X-ray Measurement of the Spin-Down of Calvera: a Radio- and Gamma-ray-Quiet Pulsar

Abstract

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-dot = (3.19+/-0.08)e-15, which corresponds to spin-down luminosity E-dot = 6.1e35 erg/s, characteristic age tau_c = P/2P-dot = 2.9e5 yr, and surface dipole magnetic field strength B_s = 4.4e11 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 < 3.3e32 erg/s, which is less than that of any pulsar of comparable E-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.