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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"

44282 results found.

  1. GRB 250830B: Swift-XRT observations
  2. EP250830a: Global MASTER-Net observations report
  3. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  4. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  5. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  6. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  7. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  8. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  9. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  10. GRB 250830B: Swift ToO observations
  11. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  12. GRB 250830B: MAXI/GSC detection
  13. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  14. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  15. The EP-WXT trigger 01709200994 is likely a flaring star
  16. GRB 250828B: Swift-BAT refined analysis
  17. EP250821a: SOAR observations
  18. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  19. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  20. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  21. GRB 250808B: SVOM detection of a burst through offline search
  22. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  23. EP250828a: Optical counterpart detection with Kinder observations
  24. EP250828a: Liverpool Telescope upper limits
  25. Swift GRB 250828B: Global MASTER-Net observations report
  26. EP250828a: Global MASTER-Net observations report
  27. EP-WXT trigger 01709200800 : KAIT optical observations
  28. EP250828a: KAIT optical upper limit
  29. EP250827a: Swift/UVOT Detection
  30. EP250828a: NOT optical counterpart confirmation
  31. EP250828a: SVOM/VT optical candidate
  32. EP250828a: Seimei/TriCCS optical counterpart detection
  33. GRB 250828B: Swift detection of a burst
  34. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  35. EP250828a: Optical upper limit with Kinder observations
  36. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  37. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  38. EP250827a: LCO observations show fading optical counterpart
  39. GRB 250828A: Fermi GBM Final Localization
  40. EP250828a: Einstein Probe detection of an X-ray transient
  41. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  42. GRID detection of GRB 250824A
  43. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  44. EP250827A: VLT/X-shooter redshift confirmation
  45. Fermi GRB 250827A: Global MASTER-Net observations report
  46. EP250827a: confirmation of optical rebrightening with LCO
  47. EP250827a: GOTO observation of the optical afterglow
  48. GRB 250826A: SVOM/GRM observation
  49. GRB 250827A: Fermi GBM Final Real-time Localization
  50. EP250827A: An optical rebrightening was detected by LCO.
  51. EP250827a: Swift-XRT counterpart detection
  52. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  53. The EP-WXT trigger 01709200800 is likely a flaring star
  54. EP250827a: TRT optical observations
  55. EP250827a: BOOTES-7 early optical dectection
  56. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  57. EP250827a: Gemini-South redshift z = 1.613
  58. EP250827a: Global MASTER-Net observations report
  59. EP250827a: Las Cumbres independent detection of the optical counterpart
  60. EP250827a: Gemini-South optical counterpart detection
  61. EP250827a: Einstein Probe detection of an X-ray transient
  62. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  63. Fermi GRB 250826A: Global MASTER-Net observations report
  64. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  65. EP250821a: Gemini GMOS Redshift Confirmation
  66. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  67. Fermi trigger No 777883624: Global MASTER-Net observations report
  68. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  69. GRB 250826A: Fermi GBM Final Real-time Localization
  70. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  71. Fermi GRB 250824B: Global MASTER-Net observations report
  72. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  73. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  74. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  75. GRB 250823A: Swift-BAT refined analysis
  76. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  77. GRB 250821B: AstroSat CZTI detection
  78. GRB 250819A: AstroSat CZTI detection
  79. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  80. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  81. GRB 250821B: Insight-HXMT detection
  82. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  83. GRB 250823A: Swift-XRT refined Analysis
  84. EP250821a: MeerKAT radio counterpart
  85. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  86. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  87. GRB 250824B: Fermi GBM Final Real-time Localization
  88. The EP-WXT trigger 01709200707 is likely a flaring star
  89. GRB 250823A: COLIBRÍ optical observations
  90. The EP-WXT trigger 01709200706 is likely a flaring star
  91. GRB 250823A: SVOM/VT optical observation
  92. GRB 250824A: Fermi GBM Final Real-time Localization
  93. GRB 250823A: Swift/UVOT Detection
  94. GRB 250823A: NOT optical observations
  95. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  96. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  97. GRB 250823A: Fermi GBM Observation
  98. GRB 250818B: MeerKAT Detection
  99. GRB 250823A: Enhanced Swift-XRT position
  100. GRB 250823A: LCOGT Optical Detection

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