199 research outputs found
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the Magnetar Candidate 1E 1048.1-5937
We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.Comment: 24 pages, 4 figures, submitted to the Astrophysical Journa
X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity
(Abridged) We report on new and archival X-ray and near-infrared observations
of the anomalous X-ray pulsar 1E 1048.1-5937 performed between 2001-2007 with
RXTE, CXO, Swift, HST, and VLT. During its ~2001-2004 active period, 1E
1048.-5937 exhibited two large, long-term X-ray pulsed-flux flares as well as
short bursts, and large (>10x) torque changes. Monitoring with RXTE revealed
that the source entered a phase of timing stability in 2004; at the same time,
a series of four simultaneous observations with CXO and HST in 2006 showed that
its X-ray flux and spectrum and near-IR flux, all variable prior to 2005,
stabilized. The near-IR flux, when detected by HST (H~22.7 mag) and VLT
(K_S~21.0 mag), was considerably fainter than previously measured. Recently, in
2007 March, this newfound quiescence was interrupted by a sudden flux
enhancement, X-ray spectral changes and a pulse morphology change, simultaneous
with a large spin-up glitch and near-IR enhancement. Our RXTE observations
revealed a sudden pulsed flux increase by a factor of ~3 in the 2-10 keV band.
In observations with CXO and Swift, we found that the total X-ray flux
increased much more than the pulsed flux, reaching a peak value of >7 times the
quiescent value (2-10 keV). With these recent data, we find a strong
anti-correlation between X-ray flux and pulsed fraction, and a correlation
between X-ray spectral hardness and flux. Simultaneously with the radiative and
timing changes, we observed a significant X-ray pulse morphology change such
that the profile went from nearly sinusoidal to having multiple peaks. We
compare these remarkable events with other AXP outbursts and discuss
implications in the context of the magnetar model and other models of AXP
emission.Comment: 13 pages (6 figures) in emulateapj style. Accepted for publication in
ApJ. New version includes referee's corrections; split Figure 1 into 2
figures; modified Figs. 4b and 6b; rearranged and renumbered of some figures
and sections; added an X-ray dataset; improved analysis of pulse morphology
and pulsed fraction; added paragraph to sec. 3.2.
The 2006-2007 Active Phase of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts,and Burst Spectral Features
After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in > 11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 0.4 - 1.8 x 10(exp 3) s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx 2 - 9 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus two emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4) x 10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. Within the framework of the magnetar model, the net spin-down of the star could be explained by regions of the superfluid that rotate. slower than the rest. The bursts, flux enhancements, and pulse morphology changes can be explained as arising from crustal deformations due to stresses imposed by the highly twisted internal magnetic field. However, unlike other AXP outbursts, we cannot account for a major twist being implanted in the magnetosphere
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