X-RAY MEASUREMENT OF THE SPIN-DOWN OF CALVERA: A RADIO- AND GAMMA-RAY-QUIET PULSAR

We measure spin-down of the 59 ms X-ray pulsar Calvera by comparing the XMM-Newton discovery data from 2009 with new Chandra timing observations taken in 2013. Its period derivative is (P) over dot = (3.19 +/- 0.08) x 10(-15), which corresponds to spin-down luminosity (E) over dot = 6.1 x 10(35) erg s(-1), characteristic age tau(c) = P/2(P) over dot = 2.9 x 10(5) yr, and surface dipole magnetic field strength B-s = 4.4 x 10(11) G. These values rule out a mildly recycled pulsar, but Calvera could be an orphaned central compact object (anti-magnetar), with a magnetic field that was initially buried by supernova debris and is now reemerging and approaching normal strength. We also performed unsuccessful searches for high-energy gamma-rays from Calvera in both imaging and timing of >100 MeV Fermi photons. Even though the distance to Calvera is uncertain by an order of magnitude, an upper limit of d < 2 kpc inferred from X-ray spectra implies a gamma-ray luminosity limit of < 3.3 x 1032 erg s(-1), which is less than that of any pulsar of comparable (E) over dot. Calvera shares some properties with PSR J1740+1000, a young radio pulsar that we show by virtue of its lack of proper motion was born outside of the Galactic disk. As an energetic, high-Galactic-latitude pulsar, Calvera is unique in being undetected in both radio and gamma-rays to faint limits, which should place interesting constraints on models for particle acceleration and beam patterns in pulsar magnetospheres.