VERITAS Detection of Historically Bright TeV Flares From LS I +61 303

ATel #6785; Jamie Holder (for the VERITAS Collaboration)
on 5 Dec 2014; 19:56 UT
Credential Certification: Jamie Holder (jholder@physics.udel.edu)

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The VERITAS collaboration reports the detection of brief and intense gamma-ray flaring activity from the binary system LS I +61 303. The flares occurred over a sharply defined phase range (from phase 0.55 to 0.65) during two orbital cycles in October and November 2014. If the source behaves similarly over the next orbit, this represents an unprecedented opportunity to study the high energy processes in this enigmatic system.

As a part of a multi-wavelength campaign with VERITAS, Swift-XRT, Ritter Observatory, and Fermi-LAT, VERITAS has been monitoring the known TeV binary source LS I +61 303 (orbital period of ~26.5 days) since October 16, 2014 (MJD 56946). In preliminary analysis, we have detected the source at a statistical significance of >15 sigma in ~20 hours of observations. During these observations, LS I +61 303 displayed relatively short (1-2 days duration), bright TeV flares with a flux peak above 25% of the Crab Nebula flux (>300 GeV). In both orbital periods sampled, these flares were centered on orbital phase = 0.6. Historically, the source has presented a flux level of 5-15% of the Crab Nebula during its active phases, making these flares the brightest ever detected from this source.

Contemporaneous light curves from Swift-XRT (0.3-10 keV) and Fermi-LAT (0.3-300 GeV) do not show evidence for similarly high emission in their respective bands, as can be seen at:
http://www.swift.psu.edu/monitoring/source.php?source=LSI+61303
and
http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/LSI_p61_303

VERITAS will continue to monitor the source during the following dates/times:

MJD Time (UTC)

57000 02:00-03:00

57001 02:00-04:00

57002 02:00-05:00

57003 03:00-05:00

We strongly encourage both contemporaneous and follow-up multiwavelength observations. Please contact Andrew W. Smith (asmith44@umd.edu) and Gernot Maier (gernot.maier@desy.de) for further information. Further details on the VERITAS observatory can be found on the VERITAS public web page.