Astron. Nachr. 320 (1999) 4/5 343

X-ray observation of the supernova remnant/pulsar association – SNR G11.2-0.3

K. Torii1, H. Tsunemi2,3,1, T. Dotani4, K. Mitsuda4, N. Kawai5,1, K. Kinugasa6, Y. Saito4,and S. Shibata7

1 Space Utilization Research Program (SURP), Tsukuba Space Center (TKSC), National Space DevelopmentAgency of Japan (NASDA), 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan

2 Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1, Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan

3 CREST, Japan Science and Technology Corporation (JST), 4-1-8 Honmachi, Kawaguchi, Saitama 332-0012,Japan

4 Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510,Japan

5 Cosmic Radiation Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, 351-0198, Japan

6 Gunma Astronomical Observatory, 6860-86 Nakayama, Takayama, Agatsuma, Gunma 377-0702, Japan7 Department of Physics, Yamagata University, 1-4-12 Koshirakawa-cho, Yamagata 990-8560, Japan

1. Introduction

Although it is widely accepted that neutron stars areborn by supernova explosions of massive progenitorstars, associations of supernova remnants (SNRs) withyoung pulsars have been studied based upon a smallnumber of prototypical objects (e.g., Weiler & Panagia1978).

Recently, X-ray observations have largely increasedthe number of young pulsars (e.g., Vasisht & Gotthelf1997; Torii, et al. 1997; Torii, et al. 1998; Marshall, et al.1998; Pavlov, et al. 1999). We can now study the earlyphase evolution of the supernova remnant / pulsar as-sociations by using these rare samples. A 65 millisecondX-ray pulsar was discovered within the SNR shell of thesupernova remnant G11.2-0.3 (Torii, et al. 1997).

Out of these pulsars, the period derivative has notyet been measured for the 65 ms pulsar within the SNRG11.2-0.3. The SNR G11.2-0.3 is a leading candidateremnant of the historical supernova in 386 AD (Clark &Stephenson 1977).

2. Observation and results

We observed the SNR G11.2-0.3 in March 1998 withthe Advanced Satellite for Cosmology and Astrophysics(ASCA) (Tanaka, Inoue, & Holt 1994) to measure theperiod derivative (P ) of the pulsar. The exposure timewas about 20 ks for each GIS. To increase the time res-olution, more telemetry bits were allocated to timinginformation than for the standard observations sacrific-ing the pulse height and the rise-time information. Theresultant time resolution was 1/2048 and 1/256 s, de-pending on the telemetry rate.

We performed epoch folding searches on the newdata around the expected period. We could significantlydetect the pulsations. We found that the pulsations weremost clearly detected above 4 keV where the contam-ination by the thermal component of the SNR shellwas negligible. The period was 64.67249(5) ms at MJD

50902.924. The pulse shape was singly peaked which wasconsistent with that observed previously (Torii, et al.1997). Combining the measured period with the previ-ous one in 1994 (Torii, et al. 1997), we have obtain theperiod derivative of P = (4.38± 0.05)× 10−14s s−1.

From the pulsar period and its derivative, the corre-sponding surface magnetic field, B = 1.7× 1012 G, andthe characteristic age, P/(2P ) = 2.4 × 104 yrs, are de-rived. In contrast to the case for the Crab Nebula, themeasured characteristic age is significantly larger thanthe historical age. If the pulsar was formed at the his-torical event, either the initial pulse period had to berather slow, or its braking index was anomalously large.Either of these properties deviates from known char-acteristics of small number of prototypical objects. Toconstrain the pulsar age and the spindown properties,further timing observations to measure the pulsar brak-ing index is desired.

Acknowledgements. The authors are grateful to all the mem-bers of the ASCA team. A part of this research has made useof data obtained through the High Energy Astrophysics Sci-ence Archive Research Center Online Service, provided bythe NASA Goddard Space Flight Center.

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