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

Abstract

Context. PSR J1048-5832 is a young radio-pulsar that has recently been detected in γ-rays with Fermi, and also in X-rays with Chandra and XMM-Newton. It powers a compact pulsar wind nebula visible in X-rays and is in many ways similar to the Vela pulsar. Aims. We present deep optical observations made with the ESO Very Large Telescope to search for optical counterparts of the pulsar and its nebula and to explore their multi-wavelength emission properties. Methods. The data were obtained in the V and R bands and were compared with archival data in other spectral domains. Results. We do not detect the pulsar in the optical and derive informative upper limits of R 28. m 1 and V 28. m 4 for its brightness. Using a red-clump star method, we estimate an interstellar extinction towards the pulsar of A V ≈ 2 mag, which is consistent with the absorbing column density derived from X-rays. The respective distance agrees with the dispersion measure distance. We reanalysed the Chandra X-ray data and compared the dereddened upper limits with the unabsorbed X-ray spectrum of the pulsar. We find that regarding its optical-X-ray spectral properties this γ-ray pulsar is not distinct from other pulsars detected in both ranges. However, like the Vela pulsar, it is very inefficient in the optical and X-rays. Among a dozen optical sources overlapping with the pulsar X-ray nebula we find one with V ≈ 26. m 9 and R ≈ 26. m 3, whose colour is slightly bluer than that of the field stars and is consistent with the peculiar colours typical for pulsar nebula features. It positionally coincides with a relatively bright feature of the pulsar X-ray nebula, resembling the Crab wisp and is located in ∼2 from the pulsar. We suggest this source as a counterpart candidate to the feature. Conclusions. Based on the substantial interstellar extinction towards the pulsar and its optical inefficiency, additional optical studies should be carried out at longer wavelengths.

Observations of three young γ-ray pulsars with the Gran Telescopio Canarias

“…The limits on the optical luminosity Lopt and on Lopt/ Ė for PSR J0631+1036 and PSR J0633+0632 are comparable, for the assumed values of distance and interstellar ex-tinction, to those of the Vela-like pulsars, which are in the range ∼ 0.04-0.92 × 10 30 erg s −1 and 9.4 × 10 −8 -1.1 × 10 −6 , respectively. This confirms, on a broader sample, that pulsars in the age range 10-100 kyrs are fainter and less efficient in the optical than the Crab-like ones (see also, Danilenko et al 2013;Kirichenko et al 2015). The limits on the Fopt/FX and Fopt/Fγ ratios for both PSR J0631+1036 and PSR J0633+0632 are also quite similar, indicating that the optical emission always tends to be less than ≈ 10 −3 and ≈ 10 −6 of the X and γ-ray ones, respectively.…”

“…Among the new γ-ray pulsars discovered by Fermi, a candidate optical counterpart has been identified for PSR J0205+6449 (Moran et al 2013), whereas for PSR B0540−69 in the Large Magellanic Cloud, only recently detected as a γ-ray pulsar (Ackermann et al 2015), the optical counterpart has been known since the early 1990s (Caraveo et al 1992), following its discovery as an X-ray and optical pulsar (Seward et al 1984;Middleditch & Pennypacker 1985). Another handful of γ-ray pulsars have been observed after their discovery by Fermi, but not detected yet, with 10mclass telescopes: PSR J1357−6429 (Mignani et al 2011), PSR J1028−5819 (Mignani et al 2012), PSR J1048−5832 (Razzano et al 2013;Danilenko et al 2013), PSR J0007+7303 , PSR J0357+3205 (De Luca et al 2011;Kirichenko et al 2014), and PSR J2021+3651 (Kirichenko et al 2015). Recently, PSR J1357−6429 might have been identified in the near infrared (Zyuzin et al 2016).…”

The γ-ray Pulsar J0633+0632 in X-rays

“…In any case, the parameters of the X-ray non-thermal emission in Table 3 are not peculiar in comparison with those for other pulsars with similarĖ Danilenko et al 2013). In addition, in Table 3, we show J0633 γ -ray luminosities L psr γ and corresponding efficiencies η psr γ = L psr γ /Ė.…”

“…These values show some dependence 12 Danilenko et al on a choice of the spectral model because in the two models the inferred distance ranges are slightly different (Table 2). In any case, the parameters of the X-ray non-thermal emission in Table 3 are not peculiar in comparison with those for other pulsars with similarĖ Danilenko et al 2013). In addition, in Table 3, we show J0633 γ -ray luminosities L psr γ and corresponding efficiencies η psr γ = L psr γ /Ė.…”

Optical Observations of PSR J2021+3651 in the Dragonfly Nebula With the GTC

“…For the 90% distance upper limit D = 3.5 kpc, upper limits on the optical luminosity and effi--15ciency in the V band, assuming a flat spectrum, are log L Opt 29.9 [ erg s −1 ] and log η Opt −6.7, respectively. In Figure 4 we compare the obtained X-ray and optical efficiencies and luminosities with the data for other pulsars observed in both ranges (Danilenko et al 2013). According to Figure 4, we can conclude that PSR J2021+3651, like the Vela pulsar, is inefficient in these ranges as compared to other substantially younger and older pulsars.…”