摘要:

We review the observational properties of the so‐called “anomalous X‐ray pulsars,” a class of young neutron stars having properties very different from most of the population.RXTEhas provided observations that have made significant progress in our understanding of these sources, which like the “soft gamma repeaters,” are today thought to be young, isolated, ultrahigh magnetic field neutron stars, or “magnetars.” We briefly discuss the major outstanding questions in this area, and what sort of future X‐ray missions would be most likely to allow progress to be made. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781041

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We carried out a long‐term timing analysis of the Anomalous X‐ray Pulsar 1RXS J170849‐400910 based on archival observations made with the Rossi X‐ray Timing Explorer between January 1998 and May 2002. We detected a new, large glitch from this source which occurred ∼ 1.5 yr after a previous such event, already reported in the literature. The second glitch was much larger than the previous one and comparable to the largest glitches observed in radio pulsars (&Dgr;v/v∼ 4 × 10−6). Its recovery was best‐fit by an exponential with a timescale ∼ 50 d, plus an apparently unrecovered 1&percent; increase in the spin‐down rate of the source. This last result needs confirmation, as a recovery timescale longer than 1 yr cannot be ruled out as yet. Timing residuals after subtraction of the two glitches show a high stability of the spin‐down of 1RXS J170849‐400910 during the ∼ 5 yrs of monitoring, with an r.m.s. ≃ 130 ms ≃ 1.1 &percent; of the rotation period. The glitch properties of this source reveal remarkable peculiarities compared to those of radio pulsars. An analysis of the glitches of 1RXS J170849‐400910 in the light of glitch models seems to hint to the presence of peculiar sources of stress within AXPs, as expected in the magnetar model. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781042

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The newly discovered X‐ray transient XTE J1810‐197 exhibits almost all characteristics of magnetars. It possesses a relatively long spin period of 5.54 s and a rapid spin down rate of ≈ 10−11s s−1, while showing no evidence for Doppler shifts due to a binary companion. This yields a magnetar‐strength dipole fieldB= 3 × 1014G and a young characteristic age &tgr; ⩽ 7600 yr. The spectrum of the source is notably soft (photon index ≈ 4) and optical observations with the 1.5 mRussian‐TurkishOptical TelescopeRTT150revealed a limiting magnitude ofRc= 21.5, both consistent with those of Soft gamma repeaters and anomalous X‐ray pulsars. However, the source shows a significant flux decline for over nine months and is present in archivalASCAandROSATobservations at nearly two orders of magnitude fainter luminosity. Putting all evidence together shows that we have found the first confirmedtransientmagnetar. This suggests the presence of other unidentified transient magnetars in a state similar to XTE J1810‐197 in its inactive phase. The detection of such sources is one of the important areas in which future X‐ray timing missions can make a significant impact. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781043

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

An outburst of several tens of SGR‐like bursts was detected from the Anomalous X‐ray Pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile and spin down of the underlying X‐ray source. We present RXTE and XMM‐Newton observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode and identify recovery time scales for each. Specifically, we observe an X‐ray flux increase (pulsed and phase‐averaged) by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within ∼2 days during which the energy spectrum hardens considerably relative to the quiescent state of the source. The second component decays over the year following the glitch/outburst according to a power law in time with an exponent −0.22. The pulsed fraction decreased initially to ∼15&percent; RMS, but recovered rapidly to the pre‐outburst level of ∼23&percent; within the first three days. The pulse profile changed significantly during the outburst, and recovered almost fully within two months of the outburst. A glitch of size &Dgr;vmax/v= (4.24±0.11) × 10−6was observed in 1E 2259+586 that preceded the onset of the observed burst activity. The glitch could not be well fit with a simple partial exponential recovery. An additional exponential rise in frequency with a time scale of 15 days resulted in a significantly better fit to the data, however, a systematic drift in the phase of the pulse profile cannot be excluded as the cause for the apparent slow rise in frequency. The changes in the source properties of 1E 2259+586 during its 2002 outburst are shown to be qualitatively similar to changes seen during/following burst activity in two Soft Gamma Repeaters (SGRs), thus further solidifying the common nature of SGRs and AXPs as magnetars. Finally, the changes in persistent emission properties coincident with burst activity in 1E 2259+586 enabled us to infer previous burst active episodes from this and other AXPs. The non‐detection of these outbursts by all‐sky gamma‐ray instruments suggests that the number of active magnetar candidates in our Galaxy is larger than previously thought. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781044

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present a statistical analysis of the X‐ray bursts observed from the 2002 June 18 outburst of the Anomalous X‐ray Pulsar (AXP) 1E 2259+586, observed with the Proportional Counter Array aboard theRossi X‐ray Timing Explorer. We show that the properties of these bursts are similar to those of Soft Gamma‐Repeaters (SGRs). The similarities we find are: the burst durations follow a log‐normal distribution which peaks at 99 ms, the differential burst fluence distribution is well described by a power law of index −1.7, the burst fluences are positively correlated with the burst durations, the distribution of waiting times is well described by a log‐normal distribution of mean 47 s, and the bursts are generally asymmetric with faster rise than fall times. However, we find several quantitative differences between the AXP and SGR bursts. Specifically, there is a correlation of burst phase with pulsed intensity, the AXP bursts we observed exhibit a wider range of durations, the correlation between burst fluence and duration is flatter than for SGRs, the observed AXP bursts are on average less energetic than observed SGR bursts, and the more energetic AXP bursts have the hardest spectra — the opposite of what is seen for SGRs. We conclude that the bursts are sufficiently similar that AXPs and SGRs can be considered united as a source class yet there are some interesting differences that may help determine what physically differentiates the two closely related manifestations of neutron stars. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781045

