1. By Scott J. Wolk and Jan Forbrich
The Radio/X-ray Connection in Young Stellar Objects in the Orion Nebula Cluster
By Scott J. Wolk and Jan Forbrich

2. Güdel (2002)

3. Classes of Young Stellar Objects (YSOs)
“class I”
Greene (2001)
“class II”
“class III”
Lada (1987)
André et al. (2000)

4. Different from other active stars (?) ((thermal) X-rays,
nonthermal radio
thermal radio
Feigelson & Montmerle (1999)
Different from
other active stars (?)
NASA/CXC/M.Weiss
X-rays and nonthermal radio emission probe the innermost regions of protostars,
but currently only radio observations offer high angular resolution (VLBI).

5. (e.g., free-free emission)
Feigelson & Montmerle (1999)
Thermal radio
(e.g., free-free emission)
Nonthermal radio
(e.g., gyrosynchrotron
emission)

6. (e.g., free-free emission)
Feigelson & Montmerle (1999)
Thermal radio
(e.g., free-free emission)
Nonthermal radio
(e.g., gyrosynchrotron
emission)
...only
~2 sources!

7. YSO Radio Emission Process: Gyrosynchrotron/non-thermal radiation
or Thermal free-free
GS identified by: Polarization, spectral index, rapid
variability, high brightness temperature
Problem (VLA): weak sources,
measurement at single frequency
Best evidence for non-thermal radiation
requires high S/N – often not the case.
Difficult to constrain the emission
processes of many weak sources.
Gs spectra flat alpha =0 in Quiescence ~1 in flare.

8. GMR A (Bower et al. 2003, Getman et al. 2003)

9. CrA: Optical image European Southern Observatory
R oph 31 radio sources,
10 with X-ray counter parts at 160 pc.
2 with circular polarization
DO AR had X-ray flare
Oph S1

10. X-ray image
NASA/CXC/CfA/J.Forbrich et al.
Forbrich & Preibisch (2007)

11. X-ray image
NASA/CXC/CfA/J.Forbrich et al.

12. X-ray image with radio data
NASA/CXC/CfA/J.Forbrich et al.
~0.1 pc
Seven objects are detected simultaneously in the X-ray, radio, and optical/infrared bands; they constitute our core sample. While most of these sources exhibit clear variability in the X-ray regime and several also display optical/infrared variability, none of them shows significant radio variability on the timescales probed. We also do not find any case of clearly time-correlated optical/infrared and X-ray variability. Remarkable intra-band variability is found for the class I protostar IRS 5 which shows much lower radio fluxes than in previous observations, and the Herbig Ae star R CrA, which displays enhanced X-ray emission during the last two epochs, but no time-correlated variations are seen for these objects in the other bands. The two components of S  CrA vary nearly synchronously in the I band.
Forbrich et al. (2006, 2007)

13. X-ray image with radio data (offset)
NASA/CXC/CfA/J.Forbrich et al.
~0.1 pc
Only IRS 5 bright enough to measure polarization  IRS 5 in synchrotron
Forbrich et al. (2006, 2007)

14. What about other clusters?
NGC 1333 & IC 348
Very few YSOs (∼5%) are detected in both bands.
We find radio variability on timescales of decades, days, and hours.
About half of the objects with X-ray and radio detections were variable at X-ray wavelengths, despite lacking large-scale flares or large variations. Variability appears to be a bigger factor affecting radio emission than X-ray emission. A star with infrared evidence for a disk, [BW88] 3, was observed in the decay phase of radio flare. In this object and another ([BW88] 1) ,
we find an inverse correlation between radio flux and spectral index, which contrasts with behavior seen in the Sun and active stars. We interpret this behavior as the repopulation of the hardest energy electrons due to particle acceleration
Forbrich, Osten & Wolk 2011
NGC 1333: 2x 40 ksec Chandra + 22h VLA (X & C in subarrays)
IC 348: 2x 40 ksec Chandra + 22h VLA (X & C in subarrays)
~5% of YSOs have Simultaneous X-ray & radio detections
→ only three class I sources detected in X-rays and radio

