Near-infrared Brightening around the Periastron Passages of the Gamma-ray Binary PSR B1259$-$63 /LS 2883

TL;DR

This study observes near-infrared brightening around periastron in the gamma-ray binary PSR B1259-63/LS 2883, revealing disk dynamics influenced by tidal interactions during the orbit.

Contribution

It provides new near-infrared observational data of the binary during periastron and proposes a model linking disk changes to tidal torque effects.

Findings

NIR brightening occurs 12-17 days after periastron.

The NIR light curve shows a characteristic color-magnitude track.

Disk variation begins in outer regions, indicating a contraction-expansion cycle.

Abstract

The binary of the pulsar PSRB1259$-$63 and the Be star LS 2883 has been observed at the 2010 and 2014 periastron passages in the near-infrared (NIR) bands using the IRSF/SIRIUS and SIRPOL. The light curves in the J-,H-, and Ks-bands are almost identical in these periastron passages. A flare starts no later than 10 days before periastron and the maximum brightening of about 0.1 magnitude is observed 12--17 days after periastron. The rising part of the light curve is steeper and reaches a peak slightly earlier in the Ks-band than in the other bands, thus a characteristic track appears on the NIR color-magnitude diagram. The time lag between the NIR light curves indicates that the variation in the Be circumstellar disk first occurs in an outer region. We propose that the initial rapid contraction followed by the gradual expansion of the disk is evoked by the rapidly changing tidal torque around periastron and the resultant change of the optically thick area causes the observed NIR light curves.