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

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