Two classes of X-ray pulsars, the anomalous X-ray pulsars and the soft gamma-ray repeaters, have been recognized in the last decade as the most promising candidates for being magnetars: isolated neutron stars powered by magnetic energy. I review the observational properties of these objects, focussing on the most recent results, and their interpretation in the magnetar model. Alternative explanations, in particular those based on accretion from residual disks, are also considered. The possible relations between these sources and other classes of neutron stars and astrophysical objects are also discussed.

The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars

The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to the fine spectroscopy (2.5 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray ($3{-}35$ keV) and optical ( V -band, 550 nm) energy ranges. INTEGRAL carries two main gamma-ray instruments, the spectrometer SPI (Vedrenne et al. [CITE]) – optimized for the high-resolution gamma-ray line spectroscopy (20 keV–8 MeV), and the imager IBIS (Ubertini et al. [CITE]) – optimized for high-angular resolution imaging (15 keV–10 MeV). Two monitors, JEM-X (Lund et al. [CITE]) in the ($3{-}35$) keV X-ray band, and OMC (Mas-Hesse et al. [CITE]) in optical Johnson V -band complement the payload. The ground segment includes the Mission Operations Centre at ESOC, ESA and NASA ground stations, the Science Operations Centre at ESTEC and the Science Data Centre near Geneva. INTEGRAL was launched on 17 October 2002. The observing programme is well underway and sky exposure (until June 2003) reaches ~1800 ks in the Galactic plane. The prospects are excellent for the scientific community to observe the high energy sky using state-of-the-art gamma-ray imaging and spectroscopy. This paper presents a high-level overview of INTEGRAL.

The INTEGRAL Mission

We present a catalog of the 26 currently known magnetars and magnetar candidates. We tabulate astrometric and timing data for all catalog sources, as well as their observed radiative properties, particularly the spectral parameters of the quiescent X-ray emission. We show histograms of the spatial and timing properties of the magnetars, comparing them with the known pulsar population, and we investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties. We find the scale height of magnetars to be in the range 20–31pc, assuming they are exponentially distributed. This range is smaller than that measured for OB stars, providing evidence that magnetars are born from the most massive O stars. From the same fits, we find that the Sun lies ∼13–22pc above the Galactic plane, consistent with previous measurements. We confirm previously identified correlations between quiescent X-ray luminosity LX and magnetic field B, as well as X-ray spectral power-law index and B, and show evidence for an excluded region in a plot of LX vs. . We also present an updated kT versus characteristic age plot, showing magnetars and high-B radio pulsars are hotter than lower-B neutron stars of similar age. Finally, we observe a striking difference between magnetars detected in the the hard X-ray and radio bands; there is a clear correlation between the hard and soft X-ray flux, whereas the radio-detected magnetars all have low soft X-ray flux suggesting, if anything, that the two bands are anti-correlated. An online version of the catalog is located at http://www.physics.mcgill.ca/~pulsar/magnetar/main.html.

https://iopscience.iop.org/article/10.1088/0067-0049/212/1/6/pdf

The mcgill magnetar catalog

We present a catalog of the 26 currently known magnetars and magnetar candidates. We tabulate astrometric and timing data for all catalog sources, as well as their observed radiative properties, particularly the spectral parameters of the quiescent X-ray emission. We show histograms of the spatial and timing properties of the magnetars, comparing them with the known pulsar population, and we investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties. We find the scale height of magnetars to be in the range 20-31 pc, assuming they are exponentially distributed. This range is smaller than that measured for OB stars, providing evidence that magnetars are born from the most massive O stars. From the same fits, we find that the Sun lies ~13-22 pc above the Galactic plane, consistent with previous measurements. We confirm previously identified correlations between quiescent X-ray luminosity L_X and magnetic field B, as well as X-ray spectral power-law index Gamma and B, and show evidence for an excluded region in a plot of L_X vs. Gamma. We also present an updated kT versus characteristic age plot, showing magnetars and high-B radio pulsars are hotter than lower-B neutron stars of similar age. Finally, we observe a striking difference between magnetars detected in the the hard X-ray and radio bands; there is a clear correlation between the hard and soft X-ray flux, whereas the radio-detected magnetars all have low soft X-ray flux suggesting, if anything, that the two bands are anti-correlated. 
An online version of the catalog is located at this http URL

