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No radio pulsations detected from AXP 1E 1048.1-5937 following a glitch

ATEL # 1056; F. Camilo (Columbia), J. Reynolds (ATNF)
on 15 Apr 2007; 2:19 UT
Password Certification: Fernando Camilo (fernando@astro.columbia.edu)

Subjects: Radio, Neutron Stars, Pulsars

Following a rotation glitch in the anomalous X-ray pulsar (AXP) 1E 1048.1-5937 that took place in late 2007 March, its X-ray flux increased (ATEL #1041, #1043), and likely so did its infrared flux (ATEL #1044). Previous radio searches of this AXP were unsuccessful (e.g., Burgay et al. 2006, MNRAS, 372, 410). However, another AXP, XTE J1810-197, was found to emit bright radio pulses (Camilo et al. 2006, Nature, 442, 892) only after a large X-ray outburst. Although the transient events in both these AXPs were very different, the recent glitch led us to search anew for pulsed radio emission from 1E 1048.1-5937.

On 2007 April 13 (MJD 54203.2) we used the ATNF Parkes telescope in Australia to search for radio emission from 1E 1048.1-5937 using its HOH receiver operating at a central frequency of 1518 MHz. We recorded data for 4.0 hr across a bandwidth of 576 MHz, sampling the polarization-summed outputs of each of 192 frequency channels every 1 ms. We analyzed the data using standard pulsar search techniques, looking for both average emission and single pulses, but found no pulsar candidate at any period, including the 6.4 s period of the AXP. The period-averaged flux density limit from this search at 1.5 GHz is 0.1 mJy for an approximately sinusoidal pulse profile, and a factor of about 3 lower for a duty cycle of 10%.

Assuming a distance of 3 kpc, the above flux density limit corresponds to a pseudo-luminosity limit of approximately 1 mJy kpc^2, smaller than the radio luminosity of virtually every known young radio pulsar. Therefore, if 1E 1048.1-5937 is presently a radio pulsar, it is likely not beaming toward the Earth. Alternatively, 1E 1048.1-5937 is not presently emitting pulsed radio emission at all.


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