The Effects of Burst Activity on Soft Gamma Repeater Pulse Properties and Persistent Emission

Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and persistent emission during episodes of intense burst activity. SGR 1900+14 has undergone large flux increases following recent burst activity. Both SGR 1900+14 and SGR 1806-20 have shown significant changes in their pulse profile and spin-down rates during the last several years. The pulse profile changes are linked with the burst activity whereas the torque variations are not directly correlated with the bursts. Here, we review the observed dynamics of the pulsed and persistent emission of SGR 1900+14 and SGR 1806-20 during burst active episodes and discuss what implications these results have for the burst emission mechanism, the magnetic field dynamics of magnetars, the nature of the torque variability, and SGRs in general.Comment: 9 pages, Woods Hole 2001 GRB and SGR Conferenc

Control of erythroid differentiation: asynchronous expression of the anion transporter and the peripheral components of the membrane skeleton in AEV- and S13-transformed cells

Chicken erythroblasts transformed with avian erythroblastosis virus or S13 virus provide suitable model systems with which to analyze the maturation of immature erythroblasts into erythrocytes. The transformed cells are blocked in differentiation at around the colony-forming unit- erythroid stage of development but can be induced to differentiate in vitro. Analysis of the expression and assembly of components of the membrane skeleton indicates that these cells simultaneously synthesize alpha-spectrin, beta-spectrin, ankyrin, and protein 4.1 at levels that are comparable to those of mature erythroblasts. However, they do not express any detectable amounts of anion transporter. The peripheral membrane skeleton components assemble transiently and are subsequently rapidly catabolized, resulting in 20-40-fold lower steady-state levels than are found in maturing erythrocytes. Upon spontaneous or chemically induced terminal differentiation of these cells expression of the anion transporter is initiated with a concommitant increase in the steady- state levels of the peripheral membrane-skeletal components. These results suggest that during erythropoiesis, expression of the peripheral components of the membrane skeleton is initiated earlier than that of the anion transporter. Furthermore, they point a key role for the anion transporter in conferring long-term stability to the assembled erythroid membrane skeleton during terminal differentiation

Probing the birth of fast rotating magnetars through high-energy neutrinos

We investigate the high-energy neutrino emission expected from newly born magnetars surrounded by their stellar ejecta. Protons might be accelerated up to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds, leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a few days after the birth of magnetars, making the characteristic soft-hard-soft behavior. Detections would be important as a clue to the formation mechanism of magnetars, although there are ambiguities coming from uncertainties of several parameters such as velocity of the ejecta. Non-detections would also lead to useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR

The 2006 Outburst of the Magnetar CXOU J164710.2-455216

We report on data obtained with the Chandra, XMM-Newton, Suzaku and Swift X-ray observatories, following the 2006 outburst of the Anomalous X-ray Pulsar CXO J164710.2-455216. We find no evidence for the very large glitch and rapid exponential decay as was reported previously for this source. We set a 3 sigma upper limit on any fractional frequency increase at the time of the outburst of Delta nu/nu < 1.5 x 10^{-5}. Our timing analysis, based on the longest time baseline yet, yields a spin-down rate for the pulsar that implies a surface dipolar magnetic field of ~9 x 10^{13} G, although this could be biased high by possible recovery from an undetected glitch. We also present an analysis of the source flux and spectral evolution, and find no evidence for long-term spectral relaxation post-outburst as was previously reported.Comment: Submitted to Ap

The Dynamic Behavior of Soft Gamma Repeaters

Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and persistent emission during episodes of intense burst activity. Both SGR 1900+14 and SGR 1806-20 have shown significant changes in their spin-down rates during the last several years, yet the bulk of this variability is not correlated with burst activity. SGR 1900+14 has undergone large changes in flux and a dramatic pulse profile change following burst activity in 1998. The flux level of SGR 1627$-$41 has been decreasing since its only recorded burst activity. Here, we review the global properties of SGRs as well as the observed dynamics of the pulsed and persistent emission properties of SGR 1900+14, SGR 1806-20 and SGR 1627-41 during and following burst active episodes and discuss what implications these results have for the burst emission mechanism, the magnetic field dynamics of magnetars, the nature of the torque variability, and SGRs in general.Comment: Invited review to appear in "High Energy Studies of Supernova Remnants and Neutron Stars" (COSPAR 2002). 12 pages, 7 figure

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.

Spatial, Temporal and Spectral Properties of X-ray Emission from the Magnetar SGR~0501+4516

SGR~0501+4516 was discovered with the Swift satellite on 2008 August 22, after it emitted a series of very energetic bursts. Since then, the source was extensively monitored with Swift, the Rossi X-ray Timing Explorer (RXTE) and observed with Chandra and XMM-Newton, providing a wealth of information about its outburst behavior and burst induced changes of its persistent X-ray emission. Here we report the most accurate location of SGR~0501+4516 (with an accuracy of 0.11'') derived with Chandra. Using the combined RXTE, Swift/X-ray Telescope, Chandra and XMM-Newton observations we construct a phase connected timing solution with the longest time baseline (~240 days) to date for the source. We find that the pulse profile of the source is energy dependent and exhibits remarkable variations associated with the SGR~0501+4516 bursting activity. We also find significant spectral evolution (hardening) of the source persistent emission associated with bursts. Finally, we discuss the consequences of the SGR~0501+4516 proximity to the supernova remnant, SNR G160.9+2.6 (HB9).Comment: Accepted for publication in the Ap

The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005

On 2004 December 27, a highly-energetic giant flare was recorded from the magnetar candidate SGR 1806-20. In the months preceding this flare, the persistent X-ray emission from this object began to undergo significant changes. Here, we report on the evolution of key spectral and temporal parameters prior to and following this giant flare. Using the Rossi X-ray Timing Explorer, we track the pulse frequency of SGR 1806-20 and find that the spin-down rate of this SGR varied erratically in the months before and after the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for a discrete jump in spin frequency at the time of the December 27th flare (|dnu/nu| < 5 X 10^-6). In the months surrounding the flare, we find a strong correlation between pulsed flux and torque consistent with the model for magnetar magnetosphere electrodynamics proposed by Thompson, Lyutikov & Kulkarni (2002). As with the flare in SGR 1900+14, the pulse morphology of SGR 1806-20 changes drastically following the flare. Using the Chandra X-ray Observatory and other publicly available imaging X-ray detector observations, we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual magnetar persistent emission spectral model of a power-law plus a blackbody provides an excellent fit to the data. We confirm the earlier finding by Mereghetti et al. (2005) of increasing spectral hardness of SGR 1806-20 between 1993 and 2004. Contrary to the direct correlation between torque and spectral hardness proposed by Mereghetti et al., we find evidence for a sudden torque change that triggered a gradual hardening of the energy spectrum on a timescale of years. Interestingly, the spectral hardness, spin-down rate, pulsed, and phase-averaged of SGR 1806-20 all peak months before the flare epoch.Comment: 37 pages, 8 figures, 8 tables. Accepted for publication in ApJ. To appear in the Oct 20 2006 editio