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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 251126A: SAO RAS optical observations
  2. GRB 251128A: GECAM-B detection
  3. GRB 251128A: SVOM/GRM observation of a long burst
  4. GRB 251128A: Insight-HXMT/HE detection
  5. SVOM GRB 251129A : MASTER optical counterpart detection
  6. GRB 251129A: Swift-XRT afterglow detection
  7. The EP-WXT trigger 01709248941 is triggered by the known source Perseus Cluster
  8. Swift trigger 1418333 is not an astrophysical source
  9. GRB 251129A: Swift ToO observations
  10. GRB 251129A / EP251129a: SVOM/VT optical fading
  11. EP251129a: Global MASTER-Net observations report
  12. GRB 251129A: Optical Observations via Virtual Telescope Project, Italy
  13. EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
  14. GRB 251129A: Correction to the position of the optical counterpar
  15. GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
  16. GRB 251128A: Fermi GBM Observation
  17. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  18. GRB 251129A: SVOM detection of a burst
  19. SVOM GRB251129A: Global MASTER-Net observations report
  20. GRB 251129A: SVOM detection of a burst
  21. GRB 251126A: Swift-BAT refined analysis
  22. GRB 251126A: TShAO, Mondy, and AbAO optical observations
  23. GRB 251128A: Swift/BAT-GUANO localization skymap of a burst
  24. Fermi GRB 251128A: Global MASTER-Net observations report
  25. GRB 251127A: Glowbug gamma-ray detection
  26. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  27. GRB 251126A: further SAO RAS optical observations
  28. GRB 250702B: detection of the compact radio counterpart 139 days after the burst
  29. GRB 251126A NUTTelA-TAO Early Measurements
  30. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  31. GRB251126A: MAO/AZT-22 optical observations
  32. GRB 251128A: Fermi GBM Final Real-time Localization
  33. GRB251126A: Continued optical observation from 1.3m DFOT
  34. GRB 251126A: Swift/UVOT Detection
  35. EP251124a: Pan-STARRS ri-band imaging and photometry
  36. GRB 251126A: Mondy and SAO RAS optical observations
  37. GRB 251126A: Swift-XRT refined Analysis
  38. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  39. GRB 251126A: NOT optical observations
  40. GRB 251126A: 1.3m DFOT optical afterglow detection
  41. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  42. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  43. GRB 251125B: GECAM-B detection
  44. Fermi GRB 251127A: Global MASTER-Net observations report
  45. GRB 251127A: Fermi GBM Final Real-time Localization
  46. GRB 251126A: Enhanced Swift-XRT position
  47. GRB 251126A: Kilonova-Catcher optical afterglow detection
  48. GRB 251126A: Asiago i-band detection
  49. GRB 251126A: Nanshan/HMT optical afterglow detection
  50. Swift GRB 251126A: Global MASTER-Net observations report
  51. GRB 251121A: Fermi GBM Observation
  52. GRB 251126A: Prompt enhanced Swift-XRT position
  53. GRB 251126A: GIT discovery of the likely optical afterglow
  54. GRB 251126A: Swift detection of a burst
  55. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  56. EP251124b follow-up observation by EP-FXT
  57. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  58. EP251124b: NOT r- and z-band optical upper limits
  59. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  60. Fermi GRB 251125B: Global MASTER-Net observations report
  61. GRB 251125B: Fermi GBM Final Real-time Localization
  62. EP251124b: Global MASTER-Net observations report
  63. EP251124b: EP-WXT detection of a fast X-ray transient
  64. EP251124a: Xinglong GWAC-F60A optical observation
  65. EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
  66. Fermi GRB 251125A: Global MASTER-Net observations report
  67. GRB 251125A: Fermi GBM Final Real-time Localization
  68. EP251124a: NOT r- and z-band optical upper limits
  69. EP251124a: Global MASTER-Net observations report
  70. EP251124a: Swift-XRT observations
  71. GRB 251124A: Fermi GBM Localization by automated pipeline
  72. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  73. EP251124a: Optical upper limit with Kinder observations
  74. GRB 251122B: Fermi GBM Final Localization
  75. EP251118A: 6 GHz VLA Detection
  76. Fermi GRB 251124a: Global MASTER-Net observations report
  77. GRB 251124a: Fermi GBM Final Localization
  78. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  79. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  80. EP251124a: GROWTH-India Telescope optical upper limits
  81. EP251124a: Einstein Probe detection of an X-ray transient
  82. GRB 251116C: Swift-XRT confirmation of fading
  83. GRB 251122A/EP251122a: FTW optical and NIR observations
  84. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  85. The EP-WXT trigger 01709248783 is likely a flaring star
  86. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  87. EP251118A: 3.6m DOT optical afterglow detection
  88. GRB 251122A / EP251122a: EP-FXT counterpart detection
  89. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  90. GRB 251122A / EP251122a: WFST optical observations
  91. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  92. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  93. GRB 251122A / EP251122a: LCO optical upper limits
  94. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  95. EP251122a: Global MASTER-Net observations report
  96. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  97. GRB 251122A / EP251122a: SVOM detection of a long burst
  98. EP251122a: Einstein Probe detection of an X-ray transient
  99. EP251118a: Continued Optical Detection with Kinder observations
  100. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search

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