The spectrum of a magnetar in the blue and ultraviolet.

I have added orient constraints, since the longer exposures here increase the size of diffraction spikes from the star DUE SOUTH of our star of interest. ----- Submission 1 (Fri May 05 21:20:40 GMT 2006) ----- ----- Attempting Submission 2 (Tue Mar 06 17:36:24 GMT 2007) ----- Assigned ID: 27 ----- Submission 1 (Fri Jan 20 23:08:18 GMT 2006) ----- Phase I Proposal 27 (myHST) successfully submitted. The spectrum of a magnetar in the blue and ultraviolet. Magnetars are natural laboratories for investigating the behaviour of matter at the very extremes of nature. The magnetar CXOU J010043.1-721134 was serendipitously discovered by WFPC2 imaging of the SMC. Because of the low reddening to this source compared to the other magnetars, this is a unique opportunity to measure the spectral shape in the blue and ultraviolet. We hope also to establish the feasibility of spectroscopic follow-up. We are asking for two orbits of ACS imaging.

We will use two orbits with ACS to accurately measure CXOU J010043.1-721134's F606W magnitude (where the only detection has been made, mF606W = 24.2) and measure the source or set good limits across the optical/UV band, using filters F330W, F435W, and F814W. A Rayleigh-Jeans form spectrum (nuF_nu ~ nu^n, n = 3) is possible given the limits in F814W previously obtained. Since it is very unlikely that the spectrum rises faster than this (it would require a very strong and broad spectral line), we predict a magnitude of mF814W = 25. We can also predict what we might might find in F435W by supposing that CXOU J010043.1?721134 has the same intrinsic B-V color as 4U 0142+61. With B-V = 2.5 (Hulleman et al., 2004) and using our new estimated reddening for 4U 0142+61 (AV = 3.5, Durant & van Kerkwijk, 2006, submitted), we find (B-V )_0 = 1.4 and thus we would predict mF435W = 25.7. For U we have no predictions, and hence for this initial study we will go as deep as possible in a single orbit. In the optical, with the WFC, a given SNR is reached much quicker than with the HRC. Only the HRC is sensitive in U, however, so we will use the WFC for one orbit and the HRC for the second. According to the ACS ETC for the WFC, 200s is required to reach SNR=20 at V=24.2 in F606W. Good measurements (SNR=10) will be reached in F435W in 530s down to 25.3mag and in F814W in 860s down to 25.0mag, respectively. These all assume CR-SPLIT=2, GAIN=2 and average conditions. In total, these three filters will take 52min to observe, or one orbit exactly, including overheads. We will use the WFC1-1K sub-array to reduce the read-out time and release more time for exposures (and eliminate the buffer dump overhead). In the second orbit, we will use the HRC to get as deep an image in F330W as possible. After accounting for overheads, 2550s remains, which reaches a detection limit (SNR=3) of U=25.3 for GAIN=2, CR-SPLIT=2. HOT STARS 12 false 0.0 false false false false false false SUPPORTED STAR NEUTRON STAR PULSAR X-RAY TRANSIENT m606-m814 < -0.3 J2000 01 00 43.1400 -72 11 33.80 J2000 ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F435W ACS/HRC Imaging No No F330W POS-TARG DITHER 0.3535 LINE false false 3 45 WFPC2-LINE 1

false

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