HAWC detection of further increase in TeV gamma-ray flux from Mrk 421

ATel #9946; I. Martinez (University of Maryland), J. Wood (University of Wisconsin), R. Lauer (University of New Mexico)
on 6 Jan 2017; 17:39 UT
Credential Certification: Robert Lauer (rjlauer@unm.edu)

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During the transit ending on Jan 6 07:21:16 UTC, the HAWC gamma-ray observatory measured an increased TeV gamma-ray flux from the direction of BL Lac Markarian 421 (z=0.031) equivalent to ~4 times the Crab Nebula flux. As reported in ATEL #9936, this follows several days of having an elevated flux (~2 Crab Units). Bellow is the progression of fluxes up to the most recent transit measurement:

Transit Starting 07:40:55 UTC on Jan 1, 2017 (MJD 57754.32):
Flux = (4.8 +/- 1.1) x10^-11 photons/cm2/s [2.5 Crab Units]

Transit Starting 07:36:59 UTC on Jan 2, 2017 (MJD 57755.32):
Flux = (3.6 +/- 1.0) x10^-11 photons/cm2/s [1.9 Crab Units]

Transit Starting 07:33:04 UTC on Jan 3, 2017 (MJD 57756.31):
Flux = (4.0 +/- 1.0) x10^-11 photons/cm2/s [2.1 Crab Units]

Transit Starting 07:29:08 UTC on Jan 4, 2017 (MJD 57757.31):
Flux = (4.1 +/- 1.0) x10^-11 photons/cm2/s [2.2 Crab Units]

Transit Starting 07:25:12 UTC on Jan 5, 2017 (MJD 57758.31):
Flux = (3.9 +/- 1.0) x10^-11 photons/cm2/s [2.0 Crab Units]

Transit Starting 07:21:16 UTC on Jan 6, 2017 (MJD 57759.30):
Flux = (7.5 +/- 1.1) x10^-11 photons/cm2/s [4.0 Crab Units]

All fluxes reported here are the integral flux above 1 TeV averaged over the 6 hour source transit obtained from a maximum likelihood fit under the assumption of a fixed spectral shape with power law index of 2.2 and exponential cut-off at 5 TeV. This shape is the current best fit for HAWC data from Markarian 421. These are preliminary values measured from a real-time analysis running at the HAWC site and may change with reprocessing.

HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico that monitors 2/3 of the sky every day with an instantaneous field of view of ~2 sr. The HAWC contact people for this analysis are Israel Martinez (imc@umd.edu), Joshua Wood (jwood22@wisc.edu), and Robert Lauer (rjlauer@unm.edu).