Fermi-LAT detection of renewed enhanced gamma-ray activity from the Crab Nebula
ATel #16387; Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Roma, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 20 Dec 2023; 15:48 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)
Subjects: Gamma Ray, Request for Observations, Transient, Pulsar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed substantial enhanced gamma-ray activity from the Crab Nebula region, beginning its increase on about December 10 and peaking on December 19, 2023 when a preliminary analysis indicates that the daily-averaged gamma-ray flux level (E>100 MeV) has been (11.5 +/- 0.7) X 10^-6 ph cm^-2 s^-1 (statistical uncertainties only). The Crab source rapidly increased from a daily-averaged gamma-ray flux level (E>100 MeV) of (5.1 +/- 0.5) X 10^-6 ph cm^-2 s^-1, detected on December 18, 2023.
The December 19 daily flux is a factor of 4.5 greater than the average gamma-ray flux of (2.47+/-0.05) X 10^-6 ph cm^-2 s^-1 reported in the fourth Fermi-LAT source catalog Data Release 3 (Abdollahi et al. 2022, ApJS, 260, 53). All fluxes given are the sums of the Crab pulsar and nebular emission, and with statistical uncertainties only. These are the highest fluxes observed for the Crab source since May 2019, i.e. after four years and a half, as reported in ATel#12753 and those related to it.
Other previous outburst observed by the LAT were published previously in ATel#12095, ATel#11412, ATel#9588, ATel#8519, ATel#6401, ATel#5971, ATel#5485, ATel#4855, ATel#4239, ATel#3284, ATel#2879, ATel#2861.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of the Crab Nebula region will continue. We encourage multifrequency observations of this gamma-ray source.
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
