Support ATel At Patreon

[ Previous | Next | ADS ]

HAWC follow up for gamma-rays emission coincident with the position of AT2018cow

ATel #11792; Jose Andres Garcia-Gonzalez (IF-UNAM), Magdalena Gonzalez (IA-UNAM), Israel Martinez (UMD), for the HAWC Collaboration
on 28 Jun 2018; 20:00 UT
Credential Certification: Israel Martinez (imc@umd.edu)

Subjects: Gamma Ray, VHE, Transient

The HAWC observatory did a follow up regarding a bright transient spatially coincident with CGCG 137-068 (60 Mpc) named ATLAS18qqn (AT2018cow) reported on ATel #11727

Considering the dates reported by the Palomar Observatory in ATel#11738 on 2018-06-13 and by NuSTAR in ATel #11775 for the observations in the X-Ray band on 2018-06-23, we performed a search at the location of the observed transient, (RA, Dec) = (244.000, 22.268) deg, for the time period defined by the dates mentioned above. We did not see a significant detection and we report daily upper limits at 95%CL as follows:

Flux Normalization at 1 TeV ( x10^-11 TeV^-1 cm^-2 s^-1 ):
2018-06-13: 2.11
2018-06-14: 2.43
2018-06-15: 2.55
2018-06-16: 5.46
2018-06-17: 1.30
2018-06-18: 3.82
2018-06-19: 2.99
2018-06-20: 0.89
2018-06-21: 4.60
2018-06-22: 5.68
2018-06-23: 3.02

All flux normalization limits are obtained from a maximum likelihood fit under the assumption of a fixed spectral shape with power law index of -2.63.

We also performed a search for transients in short timescales of 0.2s, 1s and 10s at the same location from 2018-06-13 04:07:45 UTC to 2018-06-16 10:35:02 (a total of 23.6hrs in our field of view). The time period was constrained by the Palomar 48-inch observations in ATel #11738 and the initial detection by ATLAS in ATel #11727.

We found one sub-threshold candidate of ~5 sigma pre-trials in the 1 second search and centered at 2018-06-13 05:10:01.30 UTC. This corresponds to a false alarm rate consistent with background of ~1e-2 hr^-1. For a 1s burst as nearby as CGCG 137-068 (z=0.014), and assuming a spectral index of -2, HAWC has a 5 sigma sensitivity from 1e-7 photons/cm^2 to 1e-6 photons/cm^2 above 100GeV, depending on the zenith angle.

The HAWC contact people for this analysis are Jose Andres Garcia-Gonzalez (jagarcia@fisica.unam.mx), Magdalena Gonzalez (magda@astro.unam.mx) and Israel Martinez (imc@umd.edu).

HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico, that monitors two thirds of the sky every day with an instantaneous field of view of ~2 sr.