15. What about other clusters?
LkHα101 (Osten & Wolk 2009)
6 cm LR (1017 erg s-1 Hz-1)
Figure 3. Left: plot of 6 cm radio luminosity against 6–3.6 cm spectral index, for three objects for which changes in the spectral index could be measured. Open
squares indicate data points from the first day of observations, while the filled circles denote data from the second observation. The two apparent cluster members,
[BW88] 1 and [BW88] 3,
display a statistically significant anticorrelation between luminosity and spectral index,
while the probable AGN ([BW88] 2) shows no
correlation.
Right: plot displaying 6 cm radio luminosity against 6–3.6 cm spectral index for the decays of several radio flares from nearby active stars.
Data for decays
of radio flares from HR 1099 are taken from Osten et al. (2004); data for the decay of radio flare from EV Lac is taken from Osten et al. (2005). The radio luminosities
are positively correlated with spectral index over a wide range of luminosity
AGN

16. All YSOs with Chandra and VLA detections (5 clusters)
Figure 2. Plot of the X-ray and radio luminosities of all YSOs that have been simultaneously detected in both the X-ray and radio ranges by Chandra and the VLA, excluding sources with a radio detection significance of <5σ and less than 100 counts in X-rays. The symbols “+,” “×,” and “*” indicate YSO classes I, II, and III, respectively. Apart from sources reported in this paper, and sources in ρ Oph from Gagne ́ et al. (2004), scaled to a distance of 130 pc, IRS sources are in CrA (Forbrich et al. 2007), and L1 stands for LkHα 101 (Osten & Wolk 2009). The central line marked “GB” indicates the Gu ̈del–Benz relation with its upper and lower bounds, as reported by Gu ̈del (2002), shown as dashed lines. The vertical lines indicate the 5σ sensitivities of the different observations, as converted into radio luminosities at the respective distances. The limits are strictly for the simultaneous observations only (some regions have deeper radio and/or X-ray data from separate observations). The X-ray sensitivity limits are lower than the X-ray luminosity range shown (see Table 1).
Forbrich, Osten & Wolk 2011

17. Positions of most of the VLA 3
Positions of most of the VLA 3.6 cm sources, superposed on the H image of O'Dell & Wong (1996). Sources 1, 2, 3, 4, 6, 10, and 77 fall outside the region shown. The triangles indicate time-variable sources, the diamonds indicate nonvariable sources, and the circles indicate faint sources detected in the averaged image (see Table 3). The positions of the radio sources are at the center of the symbols.
Composite of 4 VLA 3,6 cm observations
We have used 3.6 cm archival data from the VLA of the
NRAO1in its A configuration to study the cluster of radio sources in Orion and to search for new, fainter objects in a sensitive image made from concatenating all the data. The
region was observed on 1994 April 29, 1995 July 22, 1996 November 21, and 1997 January 11. The amplitude calibrator was , with an adopted flux density
The rms noise from the Zapata paper is for a single epoch (Table 1), each of these four consists of one 1 track, i.e., ~7h. In our EVLA observations, we will get four epochs with 2x1 GHz bandwidth, both in the C band, centered on 4.8 and 7.4 GHz each. The nominal sensitivity limit for the first epoch is 5 muJy, but it is likely going to be higher due to the extremely bright extended structure (aka the Orion Nebula) that will not be filtered out entirely.
Zapata et al. 2004

18. Positions of most of the VLA 3
Positions of most of the VLA 3.6 cm sources, superposed on the H image of O'Dell & Wong (1996). Sources 1, 2, 3, 4, 6, 10, and 77 fall outside the region shown. The triangles indicate time-variable sources, the diamonds indicate nonvariable sources, and the circles indicate faint sources detected in the averaged image (see Table 3). The positions of the radio sources are at the center of the symbols.
Composite of 4 VLA 3,6 cm observations
We have used 3.6 cm archival data from the VLA of the
NRAO1in its A configuration to study the cluster of radio sources in Orion and to search for new, fainter objects in a sensitive image made from concatenating all the data. The
region was observed on 1994 April 29, 1995 July 22, 1996 November 21, and 1997 January 11. The amplitude calibrator was , with an adopted flux density
The rms noise from the Zapata paper is for a single epoch (Table 1), each of these four consists of one 1 track, i.e., ~7h. In our EVLA observations, we will get four epochs with 2x1 GHz bandwidth, both in the C band, centered on 4.8 and 7.4 GHz each. The nominal sensitivity limit for the first epoch is 5 muJy, but it is likely going to be higher due to the extremely bright extended structure (aka the Orion Nebula) that will not be filtered out entirely.
Zapata et al. 2004

