Magnetar-like Emission from the Young Pulsar in Kes 75

We report detection of magnetar-like X-ray bursts from the young pulsar PSR J1846-0258, at the center of the supernova remnant Kes 75. This pulsar, long thought to be rotation-powered, has an inferred surface dipolar magnetic field of 4.9x10^13 G, higher than those of the vast majority of rotation-powered pulsars, but lower than those of the ~12 previously identified magnetars. The bursts were accompanied by a sudden flux increase and an unprecedented change in timing behavior. These phenomena lower the magnetic and rotational thresholds associated with magnetar-like behavior, and suggest that in neutron stars there exists a continuum of magnetic activity that increases with inferred magnetic field strength.Comment: 17 pages, 2 figures, accepted for publication in Science. Note: The content of this paper is embargoed until February 21, 200

Long-term X-ray changes in the emission from the anomalous X-ray pulsar 4U 0142+61

We present results obtained from X-ray observations of the anomalous X-ray pulsar (AXP) 4U 0142+61 taken between 2000-2007 using XMM-Newton, Chandra and Swift. In observations taken before 2006, the pulse profile is observed to become more sinusoidal and the pulsed fraction increased with time. These results confirm those derived using the Rossi X-ray Timing Explorer and expand the observed evolution to energies below 2 keV. The XMM-Newton total flux in the 0.5-10 keV band is observed to be nearly constant in observations taken before 2006, while an increase of ~10% is seen afterwards and coincides with the burst activity detected from the source in 2006-2007. After these bursts, the evolution towards more sinusoidal pulse profiles ceased while the pulsed fraction showed a further increase. No evidence for large-scale, long-term changes in the emission as a result of the bursts is seen. The data also suggest a correlation between the flux and hardness of the spectrum, with brighter observations on average having a harder spectrum. As pointed out by other authors, we find that the standard blackbody plus power-law model does not provide the best spectral fit to the emission from 4U 0142+61. We also report on observations taken with the Gemini telescope after two bursts. These observations show source magnitudes consistent with previous measurements. Our results demonstrate the wide range of X-ray variability characteristics seen in AXPs and we discuss them in light of current emission models for these sources.Comment: 10 pages, 9 figures, in emulateapj style. Submitted to Ap

Exceptional flaring activity of the anomalous X-ray pulsar 1E 1547.0-5408

(Abridged) We studied an exceptional period of activity of the anomalous X-ray pulsar 1E 1547.0-5408 in January 2009, during which about 200 bursts were detected by INTEGRAL. The major activity episode happened when the source was outside the field of view of all the INTEGRAL instruments. But we were still able to study the properties of 84 bursts detected simultaneously by the anti-coincidence shield of the spectrometer SPI and by the detector of the imager ISGRI. We find that the luminosity of the 22 January 2009 bursts of 1E 1547.0-5408 was > 1e42 erg/s. This luminosity is comparable to that of the bursts of soft gamma repeaters (SGR) and is at least two orders of magnitude larger than the luminosity of the previously reported bursts from AXPs. Similarly to the SGR bursts, the brightest bursts of 1E 1547.0-5408 consist of a short spike of ~100 ms duration with a hard spectrum, followed by a softer extended tail of 1-10 s duration, which occasionally exhibits pulsations with the source spin period of ~2 s. The observation of AXP bursts with luminosities comparable to the one of SGR bursts strengthens the conjecture that AXPs and SGRs are different representatives of one and the same source type.Comment: 9 pages, 10 figures, accepted to Astronomy & Astrophysic

High-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61 with ULTRACAM

We present high-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel Telescope. We detect 4U 0142+61 at magnitudes of i'=23.7+-0.1, g'=27.2+-0.2 and u'>25.8, consistent with the magnitudes found by Hulleman et al.(2004) and hence confirming their discovery of both a spectral break in the optical and a lack of long-term optical variability. We also confirm the discovery of Kern & Martin (2002) that 4U 0142+61 shows optical pulsations with an identical period (~8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is 29+-8%, 5-7 times greater than the 0.2-8 keV X-ray rms pulsed fraction. The optical and X-ray pulse profiles show similar morphologies and appear to be approximately in phase with each other, the former lagging the latter by only 0.04+-0.02 cycles. In conjunction with the constraints imposed by X-ray observations, the results presented here favour a magnetar interpretation for the anomalous X-ray pulsars.Comment: 6 pages, 4 figures, accepted for publication in MNRA

The 2009 outburst of magnetar 1E 1547-5408: Persistent radiative and burst properties

The magnetar 1E~1547$-$5408 recently exhibited two periods of outburst, beginning on 2008 October 3 and 2009 January 22. Here we present an analysis of the persistent radiative evolution and a statistical study of the burst properties during the 2009 outburst using the {\em Swift} X-ray Telescope (XRT). We find that the 1--10 keV flux increased by a factor of $\sim500$ and hardened significantly, peaking $\sim6$ hours after the onset of the outburst. The observed pulsed fraction exhibited an anti-correlation with phase-averaged flux. Properties of the several hundred X-ray bursts during the 2009 outburst were determined and compared to those from other magnetar outburst events. We find that the peaks of the bursts occur randomly in phase but that the folded counts that compose the bursts exhibit a pulse which is misaligned with the persistent pulse phase. We also report a correlation between burst hardness and flux. We compare the hardness-flux evolution of the persistent emission of both outbursts to those from other magnetars and find that although there does exist an overall trend, the degree of hardening for a given increase in flux is not uniform from source to source. These results are discussed in the context of previous results and within the magnetar model.Comment: 10 pages, 9 figures. Accepted for publication in Ap

Chandra and RXTE Observations of 1E 1547.0-5408: Comparing the 2008 and 2009 Outbursts

We present results from observations of the magnetar 1E 1547.0-5408 (SGR J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer (RXTE) following the source's outbursts in 2008 October and 2009 January. During the time span of the Chandra observations, which covers days 4 through 23 and days 2 through 16 after the 2008 and 2009 events, respectively, the source spectral shape remained stable, while the pulsar's spin-down rate in the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The lack of spectral variation suggests decoupling between magnetar spin-down and radiative changes, hence between the spin-down-inferred magnetic field strength and that inferred spectrally. We also found a strong anti-correlation between the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra data, but not in the pre-2008 measurements. We discuss these results in the context of the magnetar model.Comment: 4 figures, accepted for publication in Ap

The Long-term Radiative Evolution of Anomalous X-ray Pulsar 1E 2259+586 after its 2002 Outburst

We present an analysis of five X-ray Multi-Mirror Mission (XMM) observations of the anomalous X-ray pulsar (AXP) 1E 2259+586 taken in 2004 and 2005 during its relaxation following its 2002 outburst. We compare these data with those of five previous XMM observations taken in 2002 and 2003, and find the observed flux decay is well described by a power-law of index -0.69+/-0.03. As of mid-2005, the source may still have been brighter than preoutburst, and was certainly hotter. We find a strong correlation between hardness and flux, as seen in other AXP outbursts. We discuss the implications of these results for the magnetar model.Comment: 23 Pages, 4 figures, 3 tables, published on Ap