The McGill Magnetar Catalog

The rotation of more than 700 pulsars has been monitored using the 76-m Lovell Telescope at Jodrell Bank. Here we report on a new search for glitches in the observations, revealing 128 new glitches in the rotation of 63 pulsars. Combining these new data with those already published, we present a data base containing 315 glitches in 102 pulsars. The data base was used to study the glitch activity among the pulsar population, finding that it peaks for pulsars with a characteristic age τ c ∼ 10 kyr and decreases for longer values of τ c, disappearing for objects with τ c > 20 Myr. The glitch activity is also smaller in the very young pulsars (τ c 1 kyr). The cumulative effect of glitches, a collection of instantaneous spin-up events, acts to reduce the regular long-term spin-down rate |u ν| of the star. The percentage of |u ν| reversed by glitch activity was found to vary between 0.5 and 1.6 per cent for pulsars with spin-down rates |u ν| between 10 −14 and 3.2 × 10 −11 Hz s −1 , decreasing to less than 0.01 per cent at both higher and lower spin-down rates. These ratios are interpreted in terms of the amount of superfluid involved in the generation of glitches. In this context, the activity of the youngest pulsar studied, the Crab pulsar, may be explained by quake-like activity within the crust. Pulsars with low spin-down rates seem to exhibit mostly small glitches, matching well the decrease of their crustal superfluid. Through the analysis of glitch sizes, it was found that the particular glitching behaviour of PSR J0537−6910 and the Vela pulsar may be shared by most Vela-like pulsars. These objects present most of their glitches with characteristic frequency and frequency derivative jumps, occurring at regular intervals of time. Their behaviour is different from other glitching pulsars of similar characteristic age.

A study of 315 glitches in the rotation of 102 pulsars

We present a summary of the long-term evolution of various properties of the five non-transient anomalous X-ray pulsars (AXPs) 1E 1841–045, RXS J170849.0–400910, 1E 2259+586, 4U 0142+61, and 1E 1048.1–5937, regularly monitored with RXTE from 1996 to 2012. We focus on three properties of these sources: the evolution of the timing, pulsed flux, and pulse profile. We report several new timing anomalies and radiative events, including a putative anti-glitch seen in 1E 2259+586 in 2009, and a second epoch of very large spin-down rate fluctuations in 1E 1048.1–5937 following a large flux outburst. We compile the properties of the 11 glitches and 4 glitch candidates observed from these 5 AXPs between 1996 and 2012. Overall, these monitoring observations reveal several apparent patterns in the behavior of this sample of AXPs: large radiative changes in AXPs (including long-lived flux enhancements, short bursts, and pulse profile changes) are rare, occurring typically only every few years per source; large radiative changes are almost always accompanied by some form of timing anomaly, usually a spin-up glitch; only 20%-30% of timing anomalies are accompanied by any form of radiative change. We find that AXP radiative behavior at the times of radiatively loud glitches is sufficiently similar to suggest common physical origins. The similarity in glitch properties when comparing radiatively loud and radiatively silent glitches in AXPs suggests a common physical origin in the stellar interior. Finally, the overall similarity of AXP and radio pulsar glitches suggests a common physical origin for both phenomena.

