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New Star Observations with NuSTAR: Flares from Young Stellar Objects in the ρ Ophiuchi Cloud Complex in Hard X-Rays

Vievering, Juliana T. and Glesener, Lindsay and Grefenstette, Brian W. and Smith, David M. (2019) New Star Observations with NuSTAR: Flares from Young Stellar Objects in the ρ Ophiuchi Cloud Complex in Hard X-Rays. Astrophysical Journal, 882 (1). Art. No. 72. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20190904-152822673

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Abstract

We study the structure and dynamics of extreme flaring events on young stellar objects (YSOs) observed in hard X-rays by the Nuclear Spectroscopic Telescope Array (NuSTAR). During 2015 and 2016, NuSTAR made three observations of the star-forming region ρ Ophiuchi, each with an exposure ~50 ks. NuSTAR offers unprecedented sensitivity above ~7 keV, making this data set the first of its kind. Through improved coverage of hard X-rays, it is finally possible to directly measure the high-energy thermal continuum for hot plasmas and to sensitively search for evidence of nonthermal emission from YSO flares. During these observations, multiple flares were observed, and spectral and timing analyses were performed on three of the brightest flares. By fitting an optically thin thermal plasma model to each of these events, we found flare plasma heated to high temperatures (~40−80 MK) and determined that these events are ~1000 times brighter than the brightest flares observed on the Sun. Two of the studied flares showed excess emission at 6.4 keV, and this excess may be attributable to iron fluorescence in the circumstellar disk. No clear evidence for a nonthermal component was observed, but upper limits on nonthermal emission allow for enough nonthermal energy to account for the estimated thermal energy in the flare on protostar IRS 43, which is consistent with the standard model for solar and stellar flares.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/ab2e0dDOIArticle
ORCID:
AuthorORCID
Vievering, Juliana T.0000-0002-7407-6740
Glesener, Lindsay0000-0001-7092-2703
Grefenstette, Brian W.0000-0002-1984-2932
Smith, David M.0000-0002-0542-5759
Additional Information:© 2019 The American Astronomical Society. Received 2018 October 25; revised 2019 June 7; accepted 2019 June 26; published 2019 September 4. This work was supported by NSF grants AGS-1429512 and AGS-1752268 and by NASA Headquarters under the NASA Earth and Space Science Fellowship Program Grant 80NSSC17K0430. The authors would like to acknowledge and thank Eric Feigelson for encouraging the NuSTAR team early on to make these observations and for contributing to discussions of this analysis. Software: NuSTARDAS (v1.6.0), nuskybgd (Wik et al. 2014), XSPEC (Arnaud 1996).
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NSFAGS-1429512
NSFAGS-1752268
NASA Earth and Space Science Fellowship 80NSSC17K0430
Subject Keywords:Star forming regions; Stellar flares; Stellar x-ray flares; Pre-main sequence stars; Young stellar objects; Stellar activity
Issue or Number:1
Classification Code:Star forming regions (1565); Stellar flares (1603); Stellar x-ray flares (1637); Pre-main sequence stars (1290); Young stellar objects (1834); Stellar activity (1580)
Record Number:CaltechAUTHORS:20190904-152822673
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190904-152822673
Official Citation:Juliana T. Vievering et al 2019 ApJ 882 72
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98418
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Sep 2019 22:41
Last Modified:03 Oct 2019 21:40

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