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report on X‐ray monitoring of two isolated pulsars within the same RXTE field of view. PSR J1811‐1925 in the young supernova remnant G11.2‐0.3 has a nearly sinusoidal pulse profile with a hard pulsed spectrum (photon index &Ggr; ∼ 1.2). The pulsar is a highly efficient (∼ 1&percent; of spin‐down energy) emitter of 2–50 keV pulsed X‐rays despite having a fairly typicalB∼ 2 × 1012G magnetic field. PSR J1809‐1943/XTE J1810‐197 is a newly discovered slow (P= 5.54 s), apparently isolated X‐ray pulsar which increased in flux by a factor of 100 in 2003 January. Nine months of monitoring observations have shown a decrease in pulsed flux of ∼ 30&percent; without a significant change in its apparently thermal spectrum (kT∼ 0.7 keV) or pulse profile. During this time, the spin‐down torque has fluctuated by a factor of ∼ 2. Both the torque and the flux have remained steady for the last 3 months, at levels consistent with a magnetar interpretation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781046

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have analyzed 90 observations of the young pulsar B1509‐58 made by RXTE over 7.6 years.The pulse profile can be described as a combination of two systems. The first consists of two narrow components separated by 0.14 period with an amplitude ratio of 10:3; the second consists of a single broader component. The two systems appear to be shifting with respect to each other as a function of energy.We have derived a single timing ephemeris on the basis of the X‐ray observations, using terms up to the third derivative. There is no indication that a fourth derivative is required. The resulting value of the first braking index is consistent with that derived from radio observations, but the second braking index is twice its expected value. This casts some doubt on the significance of the pulsar’s characteristic age (1700 years).The phase residuals have been fit with sine components, resulting in an estimate of the proper motion (45±25 mas/yr at a position angle of 45±45°) and of masses and orbital radii (ranging from 0.7 to 2 AU and 0.25 to 2.5 earth masses) of planetary material — if that is the cause of these phase excursions. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781047

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

I provide a review of observations in the optical, UV (HST), and EUV (EUVEandChandraLETG) of the rapid periodic oscillations of nonmagnetic, disk‐accreting, high mass‐accretion rate cataclysmic variables (CVs), with particular emphasis on the dwarf nova SS Cyg in outburst. In addition, I drawn attention to a correlation, valid over nearly six orders of magnitude in frequency, between the frequencies of the quasi‐periodic oscillations (QPOs) of white dwarf, neutron star, and black hole binaries. This correlation identifies the high frequency quasi‐coherent oscillations (so‐called “dwarf nova oscillations”) of CVs with the kilohertz QPOs of low mass X‐ray binaries (LMXBs), and the low frequency and low coherence QPOs of CVs with the horizontal branch oscillations (or the broad noise component identified as such) of LMXBs. Assuming that the same mechanisms produce the QPOs of white dwarf, neutron star, and black hole binaries, this correlation has important implications for QPO models. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781048

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A great deal of emphasis on timing in theRXTEera has been on pushing toward higher and higher frequency phenomena, particularly kHz QPOs. However, the large areas of theRXTEpointed instruments provide another capability which is key for the understanding of accreting X‐ray pulsars — the ability to accumulate high quality spectra in a limited observing time. For the accreting X‐ray pulsars, with their relatively modest spin frequencies, this translates into an ability to study broad band spectra as a function of pulse phase. This is a critical tool, as pulsar spectra are strong functions of the geometry of the “accretion mound” and the observers’ viewing angle to the ∼1012G magnetic field. In particular, the appearance of “cyclotron lines” is sensitively dependent on the viewing geometry, which must change with the rotation of the star. These spectral features, seen in only a handful of objects, are quite important, as they give us our only direct measure of neutron star magnetic fields. Furthermore, they carry a great deal of information as to the geometry and physical conditions in the accretion mound. In this paper, we review the status of cyclotron line studies with theRXTE. We present an overview of phase‐averaged results and give examples of observations which illustrate the power of phase‐resolved spectroscopy. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781049

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

From determining the log(N)‐log(S) distribution of XRBs in the Milky Way, to testing radio/X‐ray correlations of microquasars and BHCs, studying long term variability, and acting as a trigger for observations of transient sources, the ASM on RXTE has proved an invaluable resource. I will briefly discuss some highlights of the many results that have been possible only because of the ASM. The fact that the number of papers per year (over 100) that have relied on ASM data has remained steady over the 8‐year lifetime of the RXTE is an indication of the enduring usefulness of all‐sky X‐ray monitoring. I argue that the permanent presence in space of an ASM‐like instrument is a major benefit to numerous active branches of astrophysics, that there is no substitute (ground‐based or in other parts of the electromagnetic spectrum) for this capability, and that the planning process for future missions ought to take into account the ongoing scientific need for all‐sky X‐ray monitoring. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781050

出版商:AIP    

年代:1904

数据来源: AIP