Fermi-LAT Observations of Continued Gamma-ray Activity from Nova ASASSN-16ma

ATel #9771; Kwan-Lok Li, Laura Chomiuk, and Jay Strader (Michigan State University); C. C. Cheung (NRL), P. Jean (IRAP, Toulouse), on behalf of the Fermi Large Area Telescope Collaboration; S. N. Shore (U. Pisa and INFN)
on 18 Nov 2016; 23:05 UT
Credential Certification: Laura Chomiuk (chomiuk@pa.msu.edu)

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Following the report of a sudden gamma-ray onset detection of nova ASASSN-16ma coincident with the optical peak of ~5.5 mag on November 8 (ATel #9736), ASASSN-16ma was observed to slowly decrease in gamma-rays but has remained bright enough to be detectable with Fermi-LAT over the last 9 days (test statistic, TS > 10 per day, except for November 17 with TS=5). In our preliminary stacked analysis of the LAT data from November 7 UT 00:00:00 to November 17 UT 23:14:42, the average gamma-ray flux is F(E>100 MeV) = (6.1 ± 0.5) x 10^-7 ph cm^-2 s^-1 with a photon index of 2.14 ± 0.05 (statistical errors only).

There is a clear correlation between the gamma-ray and optical light curves. Preliminary analysis indicates the daily gamma-ray light curve follows the (pre-validated AAVSO) optical light curve closely, with a general decline from F(E>100 MeV) = (9.7 ± 1.3) x 10^-7 ph cm^-2 s^-1 (assuming a single power-law with photon index = 2.2 fixed in the fit) on November 8 to (3.4 ± 2.1) x 10^-7 ph cm^-2 s^-1 on November 17. A significant 1-day gamma-ray flux dip that was observed on November 13, F(E>100 MeV) = (1.4 ± 0.7) x 10^-7 ph cm^-2 s^-1, had a corresponding dip in the optical light curve.

More multi-wavelength follow-up observations, especially in the optical (the source is currently at V~7), are strongly encouraged.

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.