State-change in the "transition" binary millisecond pulsar J1023+0038
ATel #5513; B. W. Stappers (University of Manchester), A. Archibald (ASTRON), C. Bassa (ASTRON), J. Hessels (ASTRON), G. Janssen (ASTRON), V. Kaspi (McGill University), A. Lyne (University of Manchester), A. Patruno (University of Leiden), A. B. Hill (Stanford Linear Accelerator Lab).
on 25 Oct 2013; 18:32 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Ben Stappers (ben.stappers@manchester.ac.uk)
Subjects: Radio, X-ray, Gamma Ray, Neutron Star, Transient, Pulsar
We report a change in the state of PSR J1023+0038, a source which is
believed to be transitioning from an X-ray binary to an eclipsing
binary radio millisecond pulsar (Archibald et al. 2009, Science, 324,
1411). The system was known to contain an accretion disk in 2001 but
has shown no signs of it, or of accretion, since then, rather exhibiting
all the properties of an eclipsing binary millisecond radio pulsar
(MSP). Since its discovery as an MSP in June 2007 our regular
monitoring with the Lovell Telescope (LT) at Jodrell Bank and
Westerbork Synthesis Radio Telescope (WSRT) have shown it to be a
steady radio emitter, apart from periods of orbital phase when it is
eclipsed.
However this changed on June 23rd 2013, when the LT failed to detect
PSR J1023+0038 at 1.4 GHz. Observations with the WSRT at 350 MHz and
1380 MHz showed that it was present on June 15th 2013. Since then, we
have not detected PSR J1023+0038 in any of our, at least weekly, radio
pulsar observations, including a full-orbit scan with the Green Bank
Telescope (GBT) at 2.3 GHz (August 11th 2013) and a high-frequency
scan with the Arecibo telescope (AO) (August 28th 2013) at 5 GHz. The
corresponding pulsed flux density upper limits for typical
observations at the aforementioned frequencies, assuming a 10-sigma
detection threshold, are 0.8, 0.06, 0.016 and 0.003 mJy for the WSRT,
LT, GBT and AO observations respectively. This contrasts with
representative fluxes, away from eclipse, of 16 mJy and 0.9 mJy at 350
and 1380 MHz respectively. Thus, PSR J1023+0038 disappeared as an
observable radio pulsar sometime between 19-23 June 2013.
Despite the dramatic change in the observed pulsed radio flux, daily
Swift/BAT observations show non-detections with typical upper limits
of the order of 10^35 erg s^-1 on the 15-50 keV luminosity (for
power-law model with spectral index between 1.5 and 2, N_H ~ 4.3 x 10^20
cm^-2, and an assumed source distance of 1.3 kpc) since June 1 2013. The Swift/BAT was
unable to observe the source in the period August 23 2013 to September 9 2013 due to
Solar constraints. This low level X-ray activity rules out a high
accretion rate or a thermonuclear burst. Tam et al. (2010, ApJ, 724,
207) pointed out that PSR J1023+0038 was a gamma-ray source during
2008-2010, and it appears in the 2FGL catalog of sources (Nolan et
al. 2012, ApJS, 199, 31). A binned spectral analysis shows that the
100 MeV-300 GeV flux has increased from its long-term average of
1.07(13) x 10^-8 counts cm^-2 s^-1 to 4.9(9) x 10^-8 and 7(2) x 10^-8 counts cm^-2
sec^-1 during the periods from June 21 2013 to August 17 2013 and
August 17 2013 to September 15 2013, respectively. Thus J1023 has
brightened by a factor of ~5 in the gamma-rays since the radio
pulsations disappeared.
We encourage further multi-wavelength follow-up.
The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of
an international collaboration between NASA and DOE in the U.S. and
many scientific institutions across France, Italy, Japan and Sweden.