Increased X-ray activity and likely binary period of HESS J0632+057 Observed by Swift-XRT

ATel #3152; Abe Falcone, Stephen Bongiorno, Michael Stroh (Penn State Univ.), Jamie Holder (Univ. of Delaware)
on 8 Feb 2011; 17:41 UT
Credential Certification: Abe Falcone (afalcone@astro.psu.edu)

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HESS J0632+057 (R.A. 06:32:58.3, Dec. +05:48:20), which is associated with XMMU J063259.3+054801 and Be star MWC 148 (R.A. 06:32:59.3, Dec. +05:48:01) has shown a recent increase in X-ray activity, based on Swift-XRT monitoring data. This unidentified TeV source was discovered by HESS (Aharonian et al. 2007, A&A, 469, L1), and it was proposed as a likely binary object based on a variety of features, including its unresolved, point-like nature, its spectrum, evidence of X-ray variability (Hinton et al. 2009, ApJ 690, L101), its low and variable radio flux (Skilton et al. 2009, MNRAS, 399, 317), as well as evidence of TeV variability (Acciari et al. 2009, ApJ 698, L94). Subsequent Swift observations showed that, if this was a binary object, it had a long period that was likely to be greater than 54 days (Falcone et al. 2009, ApJ 708, L52).

Swift has continued monitoring this object, and a likely period in the range of approximately 310 to 320 days has emerged. This recent rise in X-ray activity began on around MJD 55584 (23 Jan 2011) and is still ongoing as of MJD 55598 (6 Feb 2011), with a flux increase by a factor of ~3. This rise is almost identical to two similar rises that occurred ~320 days ago and ~640 days ago, respectively. Based on these past increases, along with the overall folded light curve that overlaps with this period, we expect that the flux level will begin to decay within days to ~1 week, reaching quiescent levels (~0.02 c/s in Swift XRT 0.3-10 keV band) within ~2 weeks, and then it will briefly dip below these flux levels by a factor of 2-4 before returning to the quiescent ~0.02 c/s.

Multiwavelength observations throughout the next 1-3 weeks are encouraged, particularly TeV observations and optical radial velocity measurement programs.

We thank the Swift MOC, science planning team, and PI for approving and enabling Swift ToO observations and GI program monitoring observations on this source.