On-going radio observations of PSR J1745-2900 at Effelsberg, Nancay, and Jodrell Bank: flux density estimates, polarisation properties, spin-down measurement, and the highest dispersion measure measured.

ATel #5058; Ralph Eatough (Max-Planck-Institut fuer Radioastronomie: MPIfR), Ramesh Karuppusamy (MPIfR), David Champion (MPIfR), Evan Keane (Jodrell Bank Centre for Astrophysics: JBCA), KJ Lee (MPIfR), Michael Kramer (MPIfR), Bernd Klein (MPIfR), Alex Kraus (MPIfR), Cees Bassa (JBCA), Andrew Lyne (JBCA), Ben Stappers (JBCA), Laura Spitler (MPIfR) , Paulo Freire (MPIfR), Ismael Cognard (CNRS-Orleans), Gregory Desvignes (MPIfR), Patrick Lazarus (MPIfR), Joris Verbiest (MPIfR), Andreas Brunthaler (MPIfR), Heino Falcke (ASTRON, Nijmegen)
on 8 May 2013; 21:29 UT
Credential Certification: Evan Keane (ekean@jb.man.ac.uk)

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We report on continued observations of J1745-2900, the pulsar discovered by the NuStar X-ray telescope in the direction of the Galactic centre (ATel #5020), using the Max Planck Institute for Radio Astronomy (MPIfR) Effelsberg Telescope, the CNRS Nancay Radio Telescope, and the Lovell Telescope at Jodrell Bank.

With Effelsberg, detections have now been made at 4.85 GHz (ATel #5043), 8.35GHz (ATel #5040), 14.6 GHz (this ATel), and 18.95 GHz (this ATel) (see links below to diagnostic plots at 14.6 and 18.95 GHz, NB there is no optimisation in DM possible at 18.95 GHz). We note that the pulsar was previously not visible at 4.85 and 14.6 GHz (Atel #5027). For each frequency we estimate flux densities (errors ~20%) as follows: 4.85 GHz ~ 0.1 mJy , 8.35 GHz ~ 0.2 mJy, 14.6 GHz ~ 0.2 mJy, 18.95 GHz ~0.2 mJy. Flux density estimates (including those in ATel #5053) indicate a flat or possibly rising spectrum, consistend with previous radio observations of magnetars.

Nancay has made two detections at 2.5 GHz with an estimated flux density of ~ 0.1 mJy. We also report two further non-detections at 1.5 GHz using the Lovell Telescope. The Lovell observations, with observing specifications as described in ATel #5033, were performed on May 2nd (Tobs = 3 hours) and May 3rd 2013 (Tobs = 4 hours) and yield flux density upper limits of ~0.2 mJy (for a 30% duty cycle) in both cases.

Analysis of the pulse broadening at all detected frequencies leads us to predict a scattering timescale of ~2 seconds at 1.5 GHz; making detection at this frequency difficult.

Since our first detection at Effelsberg, we have not seen any dramatic pulse shape changes like those seen in other radio-emitting magnetars, although there is some evidence of frequency evolution of the pulse profile. Also, we expect some of the baseline features visible in the 18.95 GHz profile may be real, and will continue to study these in our ongoing observations.

Observations at 4.85 and 8.35 GHz do not indicate significant linear polarisation but significant circular polarisation is observed.

A preliminary timing analysis of the Effelsberg and Nancay detections has given improved values for spin period P0, and the first radio determination of the period derivative Pdot, and the dispersion measure DM. We find P0=3.7635468(4) s and Pdot=6.5(6)E-12 s/s, implying a characteristic age of ~9 kyr and a surface magnetic field of 1.6E+14 G (roughly consistent with the X-ray observations reported in ATel #5046).

We have improved our DM estimate from ATel #5043. The DM is now well constrained to 1700(50) cm^-3 pc, making this the pulsar with the highest known DM. This suggests this pulsar is located in the Galactic centre region. Monitoring at Effelsberg will be continued to improve the timing solution.

Diagnostic Plots