The launch of the Large Area Telescope (LAT) onboard
One widely accepted version for the evolutionary scenario of fast-spinning millisecond pulsars (MSPs) is that an old neutron star has been spun up to a spin period on the order of millisecond via accretion from a companion which transferred mass and angular momentum to the pulsar. This process is usually dubbed ‘recycling’. Once the accretion has halted at some point, strongly magnetized relativistic pulsar wind will possibly carry away the pulsar rotational energy and angular momentum, meanwhile ablate and eventually evaporate its companion. The fact that the pulsar destroys what spins it up gave rise to the name ‘Black Widow’ pulsar. Our target, 2FGL J2339.7-0531, is a prototype of this sort. Studying such “near-death experience”' of these binary systems provides a wealth of information not only on the evolutionary history of isolated MSPs whose companion were gone but also on the physical details of the pulsars high energy emission properties. Multiwavelength identifications will also be of great help in understanding the radiative mechanism of such system. Up to now, all
2. MULTIWAVELENGTH OBSERVATIONS
In Kong et al. (2012), identification of lower energy counterpart of this
[Fig. 1.] Composite light curve of 2FGL J2339.7-0531. All data are folded with a Lomb-Scargle period of 4.6343 hour. The phase zero is arbitrarily defined as 55500.3867 MJD.
star from the USNO catalog. We then carried out an intensive optical monitoring campaign first with the MITSuME 50 cm telescope located at Akeno Observatory in Japan from 55452.62629 to 55521.53568 MJD. MITSuME is equipped with a tricolor camera that can perform simultaneous imaging in the g', R, and I bands. After approximately 40 days, we followed-up this source with the One-meter Telescope at Lulin Observatory in Taiwan for two nights in a row for Johnson V band and white light respectively (55494.61923- 55495.67129 MJD and 55500.43791-55501.69024 MJD) for consecutive 2 minute exposures. This optical source was then observed a few days later in white light again with the 0.8 m Tenagra Telescope in Arizona (55511.07752-55511.26798 MJD) but this time for consecutive 5 minute exposures. Lastly, we used data from Infrared Survey Facility of South African Astronomical Observatory to obtain some infrared photometry for simultaneous J, H, and K
We make use of our photometric measurement to place constraints on the orbital parameters of 2FGL J2339.7-0531 by using the ELC code of Orosz & Hauschildt (2000). This code has the ability to model binary systems including treatment of accretion disk, reflection effect, with more variety in the ways one can specify the system geometry. This code also deals with the effect of companion illumination (‘X-ray heating’) and outputs modeled light curves. We are currently excluding white light measurement since the white light calibration for the zero point magnitude is not very accurate because all the catalogs use filters. We note that in a poster presentation of Schoeder et al. in the Fourth International Fermi Symposium (2012) for another black widow system 2FGL J2215.7+5135, the amplitude of
[Fig. 2.] Composite light curve of 2FGL J2339.7-0531 along with the ELC modeling result. Timing ephemeris is the same as in Fig. 1.
the modulation and peak intensity of their observations performed between 2010-2011 are both larger than our measurement performed in 2012. Similar feature was also observed for the optical counterpart of 1FGL J1311.7- 3429 which shows significant epoch to epoch variablity up to > 1 mag and 0.5 mag respectively over a span of two months (Kataoka et el. 2012). This might be an important implication that the system parameters change as the binary system evolves and we are actually witnessing the timeevolution of the stripping of the companion. We therefore propose to fit these lightcurves separately as different groups: first with observations in between 55450-55500 MJD, and then with those Ishigaki observations performed in between 55833.75618--55835.07004 MJD, in order to trace the system evolution. For the fits, we adjust the effective temperature (Teff) of the companion, the mass ratio (Q), and the inclination angle (
Shown in Fig. 2 is the ELC modeling result of the two epochs. Comparing the fitted parameters of two epochs we suggest that the system switched from Teff = 5500 K to Teff = 5300 K, and from