Simultaneous Multi-band Radio & X-ray Observations of the Galactic Center Magnetar SGR 1745$-$2900

Abstract

We report on multi-frequency, wideband radio observations of the Galactic Center magnetar (SGR 1745$-$2900) with the Green Bank Telescope for $\sim$100 days immediately following its initial X-ray outburst in April 2013. We made multiple simultaneous observations at 1.5, 2.0, and 8.9 GHz, allowing us to examine the magnetar's flux evolution, radio spectrum, and interstellar medium parameters (such as the dispersion measure (DM), the scattering timescale and its index). During two epochs, we have simultaneous observations from the Chandra X-ray Observatory, which permitted the absolute alignment of the radio and X-ray profiles. As with the two other radio magnetars with published alignments, the radio profile lies within the broad peak of the X-ray profile, preceding the X-ray profile maximum by $\sim$0.2 rotations. We also find that the radio spectral index $\gamma$ is significantly negative between $\sim$2 and 9 GHz; during the final $\sim$30 days of our observations $\gamma \sim -1.4$, which is typical of canonical pulsars. The radio flux has not decreased during this outburst, whereas the long-term trends in the other radio magnetars show concomitant fading of the radio and X-ray fluxes. Finally, our wideband measurements of the DMs taken in adjacent frequency bands in tandem are stochastically inconsistent with one another. Based on recent theoretical predictions, we consider the possibility that the dispersion measure is frequency-dependent. Despite having several properties in common with the other radio magnetars, such as $L_{\text{X,qui}}/L_{\text{rot}}\lesssim 1$, an increase in the radio flux during the X-ray flux decay has not been observed thus far in other systems.

15 pages, 9 figures, 3 tables; accepted to ApJ

References in corpus (21)

• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• Transient pulsed radio emission from a magnetar
• Untwisting magnetospheres of neutron stars
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• The magnetar 1E 1547.0-5408: radio spectrum, polarimetry, and timing
• Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations
• Radio emission evolution, polarimetry and multifrequency single pulse analysis of the radio magnetar PSR J1622-4950
• Scatter broadening measurements of 124 pulsars at 327 MHz
• The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
• Outburst of the 2 s Anomalous X-ray Pulsar 1E 1547.0-5408
• Discovery of two pulsars towards the Galactic Centre
• Timing and Flux Evolution of the Galactic Center Magnetar SGR J1745-2900
• The fundamental plane for radio magnetars
• Radio spectrum of the AXP J1810-197 and of its profile components
• The analysis of the largest sample of multi-frequency pulsar scatter time estimates
• Pulsars with gigahertz-peaked spectra
• The X-ray outburst of the Galactic Centre magnetar SGR J1745-2900 during the first 1.5 year
• Flux-density spectral analysis for several pulsars and two newly-identified gigahertz-peaked spectra
• The effect of Pulse profile evolution on Pulsar Dispersion Measure
• Flux density measurements of GPS candidate pulsars at 610 MHz using interferometric imaging technique

Cited by in corpus (26)

• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• Magnetars
• The NANOGrav 12.5-year Data Set: Wideband Timing of 47 Millisecond Pulsars
• Radio disappearance of the magnetar XTE J1810-197 and continued X-ray timing
• Magnetars: a short review and some sparse considerations
• Wideband polarized radio emission from the newly revived magnetar XTE J1810$-$197
• Resonant Inverse Compton Scattering Spectra from Highly-magnetized Neutron Stars
• Detection of the magnetar SGR J1745-2900 up to 291 GHz with evidence of polarized millimetre emission
• Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900
• Chandra monitoring of the Galactic Centre magnetar SGR J1745-2900 during the initial 3.5 years of outburst decay
• The dynamic magnetosphere of Swift J1818.0$-$1607
• Dispersion by pulsars, magnetars, fast radio bursts and massive electromagnetism at very low radio frequencies
• Gigahertz-peaked spectra pulsars and thermal absorption model
• Radio Properties of Rotating Radio Transients: Single Pulse Spectral and Wait Time Analyses
• Simultaneous 2.25/8.60 GHz observations of the newly discovered magnetar -- Swift J1818.0-1607
• Observations of Radio Magnetars with the Deep Space Network
• Paving the way to simultaneous multi-wavelength astronomy
• The X-ray outburst of the Galactic Center magnetar over six years of Chandra observations
• Multi-frequency radio observations of the radio-loud magnetar XTE J1810-197
• High Frequency Radio Observations of Two Magnetars, PSR J1622$-$4950 and 1E 1547.0$-$5408
• VLA Observations of Single Pulses from the Galactic Center Magnetar
• Single-pulse observations of the Galactic Center magnetar PSR J1745$-$2900 at 3.1 GHz
• Relativistic scattering of a fast spinning neutron star by a massive black hole
• The uGMRT observations of three new GPS pulsars
• Phase-Resolved Spectroscopy of the Magnetar SGR J1745-2900 Based on Data from the NuSTAR Observatory
• A month of monitoring the new magnetar Swift J1555.2-5402 during an X-ray outburst