On the radio-X-ray connection in young stellar objects in the Orion nebula cluster

Author(s)

J. Forbrich, S. J. Wolk

Abstract

Context. Both X-ray and radio observations offer insight into the

high-energy processes of young stellar objects (YSOs). The observed

thermal X-ray emission can be accompanied by both thermal and nonthermal

radio emission. Due to variability, simultaneous X-ray and radio

observations are a priori required, but only a comparably small number

of YSOs have been studied in this way. Results have been inconclusive

due to the even smaller number of YSOs that were simultaneously detected

in X-ray and radio observations. Aims: We use archival X-ray and

radio observations of the Orion nebula cluster (ONC) to significantly

enlarge the sample size of known YSOs with both X-ray and radio

detections. Methods: We study the ONC using multi-epoch

non-simultaneous archival Chandra X-ray and NRAO Very Large Array (VLA)

single-band radio data. The multiple epochs allow us to reduce the

impact of variability by obtaining approximated quiescent fluxes.

Results: We find that only a small fraction of the X-ray sources (7%)

have radio counterparts, even if 60% of the radio sources have X-ray

counterparts. YSOs with detections in both bands thus constitute a small

minority of the cluster. The radio flux density is typically too low to

distinguish thermal and nonthermal radio sources. Only a small fraction

of the YSOs with detections in both bands are compatible with the

empirical "Güdel-Benz" (GB) relation. Most of the sources not

compatible with the GB relation are proplyds, and thus likely thermal

sources, but only a fraction of the proplyds is detected in both bands,

such that the role of these sources is inconclusive. Conclusions:

While the radio sources appear to be globally unrelated to the X-ray

sources, the X-ray dataset clearly is much more sensitive than the radio

data. We find tentative evidence that known non-thermal radio sources

and saturated X-ray sources are indeed close to the empirical relation,

even if skewed to higher radio luminosities, as they are expected to be.

Most of the sources that are clearly incompatible with the empirical

relation are proplyds that could instead plausibly be thermal radio

sources. The newly expanded Karl G. Jansky Very Large Array with its

significantly enhanced continuum sensitivity is beginning to provide an

ideal tool for addressing this issue. Combined X-ray and radio studies

of YSOs using older VLA data are clearly limited by the typically low

signal-to-noise of the radio detections, providing insufficient

information to disentangle thermal and nonthermal sources.

Organisation(s)

Department of Astrophysics

External organisation(s)

Harvard-Smithsonian Center for Astrophysics

Journal

Astronomy & Astrophysics

Volume

551

No. of pages

6

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/201220579

Publication date

03-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics, 103003 Astronomy

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/d2bed746-01e2-464f-ae7c-c19d7f9de89e