Possible optical counterpart of PSR J1357−6429

Abstract

Context. PSR J1357−6429 is a Vela-like radio pulsar that has been recently detected in X-rays and γ-rays. It powers a compact taillike X-ray pulsar wind nebula and X-ray-radio plerion associated with an extended TeV source HESS J1356−645. Aims. We present our deep optical observations with the Very Large Telescope to search for an optical counterpart of the pulsar and its nebula. Methods. The observations were carried out using a direct imaging mode in the V, R, and I bands. We also analysed archival X-ray data obtained with Chandra and XMM-Newton. Results. In all three optical bands, we detect a point-like source with V = 27.3 ± 0.3, R = 25.52 ± 0.07, and I = 24.13 ± 0.05, whose position is within the 1σ error circle of the X-ray position of the pulsar, and whose colours are distinct from those of ordinary stars. We consider it as a candidate optical counterpart of the pulsar. If it is indeed the counterpart, its 5σ offset from the radio pulsar position, measured about 9 yr earlier, implies that the transverse velocity of the pulsar is in the range of 1600-2000 km s −1 at the distance of 2-2.5 kpc, making it the fastest moving pulsar known. The direction of the estimated proper motion coincides with the extension of the pulsar's X-ray tail, suggesting that this is a jet. The tentative optical luminosity and efficiency of the pulsar are similar to those of the Vela pulsar, which also supports the optical identification. However, the candidate undergoes an unusually steep dereddened flux increase towards the infrared with a spectral index α ν ∼ 5, that is not typical of optical pulsars. It implies a strong double-knee spectral break in the pulsar emission between the optical and X-rays. The reasons for the spectral steepness are unclear. It may be caused by a nebula knot projected onto the jet and strongly overlapping with the pulsar, as observed for the Crab, where the knot has a significantly steeper spectrum than the pulsar. We find no other signs of the pulsar nebula in the optical. Alternatively, the detected source may be a faint AGN, that has not yet been seen at other wavelengths. Conclusions. The position and peculiar colours of the detected source suggest that it is an optical counterpart of the pulsar. Further high spatial-resolution infrared observations can help to verify its real nature.

Deep optical imaging of theγ-ray pulsar J1048–5832 with the VLT

“…Comparing this together with our constraints of optical luminosity L opt < ∼ 10 28.9 erg s −1 and the efficiency of transformation of its spindown luminosityĖ to optical photons L opt /Ė < ∼ 10 −7.4 with the data available for other pulsars detected in the optical and X-rays (Zharikov et al 2004;Danilenko et al 2012), we conclude that, like the Vela pulsar, PSR J1048-5832 is rather inefficient in the optical and X-rays (Fig. 7).…”

THE SECOND FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS

“…In these circumstances, the favored techniques are unbinned tests for periodic signals. We use the H-test (de Jager et al 1989;de Jager & Büsching 2010), a statistical test for discarding the null hypothesis that a set of photon phases is uniformly distributed. For N γ gamma-rays, the H-test statistic is H ≡ max(Z 2 m − 4 × (m − 1), 1 m 20), with Z 2 m ≡ (2/N γ ) m k=1 α 2 k +β 2 k , and α k and β k the empirical trigonometric coefficients α k ≡ N γ i=1 sin(2πkφ i ) and β k ≡ N γ i=1 cos(2πkφ i ).…”

“…A quick-look survey carried out with 2-4 m class telescopes did not discover any potential counterparts (Collins et al 2011). Dedicated follow-up observations with either the Hubble Space Telescope or 8 m-class telescopes have been made in a few cases, e.g., for PSR B1055−52 (Mignani et al 2010b(Mignani et al , 2010a, PSR J1357−6429 Danilenko et al 2012), PSR J1048−5832 Razzano et al 2013), PSR J1028−5819 (Mignani et al 2012b), PSR J0205+6449 (Shearer et al 2013), and PSR J0007+7303 (Mignani et al 2013b). Apart from PSR B1055−52 for which an optical counterpart had been previously identified, new counterparts were detected only for PSR J1357−6429 and PSR J0205+6449.…”

Near-infrared observations of PSR J1357−6429

“…′′ 2 obtained by Danilenko et al (2012). We selected fifteen common isolated unsaturated stars as secondary astrometric standards in this frame and in the best-quality near-IR resulting image obtained in the K s band.…”

“…The J1357 field was observed in the optical V RI bands with the ESO Very Large Telescope (VLT) in 2009 (Mignani et al 2011;Danilenko et al 2012). Danilenko et al (2012) detected a point source in all these bands within 1σ uncertainties of the pulsar X-ray position and suggested it as a pulsar optical counterpart candidate.…”