Renewed IR and optical activity of SAX J2103.5+4545

ATel #6262; A. Camero-Arranz (IEEC/ICE), C. Zurita (IAC), J. Fabregat (University of Valencia), M. H. Finger (USRA), and V. Peris (University of Valencia) on behalf of a larger collaboration
on 24 Jun 2014; 10:44 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Ascension Camero-Arranz (camero@ice.cat)

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We report on recent multiwavelength observations of the binary system SAX J2103.5+4545. The IR and optical photometry were obtained with the 1.5-m TCS and 80-cm IAC80 telescopes at the Observatorio del Teide on Tenerife (Spain). They show an infrared enhancement of the counterpart CGS 03588-00834, with the brightness varying from J = 11.85±0.03 mag,H = 11.41±0.07 mag, and Ks = 11.29±0.08 mag (2013-09-11 01:49:26.400 UT; MJD 56546.076), to J = 11.16±0.03 mag, H = 10.73±0.03 mag, and Ks = 10.38±0.03 mag (2014-04-05 04:30:43.200 UT; MJD 56752.188). A similar behavior was observed during the 2012 episode (ATel #4187). The IR brightening of the system may be interpreted as reprocessing of matter ejected from the donor star, which in turn would provide the material for the Be disk formation. In addition, the optical magnitudes changed from being B=15.56±0.01 mag and V=14.559±0.007 mag (2013-09-19 22:43:40.800 UT; MJD 56554.947), to B=15.069±0.003 mag and V=13.926±0.002 mag (2014-06-05 03:50:24.000 UT; MJD 56813.160). Although the current behavior of this source so far resembles the activity displayed in 2012 (see ATels #4068 and #6019), the intensity in the BV filters is the brightest ever reported for this source.

Optical spectroscopic observations performed with the spectrograph located at the 51 cm telescope of the Observatorio de Aras de los Olmos of the University of Valencia on 2014-06-03 00:02:52.800 UT(MJD 56811.002) found the Hα line in emission. The equivalent width of this line was -1.5±1.0 Å. This finding supports the presence of a circumstelar disk around the Be star.

Recent X-ray observations by Swift/BAT also show a recent flux enhancement from the compact object of this system. INTEGRAL IBIS/ISGRI detected renewed X-ray activity from this source on 2014-05-20 and 2014-05-21 (ATel #6154). Fermi/GBM initially detected pulsations from the neutron star on 2014-04-12 (MJD 56759.4) with a frequency of 2.8473(3) mHz, changing to 2.8507(2) mHz on 2014-06-03 (MJD 56798.6).

GBM Pulsar Project