IS SGR 0418+5729 INDEED A WANING MAGNETAR?

Journal Article · Thu Oct 20 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/740/2/105; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21587334

Turolla, R ^[1]; Zane, S ^[2]; Pons, J A ^[3]; Esposito, P ^[4]; Rea, N ^[5]

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1. Department of Physics, University of Padova, Via Marzolo 8, I-35131 Padova (Italy)
2. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT (United Kingdom)
3. Department de Fisica Aplicada, Universitat d'Alacant, Ap. Correus 99, 03080 Alacant (Spain)
4. INAF-Astronomical Observatory of Cagliari, Localita Poggio dei Pini, Strada 54, I-09012 Capoterra (Italy)
5. Institut de Ciencies de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5-parell, E-08193 Barcelona (Spain)

SGR 0418+5729 is a transient soft gamma-ray repeater which underwent a major outburst in 2009 June, during which the emission of short bursts was observed. Its properties appeared quite typical of other sources of the same class until long-term X-ray monitoring failed to detect any period derivative. The present upper limit on P-dot implies that the surface dipole field is B{sub p} {approx}< 7.5 x 10{sup 12} G, well below those measured in other soft gamma-ray repeaters (SGRs) and in the Anomalous X-ray Pulsars (AXPs), a group of similar sources. Both SGRs and AXPs are currently believed to be powered by ultra-magnetized neutron stars (magnetars, B{sub p} {approx} 10{sup 14}-10{sup 15} G). SGR 0418+5729 hardly seems to fit in such a picture. We show that the magneto-rotational properties of SGR 0418+5729 can be reproduced if this is an aged magnetar, {approx}1 Myr old, which experienced substantial field decay. The large initial toroidal component of the internal field required to match the observed properties of SGR 0418+5729 ensures that crustal fractures, and hence bursting activity, can still occur at the present time. The thermal spectrum observed during the outburst decay is compatible with the predictions of a resonant Compton scattering model (as in other SGRs/AXPs) if the field is low and the magnetospheric twist is moderate.

• OSTI ID: 21587334
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 740; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
GAMMA RADIATION
IONIZING RADIATIONS
NEUTRON STARS
PULSARS
RADIATIONS
STARS