Swift detects BL Lacertae in an historic high state in X-rays

ATel #4627; Dirk Grupe (Pennsylvania State University) and Ann E. Wehrle (Space Science Institute)
on 7 Dec 2012; 20:04 UT
Credential Certification: Dirk Grupe (grupe@astro.psu.edu)

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We report on an unprecedented high flux in X-rays in BL Lacertae (22h 02m 43a, +42d 16m 40s) seen by Swift on 2012 December 05, exceeding the previous high X-ray flux reported in our ATEL 4557. This high X-ray flux was accompanied by fairly bright optical and ultraviolet emission. We are currently monitoring BL Lacertae daily with Swift. On 2012 December 05 Swift observed BL Lacertae starting at 07:08 UT for a total of 1162s and detected it with the X-Ray Telescope with a count rate of 1.49+/-0.07 counts/s (corresponding to a flux in the 0.3-10 keV band of 7.92e-14 W/m2). On our most recent observation on December 06, however, it was again down to 0.8 counts/s in the XRT. The X-ray light curve of BL Lacertae can be found at: http://www.swift.psu.edu/monitoring/source.php?source=BLLacertae Swift UVOT observed BL Lacertae in all 6 filters. On 2012 December 06, we found that in all 6 filters BL Lac had become brighter by 0.6 to 1.0 magnitude compared to the previous day. We will continue monitoring BL Lacertae with daily cadence through at least December 21. On December 11-12, we are conducting a multi-wavelength observing campaign of BL Lacertae including Swift, Herschel, and NuSTAR. The Swift-Herschel campaign leader is Ann Wehrle (awehrle@spacescience.org). We encourage ground-based observations of BL Lacertae in this unusual high state. We thank the Swift PI Neil Gehrels, the Observation Duty Scientists and the science planners. We also thank A. Falcone and M. Stroh (Penn State) for use of their Swift monitoring program webpage at http://www.swift.psu.edu/monitoring/. At Penn State we acknowledge support from the NASA Swift program through contract NAS5-00136.