Volume 493, Number 1, January I 2009
|Page(s)||119 - 125|
|Section||Interstellar and circumstellar matter|
|Published online||20 November 2008|
Mid-infrared VISIR and Spitzer observations of the surroundings of the magnetar SGR 1806-20*
Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, IRFU/Service d'Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: [frahoui;chaty;pierrre-olivier.lagage]@cea.fr
2 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago de Chile
Accepted: 23 October 2008
Context. SGR 1806-20 is the soft gamma-ray repeater that has exhibited the highest activity since its discovery, including a giant flare in 2004 December 27. Previous studies of this source – probably a magnetar – have shown that it was associated with a massive star cluster embedded in a gas and dust cloud. Moreover, several stars in the cluster are peculiar hypergiants – luminous blue variable (LBV) and Wolf-Rayet stars – exhibiting strong and likely dusty stellar winds.
Aims. We aimed at studying the mid-infrared emission of the stars associated with the same cluster as SGR 1806-20, to detect variations that could be due to the high-energy activity of the magnetar through interaction with the dust. We also studied the morphology of the cloud close to the centre of the cluster.
Methods. We carried out mid-infrared observations of SGR 1806-20 and its environment, with the highest spatial resolution in this domain to date, using ESO/VISIR in 2005 and 2006, and we retrieved Spitzer/IRAC-MIPS archival data of the same field. We performed broadband photometry of three stars – LBV 1806-20, a WC9 and an O/B supergiant – on our VISIR images, as well as on the IRAC data. We then built and fitted their broadband spectral energy distributions with a combination of two absorbed black bodies, representing their stellar components, as well as a possible mid-infrared excess, to derive their physical parameters.
Results. We show that LBV 1806-20 and the WC9 star exhibit a mid-infrared excess, likely because of the presence of circumstellar dust related to their winds. We also show that only LBV 1806-20 has had a variable flux over a period of two years, variability that is due to its LBV nature rather than to a heating of the gas and dust cloud by the high-energy emission of SGR 1806-20. Finally, differences in the intrinsic absorptions of the three stars show an inhomogeneous structure of the density of the gas and dust cloud in the massive star cluster.
Key words: stars: neutron / infrared: stars / dust, extinction / open clusters and associations: general / stars: early-type / supergiants
© ESO, 2008
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.