Multi-wavelength sources in the vicinity of LS I +61 303
Alvaro J. MuÃ±oz-Arjonilla (UJA), Victor Zabalza (UB), Josep MartÃ­ (UJA), Jorge A. Combi (UJA), Pedro L. Luque-Escamilla (UJA), Juan R. SÃ¡nchez-Sutil (FAEG, UJA), Josep M. Paredes (UB)
Recently, a SGR-like burst was detected by the Swift BAT on 2008 September 10th (de Pasquale et al. GCN 8209). The BAT on-board location of the burst was placed at 140 arcsec from LS I +61 303 with a 3 arcmin location error. The ground calculated location was refined to an error of 2.2 arcmin placed at 88 arcsec from the High Mass X-ray Binary (Barthelmy et al. GCN 8215). It has been proposed that this burst has been associated to magnetar-like activity linked to the presence of a young highly magnetized pulsar in the binary system (Dubus & Giebels, Atel #1715). In addition, an unusual X-ray activity (hard high flux and QPOs) on 2008 August 21 has been reported by Ray et al. (Atel #1730). Rea & Torres (ATel #1731) point out a population of faint X-ray sources in the vicinity of LS I +61 303 which might be the quiescent counterpart of a new transient magnetar. As part of an on-going multiwavelength study of the LS I +61 303 environment, and using archive Very Large Array (VLA) data (MuÃ±oz-Arjonilla et al. 2008, in prep.), we have obtained one of the deepest (rms 13 microJy) radio maps of the surroundings of this gamma-ray binary. In addition to LS I +61 303, our 6 cm VLA map displays 16 compact radio sources within a 10 arcmin field of view with a peak flux density above four times the rms noise. The relevant part of this map covering the Swift BAT error circles (GCN 8209 and 8215) can be found here. Three compact radio sources (labelled 03, 09 and 11) are located within or very close to the refined BAT location. Their 6 cm flux densities are measured to be 0.15, 0.17 and 0.17 mJy, respectively. If either the SGR-like burst behavior or the X-ray activity presenting QPOs are not connected with LS I +61 303, then these radio sources appear as potential alternative counterparts for such detections. Furthermore, we have obtained near infrared JHKs observations of the region with the 3.5 m telescope at CAHA. As a result, radio source 03 has a bright star-like counterpart with about J=11.4, H=10.3 and Ks=10.0 mag. Source 09 is also consistent with a J=19.2, H=17.8 and Ks=16.7 mag point like source. We have also obtained an X-ray source list from the Chandra ACIS-I obsid 6585 (performed on 2006 April 7th, Paredes et al. 2007, ApJ, 664, L39) with the CIAO tool wavdetect. We have used an exposure map to obtain photon fluxes and used wavelet scales according to the range of PSF sizes in the box shown. In the map of the region, the red crosses show the X-ray sources with a signal-to-noise-ratio above 3. Interestingly, one of these X-ray sources is consistent with the VLA radio source #11 quoted above. The X-ray flux of this source in the 0.3-10 keV band is (3.07+/-0.82)*10^-6 ph/cm^2/s. This radio/X-ray emitter appears thus as an intriguing object whose connection with the SGR-like behaviour cannot be excluded. This object was already reported in the VLA observations by Marti et al. (1998, A&A, 329, 951) with extended radio emission around it (source D in their Table 1). No near infrared counterpart was detected in our CAHA observations brighter than about Ks=18 mag. Further observations are required in order to finally solve the nature of radio sources reported in this telegram.
radio,infra-red,x-ray,gamma ray,binary,magnetar,pulsar,soft gamma-ray repeater,star,transient