Psr j0357+3205: The Tail of the Turtle

Abstract

Using a new XMM-Newton observation, we have characterized the X-ray properties of the middle-aged radio-quiet γ-ray pulsar J0357+3205 (named Morla) and its tail. The X-ray emission from the pulsar is consistent with a magnetospheric non-thermal origin plus a thermal emission from a hot spot (or hot spots). The lack of a thermal component from the whole surface makes Morla the coldest neutron star in its age range. We found marginal evidence for a double-peaked modulation of the X-ray emission. The study of the 9'-long tail confirmed the lack of extended emission near the pulsar itself. The tail shows a very asymmetric brightness profile and its spectrum lacks any spatial variation. We found the nebular emission to be inconsistent with a classical bow-shock, ram-pressure dominated pulsar wind nebula. We propose thermal bremsstrahlung as an alternative mechanism for Morla's tail emission. In this scenario, the tail emission comes from the shocked interstellar medium (ISM) material heated up to X-ray temperatures. This can fully explain the peculiar features of the tail, assuming a hot, moderately dense interstellar medium around the pulsar. For a bremsstrahlungemitting tail, we can estimate the pulsar distance to be between 300 and 900 pc. A pulsar velocity of ∼1900 km s −1 is required -which would make Morla the pulsar with the largest velocity -and high inclination angles (>70 • ) are preferred.We propose Morla's nebula as the first example of a new "turtle's tail" class of thermally-emitting nebulae associated to high velocity pulsars.

The Tale of the Two Tails of the Oldish PSR J2055+2539

“…Next, using the pulsar column density, we can get an estimate of its distance with respect to the edge of the Galaxy. Such an estimate could be refined if bright X-ray-emitting and optical- emitting stars (with known distances) were also present (see, e.g., Marelli et al 2013Marelli et al , 2014aMarelli et al , 2014b. The spatial resolution of this measurement is much higher than the one from the 21 cm H I sky survey of Kalberla et al (2005).…”

“…Much less obvious is another elongated extended emission protruding from J2055 thatis visible southeast to northwest. Unfortunately, this fainter secondary feature is heavily contaminated by bright point sources, hampering a classical analysis (see, e.g., Marelli et al 2013).…”

“…We note that the low-energetic J2055 is close to the death line for the production of e + -(responsible for polar heating) by curvature radiation photons, thus making this type of emission unlikely. A pulsar with comparable energetics, J0357+3205, shows reduced polar cap heating (Marelli et al 2013). The nonthermal luminosity of J2055 is in agreement with the empirical relation between the X-ray luminosity of rotation-powered pulsars and their spindown luminosity (Possenti et al 2002;Kargaltsev & Pavlov 2008b).…”

“…Taking into account the spectral best-fit values and following Marelli et al (2013), this implies an ISM temperature of ¶50,000 K, depending on the inclination of the nebula. The pulsar velocity along the plane of the sky would be ∼2300 km s −1 , one of the highest values for a pulsar.…”

“…One of the newly discovered pulsars, PSR J0357+3205 ), revealed a bright tail that cannot be interpreted in the framework of synchrotron PWNe, owingto the low energetics of the leading pulsar and to a peculiar shape (De Luca et al 2011). Alternatively, a new model for pulsar nebulae was proposed, involving bremsstrahlung thermal emission from the ISM, shocked by the supersonically moving pulsar, accounting for all the characteristics of the nebula (Marelli et al 2013). The cooldown time for this emission is orders of magnitude longer than for the synchrotron model, thus implying a lack of spectral variation along the tail.…”