NuSTAR detects extreme X-ray flaring of Mrk 421
ATel #4974; Mislav Balokovic (Caltech), Amy Furniss (UCSC), Grzegorz Madejski (KIPAC/Stanford), Fiona Harrison (Caltech)
on 13 Apr 2013; 00:00 UT
Credential Certification: Amy Furniss (firstname.lastname@example.org)
Subjects: X-ray, Request for Observations, AGN, Blazar
We report extreme brightening of the nearby BL Lac object Mrk 421 with NuSTAR. NuSTAR is a focusing hard X-ray telescope observing in the 3-79 keV band with unprecedented sensitivity (Harrison et al. 2013, arXiv:1301.7307). Mrk 421 has been the subject of a monitoring campaign with NuSTAR since the beginning of January 2013.
Latest observations performed between 4-10-2013 UT 21:25 and 4-12-2013 UT 09:35 show extreme brightening up to flux levels that have not been observed before for this object. NuSTAR count rates increased from about 6 counts per second per module in the NuSTAR band on 4-11-2013 UT 08:45, to over 34 counts per second per module on 4-12-2013 UT 08:57. The count rate had a steadily increasing trend up to the end of the NuSTAR observation, with multiple short outbursts and flux-doubling timescale of about 7 hours. For comparison, the earlier NuSTAR observations of Mrk 421 in 2013 had mean count rates of about 3, and as low as 0.3, counts per second per module. Latest count rates imply flux in excess of 2.0e-9 erg/s/cm2 in the 2-10 keV band, higher than flux levels previously observed during giant flares. We strongly encourage multiwavelength observations of Mrk 421 during this extreme event.