SimultaneousSwiftX-ray and UV views of comet C/2007 N3 (Lulin)

Abstract

Aims. We present an analysis of simultaneous X-Ray and UV observations of comet C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using the Swift observatory. Methods. For our X-ray observations, we used basic transforms to account for the movement of the comet to allow the combination of all available data to produce an exposure-corrected image. We fit a simple model to the extracted spectrum and measured an X-ray flux of 4.3 ± 1.3 × 10 −13 erg cm −2 s −1 in the 0.3 to 1 keV band. In the UV, we acquired large-aperture photometry and used a coma model to derive water production rates given assumptions regarding the distribution of water and its dissociation into OH molecules about the comet's nucleus. Results. We compare and discuss the X-ray and UV morphology of the comet. We show that the peak of the cometary X-ray emission is offset sunward of the UV peak emission, assumed to be the nucleus, by approximately 35 000 km. The offset observed, the shape of X-ray emission and the decrease of the X-ray emission comet-side of the peak, suggested that the comet was indeed collisionally thick to charge exchange, as expected from our measurements of the comet's water production rate (6-8 ×10 28 mol s −1 ). The X-ray spectrum is consistent with solar wind charge exchange emission, and the comet most likely interacted with a solar wind depleted of very highly ionised oxygen. We show that the measured X-ray lightcurve can be very well explained by variations in the comet's gas production rates, the observing geometry and variations in the solar wind flux.

Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)

“…Several papers have resulted from these efforts, and many more preliminary results were presented at meetings or in IAU Circulars. Production rates and/or compositional studies, mostly by means of spectroscopy, were obtained from the UV and visible (Combi et al 2009a,b;Bodewits et al 2011;Carter et al 2012;Morgenthaler et al 2009), to the near-IR (Woodward et al 2011, Gibb et al 2012, Kobayashi et al 2009Ootsubo et al 2010), and the mm and radio (Biver et al 2009;Charnley et al 2009;Lovell & Howell 2009). Photometry of the dust was obtained (Joshi et al 2011) along with polarimetry in both the visible and IR (Woodward et al 2011), while imaging in the visible was also acquired (Hicks et al 2009).…”

Survey of cometary CO2, CO, and particulate emissions using the Spitzer Space Telescope

“…For C/2006 W3, Q is based on OH fromBockelée-Morvan et al (2010). For C/2007 N3, Q is based on OH fromCarter et al (2012). For 29P and 118P, Q is based on H2O fromOotsubo et al (2012).b From A'Hearn et al (1995); taxonomic class D=depleted (lower abundance of carbon-chain molecules, and low CN/OH), T=typical (in terms of carbon-bearing molecules per unit OH)…”

Cometary Charge Exchange Diagnostics in UV and X-ray

“…In very active comets (gas production rates of 10 29 molecules s −1 or more, ) observed at phase angles of about 90 degrees, the X-ray emission maps a spherical gas distribution resulting in a characteristic sunward, crescent shape as seen by a remote observer, indicating a coma that is collisionally thick to charge exchange. A good example results from the combined observations of comet 2007/N3 (Lulin), shown in Figure 1 (Carter et al 2012). The Swift observatory is equipped with boresighted UV and X-ray instruments, allowing for 1 Unsuccessful attempts to detect X-rays in comets were made using the Einstein satellite, the Rossi X-ray Timing Explorer, and the ASCA observatory (Krasnopolsky et al 2004).…”

“…Secondly, the size of the cometary atmosphere (on the order of 10 5 km) allows remote tracking of the ions as they penetrate into the comet's atmosphere, offering a closeup view on the interaction of the two plasmas. Thirdly, since the first observations of cometary X-ray emission, more than 20 comets have been observed with various Xray and UV observatories including ROSAT (Dennerl et al 1997;Lisse et al 1996), EUVE (Mumma et al 1997) Swift observations of comet 2007/N3 (Lulin), adapted from Carter et al (2012). The Swift satellite allows for simultaneous mapping of OH in the neutral coma (blue) and charge exchange X-ray emission (red).…”

“…The peak X-ray brightness is offset by about 35,000 km towards the Sun. Lisse et al 2001;Wolk et al 2009), CHIPS (Sasseen et al 2006), FUSE (Feldman 2005), XMM-Newton (Dennerl 2012;Schultz et al 2006), Suzaku (Brown et al 2010), and Swift (Carter et al 2012;Willingale et al 2006) 1 . This observational sample offers a broad variety of comets, solar wind environments and observational conditions, clearly demonstrating that cometary charge exchange emission provides a wealth of diagnostics, which are visible as spatial, temporal, and spectral emission manifestations.…”