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; 02:19 UT
Credential Certification: Fernando Camilo (fernando@astro.columbia.edu)
Subjects: Radio, Neutron Star, Pulsar
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.
