X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity

Abstract

(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.

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. 3.2.6

References in corpus (13)

• Corona of Magnetars
• A Debris Disk Around An Isolated Young Neutron Star
• Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
• 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
• Distances to Anomalous X-ray Pulsars using Red Clump Stars
• Modelling mid-Z element atmospheres for strongly-magnetized neutron stars
• The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
• The Anatomy of a Magnetar: XMM Monitoring of the Transient Anomalous X-ray Pulsar XTE J1810-197
• Extinction Columns and Intrinsic X-ray Spectra of the Anomalous X-ray Pulsars
• Swift and Chandra confirm the intensity-hardness correlation of the AXP 1RXS J170849.0-400910
• Optical/Infrared Observations of the Anomalous X-ray Pulsar 1E 1048.1-5937 During Its 2007 X-Ray Flare
• Glitches in Anomalous X-ray Pulsars
• The Long-term Radiative Evolution of Anomalous X-ray Pulsar 1E 2259+586 after its 2002 Outburst

Cited by in corpus (26)

• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• Magnetar-like Emission from the Young Pulsar in Kes 75
• Resonant cyclotron scattering in magnetars' emission
• Timing and Flux Evolution of the Galactic Center Magnetar SGR J1745-2900
• Electrodynamics of Magnetars III: Pair Creation Processes in an Ultrastrong Magnetic Field and Particle Heating in a Dynamic Magnetosphere
• Repeated, Delayed Torque Variations Following X-ray Flux Enhancements in the Magnetar 1E1048.1$-$5937
• NuSTAR observations of X-ray bursts from the magnetar 1E 1048.1-5937
• A glitch and an anti-glitch in the anomalous X-ray pulsar 1E 1841-045
• Optical pulsations from the anomalous X-ray pulsar 1E 1048.1-5937
• Two new outbursts and transient hard X-rays from 1E 1048.1$-$5937
• Optical/Infrared Observations of the Anomalous X-ray Pulsar 1E 1048.1-5937 During Its 2007 X-Ray Flare
• Where are the magnetar binary companions? Candidates from a comparison with binary population synthesis predictions
• Pair Plasma in Super-QED Magnetic Fields and the Hard X-ray/Optical Emission of Magnetars
• A systematic study of soft X-ray pulse profiles of magnetars in quiescence
• New candidates for magnetar counterparts from a deep search with the Hubble Space Telescope
• Searching for X-ray Variability in the Glitching Anomalous X-ray Pulsar 1E 1841-045 in Kes 73
• X-Ray Observations of Magnetar SGR 0501+4516 from Outburst to Quiescence
• Activity from Magnetar Candidate 4U 0142+61: Bursts and Emission Lines
• Long-term XMM-Newton view of magnetar CXOU J010043.1$-$721134: Comprehensive spectral and temporal results
• Mapping the Surface of the Magnetar 1E 1048.1-5937 in Outburst and Quiescence Through Phase Resolved X-ray Spectroscopy
• A high-magnetic-field radio pulsar survey with Swift/XRT
• The Long-term Radiative Evolution of Anomalous X-ray Pulsar 1E 2259+586 after its 2002 Outburst
• 4XMM J175136.8-275858: A New Magnetar Candidate?
• The short bursts in SGR 1806-20, 1E 1048-5937 and SGR 0501+4516
• The Broad-band Noise Characteristics of Selected Anomalous X-Ray Pulsars and Soft Gamma-ray Repeaters
• The Fast Radio Burst-emitting magnetar SGR 1935+2154 -- proper motion and variability from long-term Hubble Space Telescope monitoring