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Register a new userHubble Space Telescope non-detection of PSR J2144-3933: the coldest known neutron star
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We report non-detections of the $sim 3times 10^8$ yr old, slow, isolated, rotation-powered pulsar PSR J2144$-$3933 in observations with the Hubble Space Telescope in one optical band (F475X) and two far-ultraviolet bands (F125LP and F140LP), yielding upper bounds $F_{rm F475X}< 22.7$ nJy, $F_{rm F125LP}< 5.9$ nJy, $F_{rm F140LP}< 19.5$ nJy, at the pivot wavelengths 4940 AA, 1438 AA and 1528 AA, respectively. Assuming a blackbody spectrum, we deduce a conservative upper bound on the surface (unredshifted) temperature of the pulsar of $T<42,000$ K. This makes PSR~J2144--3933 the coldest known neutron star, allowing us to study thermal evolution models of old neutron stars. This temperature is consistent with models with either direct or modified Urca reactions including rotochemical heating, and, considering frictional heating from the motion of neutron vortex lines, it puts an upper bound on the excess angular momentum in the neutron superfluid, $J<10^{44},mathrm{erg,s}$.
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The partially screened vacuum gap model (PSG) for the inner acceleration region in normal radio pulsars, a variant of the pure vacuum gap model, attempts to account for the observed thermal X-ray emission from polar caps and the subpulse drifting timescales. We have used this model to explain the presence of death lines, and extreme location of PSR J2144$-$3933 in the $P-dot{P}$ diagram. This model requires maintaining the polar cap near a critical temperature and the presence of non-dipolar surface magnetic field to form the inner acceleration region. In the PSG model, thermostatic regulation is achieved by sparking discharges which are a feature of all vacuum gap models. We demonstrate that non-dipolar surface magnetic field reduces polar cap area in PSR J2144$-$3933 such that only one spark can be produced and is sufficient to sustain the critical temperature. This pulsar has a single component profile over a wide frequency range. Single-pulse polarimetric observations and the rotating vector model confirm that the observers line-of-sight traverses the emission beam centrally. These observations are consistent with a single spark operating within framework of the PSG model leading to single-component emission. Additionally, single-pulse modulations of this pulsar, including lack of subpulse drifting, presence of single-period nulls and microstructure, are compatible with a single spark either in PSG or in general vacuum gap models.
We reinvestigate the radio pulsar ``death lines within the framework of two different types of polar cap acceleration models, i.e., the vacuum gap model and the space-charge-limited flow model, with either curvature radiation or inverse Compton scattering photons as the source of pairs. General relativistic frame-dragging is taken into account in both models. We find that the inverse Compton scattering induced space-charge-limited flow model can sustain strong pair production in some long-period pulsars, which allows the newly detected 8.5s pulsar PSR J2144-3933 to be radio loud, without assuming a special neutron star equation-of-state or ad hoc magnetic field configurations.
In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930$-$1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are characterized by short orbital periods, rapid spin periods and eccentric orbits. However, J1930$-$1852 has the longest spin period ($P_{rm spin}sim$185 ms) and orbital period ($P_{rm b}sim$45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930$-$1852, $dot{omega}=0.00078$(4) deg/yr, which implies a total mass (M$_{rm{tot}}=2.59$(4) M$_{odot}$) consistent with other DNS systems. The $2sigma$ constraints on M$_{rm{tot}}$ place limits on the pulsar and companion masses ($m_{rm p}<1.32$ M$_{odot}$ and $m_{rm c}>1.30$ M$_{odot}$ respectively). J1930$-$1852s spin and orbital parameters challenge current DNS population models and make J1930$-$1852 an important system for further investigation.
We present Spitzer Space Telescope 3.6 and 4.5 micron observations of the binary neutron star merger GW170817 at 43, 74, and 264 days post-merger. Using the final observation as a template, we uncover a source at the position of GW170817 at 4.5 micron with a brightness of 22.9+/-0.3 AB mag at 43 days and 23.8+/-0.3 AB mag at 74 days (the uncertainty is dominated by systematics from the image subtraction); no obvious source is detected at 3.6 micron to a 3-sigma limit of >23.3 AB mag in both epochs. The measured brightness is dimmer by a factor of about 2-3 times compared to our previously published kilonova model, which is based on UV, optical, and near-IR data at <30 days. However, the observed fading rate and color (m_{3.6}-m_{4.5}> 0 AB mag) are consistent with our model. We suggest that the discrepancy is likely due to a transition to the nebular phase, or a reduced thermalization efficiency at such late time. Using the Spitzer data as a guide, we briefly discuss the prospects of observing future binary neutron star mergers with Spitzer (in LIGO/Virgo Observing Run 3) and the James Webb Space Telescope (in LIGO/Virgo Observing Run 4 and beyond).
We report on detection of the double pulsar system J0737-3039 in the far-UV with the ACS/SBC detector aboard HST. We measured the energy flux F = 4.5+/-1.0e-17 erg cm-2s-1 in the 1250-1550 AA band, which corresponds to the extinction-corrected luminosity L~1.5e28 erg s-1 for the distance d=1.1 kpc and a plausible reddening E(B-V)=0.1. If the detected emission comes from the entire surface of one of the neutron stars with a 13 km radius, the surface blackbody temperature is in the range T~2-5e5 K for a reasonable range of interstellar extinction. Such a temperature requires an internal heating mechanism to operate in old neutron stars, or it might be explained by heating of the surface of the less energetic Pulsar B by the relativistic wind of Pulsar A. If the far-UV emission is non-thermal (e.g., produced in the magnetosphere of Pulsar A), its spectrum exhibits a break between the UV and X-rays.
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