19. Results
70 radio sources were detected in the primary VLA field of the 3.6 cm observations
rms noise ~0.05 mJy  but high free-free background
11 known class I/II YSOs
623 X-ray source in that field
850 ks observation sensitive to log LX~27
Note: LX gives a rough estimate of stellar parameters
Only 46 detected in both.
5 Class II YSOs
1 Class I
65% or radio source
7% of X-ray
that Zapata et al. (2004) find circular polarization, indicative o0 non-thermal gyrosynchrotron radiation, only toward GMR A
GMR 12(~O9), G, and F are detected in VLBI and are NT/GS

20. X-ray and Radio detection rates
Fig. 1.— Left panel: Histogram of the radio luminosities of all sources detected by Zapata et al. (2004) (empty histogram) and those with X-ray counterparts (hashed histogram). Right panel: Histogram of the
COUP X-ray luminosities in the area probed by Zapata et al. (2004) with the VLA (empty histogram) and those with radio counterparts (hashed histogram) on a logarithmic scale.

21. (Lack of) Impact of X-ray parameters on radio detection
Histograms of the distributions of NH (left), kT 1 (center), and < E > (right) for the COUP
sources contained in the VLA primary beam area (empty histograms) and the COUP sources with radio
counterparts (filled histograms).

22. LX vs. LR diagram for the ONC
LX vs. LR diagram of the ONC, based on COUP X-ray data and radio observations reported by
Zapata et al. (2004). The small dots in straight lines at low X-ray and radio luminosities denote nondetections
with a nominal upper limit. The squares mark sources with LX/Lbol information. Proplyds from Kastner
et al. (2005) are marked by ‘x’. Some sources are marked with their GMR names (see text) and the only
two (possibly) extragalactic sources from Getman et al. (2005b) are marked by ‘EG’.

23. What do we know?
We usually don’t see YSOs in the radio, but when we do they are over bright
We don’t know:
Their YSO Class
Radio Spectrum
The radio signal is sometimes gyrosynchrotron
GMR A, CRA IRS 5
Other sources could be too, not enough S/N
Optical depth could delay one of the signals
Could be thermal free-free
Free-free should be bright.
26/15 ARE proplyds
But most (109) proplyds are not detected and most radio sources are not proplyds.
“My friend”
Lack of correlation does not imply lack of causality
Propylds = PIGS partially ionized globules

24. VLA JVLA
The New Yorker

25. Conclusions
With Chandra and XMM-Newton, the number of X-ray detected YSOs has gone through the roof. Yet, the number of radio-detected YSOs has barely changed.
Observations (simultaneous) of the ONC, (NGC 1333, Lk Ha101, CrA, r Oph and IC 348) are limited by the radio sensitivity; only a very low detection fraction of YSOs in both bands is found.
The NRAO Very Large Array is history – it is right now being transformed into the Jansky Very Large Array, a very different instrument (much better to prove the kind of emission!).

27. NGC 1333 & IC 348
NGC 1333: 2x 40 ksec Chandra + 22h VLA (X & C in subarrays)
IC 348: 2x 40 ksec Chandra + 22h VLA (X & C in subarrays)

28. NGC 1333 & IC 348
Class I sources (Gutermuth et al. 2008, Muench et al. 2007)

29. What about other clusters?
ρ Oph (Gagné et al. 2004), LkHα101 (Osten & Wolk 2009)
Class I protostars first detected in X-rays and radio in CrA.
→ try even more prominent (and compact) star-forming regions
NGC 1333
IC 348

30. Developments since 1999
1) With Chandra and XMM-Newton, the number of X-ray detected
YSOs has gone through the roof. Yet, the number of radio-detected
YSOs has barely changed.
2) The (still growing) legacy of the Spitzer Space Telescope has
provided us with a consistent roadmap to look for YSOs. We now
Know much better where to look.
3) The NRAO Very Large Array is history – it is right now being
transformed into the Expanded Very Large Array, a very different
instrument.

31. All Class I sources in VLA FOV

32. All Class I sources in VLA FOV
α < -0.78
α > 0.15
α = 0.25
(?)

33. X-ray image
NASA/CXC/CfA/J.Forbrich et al.

36. Feigelson & Montmerle (1999)

37. EVLA Observations
1) 2 Ghz vs. 100 MHz
2) 24 hours within one week 3)

38. CrA: Optical image European Southern Observatory
R oph 31 radio sources,
10 with X-ray counter parts at 160 pc.
2 with circular polarization
DO AR had X-ray flare
Oph S1

39. Mid-infrared image
NASA/CXC/CfA/IRAC GTO Team

40. GMR A
Bower