θ = 0.35º
Figure 8.4: Schematic view of the maximum possible extension that MAGIC can assumed for a source taken inwobblemode. Both W1 and W2 are depicted simultaneously. From W1, the ON region (green) is taken while W2 provides the OFF region (red) at the same distance, d, from the camera center. An intrinsic radius of the source of∼0.16◦leads to aθ2cut of 0.12 deg2, i.e.θ=0.35◦, taken into account a PSF of 0.07◦. The normalization region is shown in blue between the ON and OFF regions.
X-ray Observatory revealed the existence of a point-like source, CXO J200423.4+333907 (see Figure 8.5), reported by Cameron & Kulkarni (2007). This source was at 3.6” from the previously detected Be star, turning a binary system composed by both of them impossible. However, NIR observations with the Keck Observatory’s Laser Guide Star Adaptive Optics (LGS-AO) system showed in turn a relatively bright counterpart around the X-ray source, which was consistent with a highly obscured B-star. This way, Cameron & Kulkarni (2007) suggested that the X-ray binary (comprised by CXO J200423.4+333907 and a B-star) was the dominant source that powers the radio/optical nebula G70.7+1.2, moving into the molecular cloud from its far side. On the other hand, the Be star could create a reflection nebula on the near side. An unidentifiedFermi-LAT source included in the Second Fermi-LAT catalog (2FGL) catalog, 2FGL J2004.3+3339, was detected at the position of the X-ray source. This discovery reinforced the idea of the binary scenario, although not pulsation was reported so far. In turn, coincident with the Fermi-LAT source, a hotspot at the level of 3–4σwas detected on the re-analysis of the 8-years data sample
from the Milagro gamma-ray Observatory, whose position was not confirmed by the 2HWC catalog.
MAGIC pointed to theFermi-LAT source and amounted a total of∼ 55 hours (after quality cuts). The data was recorded between April 2015 and August 2016 within an extended zenith range of (5, 50)◦.
CXO J200423.4+333907
Be-star
Figure 8.5: LGS-AO NIR image from G70.7+1.2 with the diffuse Chandra X-ray counterparts, taken from Cameron & Kulkarni (2007). The red circle corresponds to the X-ray source CXO J200423.4+333907. The Be-star, at 3.6” from the X-ray point-like source, is highlighted in blue. The distance between the expected binary system and the center of the diffuse X-ray emission is around 20”.
8.2.2 2HWC J1907 + 084
∗2HWC J1907+084∗ is located at 0.79◦ from 1HWC J1904+080c (RA = 286.1◦, Dec = 8.1◦).
The latter was included in the first HAWC survey (Abeysekara et al. 2016) and previously reported within a list of interesting candidates via private communication to all collaboration HAWC had a MoU with, including MAGIC. The list was composed of 6 new TeV candidates (1 extragalactic and 5 galactic sources) with significance above 4.2σ obtained after 9 months of observations with the HAWC-111 configuration. The PSF at a 68% radius containment for this HAWC analysis was 0.8◦and the systematic uncertainty on the location was expected to be
< 0.2◦. The flux for all candidates above 1 TeV was∼ 20% C.U. (with a systematic uncertainty on the flux of∼ 40%). The chosen candidate by MAGIC, 1HWC J1904+080c, presented 5.2σ pre-trials, which decreased up to 3.9σafter trials, as shown later on in Abeysekara et al. (2016).
The coordinates were not coincident with any known TeV source, but it was close (at 0.3◦, co-incident within the errors) to a Fermi-LAT hotspot (< 5σ), 3FGL J1904.9+0818 (Acero et al.
2015).
A point-like source with a flux of∼ 20% C.U. in the TeV regime is detectable by MAGIC in less than an hour. However, given the poor HAWC PSF in this analysis, the candidate could be extended and, in turn, presented a high systematic uncertainty on the flux. Thus, MAGIC asked
for observing 1HWC J1904+080c 5 hours, extendable another 5 hours if a significance of 3σ was reached. Finally, MAGIC performed follow-up observations of the 1HWC candidate from 10th May of 2015 to 19th May 2015, for 6 non-consecutive nights at a medium Zd range of (30, 50)◦. After disposing of the data affected by non-optimal weather conditions, the total amount of time reached 4.2 hours.
