Recent extended period of High Activity of Mrk 421 measured by HAWC

ATel #13917; jagarcia@fisica. unam. mx, ITESM-EIC, anteus79@tec. mx),Israel Martinez (UMD, imc@umd. edu) on behalf of the HAWC Collaboration
on 3 Aug 2020; 23:50 UT
Credential Certification: José Andrés García-González (jagarcia@fisica.unam.mx)

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In the past week the HAWC gamma-ray observatory has observed an increased TeV gamma-ray emission from Markarian 421, with a highest flux above 1 TeV of (13.74 +/- 1.66) X 10^-11 cm^-2s^-1 ( 7.8 equivalent Crab units) between 2020-07-31 17:47:05 and 2020-07-31 20:55:04 UTC.

This new increase in the integrated flux has been preceded for an extended period of high activity that started in Jun 14th and has continued almost uninterrupted since then (see for ref. #Atel 13808, #Atel 13831 and #Atel 13875).

The summary of this new extended period is as follows:

Duration of each full transit is 6.2 hr.

MJD 59059 (2020-07-29 17:54:57 - 2020-07-30 00:10:55 UTC) Preliminary flux level: 3.56 +/- 0.89 X 10^-11 cm^-2s^-1 [>1 TeV] (2.0 CU)

MJD 59060 (2020-07-30 17:51:01 - 2020-07-31 00:06:59 UTC) Preliminary flux level: 5.90 +/- 1.02 X 10^-11 cm^-2s^-1 [>1 TeV] (3.3 CU)

MJD 59061 (2020-07-31 17:47:05 - 2020-08-01 00:03:03 UTC) Preliminary flux level: 13.20 +/- 1.15 X 10^-11 cm^-2s^-1 [>1 TeV] (7.45 CU)

MJD 59062 (2020-08-01 17:43:09 - 2020-08-01 23:59:07 UTC) Preliminary flux level: 7.70 +/ 1.05 X 10^-11 cm^-2s^-1 [>1 TeV] (4.35 CU)

HAWC continuously monitors this source and will keep reporting in case that the enhanced activity follows. Follow-up observations are encouraged. All flux values are 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. A preliminary plot showing the source activity from the beginning of the high activity to this ATel may be found at https://data.hawc-observatory.org/atels/2020-06-14to08-01_HAWC_Markarian421_halfTransits.png.

The HAWC contact people for this analysis are Jose Andres Garcia-Gonzalez (IF-UNAM, jagarcia@fisica.unam.mx, ITESM-EIC, anteus79@tec.mx) and Israel Martinez (UMD, imc@umd.edu). HAWC is a TeV gamma-ray water Cherenkov array located in the state of Puebla, Mexico, that monitors two thirds of the sky every day with an instantaneous field of view of ~2 sr.