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

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