https://iopscience.iop.org/article/10.1088/0004-637X/784/1/37/pdf

16 yr of RXTE Monitoring of Five Anomalous X-Ray Pulsars

We report on 8.7 and 7.6 yr of Rossi X-Ray Timing Explorer (RXTE) observations of the anomalous X-ray pulsars (AXPs) RXS J170849.0–400910 and 1E 1841–045, respectively. These observations have allowed us to study the long-term timing, pulsed flux, and pulse profile evolution of these objects. We report on four new glitches, one from RXS J170849.0–400910 and three from 1E 1841–045. With nearly all known persistent AXPs now seen to glitch, such behavior is clearly generic to this source class. We show that in terms of fractional frequency change, AXPs are among the most actively glitching neutron stars, with glitch amplitudes in general larger than in radio pulsars. However, in terms of absolute glitch amplitude, AXP glitches are unremarkable. Unlike radio pulsar glitches, AXP glitches can sometimes, though not always, be accompanied by radiative events. We show that the largest observed AXP glitches have recoveries that are unusual among those of radio pulsar glitches, with the combination of recovery time scale and fraction yielding changes in spin-down rates following the glitch similar to, or larger than, the long-term average. We also observed a large long-term fractional increase in the magnitude of the spin-down rate of 1E 1841–045, following its largest glitch, with $Δ d{ν }/d{ν } = 0.1$ -->. These observations are challenging to interpret in standard glitch models, as is the frequent occurence of large glitches given AXPs' high measured temperatures. We speculate that the stellar core may be involved in the largest AXP glitches.

Glitches in anomalous x-ray pulsars

We present a summary of the long-term evolution of various properties of the five non-transient Anomalous X-ray Pulsars (AXPs) 1E 1841-045, RXS J170849.0-400910, 1E 2259+586, 4U 0142+61, and 1E 1048.1-5937, regularly monitored with RXTE from 1996 to 2012. We focus on three properties of these sources: the evolution of the timing, pulsed flux, and pulse profile. We report several new timing anomalies and radiative events, including a putative anti-glitch seen in 1E 2259+586 in 2009, and a second epoch of very large spin-down rate fluctuations in 1E 1048.1-5937 following a large flux outburst. We compile the properties of the 11 glitches and 4 glitch candidates observed from these 5 AXPs between 1996 and 2012. Overall, these monitoring observations reveal several apparent patterns in the behavior of this sample of AXPs: large radiative changes in AXPs (including long-lived flux enhancements, short bursts, and pulse profile changes) are rare, occurring typically only every few years per source; large radiative changes are almost always accompanied by some form of timing anomaly, usually a spin-up glitch; only 20-30% of timing anomalies are accompanied by any form of radiative change. We find that AXP radiative behavior at the times of radiatively loud glitches is sufficiently similar to suggest common physical origins. The similarity in glitch properties when comparing radiatively loud and radiatively silent glitches in AXPs suggests a common physical origin in the stellar interior. Finally, the overall similarity of AXP and radio pulsar glitches suggests a common physical origin for both phenomena.

