Continued flaring activity at TeV energies from Mrk 421 measured by HAWC

ATel #13924; Jose Andres Garcia-Gonzalez (IF-UNAM, jagarcia@fisica. unam. mx, ITESM-EIC, anteus79@tec. mx), Israel Martinez (UMD, imc@umd. edu) on behalf of the HAWC Collaboration
on 8 Aug 2020; 02:08 UT
Credential Certification: José Andrés García-González (jagarcia@fisica.unam.mx)

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After the increase of activity of Markarian 421 from the past week, the HAWC gamma-ray observatory has observed a new period of high activity from the source, with the highest flux happening between 2020-08-05 17:27:25 and 2020-08-05 20:35:24 UTC with a value of (14.47 +/- 1.68) X 10^-11 cm^-2s^-1 above 1 TeV ( 8.2 equivalent Crab units).

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 , #Atel 13875 and #Atel 13917)

The summary of this new extended period is as follows:

Duration of each full transit is 6.2 hr.

MJD 59064 (2020-08-03 17:35:17 - 2020-08-03 23:51:15 UTC) Preliminary flux level: 9.30 +/- 1.07 X 10^-11 cm^-2s^-1 [>1 TeV] (5.25 CU)

MJD 59065 (2020-08-04 17:31:21 - 2020-08-04 23:47:19 UTC) Preliminary flux level: 6.21 +/- 0.94X 10^-11 cm^-2s^-1 [>1 TeV] (3.5 CU)

MJD 59066 (2020-08-05 17:27:25 - 2020-08-05 23:43:23 UTC) Preliminary flux level: 13.09 +/- 1.16X 10^-11 cm^-2s^-1 [>1 TeV] (7.4 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/2020-06-14to08-05_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.