Discovery of 59 ms pulsations from 1RXS J141256.0+792204 (Calvera)

We report on the results of a multi-wavelength study of the compact object candidate 1RXS J141256.0+792204 (Calvera). Calvera was observed in the X-rays with XMM-Newton/EPIC twice for a total exposure time of ~50 ks. The source spectrum is thermal and well reproduced by a two-component model composed of either two (absorbed) hydrogen atmosphere models or two blackbodies with temperatures kT1~ 55/150 eV, kT2~ 80/250 eV, respectively (as measured at infinity). Evidence was found for an absorption feature at ~0.65 keV while no power-law high-energy tail is statistically required. Using pn and MOS data we discovered pulsations in the X-ray emission at a period P = 59.2 ms. The detection is highly significant (≳11σ), and unambiguously confirms the neutron star nature of Calvera. The pulse profile is nearly sinusoidal, with a pulsed fraction of ~18 per cent. We looked for the timing signature of Calvera in the Fermi Large Area Telescope (LAT) data base and found a significant (~5σ) pulsed signal at a period coincident with the X-ray value. The gamma-ray timing analysis yielded a tight upper limit on the period derivative, s s-1 ( erg s-1, B <5 × 1010 G for magneto-dipolar spin-down). Radio searches at 1.36 GHz with the 100-m Effelsberg radio telescope yielded negative results, with a deep upper limit on the pulsed flux of 0.05 mJy. Diffuse, soft (