A complete radio study of SNR G15.4+0.1 from new GMRT observations

SUPAN L.; CASTELLETTI G.; JOSHI B.C., SURNIS M.; SUPANITSKY D.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2015 vol. 576 p. 1 - 11

0004-6361

Aims. The supernova remnant (SNR) G15.4+0.1 is considered to be the possible counterpart of the γ-ray source HESS J1818-154.With the goal of getting a complete view of this remnant and understanding the nature of the γ-ray flux, we conducted a detailedradio study that includes the search for pulsations and a model of the broadband emission for the SNR G15.4+0.1/HESS J1818-154system.Methods. Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz towards G15.4+0.1 were carried outwith the Giant Metrewave Radio Telescope (GMRT). We correlated the new radio data with observations of the source at X-ray andinfrared wavelengths from XMM-Newton and Herschel observatories, respectively. To characterize the neutral hydrogen (HI) mediumtowards G15.4+0.1, we used data from the Southern Galactic Plane Survey.We modelled the spectral energy distribution (SED) usingboth hadronic and leptonic scenarios.Results. From the combination of the new GMRT observations with existing data, we derived a continuum spectral index alpha=-0.62 +/- 0.03 for the whole remnant. The local synchrotron spectra of G15.4+0.1, calculated from the combination of the GMRT datawith 330 MHz observations from the Very Large Array, tends to be flatter in the central part of the remnant, accompanying the regionwhere the blast wave is impinging molecular gas. No spectral index trace was found indicating the radio counterpart to the pulsar windnebula proposed from X-ray observations. In addition, the search for radio pulsations yielded negative results. Emission at far-infraredwavelengths is observed in the region where the SNR shock is interacting with dense molecular clumps.We also identified HI featuresforming a shell that wraps most of the outer border of G15.4+0.1. Characteristic parameters were estimated for the shocked HI gas.We found that either a purely hadronic or leptonic model is compatible with the broadband emission known so far.