Long-term monitoring of PSR J2021+4026 in the heart of the Cygnus region with the Fermi Large Area Telescope unveiled a sudden decrease in flux above 100 MeV over a timescale shorter than a week. The "jump" was near MJD 55850 (2011 October 16), with the flux decreasing from (8.33+/-0.08) x 10(-10) erg cm(-2) s(-1) to (6.86+/-0.13) x 10(-10) erg cm(-2) s(-1). Simultaneously, the frequency spindown rate increased from (7.8 +/- 0.1) x 10(-13) Hz s(-1) to (8.1 +/- 0.1) x 10(-13) Hz s(-1). Significant (>5 sigma) changes in the pulse profile and marginal (<3 sigma) changes in the emission spectrum occurred at the same time. There is also evidence for a small, steady flux increase over the 3 yr preceding MJD 55850. This is the first observation at gamma-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed gamma-ray emission is due to a change in emission beaming and we speculate that it is precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current.
PSR J2021+4026 IN THE GAMMA CYGNI REGION: THE FIRST VARIABLE gamma-RAY PULSAR SEEN BY THE Fermi LAT
FUSCO, Piergiorgio;LOPARCO, FRANCESCO;RAINO', SILVIA;SPINELLI, Paolo;
2013-01-01
Abstract
Long-term monitoring of PSR J2021+4026 in the heart of the Cygnus region with the Fermi Large Area Telescope unveiled a sudden decrease in flux above 100 MeV over a timescale shorter than a week. The "jump" was near MJD 55850 (2011 October 16), with the flux decreasing from (8.33+/-0.08) x 10(-10) erg cm(-2) s(-1) to (6.86+/-0.13) x 10(-10) erg cm(-2) s(-1). Simultaneously, the frequency spindown rate increased from (7.8 +/- 0.1) x 10(-13) Hz s(-1) to (8.1 +/- 0.1) x 10(-13) Hz s(-1). Significant (>5 sigma) changes in the pulse profile and marginal (<3 sigma) changes in the emission spectrum occurred at the same time. There is also evidence for a small, steady flux increase over the 3 yr preceding MJD 55850. This is the first observation at gamma-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed gamma-ray emission is due to a change in emission beaming and we speculate that it is precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
