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Register a new userSignatures of Intra-binary shock emission in the black widow pulsar binary PSR J2241-5236
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We report on high-energy properties of the black widow pulsar PSR J2241$-$5236 in the X-ray and the Fermi-LAT (GeV gamma-ray) bands. In the LAT band, the phase-averaged gamma-ray light curve shows orbital modulation below $sim$1 GeV with a chance probability ($p$) monotonically decreasing with time to $psim 10^{-5}$. The peak of the light curve is near the superior conjunction of the pulsar (binary phase $phi_{rm B}approx 0.25$). We attribute the modulation to the intra-binary shock (IBS) emission and search for IBS signatures in the archival X-ray data. We find that the X-ray spectral fit requires a non-thermal component, which implies a possible IBS origin of the X-rays. We discuss our observations in the context of IBS scenarios.
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We present simultaneous multiwavelength observations of the 4.66 ms redback pulsar PSR J1048+2339. We performed phase-resolved spectroscopy with the Very Large Telescope (VLT) searching for signatures of a residual accretion disk or intra-binary shock emission, constraining the companion radial velocity semi-amplitude ($K_2$), and estimating the neutron star mass ($M_{rm NS}$). Using the FORS2-VLT intermediate-resolution spectra, we measured a companion velocity of $291 < K_2 < 348$ km s$^{-1}$ and a binary mass ratio of $0.209 < q < 0.250$. Combining our results for $K_2$ and $q$, we constrained the mass of the neutron star and the companion to $(1.0 < M_{rm NS} < 1.6){rm sin}^{-3}i,M_{odot}$ and $(0.24 < M_2 < 0.33){rm sin}^{-3}i,M_{odot}$, respectively, where $i$ is the system inclination. The Doppler map of the H$alpha$ emission line exhibits a spot feature at the expected position of the companion star and an extended bright spot close to the inner Lagrangian point. We interpret this extended emission as the effect of an intra-binary shock originating from the interaction between the pulsar relativistic wind and the matter leaving the companion star. The mass loss from the secondary star could be either due to Roche-lobe overflow or to the ablation of its outer layer by the energetic pulsar wind. Contrastingly, we find no evidence for an accretion disk. We report on the results of the SRT and the LOFAR simultaneous radio observations at three different frequencies (150 MHz, 336 MHz, and 1400 MHz). No pulsed radio signal is found in our search. This is probably due to both scintillation and the presence of material expelled from the system which can cause the absorption of the radio signal at low frequencies. Finally, we report on an attempt to search for optical pulsations using IFI+Iqueye mounted at the 1.2 m Galileo telescope at the Asiago Observatory.
We present optical time-resolved multi-band photometry of the black widow binary millisecond pulsar J2052+1219 using direct-imaging observations with the 2.1m telescope of Observatorio Astronomico Nacional San Pedro Martir, Mexico (OAN-SPM). The observations revealed a variable optical source whose position and periodicity P = 2.752h coincide with the pulsar coordinates and the orbital period obtained from radio timing. This allowed us to identify it with the binary companion of the pulsar. We reproduce light curves of the source modelling the companion heating by the pulsar and accounting for the system parameters obtained from the radio data. As a result, we independently estimate the distance to the system of 3.94(16) kpc, which agrees with the dispersion measure distance. The companion star size is 0.12-0.15 Rsun, close to filling its Roche lobe. It has a surface temperature difference of about 3000 K between the side facing the pulsar and the back side. We summarise characteristics of all black widow systems studied in the optical and compare them with the PSR J2052+1219 parameters derived from our observations.
B1957+20 is a millisecond pulsar located in a black widow type compact binary system with a low mass stellar companion. The interaction of the pulsar wind with the companion star wind and/or the interstellar plasma is expected to create plausible conditions for acceleration of electrons to TeV energies and subsequent production of very high energy {gamma} rays in the inverse Compton process. We performed extensive observations with the MAGIC telescopes of B1957+20. We interpret results in the framework of a few different models, namely emission from the vicinity of the millisecond pulsar, the interaction of the pulsar and stellar companion wind region, or bow shock nebula. No significant steady very high energy {gamma}-ray emission was found. We derived a 95% confidence level upper limit of 3.0 x 10 -12 cm -2 s -1 on the average {gamma}-ray emission from the binary system above 200 GeV. The upper limits obtained with MAGIC constrain, for the first time, different models of the high-energy emission in B1957+20. In particular, in the inner mixed wind nebula model with mono-energetic injection of electrons, the acceleration efficiency of electrons is constrained to be below ~(2-10)% of the pulsar spin down power. For the pulsar emission, the obtained upper limits for each emission peak are well above the exponential cut-off fits to the Fermi-LAT data, extrapolated to energies above 50 GeV. The MAGIC upper limits can rule out a simple power-law tail extension through the sub-TeV energy range for the main peak seen at radio frequencies.
We report the optical identification of the companion to the {it Fermi} black widow millisecond pulsar PSR J1544+4937. We find a highly variable source on Keck LRIS images at the nominal pulsar position, with 2 magnitude variations over orbital period in the B, g, R, and I bands. The nearly achromatic light curves are difficult to explain with a simply irradiated hemisphere model, and suggest that the optical emission is dominated by a nearly isothermal hot patch on the surface of the companion facing the pulsar. We roughly constrain the distance to PSR J1544+4937 to be between 2 and 5 kpc. A more reliable distance measurement is needed in order to constrain the composition of the companion.
One of the major challenges for pulsar timing array (PTA) experiments is the mitigation of the effects of the turbulent interstellar medium (ISM) from timing data. These can potentially lead to measurable delays and/or distortions in the pulse profiles and scale strongly with the inverse of the radio frequency. Low-frequency observations are therefore highly appealing for characterizing them. However, in order to achieve the necessary time resolution to resolve profile features of short-period millisecond pulsars, phase-coherent de-dispersion is essential, especially at frequencies below $300$ MHz. We present the lowest-frequency ($80$-$220$ MHz), coherently de-dispersed detections of one of the most promising pulsars for current and future PTAs, PSR J2241$-$5236, using our new beam-former software for the MWAs voltage capture system (VCS), which reconstructs the time series at a much higher time resolution of $sim 1 mu$s by re-synthesizing the recorded voltage data at $10$-kHz/$100$-$mu$s native resolutions. Our data reveal a dual-precursor type feature in the pulse profile that is either faint or absent in high-frequency observations from Parkes. The resultant high-fidelity detections have enabled dispersion measure (DM) determinations with very high precision, of the order of $(2$-$6)times10^{-6}$ $rm pc,cm^{-3}$, owing to the microsecond level timing achievable for this pulsar at the MWAs low frequencies. This underscores the usefulness of low-frequency observations for probing the ISM toward PTA pulsars and informing optimal observing strategies for PTA experiments.
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