ATel #595 and #597).
| An additional Hα emission component in LS I +61°303: Further evidence for the Hα emission related to the neutron star
A long-term program has been established since 1992 to monitor more thana dozen of observable X-ray binaries. We present the long-termspectroscopic results of the Be/X-ray binary, LS I +61°303. TheHα emission line, usually observed as a double-peaked profile witha dominant red peak, varies noticeably during our program. While theblue peak of the Hα emission line decreases gradually, the redpeak increases considerably in 2002 October observational run andremains relatively unchanged in 2004 September run. We attribute thesevariations to the asymmetric perturbation in the Be envelope. Finally,we report on the discovery of a two-component structure in the Hαemission line when close to the apastron. In addition to the originaldouble-peaked Hα emission component, an additional emissioncomponent emerges at the center part of the emission line, which couldoriginate in the accretion disc around the neutron star.
| Hard Spectra of X-ray Pulsars from INTEGRAL Data
We present spectra for 34 accretion-powers X-ray pulsars and onemillisecond pulsar that were within the field of view of the INTEGRALobservatory over two years (December 2002 January 2005) of its in-orbitoperation and that were detected by its instruments at a statisticallysignificant level (> 8σ in the energy range 18 60 keV). Thereare seven recently discovered objects of this class among the pulsarsstudied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR J16358-4726, AXJ163904-4642, IGR J16465-4507, SAX/IGR J18027-2017, and AX J1841.0-0535.We have also obtained hard X-ray (>20 keV) spectra for theaccretion-powered pulsars RX J0146.9+6121, AX J1820.5-1434, and AXJ1841.0-0535 for the first time. We analyze the evolution of spectralparameters as a function of the intensity of the sources and comparethese with the results of previous studies.
| Constraining the Nature of the Galactic Center X-Ray Source Population
We searched for infrared counterparts to the cluster of X-ray pointsources discovered by Chandra in the Galactic center region (GCR). Whilethe sources could be white dwarfs, neutron stars, or black holesaccreting from stellar companions, their X-ray properties are consistentwith magnetic cataclysmic variables (CVs), or high-mass X-ray binaries(HMXBs) at low accretion rates. A direct way to decide between thesepossibilities, and hence between alternative formation scenarios, is tomeasure or constrain the luminosity distribution of the companions.Using infrared (J, H, K, Brγ) imaging, we searched forcounterparts corresponding to typical HMXB secondaries: spectral type B0V with K<15 at the GCR. We found no significant excess of brightstars in Chandra error circles, indicating that HMXBs are not thedominant X-ray source population and that they account for fewer than10% of the hardest X-ray sources.
| Suzaku detection of cyclotron line near 50 keV for A0535+26
We report on the Suzaku detection of a cyclotron resonance absorptionfeature from the transient binary X-ray pulsar A0535+26. Since themiddle of August, the Suzaku X-ray Observatory (launched on 2005 July10) has made regular observations using the X-ray telescope (XRT) plusX-ray CCD camera (XIS) system sensitive over 0.3-10 keV, and the HardX-ray detector (HXD) covering 10-600 keV. A0535+26 was observed withSuzaku for 20 ksec on 2005 September 14, and was clearly detected withboth instruments.
| RXTE confirms cyclotron line near 50 keV for A 0535+26
The cyclotron feature near 50 keV in the spectrum of A 0535+26 measuredwith Integral (Atel #601) is visible in the count rate spectra ofRXTE/HEXTE data from the current outburst. The feature is significantat the 17 sigma level in the 2.7-150 keV PCA/HEXTE energy spectrum fromobservations on August 28 between 13:55 and 14:54 UT. Using a MPLCUT(Coburn et. al. 2002, ApJ, 580, 394) continuum model and a Gaussianabsorption line model for the cyclotron feature, we find the followingline parameters: centroid energy 48.5+-0.7 keV, sigma 5.9+0.5-0.9 keV,and depth 0.75+-0.07.
| Integral observes possible cyclotron line at 47 keV for 1A 0535+262
The Be/X-ray binary 1A 0535+262 is known as the accreting X-ray pulsarwith the highest observed magnetic field. Usually the field strength isquoted 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 etal., 1995, ApJ 438, L25). Observations by HEXE and TTM on Mir/Kvant ofanother 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).
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Toro |
| Ascensione retta: | 05h38m54.57s |
| Declinazione: | +26°18'56.8" |
| Magnitudine apparente: | 9.199 |
| Moto proprio RA: | -2.7 |
| Moto proprio Dec: | -4.6 |
| B-T magnitude: | 9.761 |
| V-T magnitude: | 9.246 |
Cataloghi e designazioni:
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