Publication Date:
2016-12-30
Description:
We present the discovery of a variable optical counterpart to the unidentified gamma-ray source 3FGL J0212.1+5320 and argue that this is a new compact binary millisecond pulsar (MSP) candidate. We show 3FGL J0212.1+5320 hosts a semidetached binary with a 0.869 55 ± 0.000 15 d orbital period and an F6-type companion star at an estimated distance of D = 1.1 ± 0.2 kpc, with a radial velocity curve semi-amplitude K 2 = 214.1 ± 5.0 km s –1 and a projected rotational velocity of V sin ( i ) = 73.2 ± 1.6 km s –1 . We find a hard X-ray source at the same location with a 0.5–10 keV luminosity L X = 2.6 x 10 32 ( D /1.1 kpc) 2 erg s –1 , which strengthens the MSP identification. Our results imply a mass ratio q = M 2 / M 1 = 0.26 $^{+0.02}_{-0.03}$ if the companion star fills its Roche lobe, and q 0.26 in any case. This classifies 3FGL J0212.1+5320 as a ‘redback’ binary MSP; if its MSP nature is confirmed, this will be the brightest compact binary MSP in the optical band ( r '' ~= 14.3 mag) and will have the longest orbital period among Galactic field systems (nearly 21 h). Based on the light curve peak-to-peak amplitude ( r = 0.19 mag), we further suggest that the orbital inclination is high and the putative pulsar mass is close to canonical ( M 1 ~= 1.3–1.6 M ). Finally, we discuss the lack of heating signatures and asymmetric optical light curves in the context of other redback MSPs.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
