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No radio pulsations detected from SGR 1627-41 following renewed X-ray activity

ATEL # 1558; F. Camilo (Columbia U.), J. Sarkissian (ATNF)
on 4 Jun 2008; 23:42 UT
Password Certification: Fernando Camilo (fernando@astro.columbia.edu)

Subjects: Radio, X-ray, Neutron Stars, Pulsars, Soft Gamma-ray Repeaters, Transients

Starting on May 28, 2008, the SGR 1627-41 displayed X-ray bursting and enhanced flux after nearly 10 years of relative inactivity (ATEL #1548, #1549, #1555). Two magnetars are known to emit radio pulses (Camilo et al. 2007, ApJ, 666, L93), and in at least one case these are transient and have followed an X-ray outburst after many years in quiescence (Camilo et al. 2006, Nature, 442, 892). Therefore, although previous radio searches of SGR 1627-41 have been unsuccessful, we are searching for radio emission following its recent renewed burst of activity.

On May 30 and again on June 1, 2008, we used the ATNF Parkes telescope in Australia to search for radio emission from SGR 1627-41 using its multibeam receiver operating at a central frequency of 1374 MHz. We recorded data for 30 min on each occasion across a bandwidth of 288 MHz, with time and frequency resolution of, respectively, 1 ms and 3 MHz. We analyzed the data using standard pulsar search techniques, looking for both average emission and single dispersed pulses, but found no pulsar candidate at any period, including the tentative 6.4 s period of the SGR. The period-averaged flux density limit from these searches at 1.4 GHz is 0.5 mJy for an approximately sinusoidal pulse profile, and a factor of about 3 lower for a duty cycle of 10%.

Assuming a distance of 11 kpc, the above flux density limit for 10% duty cycle corresponds to a pseudo-luminosity limit of approximately 20 mJy kpc^2. This limit is only somewhat constraining: it is significantly smaller than the 1.4 GHz luminosity of both known radio magnetars at their peak (~100-200 mJy kpc^2), but is much larger than the smallest known luminosities of ordinary young pulsars (~1 mJy kpc^2). Further observations are planned.


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