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Register a new userDiscovery of synchronous X-ray and radio moding of PSR B0823+26
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Willem Hermsen Wim Hermsen
Publication date
2018
fields
Physics
and research's language is
English
Authors
W. Hermsen
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Simultaneous observations of PSR B0823+26 with ESAs XMM-Newton, the Giant Metrewave Radio Telescope and international stations of the Low Frequency Array revealed synchronous X-ray/radio switching between a radio-bright (B) mode and a radio-quiet (Q) mode. During the B mode we detected PSR B0823+26 in 0.2$-$2 keV X-rays and discovered pulsed emission with a broad sinusoidal pulse, lagging the radio main pulse by 0.208 $pm$ 0.012 in phase, with high pulsed fraction of 70$-$80%. During the Q mode PSR B0823+26 was not detected in X-rays (2 $sigma$ upper limit a factor ~9 below the B-mode flux). The total X-ray spectrum, pulse profile and pulsed fraction can globally be reproduced with a magnetized partially ionized hydrogen atmosphere model with three emission components: a primary small hot spot ($T$$sim$3.6$times10^6$ K, $R$$sim$17 m), a larger cooler concentric ring ($T$$sim$1.1$times10^6$ K, $R$$sim$280 m) and an antipodal hot spot ($T$$sim$1.1$times10^6 $ K, $R$$sim$100 m), for the angle between the rotation axis and line of sight direction $sim66^circ$. The latter is in conflict with the radio derived value of $(84pm0.7)^circ$. The average X-ray flux within hours-long B-mode intervals varied by a factor $pm$20%, possibly correlated with variations in the frequency and lengths of short radio nulls or short durations of weak emission. The correlated X-ray/radio moding of PSR B0823+26 is compared with the anti-correlated moding of PSR B0943+10, and the lack of X-ray moding of PSR B1822-09. We speculate that the X-ray/radio switches of PSR B0823+26 are due to variations in the rate of accretion of material from the interstellar medium through which it is passing.
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We present results of the analysis of interstellar scintillation in PSR B0823+26. Observations were conducted at a frequency of 1.7 GHz using the 32-m Torun Centre for Astronomy radio telescope. More than 50 observing sessions, lasting on average 10 h, were conducted between 2003 and 2006. We found interstellar scintillation parameters by means of dynamic spectrum analysis as well as structure function analysis of the flux density variations. We identified two distinctive time-scales, which we believe to be the time-scales of diffractive and refractive scintillation. Our results show that at the given frequency the diffractive time-scale in PSR B0823+26 is $tau_{diss} = 19.3^{+1.7}_{-1.6}$ min, the refractive time-scale is $tau_{riss} = 144 pm 23$ min and the decorrelation bandwidth is $B_{iss} = 81 pm 3$ MHz.
We report on a detailed analysis of the radio emission during the different modes of the pulsar J0826+2637 (B0823+26), observed using the Giant Meterwave Radio Telescope at 306-339 MHz observing frequencies. The pulsar profile has a postcursor and interpulse emission in addition to the main pulse. The single pulses showed the presence of nulling, periodic fluctuation in the emission as well as two prominent modes. In addition the pulsar also showed the presence of a null state where no emission was seen for roughly an hour which was immediately followed by a short duration ($sim$5 minutes) bright state termed the Q-bright state. The nulling varied significantly in the two modes, from a few percent nulls in B-mode to more than 90 percent nulling during the Q-mode. Additionally, the pulsar showed the presence of low level emission in both the interpulse and postcursor components when the main pulse nulled in B-mode. We detected periodic fluctuations in both the main pulse and postcursor during B-mode which were most likely a form of periodic amplitude modulation unrelated to subpulse drifting. We have also detected the appearance of periodicity during the transitions from the null to the burst states in the Q-mode, which was longer than the B-mode modulations. Our analysis further revealed a significant increase in the main pulse and post-cursor intensity during the transition from the Q-mode to the short duration Q-bright mode. On the other hand no commensurate variation was visible in the interpulse intensity.
PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over timescales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Here we report on the LOFAR discovery that PSR B0823+26 has a weak and sporadically emitting quiet (Q) emission mode that is over 100 times weaker (on average) and has a nulling fraction forty-times greater than that of the more regularly-emitting bright (B) mode. Previously, the pulsar has been undetected in the Q-mode, and was assumed to be nulling continuously. PSR B0823+26 shows a further decrease in average flux just before the transition into the B-mode, and perhaps truly turns off completely at these times. Furthermore, simultaneous observations taken with the LOFAR, Westerbork, Lovell, and Effelsberg telescopes between 110 MHz and 2.7 GHz demonstrate that the transition between the Q-mode and B-mode occurs within one single rotation of the neutron star, and that it is concurrent across the range of frequencies observed.
We report on simultaneous X-ray and radio observations of the mode-switching pulsar PSR B0943+10 obtained with the XMM-Newton satellite and the LOFAR, LWA and Arecibo radio telescopes in November 2014. We confirm the synchronous X-ray/radio switching between a radio-bright (B) and a radio-quiet (Q) mode, in which the X-ray flux is a factor ~2.4 higher than in the B-mode. We discovered X-ray pulsations, with pulsed fraction of 38+/-5% (0.5-2 keV), during the B-mode, and confirm their presence in Q-mode, where the pulsed fraction increases with energy from ~20% up to ~65% at 2 keV. We found marginal evidence for an increase in the X-ray pulsed fraction during B-mode on a timescale of hours. The Q-mode X-ray spectrum requires a fit with a two-component model (either a power-law plus blackbody or the sum of two blackbodies), while the B-mode spectrum is well fit by a single blackbody (a single power-law is rejected). With a maximum likelihood analysis, we found that in Q-mode the pulsed emission has a thermal blackbody spectrum with temperature ~3.4x10^6 K and the unpulsed emission is a power-law with photon index ~2.5, while during B-mode both the pulsed and unpulsed emission can be fit by either a blackbody or a power law with similar values of temperature and photon index. A Chandra image shows no evidence for diffuse X-ray emission. These results support a scenario in which both unpulsed non-thermal emission, likely of magnetospheric origin, and pulsed thermal emission from a small polar cap (~1500 m^2) with a strong non-dipolar magnetic field (~10^{14} G), are present during both radio modes and vary in intensity in a correlated way. This is broadly consistent with the predictions of the partially screened gap model and does not necessarily imply global magnetospheric rearrangements to explain the mode switching.
We present X-ray and radio monitoring observations of the gamma-ray binary PSR J2032+4127/MT91 213 during its periastron passage in late 2017. Dedicated Chandra, XMM-Newton,NuSTAR X-ray observations and VLA radio observations of this long orbit (50 years), 143 ms pulsar/Be star system clearly revealed flux and spectral variability during the passage. The X-ray spectrum hardened near periastron, with a significant decrease in the power-law photon index from Gamma ~ 2 to 1.2 and evidence of an increased absorption column density. We identified a possible spectral break at a few keV in the spectrum that suggests synchrotron cooling. A coincident radio and X-ray flare occurred one week after periastron, which is possibly the result of the pulsar wind interacting with the Be stellar disk and generating synchrotron radiation. However, a multi-wavelength comparison indicate that the X-ray and radio spectra cannot be simply connected by a single power-law component. Hence, the emission in these two energy bands must originate from different particle populations.
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