First report of the Fermi-LAT monitoring campaign of Galactic novae: OGLE-2016-NOVA-02 and Nova Sco 2016

ATel #9311; K. L. Li and L. Chomiuk (Michigan State University)
on 3 Aug 2016; 22:58 UT
Credential Certification: K. L. Li (lilirayhk@gmail.com)

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Classical novae have been proven to be a distinct GeV gamma-ray source class since the first Fermi-LAT detection of V407 Cygni 2010 (Fermi-LAT Collaboration 2014). However, still many similar novae have not been detected in GeV. Motivated by whether strong gamma-ray emissions are common among ordinary novae, we have recently initiated a Fermi-LAT monitoring program that performs deep gamma-ray observations on all Galactic novae (~10 per year, on average) with Fermi-LAT ToO time. The program aims for more gamma-ray detections of novae and deep limits of those LAT-undetected, which are both crucial to understanding the GeV picture of novae. Here we report the very first result of the campaign on the two recently-discovered novae, Nova Sco 2016 (CBET 4285) and OGLE-2016-NOVA-02 (ATel #9246).

Two respective ToOs for Sco 2016 and OGLE-02 2016 (each has a duration of 1 week and an on-source time of 430ks) were triggered within a week since the optical discoveries. Using the Fermi-LAT data (100MeV-300GeV) collected since the nova discovery dates until the ends of the ToOs, no significant gamma-ray detections have been seen at the optical positions. Assuming a simple power-law with a photon index of -2.2, we derived 95% upper-limits for them, which are 6.9e-08 ph/cm^2/s (Sco 2016) and 6.2e-08 ph/cm^2/s (OGLE-02 2016), based on a Baysian upper limit method. Both limits are significantly lower than the typical flux level of those Fermi-detected novae (~1e-7 ph/cm^2/s; Fermi-LAT Collaboration 2014).

The campaign is still on-going and we stay alert for further Fermi-LAT observing opportunities on other novae. We gratefully acknowledge the Fermi-LAT team for the execution of our ToO requests.