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X-ray and Ultraviolet detection of the new FU Orionis object HBC 722

ATEL # 3040; D. Pooley (Eureka Scientific/UT Austin) and J. Green (UT Austin)
on 18 Nov 2010; 20:19 UT
Password Certification: dave pooley (

Subjects: Ultra-Violet, X-ray, Variables

We report the results of a Swift target of opportunity observation of HBC 722 (ATel #2801, #2808, #2819, #2854) that started 2010-Nov-17.02 UT.

The object is detected in 4217.8 sec of exposure with the Swift X-ray Telescope (XRT) with 22.6 +/- 5.2 net counts in the 0.2-10 keV band. This is the first X-ray detection of an FUor during outburst. We performed a preliminary spectral analysis using a thermal bremsstrahlung model and assuming an absorbing column density of 5e21 cm^-2 (based on an A_V of 3.1). We find a best-fit temperature of kT = 2.6 keV and an unabsorbed 0.2-10 keV flux of 4.6e-13 erg/cm^2/s. Given the paucity of counts, the uncertainties on these spectral fitting results are large.

The object is also detected with the Swift Ultraviolet/Optical Telescope (UVOT) using the UVW2 filter, which has a central wavelength of 192.8 nm. The instrumental magnitude is 19.26 +/- 0.05, corresponding to a flux density of (1.07 +/- 0.05) x 10^-16 erg/cm^2/s/A.

Further X-ray and UV observations are strongly encouraged.

We thank Neil Gehrels and the Swift team for approving the ToO request and making these observations possible.

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