8.3 Results
8.3.1 2HWC J2006 + 341
No significant detection was found in the direction of 2HWC J2006+341 under any of the as-sumptions, point-like or extended source. Integral ULs at a 95% C.L. were computed adopting a power-law distribution with photon indexΓ = 2.64, as suggested by HAWC analysis. Account-ing for the energy threshold at the maximum moonlight level (decent moon,Eth∼220±10 GeV) and the fact that the sources were detected by HAWC in the TeV regime, integral ULs are given for energies above 300 GeV. For the point-like analysis, this UL was set to 1.8×10−12 photons cm−2s−1, while for the extended hypothesis, it increases slightly to 3.8×10−12photons cm−2s−1. Differential ULs for 2HWC J2006+341 were computed as well and can be found in Table 8.3.
The integral UL for a point-like source at the position of G70.7+1.2, for energies above 300 GeV and assuming a power-law distribution withΓ = 2.6, is 1.0×10−12photons cm−2s−1. Left panel on Figure 8.2 shows the skymap in the FoV of G70.7+1.2, where 2HWC J2006+341 is tagged in green. The skymap is computed assuming point-like source for a blind scan (without assuming the position of any source). No hotspot arises at the position or nearby 2HWC J2006+341.
Figure 8.6: Zoom view of the skymap centered in G70.7+1.2 (cyan). The hotspot at the level of 4σ (green) is located at∼ 0.12◦from the nominal posi-tion. The radius of the circles indicates the MAGIC PSF of 0.10◦.
However, a hotspot appears close to the nominal position of G70.7+1.2. With approximately RA = 301.02◦and Dec = 33.57◦, this hotspot is located at ∼ 0.12◦ from 2FGL J2004.3+3339. It corresponds to point-like emis-sion since it is contained in the PSF of MAGIC (see zoom view in Figure 8.6). To get an estimation of the significance at this position, again OfWP was used in Odie. In this case, the standard FR cuts were applied, which led to a significance of around 3σ.
Table 8.3:MAGIC 95% CL differential flux ULs for 2HWC J2006+341 and 2HWC J1907+084∗for both point-like (. 0.10◦) and extended (∼ 0.16◦) radius assumptions, considering a power-law spectrum with spectral index of Γ = 2.64 andΓ = 3.25, respectively. ULs beyond ∼ 4.7 TeV are not computed for J1907+084∗due to low statistics.
Energy range Differential flux UL for J2006+341 Differential flux UL for J1907+084∗ [GeV] [×10−13TeV−1cm−2s−1] [×10−13TeV−1 cm−2s−1]
Point-like Extended Point-like Extended
300 – 475.5 25.7 45.7 12.1 41.2
475.5 – 753.6 9.1 61.9 4.8 5.9
753.6 – 1194.3 2.9 15.0 3.2 3.0
1194.3 – 1892.9 2.2 7.1 0.6 2.1
1892.9 – 3000 0.4 1.9 0.2 0.7
3000 – 4754.7 0.3 0.8 0.04 0.3
4754.7 – 7535.7 0.1 0.3 – –
8.3.2 2HWC J1907 + 084
∗No excess was found in the direction of 2HWC J1907+084∗. The 95% C.L. integral ULs were again computed for energies greater than 300 GeV, but assuming a photon index of 3.25, fol-lowing HAWC results (see Table 8.1). The integral ULs are 9.7×10−13 photons cm−2 s−1 and 1.4×10−12photons cm−2s−1, for the point-like and radius 0.16◦hypothesis, respectively. Under the same conditions, differential ULs were calculated, which are listed in Table 8.3.
1HWC J1904+080c was not detected either. The corresponding integral UL at E > 300 GeV, assuming point-like source defined by a power-law distribution withΓ = 2.6, is 4.1×10−12 photons cm−2. The skymap of the FoV shown in Figure 8.2 does not reveal any significant area around the 1HWC or the 2HWC candidates.
8.4 Discussion
Given that the largest population of TeV emitter in our Galaxy are PWNe, it would not be im-probable that our selected candidates belong to this type of sources. However, the non-detection at lower energies neither with MAGIC orFermi-LAT (see Ahnen et al. 2017 for more information on theFermi-LAT analysis and results), complicates disentangling the nature of these sources. To delve more into the possible PWN nature, I looked for detected pulsars nearby the position of the selected candidates using the Australia Telescope National Facility (ATNF) catalog1(Manchester et al. 2005).
For 2HWC J2006+341, the closest pulsar (and the only one within a 1◦ radius) is PSR J2004+3429, which lays at ∼ 0.4◦ from the 2HWC position. This pulsar is located at a
dis-1http://www.atnf.csiro.au/people/pulsar/psrcat/