16 Years of RXTE Monitoring of Five Anomalous X-ray Pulsars

4U 0142+61 is one of the Anomalous X-ray Pulsars exhibiting hard X-ray emission above 10 keV discovered with INTEGRAL In this paper we present detailed spectral and temporal characteristics both in the hard X-ray (> 10 keV) and soft X-ray (<10 keV) domains obtained using data from INTEGRAL, XMM-Newton, ASCA and RXTE Accumulating data collected over four years with the imager IBIS-ISGRI aboard INTEGRAL, the time-averaged total spectrum shows a power-law like shape with photon index Gamma = 093 +/- 006 4U 0142+61 is detected up to 229 keV and the flux between 20 keV and 229 keV is (1501 +/- 082) x 10(-11) erg cm(-2) s(-1), which exceeds the energy flux in the 2-10 keV band by a factor of similar to 23 Using simultaneously collected data with the spectrometer SPI of INTEGRAL the combined total spectrum yields the first evidence for a spectral break above 100 keV Assuming a logparabolic function for the spectral shape above 20 keV the peak energy of 4U 0142+61 is 228(-41)(+65) keV There is no evidence for significant long-term time variability of the total emission from 4U 0142+61 Both the total flux and the spectral index are stable within the 17% level (1 sigma) Pulsed emission is measured with ISGRI up to 160 keV The 20-160 keV profile shows a broad double-peaked pulse with a 62 sigma detection significance The total pulsed spectrum can be described with a very hard power-law shape with a photon index G = 040 +/- 015 and a 20-150 keV flux of (268 +/- 134) x 10(-11) erg cm(-2) s(-1) To perform accurate phase-resolved spectroscopy over the total X-ray window, we produced pulse profiles in absolute phase for INTEGRAL-ISGRI, RXTE-PCA, XMM-Newton-PN and ASCA-GIS The two known pulses in all soft X-ray profiles below 10 keV are located in the same phases Three XMM-Newton observations in 2003-2004 show statistically identical profiles However, we find a significant profile morphology change between an ASCA-GIS observation in 1999 following a possible glitch of 4U 0142+61 This change can be accounted for by differences in relative strengths and spectral shapes (08-10 keV) of the two pulses The principle peak in the INTEGRAL pulse profile above 20 keV is located at the same phase as one of the pulses detected below 10 keV The second pulse detected with INTEGRAL is slightly shifted with respect to the second peak observed in the soft X-ray band We performed consistent phase-resolved spectroscopy over the total high-energy band and identify at least three genuinely different pulse components with different spectra The high level of consistency between the detailed results from the four missions is indicative of a remarkably stable geometry underlying the emission scenario Finally, we discuss the derived detailed characteristics of the high-energy emission of 4U 0142+61 in relation to three models for the non-thermal hard X-ray emission

/pdf/detailed-high-energy-characteristics-of-axp-4u-0142-61-multi-40evngn9pj.pdf

Detailed high-energy characteristics of AXP 4U 0142+61: Multi-year observations with INTEGRAL, RXTE, XMM-Newton, and ASCA

After three years of no unusual activity, Anomalous X-ray Pulsar 1E 1048.1 - 5937 reactivated in 2007 March. We report on the detection of a large glitch ({delta}{nu}/{nu} = 1.63(2) x 10{sup -5}) on 2007 March 26 (MJD 54185.9), contemporaneous with the onset of a pulsed-flux flare, the third flare observed from this source in 10 years of monitoring with the Rossi X-ray Timing Explorer (RXTE). Additionally, we report on a detailed study of the evolution of the timing properties, the pulsed flux, and the pulse profile of this source as measured by RXTE from 1996 July to 2008 January. In our timing study, we attempted phase-coherent timing of all available observations. We show that in 2001 a timing anomaly of uncertain nature occurred near the rise of the first pulsed flux flare; we show that a likely glitch ({delta}{nu}/{nu} = 2.91(9) x 10{sup -6}) occurred in 2002, near the rise of the second flare, and we present a detailed description of the variations in the spin down. In our pulsed flux study, we compare the decays of the three flares and discuss changes in the hardness ratio. In our pulse profile study, we show that the profile exhibited large more » variations near the peak of the first two flares, and several small short-term profile variations during the most recent flare. Finally, we report on the discovery of a small burst 27 days after the peak of the last flare, the fourth burst discovered from this source. We discuss the relationships between the observed properties in the framework of the magnetar model. « less

Rim Dib

Papers

16 yr of RXTE Monitoring of Five Anomalous X-Ray Pulsars

Glitches in anomalous x-ray pulsars

16 Years of RXTE Monitoring of Five Anomalous X-ray Pulsars

Detailed high-energy characteristics of AXP 4U 0142+61: Multi-year observations with INTEGRAL, RXTE, XMM-Newton, and ASCA

Rossi x-ray timing explorer monitoring of the anomalous x-ray pulsar 1e 1048.1 – 5937: long-term variability and the 2007 march event