Fermi-LAT detection of a very bright Gamma-ray Onset from the Galactic Nova ASASSN-16ma
ATel #9736; Kwan-Lok Li, Laura Chomiuk, and Jay Strader (Michigan State University)
on 8 Nov 2016; 20:45 UT
Credential Certification: K. L. Li (lilirayhk@gmail.com)
Subjects: Gamma Ray, Nova
Referred to by ATel #: 9771
We report the detection of gamma-ray emission from ASASSN-16ma, spectroscopically classified as a classical nova (ATel #9669 and ATel #9678).
Because of the close proximity to TCP J18102829-2729590 (separated from ASAS-SN 16ma by 2.5 degrees), ASASSN-16ma is under our Fermi ToO monitoring triggered for TCP J18102829-2729590 since 2016-10-25 (ATel #9699). While there is no significant detection in the interval between 2016-10-25 (the discovery date of ASAS-SN 16ma; ATel #9669) and 2016-11-07, strong gamma-ray emission is clearly detected with Fermi/LAT data on 2016-11-08 (the last day of the ToO; this detection is seen in about 0.5 days of data) with TS = 161 (corresponding to a significance of ~12 sigma).
No cataloged gamma-ray sources can be found within 1 degree of ASASSN-16ma in the 3FGL catalog (the closest source is 3FGL J1816.2-2726, which is an unassociated gamma-ray source 1.4 degrees away).
The new gamma-ray source can be described by a simple power law with a photon index of -2.0+/-0.1 and a photon flux of F(100 MeV-300 GeV) = (9.7+/-1.8)10^-7 ph/cm^2/s. This is potentially the most sudden onset of gamma-ray emission observed in a nova to date and among the brightest Galactic transients discovered by Fermi-LAT so far.
We note that the AAVSO light curve indicates that optical brightness of this source has increased substantially in the last few days, to at least V~5.5, and this increase in the optical brightness may be connected to the detection of gamma-rays.
We will continue to monitor the nova with Fermi. Meanwhile, more multi-wavelength follow-up observations are strongly encouraged. We thank the Fermi Science Support Center, supported by the Flight Operations Team, for scheduling these observations.
The Fermi-LAT count maps of ASASSN-16ma
