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تسجيل مستخدم جديدMulti-wavelength observations of 3FGL J2039.6-5618: a candidate redback millisecond pulsar
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We present multi-wavelength observations of the unassociated gamma-ray source 3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source gamma-ray properties suggest that it is a pulsar, most likely a millisecond pulsar, for which neither radio nor $gamma$-ray pulsations have been detected yet. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several candidate X-ray counterparts within/close to the gamma-ray error box. The brightest of these X-ray sources is variable with a period of 0.2245$pm$0.0081 d. Its X-ray spectrum can be described by a power law with photon index $Gamma_X =1.36pm0.09$, and hydrogen column density $N_{rm H} < 4 times 10^{20}$ cm$^{-2}$, which gives an unabsorbed 0.3--10 keV X-ray flux of $1.02 times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. Observations with the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) discovered an optical counterpart to this X-ray source, with a time-average magnitude $gsim 19.5$. The counterpart features a flux modulation with a period of 0.22748$pm$0.00043 d that coincides, within the errors, with that of the X-ray source, confirming the association based on the positional coincidence. We interpret the observed X-ray/optical periodicity as the orbital period of a close binary system where one of the two members is a neutron star. The light curve profile of the companion star, with two asymmetric peaks, suggests that the optical emission comes from two regions at different temperatures on its tidally-distorted surface. Based upon its X-ray and optical properties, we consider this source as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to be a new redback system.
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We present a multi-wavelength study of the unidentified Fermi object, 3FGL J0212.1+5320. Within the 95% error ellipse, Chandra detects a bright X-ray source (i.e., F(0.5-7keV) = 1.4e-12 erg/cm^2/s), which has a low-mass optical counterpart (M < 0.4 M
sun and T ~ 6000 K). A clear ellipsoidal modulation is shown in optical/infrared at 20.87 hours. The gamma-ray properties of 3FGL J0212.1+5320 are all consistent with that of a millisecond pulsar, suggesting that it is a gamma-ray redback millisecond pulsar binary with a low-mass companion filling > 64% of the Roche-lobe. If confirmed, it will be a redback binary with one of the longest orbital periods known. Spectroscopic data taken in 2015 from the Lijiang observatory show no evidence of strong emission lines, revealing that the accretion is currently inactive (the rotation-powered pulsar state). This is consistent with the low X-ray luminosities (Lx ~ 10^32 erg/s) and the possible X-ray modulation seen by Chandra and Swift. Considering that the X-ray luminosity and the high X-ray-to-gamma-ray flux ratio (8%) are both comparable to that of the two known gamma-ray transitional millisecond pulsars, we suspect that 3FGL J0212.1+5320 could be a potential target to search for future transition to the accretion active state.
Linares et al. (2016) obtained quasi-simultaneous g, r and i-band light curves and an absorption line radial velocity curve of the secondary star in the redback system 3FGL J0212.1+5320. The light curves showed two maxima and minima primarily due to
the secondary stars ellipsoidal modulation, but with unequal maxima and minima. We fit these light curves and radial velocities with our X-ray binary model including either a dark solar-type star spot or a hot spot due to off-centre heating from an intrabinary shock, to account for the unequal maxima. Both models give a radial velocity semi-amplitude and rotational broadening that agree with the observations. The observed secondary stars effective temperature is best matched with the value obtained using the hot spot model, which gives a neutron star and secondary star mass of $M_{rm 1}$=1.85$^{+0.32}_{-0.26}$ $M_{odot}$and $M_{rm 2}$=0.50$^{+0.22}_{-0.19}$ $M_{odot}$, respectively.
We have discovered a new candidate redback millisecond pulsar binary near the center of the error ellipse of the bright unassociated Fermi-LAT $gamma$-ray source 4FGL J0940.3-7610. The candidate counterpart is a variable optical source that also show
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