Simultaneous multifrequency radio observations of the Galactic Centre magnetar SGR J1745-2900

Abstract

We report on simultaneous observations of the magnetar SGR J1745-2900 at frequencies $\nu =2.54$ to $225\mathrm{GHz}$ using the Nancay 94-m equivalent, Effelsberg 100-m, and IRAM 30-m radio telescopes. We detect SGR J1745-2900 up to 225 GHz, the highest radio frequency detection of pulsed emission from a neutron star to date. Strong single pulses are also observed from 4.85 up to 154 GHz. At the millimetre band we see significant flux density and spectral index variabilities on time scales of tens of minutes, plus variability between days at all frequencies. Additionally, SGR J1745-2900 was observed at a different epoch at frequencies 296 to 472 GHz using the APEX 12-m radio telescope, with no detections. Over the period MJD 56859.83-56862.93 the fitted spectrum yields a spectral index of $⟨\alpha ⟩=-0.4\pm 0.1$ for a reference flux density $⟨S_{154}⟩=1.1\pm 0.2\mathrm{mJy}$ (with $S_{\nu }\propto {\nu }^{\alpha })$, a flat spectrum alike those of the other radio-loud magnetars. These results show that strongly magnetized neutron stars can be effective radio emitters at frequencies notably higher to what was previously known and that pulsar searches in the Galactic Centre are possible in the millimetre band.

5 pages, 3 figures. Published in MNRAS Letters; v2: minor typos corrected, one reference updated

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• Quasi-periodic sub-pulse structure as a unifying feature for radio-emitting neutron stars
• The dynamic magnetosphere of Swift J1818.0$-$1607
• Dispersion by pulsars, magnetars, fast radio bursts and massive electromagnetism at very low radio frequencies
• Multi-epoch searches for relativistic binary pulsars and fast transients in the Galactic Centre
• Detection of the magnetar XTE J1810-197 at 150 and 260 GHz with the NIKA2 Kinetic Inductance Detector camera
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• Submillimeter pulsations from the magnetar XTE J1810-197
• Detection of a dense group of hyper-compact radio sources in the central parsec of the Galaxy
• Coherent radio emission from a twisted magnetosphere after magnetar-quake
• High Frequency Radio Observations of Two Magnetars, PSR J1622$-$4950 and 1E 1547.0$-$5408
• VLA Observations of Single Pulses from the Galactic Center Magnetar
• $4-8\mathrm{GHz}$ Spectro-temporal Emission from the Galactic Center Magnetar $\mathrm{PSR}J1745-2900$
• X-ray burst and persistent emission properties of the magnetar SGR 1830-0645 in outburst
• Superdense beaming of axion dark matter in the vicinity of the light cylinder of pulsars
• The High Frequency Radio Emission of the Galactic Center Magnetar SGR J1745-29 During a Transitional Period
• ALMA discovery of Punctum -- a highly polarized mm source in nuclear starburst galaxy NGC 4945
• Retuning radio astronomy for axion dark matter with neutron stars
• Tera-Hertz Counterparts to Fast Radio Bursts from Coherent Cherenkov Radiation by Tilted Bunches