Volume 564, April 2014
|Number of page(s)||6|
|Section||Stellar structure and evolution|
|Published online||11 April 2014|
Ioffe Physical-Technical Institute,
e-mail: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org, email@example.com; firstname.lastname@example.org
2 St. Petersburg State Polytechnical University, Politekhnicheskaya 29, 195251 St. Petersburg, Russia
3 Observatorio Astronómico Nacional SPM, Instituto de Astronomía, Universidad Nacional Autónomia de Mexico, Ensenada, BC, Mexico
Received: 8 September 2013
Accepted: 6 February 2014
Context. A middle-aged radio-quiet pulsar J0357+3205 was discovered in gamma rays with Fermi and later in X-rays with Chandra and XMM-Newton observatories. It produces an unusual thermally emitting pulsar wind nebula that is observed in X-rays.
Aims. Deep optical observations were obtained to search for the pulsar optical counterpart and its nebula using the Gran Telescopio Canarias (GTC).
Methods. The direct imaging mode in the Sloan g′ band was used. Archival X-ray data were reanalysed and compared with the optical data.
Results. No pulsar optical counterpart was detected down to g′ 281. No pulsar nebula was identified in the optical either. We confirm early results that the X-ray spectrum of the pulsar consists of a nonthermal power-law component of the pulsar magnetospheric origin dominating at high energies and a soft thermal component from the neutron star surface. Using magnetised, partially ionised hydrogen atmosphere models in X-ray spectral fits, we found that the thermal component can come from the entire surface of the cooling neutron star with a temperature of 36 eV, making it one of the coldest among cooling neutron stars known. The surface temperature agrees with the standard neutron star cooling scenario. The optical upper limit does not put any additional constraints on the thermal component, however it does imply a strong spectral break for the nonthermal component between the optical and X-rays as is observed in other middle-aged pulsars.
Conclusions. The thermal emission from the entire surface of the neutron star very likely dominates the nonthermal emission in the UV range. Observations of PSR J0357+3205 in this range are promising to put more stringent constraints on its thermal properties.
Key words: stars: neutron / pulsars: general
Based on observations made with the Gran Telescopio Canarias (GTC), instaled in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma under Programme GTC3-12BMEX.
The reduced optical imaging data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/564/A81
© ESO, 2014
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