Refined Constraints on the Hard X-ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset
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arXiv
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| Formato: | Preprint |
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2026
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| author | Baring, Matthew G. Casey, Jacob Chun, Sohee Gau, Ephraim Hakamata, Tomohiro Hu, Kun Ishi, Daiki Kislat, Fabian Kiss, Mózsi Kole, Merlin Krawczynski, Henric Kuramoto, Haruki Lisalda, Lindsey Liu, Bingkun Maeda, Yoshitomo Matsumoto, Hironori Menon, Shravan Vengalil Miyazawa, Takuya Murakami, Kaito Okajima, Takashi Pearce, Mark Rauch, Brian Shirahama, Kentaro Spooner, Sean Takahashi, Hiromitsu Takatsuka, Sayana Uchida, Yuusuke Varun West, Andrew Thomas |
| author_facet | Baring, Matthew G. Casey, Jacob Chun, Sohee Gau, Ephraim Hakamata, Tomohiro Hu, Kun Ishi, Daiki Kislat, Fabian Kiss, Mózsi Kole, Merlin Krawczynski, Henric Kuramoto, Haruki Lisalda, Lindsey Liu, Bingkun Maeda, Yoshitomo Matsumoto, Hironori Menon, Shravan Vengalil Miyazawa, Takuya Murakami, Kaito Okajima, Takashi Pearce, Mark Rauch, Brian Shirahama, Kentaro Spooner, Sean Takahashi, Hiromitsu Takatsuka, Sayana Uchida, Yuusuke Varun West, Andrew Thomas |
| contents | We present updated hard X-ray polarization measurements of the Crab pulsar and nebula obtained with the balloon-borne polarimeter XL-Calibur in the ~19-64 keV energy range. During the flight, intermittent GPS-failure resulted in poorly constrained timing for ~38% of the Crab dataset. By implementing a new phase-recovery method that reconstructs timing during extended GPS-off intervals, phase tag data is recovered for ~95% of the GPS-off dataset, increasing the precision of the phase-resolved analysis. Phase-information for the data is recovered by using the Crab pulsar, with its 33 ms period, as an external timing source. Using a Markov-Chain Monte-Carlo framework to jointly fit phase offsets and frequency derivatives, sufficient phase accuracy is achieved, across multiple periods without GPS for a phase-resolved analysis. This enables inclusion of nearly the full dataset in the polarization study. The polarization degree of the nebular emission is found to be (27.7${\pm}$4.9)% at a polarization angle of 127.2°${\pm}$5.1° confirming previous XL-Calibur results and remaining aligned with the Crab's spin axis, consistent with synchrotron emission from the inner nebula. Phase-resolved measurements show that the off-pulse and bridge intervals exhibit a strong polarization, while the pulsar peaks, although weakly constrained, remain in agreement with the softer-energy trends of IXPE. These findings reinforce a scenario in which hard X-ray emission arises primarily in the nebular torus and wind regions. The successful recovery of precise phase tagging from GPS-off data demonstrates the capacity to use the pulsar as an external clock even in the case of sparsely populated data. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_15501 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Refined Constraints on the Hard X-ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset Baring, Matthew G. Casey, Jacob Chun, Sohee Gau, Ephraim Hakamata, Tomohiro Hu, Kun Ishi, Daiki Kislat, Fabian Kiss, Mózsi Kole, Merlin Krawczynski, Henric Kuramoto, Haruki Lisalda, Lindsey Liu, Bingkun Maeda, Yoshitomo Matsumoto, Hironori Menon, Shravan Vengalil Miyazawa, Takuya Murakami, Kaito Okajima, Takashi Pearce, Mark Rauch, Brian Shirahama, Kentaro Spooner, Sean Takahashi, Hiromitsu Takatsuka, Sayana Uchida, Yuusuke Varun West, Andrew Thomas High Energy Astrophysical Phenomena We present updated hard X-ray polarization measurements of the Crab pulsar and nebula obtained with the balloon-borne polarimeter XL-Calibur in the ~19-64 keV energy range. During the flight, intermittent GPS-failure resulted in poorly constrained timing for ~38% of the Crab dataset. By implementing a new phase-recovery method that reconstructs timing during extended GPS-off intervals, phase tag data is recovered for ~95% of the GPS-off dataset, increasing the precision of the phase-resolved analysis. Phase-information for the data is recovered by using the Crab pulsar, with its 33 ms period, as an external timing source. Using a Markov-Chain Monte-Carlo framework to jointly fit phase offsets and frequency derivatives, sufficient phase accuracy is achieved, across multiple periods without GPS for a phase-resolved analysis. This enables inclusion of nearly the full dataset in the polarization study. The polarization degree of the nebular emission is found to be (27.7${\pm}$4.9)% at a polarization angle of 127.2°${\pm}$5.1° confirming previous XL-Calibur results and remaining aligned with the Crab's spin axis, consistent with synchrotron emission from the inner nebula. Phase-resolved measurements show that the off-pulse and bridge intervals exhibit a strong polarization, while the pulsar peaks, although weakly constrained, remain in agreement with the softer-energy trends of IXPE. These findings reinforce a scenario in which hard X-ray emission arises primarily in the nebular torus and wind regions. The successful recovery of precise phase tagging from GPS-off data demonstrates the capacity to use the pulsar as an external clock even in the case of sparsely populated data. |
| title | Refined Constraints on the Hard X-ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2604.15501 |