Candidate counterparts to the soft gamma-ray flare in the direction of LS I +61 303

Abstract

Context. A short duration burst reminiscent of a soft gamma-ray repeater/anomalous X-ray pulsar behaviour was detected in the direction of LS I +61 303 by the Swift satellite. While the association with this well known gamma-ray binary is likely, a different origin cannot be excluded. Aims. We explore the error box of this unexpected flaring event and establish the radio, near-infrared and X-ray sources in our search for any peculiar alternative counterpart. Methods. We carried out a combined analysis of archive Very Large Array radio data of LS I +61 303 sensitive to both compact and extended emission. We also reanalysed previous near infrared observations with the 3.5 m telescope of the Centro Astronómico Hispano Alemán and X-ray observations with the Chandra satellite. Results. Our deep radio maps of the LS I +61 303 environment represent a significant advancement on previous work and 16 compact radio sources in the LS I +61 303 vicinity are detected. For some detections, we also identify near infrared and X-ray counterparts. Extended emission features in the field are also detected and confirmed. The possible connection of some of these sources with the observed flaring event is considered. Based on these data, we are unable to claim a clear association between the Swift-BAT flare and any of the sources reported here. However, this study represents the most sophisticated attempt to determine possible alternative counterparts other than LS I +61 303.

Identification of the optical and near-infrared counterpart of GRS 1758-258

“…Sometimes, several observations can be combined to produce a single deep radio map and reanalyzed with an aim different from the one it was originally planned. Similar approaches have been conducted by our group for X-ray binaries showing how useful archival data can be (see e. g. Sánchez-Sutil et al 2008;Muñoz-Arjonilla et al 2009). …”

A Magnetar-Like Event From Ls I +61°303 and Its Nature as a Gamma-Ray Binary

“…2), translating in a count-rate of 0.0010 ± 0.0002 counts s −1 . No radio, infrared or optical counterparts have been detected for this source despite the deep archival observations covering this field of view (see Muñoz-Arjonilla et al 2009; this source corresponds to their #12 of Table 3). Thus, formally we can not exclude that the faint X-ray source detected by Chandra at the limit of the 1σ positional uncertainty of the burst (see Fig.…”

Radio pulsations from a neutron star within the gamma-ray binary LS I +61$^{\circ}$ 303

“…Finally, we ponder how likely could it be that within this spatial extent, FAST is actually detecting a different pulsar lying within the angular resolution (at the L-band) of FAST, ∼ 2.9 38 . For LS I +61 • 303 in particular, a similar issue appeared when analyzing the magnetar-like flares detected from the same region [10][11][12] . Swift, the X-ray satellite that observed them, had a ∼ 1.4 positional uncertainty and no other candidate different from LS I +61 • 303 was found.…”

“…A reanalysis of the flare data, as well as a subsequent 96 ks observations with the Chandra X-ray telescope, did not reveal any other candidate in that region either 13 . Neither it did a combined analysis of archive Very Large Array radio data nor near infrared observations 12 . These studies concluded that the simplest explanation is that LS I +61 • 303 was the origin of the flares.…”

“…LS I +61 • 303 also shows superorbital variability 3,[6][7][8][9] . A couple of energetic (∼ 10 37 erg s −1 ), short, magnetar-like bursts have been plausibly ascribed to it [10][11][12][13] . LS I +61 • 303's phenomenology has been put under theoretical scrutiny for decades, but the lack of certainty regarding the nature of the compact object in the binary has prevented advancing our understanding of the source.…”